// Copyright 2018 The Bazel Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package build.bazel.remote.execution.v2;

import "build/bazel/semver/semver.proto";
import "google/api/annotations.proto";
import "google/longrunning/operations.proto";
import "google/protobuf/any.proto";
import "google/protobuf/duration.proto";
import "google/protobuf/timestamp.proto";
import "google/protobuf/wrappers.proto";
import "google/rpc/status.proto";

option csharp_namespace = "Build.Bazel.Remote.Execution.V2";
option go_package = "github.com/bazelbuild/remote-apis/build/bazel/remote/execution/v2;remoteexecution";
option java_multiple_files = true;
option java_outer_classname = "RemoteExecutionProto";
option java_package = "build.bazel.remote.execution.v2";
option objc_class_prefix = "REX";


// The Remote Execution API is used to execute an
// [Action][build.bazel.remote.execution.v2.Action] on the remote
// workers.
//
// As with other services in the Remote Execution API, any call may return an
// error with a [RetryInfo][google.rpc.RetryInfo] error detail providing
// information about when the client should retry the request; clients SHOULD
// respect the information provided.
service Execution {
  // Execute an action remotely.
  //
  // In order to execute an action, the client must first upload all of the
  // inputs, the
  // [Command][build.bazel.remote.execution.v2.Command] to run, and the
  // [Action][build.bazel.remote.execution.v2.Action] into the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage].
  // It then calls `Execute` with an `action_digest` referring to them. The
  // server will run the action and eventually return the result.
  //
  // The input `Action`'s fields MUST meet the various canonicalization
  // requirements specified in the documentation for their types so that it has
  // the same digest as other logically equivalent `Action`s. The server MAY
  // enforce the requirements and return errors if a non-canonical input is
  // received. It MAY also proceed without verifying some or all of the
  // requirements, such as for performance reasons. If the server does not
  // verify the requirement, then it will treat the `Action` as distinct from
  // another logically equivalent action if they hash differently.
  //
  // Returns a stream of
  // [google.longrunning.Operation][google.longrunning.Operation] messages
  // describing the resulting execution, with eventual `response`
  // [ExecuteResponse][build.bazel.remote.execution.v2.ExecuteResponse]. The
  // `metadata` on the operation is of type
  // [ExecuteOperationMetadata][build.bazel.remote.execution.v2.ExecuteOperationMetadata].
  //
  // If the client remains connected after the first response is returned after
  // the server, then updates are streamed as if the client had called
  // [WaitExecution][build.bazel.remote.execution.v2.Execution.WaitExecution]
  // until the execution completes or the request reaches an error. The
  // operation can also be queried using [Operations
  // API][google.longrunning.Operations.GetOperation].
  //
  // The server NEED NOT implement other methods or functionality of the
  // Operations API.
  //
  // Errors discovered during creation of the `Operation` will be reported
  // as gRPC Status errors, while errors that occurred while running the
  // action will be reported in the `status` field of the `ExecuteResponse`. The
  // server MUST NOT set the `error` field of the `Operation` proto.
  // The possible errors include:
  //
  // * `INVALID_ARGUMENT`: One or more arguments are invalid.
  // * `FAILED_PRECONDITION`: One or more errors occurred in setting up the
  //   action requested, such as a missing input or command or no worker being
  //   available. The client may be able to fix the errors and retry.
  // * `RESOURCE_EXHAUSTED`: There is insufficient quota of some resource to run
  //   the action.
  // * `UNAVAILABLE`: Due to a transient condition, such as all workers being
  //   occupied (and the server does not support a queue), the action could not
  //   be started. The client should retry.
  // * `INTERNAL`: An internal error occurred in the execution engine or the
  //   worker.
  // * `DEADLINE_EXCEEDED`: The execution timed out.
  // * `CANCELLED`: The operation was cancelled by the client. This status is
  //   only possible if the server implements the Operations API CancelOperation
  //   method, and it was called for the current execution.
  //
  // In the case of a missing input or command, the server SHOULD additionally
  // send a [PreconditionFailure][google.rpc.PreconditionFailure] error detail
  // where, for each requested blob not present in the CAS, there is a
  // `Violation` with a `type` of `MISSING` and a `subject` of
  // `"blobs/{digest_function/}{hash}/{size}"` indicating the digest of the
  // missing blob. The `subject` is formatted the same way as the
  // `resource_name` provided to
  // [ByteStream.Read][google.bytestream.ByteStream.Read], with the leading
  // instance name omitted. `digest_function` MUST thus be omitted if its value
  // is one of MD5, MURMUR3, SHA1, SHA256, SHA384, SHA512, or VSO.
  //
  // The server does not need to guarantee that a call to this method leads to
  // at most one execution of the action. The server MAY execute the action
  // multiple times, potentially in parallel. These redundant executions MAY
  // continue to run, even if the operation is completed.
  rpc Execute(ExecuteRequest) returns (stream google.longrunning.Operation) {
    option (google.api.http) = { post: "/v2/{instance_name=**}/actions:execute" body: "*" };
  }

  // Wait for an execution operation to complete. When the client initially
  // makes the request, the server immediately responds with the current status
  // of the execution. The server will leave the request stream open until the
  // operation completes, and then respond with the completed operation. The
  // server MAY choose to stream additional updates as execution progresses,
  // such as to provide an update as to the state of the execution.
  rpc WaitExecution(WaitExecutionRequest) returns (stream google.longrunning.Operation) {
    option (google.api.http) = { post: "/v2/{name=operations/**}:waitExecution" body: "*" };
  }
}

// The action cache API is used to query whether a given action has already been
// performed and, if so, retrieve its result. Unlike the
// [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage],
// which addresses blobs by their own content, the action cache addresses the
// [ActionResult][build.bazel.remote.execution.v2.ActionResult] by a
// digest of the encoded [Action][build.bazel.remote.execution.v2.Action]
// which produced them.
//
// The lifetime of entries in the action cache is implementation-specific, but
// the server SHOULD assume that more recently used entries are more likely to
// be used again.
//
// As with other services in the Remote Execution API, any call may return an
// error with a [RetryInfo][google.rpc.RetryInfo] error detail providing
// information about when the client should retry the request; clients SHOULD
// respect the information provided.
service ActionCache {
  // Retrieve a cached execution result.
  //
  // Implementations SHOULD ensure that any blobs referenced from the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage]
  // are available at the time of returning the
  // [ActionResult][build.bazel.remote.execution.v2.ActionResult] and will be
  // for some period of time afterwards. The lifetimes of the referenced blobs SHOULD be increased
  // if necessary and applicable.
  //
  // Errors:
  //
  // * `NOT_FOUND`: The requested `ActionResult` is not in the cache.
  rpc GetActionResult(GetActionResultRequest) returns (ActionResult) {
    option (google.api.http) = { get: "/v2/{instance_name=**}/actionResults/{action_digest.hash}/{action_digest.size_bytes}" };
  }

  // Upload a new execution result.
  //
  // In order to allow the server to perform access control based on the type of
  // action, and to assist with client debugging, the client MUST first upload
  // the [Action][build.bazel.remote.execution.v2.Execution] that produced the
  // result, along with its
  // [Command][build.bazel.remote.execution.v2.Command], into the
  // `ContentAddressableStorage`.
  //
  // Server implementations MAY modify the
  // `UpdateActionResultRequest.action_result` and return an equivalent value.
  //
  // Errors:
  //
  // * `INVALID_ARGUMENT`: One or more arguments are invalid.
  // * `FAILED_PRECONDITION`: One or more errors occurred in updating the
  //   action result, such as a missing command or action.
  // * `RESOURCE_EXHAUSTED`: There is insufficient storage space to add the
  //   entry to the cache.
  rpc UpdateActionResult(UpdateActionResultRequest) returns (ActionResult) {
    option (google.api.http) = { put: "/v2/{instance_name=**}/actionResults/{action_digest.hash}/{action_digest.size_bytes}" body: "action_result" };
  }
}

// The CAS (content-addressable storage) is used to store the inputs to and
// outputs from the execution service. Each piece of content is addressed by the
// digest of its binary data.
//
// Most of the binary data stored in the CAS is opaque to the execution engine,
// and is only used as a communication medium. In order to build an
// [Action][build.bazel.remote.execution.v2.Action],
// however, the client will need to also upload the
// [Command][build.bazel.remote.execution.v2.Command] and input root
// [Directory][build.bazel.remote.execution.v2.Directory] for the Action.
// The Command and Directory messages must be marshalled to wire format and then
// uploaded under the hash as with any other piece of content. In practice, the
// input root directory is likely to refer to other Directories in its
// hierarchy, which must also each be uploaded on their own.
//
// For small file uploads the client should group them together and call
// [BatchUpdateBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchUpdateBlobs].
//
// For large uploads, the client must use the
// [Write method][google.bytestream.ByteStream.Write] of the ByteStream API.
//
// For uncompressed data, The `WriteRequest.resource_name` is of the following form:
// `{instance_name}/uploads/{uuid}/blobs/{digest_function/}{hash}/{size}{/optional_metadata}`
//
// Where:
// * `instance_name` is an identifier, possibly containing multiple path
//   segments, used to distinguish between the various instances on the server,
//   in a manner defined by the server. If it is the empty path, the leading
//   slash is omitted, so that  the `resource_name` becomes
//   `uploads/{uuid}/blobs/{digest_function/}{hash}/{size}{/optional_metadata}`.
//   To simplify parsing, a path segment cannot equal any of the following
//   keywords: `blobs`, `uploads`, `actions`, `actionResults`, `operations`,
//   `capabilities` or `compressed-blobs`.
// * `uuid` is a version 4 UUID generated by the client, used to avoid
//   collisions between concurrent uploads of the same data. Clients MAY
//   reuse the same `uuid` for uploading different blobs.
// * `digest_function` is a lowercase string form of a `DigestFunction.Value`
//   enum, indicating which digest function was used to compute `hash`. If the
//   digest function used is one of MD5, MURMUR3, SHA1, SHA256, SHA384, SHA512,
//   or VSO, this component MUST be omitted. In that case the server SHOULD
//   infer the digest function using the length of the `hash` and the digest
//   functions announced in the server's capabilities.
// * `hash` and `size` refer to the [Digest][build.bazel.remote.execution.v2.Digest]
//   of the data being uploaded.
// * `optional_metadata` is implementation specific data, which clients MAY omit.
//   Servers MAY ignore this metadata.
//
// Data can alternatively be uploaded in compressed form, with the following
// `WriteRequest.resource_name` form:
// `{instance_name}/uploads/{uuid}/compressed-blobs/{compressor}/{digest_function/}{uncompressed_hash}/{uncompressed_size}{/optional_metadata}`
//
// Where:
// * `instance_name`, `uuid`, `digest_function` and `optional_metadata` are
//   defined as above.
// * `compressor` is a lowercase string form of a `Compressor.Value` enum
//   other than `identity`, which is supported by the server and advertised in
//   [CacheCapabilities.supported_compressor][build.bazel.remote.execution.v2.CacheCapabilities.supported_compressor].
// * `uncompressed_hash` and `uncompressed_size` refer to the
//   [Digest][build.bazel.remote.execution.v2.Digest] of the data being
//   uploaded, once uncompressed. Servers MUST verify that these match
//   the uploaded data once uncompressed, and MUST return an
//   `INVALID_ARGUMENT` error in the case of mismatch.
//
// Note that when writing compressed blobs, the `WriteRequest.write_offset` in
// the initial request in a stream refers to the offset in the uncompressed form
// of the blob. In subsequent requests, `WriteRequest.write_offset` MUST be the
// sum of the first request's 'WriteRequest.write_offset' and the total size of
// all the compressed data bundles in the previous requests.
// Note that this mixes an uncompressed offset with a compressed byte length,
// which is nonsensical, but it is done to fit the semantics of the existing
// ByteStream protocol.
//
// Uploads of the same data MAY occur concurrently in any form, compressed or
// uncompressed.
//
// Clients SHOULD NOT use gRPC-level compression for ByteStream API `Write`
// calls of compressed blobs, since this would compress already-compressed data.
//
// When attempting an upload, if another client has already completed the upload
// (which may occur in the middle of a single upload if another client uploads
// the same blob concurrently), the request will terminate immediately without
// error, and with a response whose `committed_size` is the value `-1` if this
// is a compressed upload, or with the full size of the uploaded file if this is
// an uncompressed upload (regardless of how much data was transmitted by the
// client). If the client completes the upload but the
// [Digest][build.bazel.remote.execution.v2.Digest] does not match, an
// `INVALID_ARGUMENT` error will be returned. In either case, the client should
// not attempt to retry the upload.
//
// Small downloads can be grouped and requested in a batch via
// [BatchReadBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchReadBlobs].
//
// For large downloads, the client must use the
// [Read method][google.bytestream.ByteStream.Read] of the ByteStream API.
//
// For uncompressed data, The `ReadRequest.resource_name` is of the following form:
// `{instance_name}/blobs/{digest_function/}{hash}/{size}`
// Where `instance_name`, `digest_function`, `hash` and `size` are defined as
// for uploads.
//
// Data can alternatively be downloaded in compressed form, with the following
// `ReadRequest.resource_name` form:
// `{instance_name}/compressed-blobs/{compressor}/{digest_function/}{uncompressed_hash}/{uncompressed_size}`
//
// Where:
// * `instance_name`, `compressor` and `digest_function` are defined as for
//   uploads.
// * `uncompressed_hash` and `uncompressed_size` refer to the
//   [Digest][build.bazel.remote.execution.v2.Digest] of the data being
//   downloaded, once uncompressed. Clients MUST verify that these match
//   the downloaded data once uncompressed, and take appropriate steps in
//   the case of failure such as retrying a limited number of times or
//   surfacing an error to the user.
//
// When downloading compressed blobs:
// * `ReadRequest.read_offset` refers to the offset in the uncompressed form
//   of the blob.
// * Servers MUST return `INVALID_ARGUMENT` if `ReadRequest.read_limit` is
//   non-zero.
// * Servers MAY use any compression level they choose, including different
//   levels for different blobs (e.g. choosing a level designed for maximum
//   speed for data known to be incompressible).
// * Clients SHOULD NOT use gRPC-level compression, since this would compress
//   already-compressed data.
//
// Servers MUST be able to provide data for all recently advertised blobs in
// each of the compression formats that the server supports, as well as in
// uncompressed form.
//
// The lifetime of entries in the CAS is implementation specific, but it SHOULD
// be long enough to allow for newly-added and recently looked-up entries to be
// used in subsequent calls (e.g. to
// [Execute][build.bazel.remote.execution.v2.Execution.Execute]).
//
// Servers MUST behave as though empty blobs are always available, even if they
// have not been uploaded. Clients MAY optimize away the uploading or
// downloading of empty blobs.
//
// As with other services in the Remote Execution API, any call may return an
// error with a [RetryInfo][google.rpc.RetryInfo] error detail providing
// information about when the client should retry the request; clients SHOULD
// respect the information provided.
service ContentAddressableStorage {
  // Determine if blobs are present in the CAS.
  //
  // Clients can use this API before uploading blobs to determine which ones are
  // already present in the CAS and do not need to be uploaded again.
  //
  // Servers SHOULD increase the lifetimes of the referenced blobs if necessary and
  // applicable.
  //
  // There are no method-specific errors.
  rpc FindMissingBlobs(FindMissingBlobsRequest) returns (FindMissingBlobsResponse) {
    option (google.api.http) = { post: "/v2/{instance_name=**}/blobs:findMissing" body: "*" };
  }

  // Upload many blobs at once.
  //
  // The server may enforce a limit of the combined total size of blobs
  // to be uploaded using this API. This limit may be obtained using the
  // [Capabilities][build.bazel.remote.execution.v2.Capabilities] API.
  // Requests exceeding the limit should either be split into smaller
  // chunks or uploaded using the
  // [ByteStream API][google.bytestream.ByteStream], as appropriate.
  //
  // This request is equivalent to calling a Bytestream `Write` request
  // on each individual blob, in parallel. The requests may succeed or fail
  // independently.
  //
  // Errors:
  //
  // * `INVALID_ARGUMENT`: The client attempted to upload more than the
  //   server supported limit.
  //
  // Individual requests may return the following errors, additionally:
  //
  // * `RESOURCE_EXHAUSTED`: There is insufficient disk quota to store the blob.
  // * `INVALID_ARGUMENT`: The
  // [Digest][build.bazel.remote.execution.v2.Digest] does not match the
  // provided data.
  rpc BatchUpdateBlobs(BatchUpdateBlobsRequest) returns (BatchUpdateBlobsResponse) {
    option (google.api.http) = { post: "/v2/{instance_name=**}/blobs:batchUpdate" body: "*" };
  }

  // Download many blobs at once.
  //
  // The server may enforce a limit of the combined total size of blobs
  // to be downloaded using this API. This limit may be obtained using the
  // [Capabilities][build.bazel.remote.execution.v2.Capabilities] API.
  // Requests exceeding the limit should either be split into smaller
  // chunks or downloaded using the
  // [ByteStream API][google.bytestream.ByteStream], as appropriate.
  //
  // This request is equivalent to calling a Bytestream `Read` request
  // on each individual blob, in parallel. The requests may succeed or fail
  // independently.
  //
  // Errors:
  //
  // * `INVALID_ARGUMENT`: The client attempted to read more than the
  //   server supported limit.
  //
  // Every error on individual read will be returned in the corresponding digest
  // status.
  rpc BatchReadBlobs(BatchReadBlobsRequest) returns (BatchReadBlobsResponse) {
    option (google.api.http) = { post: "/v2/{instance_name=**}/blobs:batchRead" body: "*" };
  }

  // Fetch the entire directory tree rooted at a node.
  //
  // This request must be targeted at a
  // [Directory][build.bazel.remote.execution.v2.Directory] stored in the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage]
  // (CAS). The server will enumerate the `Directory` tree recursively and
  // return every node descended from the root.
  //
  // The GetTreeRequest.page_token parameter can be used to skip ahead in
  // the stream (e.g. when retrying a partially completed and aborted request),
  // by setting it to a value taken from GetTreeResponse.next_page_token of the
  // last successfully processed GetTreeResponse).
  //
  // The exact traversal order is unspecified and, unless retrieving subsequent
  // pages from an earlier request, is not guaranteed to be stable across
  // multiple invocations of `GetTree`.
  //
  // If part of the tree is missing from the CAS, the server will return the
  // portion present and omit the rest.
  //
  // Errors:
  //
  // * `NOT_FOUND`: The requested tree root is not present in the CAS.
  rpc GetTree(GetTreeRequest) returns (stream GetTreeResponse) {
    option (google.api.http) = { get: "/v2/{instance_name=**}/blobs/{root_digest.hash}/{root_digest.size_bytes}:getTree" };
  }
}

// The Capabilities service may be used by remote execution clients to query
// various server properties, in order to self-configure or return meaningful
// error messages.
//
// The query may include a particular `instance_name`, in which case the values
// returned will pertain to that instance.
service Capabilities {
  // GetCapabilities returns the server capabilities configuration of the
  // remote endpoint.
  // Only the capabilities of the services supported by the endpoint will
  // be returned:
  // * Execution + CAS + Action Cache endpoints should return both
  //   CacheCapabilities and ExecutionCapabilities.
  // * Execution only endpoints should return ExecutionCapabilities.
  // * CAS + Action Cache only endpoints should return CacheCapabilities.
  //
  // There are no method-specific errors.
  rpc GetCapabilities(GetCapabilitiesRequest) returns (ServerCapabilities) {
    option (google.api.http) = {
      get: "/v2/{instance_name=**}/capabilities"
    };
  }
}

// An `Action` captures all the information about an execution which is required
// to reproduce it.
//
// `Action`s are the core component of the [Execution] service. A single
// `Action` represents a repeatable action that can be performed by the
// execution service. `Action`s can be succinctly identified by the digest of
// their wire format encoding and, once an `Action` has been executed, will be
// cached in the action cache. Future requests can then use the cached result
// rather than needing to run afresh.
//
// When a server completes execution of an
// [Action][build.bazel.remote.execution.v2.Action], it MAY choose to
// cache the [result][build.bazel.remote.execution.v2.ActionResult] in
// the [ActionCache][build.bazel.remote.execution.v2.ActionCache] unless
// `do_not_cache` is `true`. Clients SHOULD expect the server to do so. By
// default, future calls to
// [Execute][build.bazel.remote.execution.v2.Execution.Execute] the same
// `Action` will also serve their results from the cache. Clients must take care
// to understand the caching behaviour. Ideally, all `Action`s will be
// reproducible so that serving a result from cache is always desirable and
// correct.
message Action {
  // The digest of the [Command][build.bazel.remote.execution.v2.Command]
  // to run, which MUST be present in the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage].
  Digest command_digest = 1;

  // The digest of the root
  // [Directory][build.bazel.remote.execution.v2.Directory] for the input
  // files. The files in the directory tree are available in the correct
  // location on the build machine before the command is executed. The root
  // directory, as well as every subdirectory and content blob referred to, MUST
  // be in the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage].
  Digest input_root_digest = 2;

  reserved 3 to 5; // Used for fields moved to [Command][build.bazel.remote.execution.v2.Command].

  // A timeout after which the execution should be killed. If the timeout is
  // absent, then the client is specifying that the execution should continue
  // as long as the server will let it. The server SHOULD impose a timeout if
  // the client does not specify one, however, if the client does specify a
  // timeout that is longer than the server's maximum timeout, the server MUST
  // reject the request.
  //
  // The timeout is only intended to cover the "execution" of the specified
  // action and not time in queue nor any overheads before or after execution
  // such as marshalling inputs/outputs. The server SHOULD avoid including time
  // spent the client doesn't have control over, and MAY extend or reduce the
  // timeout to account for delays or speedups that occur during execution
  // itself (e.g., lazily loading data from the Content Addressable Storage,
  // live migration of virtual machines, emulation overhead).
  //
  // The timeout is a part of the
  // [Action][build.bazel.remote.execution.v2.Action] message, and
  // therefore two `Actions` with different timeouts are different, even if they
  // are otherwise identical. This is because, if they were not, running an
  // `Action` with a lower timeout than is required might result in a cache hit
  // from an execution run with a longer timeout, hiding the fact that the
  // timeout is too short. By encoding it directly in the `Action`, a lower
  // timeout will result in a cache miss and the execution timeout will fail
  // immediately, rather than whenever the cache entry gets evicted.
  google.protobuf.Duration timeout = 6;

  // If true, then the `Action`'s result cannot be cached, and in-flight
  // requests for the same `Action` may not be merged.
  bool do_not_cache = 7;

  reserved 8; // Used for field moved to [Command][build.bazel.remote.execution.v2.Command].

  // An optional additional salt value used to place this `Action` into a
  // separate cache namespace from other instances having the same field
  // contents. This salt typically comes from operational configuration
  // specific to sources such as repo and service configuration,
  // and allows disowning an entire set of ActionResults that might have been
  // poisoned by buggy software or tool failures.
  bytes salt = 9;

  // The optional platform requirements for the execution environment. The
  // server MAY choose to execute the action on any worker satisfying the
  // requirements, so the client SHOULD ensure that running the action on any
  // such worker will have the same result.  A detailed lexicon for this can be
  // found in the accompanying platform.md.
  // New in version 2.2: clients SHOULD set these platform properties as well
  // as those in the [Command][build.bazel.remote.execution.v2.Command]. Servers
  // SHOULD prefer those set here.
  Platform platform = 10;
}

// A `Command` is the actual command executed by a worker running an
// [Action][build.bazel.remote.execution.v2.Action] and specifications of its
// environment.
//
// Except as otherwise required, the environment (such as which system
// libraries or binaries are available, and what filesystems are mounted where)
// is defined by and specific to the implementation of the remote execution API.
message Command {
  // An `EnvironmentVariable` is one variable to set in the running program's
  // environment.
  message EnvironmentVariable {
    // The variable name.
    string name = 1;

    // The variable value.
    string value = 2;
  }

  // The arguments to the command.
  //
  // The first argument specifies the command to run, which may be either an
  // absolute path, a path relative to the working directory, or an unqualified
  // path (without path separators) which will be resolved using the operating
  // system's equivalent of the PATH environment variable. Path separators
  // native to the operating system running on the worker SHOULD be used. If the
  // `environment_variables` list contains an entry for the PATH environment
  // variable, it SHOULD be respected. If not, the resolution process is
  // implementation-defined.
  //
  // Changed in v2.3. v2.2 and older require that no PATH lookups are performed,
  // and that relative paths are resolved relative to the input root. This
  // behavior can, however, not be relied upon, as most implementations already
  // followed the rules described above.
  repeated string arguments = 1;

  // The environment variables to set when running the program. The worker may
  // provide its own default environment variables; these defaults can be
  // overridden using this field. Additional variables can also be specified.
  //
  // In order to ensure that equivalent
  // [Command][build.bazel.remote.execution.v2.Command]s always hash to the same
  // value, the environment variables MUST be lexicographically sorted by name.
  // Sorting of strings is done by code point, equivalently, by the UTF-8 bytes.
  repeated EnvironmentVariable environment_variables = 2;

  // A list of the output files that the client expects to retrieve from the
  // action. Only the listed files, as well as directories listed in
  // `output_directories`, will be returned to the client as output.
  // Other files or directories that may be created during command execution
  // are discarded.
  //
  // The paths are relative to the working directory of the action execution.
  // The paths are specified using a single forward slash (`/`) as a path
  // separator, even if the execution platform natively uses a different
  // separator. The path MUST NOT include a trailing slash, nor a leading slash,
  // being a relative path.
  //
  // In order to ensure consistent hashing of the same Action, the output paths
  // MUST be sorted lexicographically by code point (or, equivalently, by UTF-8
  // bytes).
  //
  // An output file cannot be duplicated, be a parent of another output file, or
  // have the same path as any of the listed output directories.
  //
  // Directories leading up to the output files are created by the worker prior
  // to execution, even if they are not explicitly part of the input root.
  //
  // DEPRECATED since v2.1: Use `output_paths` instead.
  repeated string output_files = 3;

  // A list of the output directories that the client expects to retrieve from
  // the action. Only the listed directories will be returned (an entire
  // directory structure will be returned as a
  // [Tree][build.bazel.remote.execution.v2.Tree] message digest, see
  // [OutputDirectory][build.bazel.remote.execution.v2.OutputDirectory]), as
  // well as files listed in `output_files`. Other files or directories that
  // may be created during command execution are discarded.
  //
  // The paths are relative to the working directory of the action execution.
  // The paths are specified using a single forward slash (`/`) as a path
  // separator, even if the execution platform natively uses a different
  // separator. The path MUST NOT include a trailing slash, nor a leading slash,
  // being a relative path. The special value of empty string is allowed,
  // although not recommended, and can be used to capture the entire working
  // directory tree, including inputs.
  //
  // In order to ensure consistent hashing of the same Action, the output paths
  // MUST be sorted lexicographically by code point (or, equivalently, by UTF-8
  // bytes).
  //
  // An output directory cannot be duplicated or have the same path as any of
  // the listed output files. An output directory is allowed to be a parent of
  // another output directory.
  //
  // Directories leading up to the output directories (but not the output
  // directories themselves) are created by the worker prior to execution, even
  // if they are not explicitly part of the input root.
  //
  // DEPRECATED since 2.1: Use `output_paths` instead.
  repeated string output_directories = 4;

  // A list of the output paths that the client expects to retrieve from the
  // action. Only the listed paths will be returned to the client as output.
  // The type of the output (file or directory) is not specified, and will be
  // determined by the server after action execution. If the resulting path is
  // a file, it will be returned in an
  // [OutputFile][build.bazel.remote.execution.v2.OutputFile] typed field.
  // If the path is a directory, the entire directory structure will be returned
  // as a [Tree][build.bazel.remote.execution.v2.Tree] message digest, see
  // [OutputDirectory][build.bazel.remote.execution.v2.OutputDirectory]
  // Other files or directories that may be created during command execution
  // are discarded.
  //
  // The paths are relative to the working directory of the action execution.
  // The paths are specified using a single forward slash (`/`) as a path
  // separator, even if the execution platform natively uses a different
  // separator. The path MUST NOT include a trailing slash, nor a leading slash,
  // being a relative path.
  //
  // In order to ensure consistent hashing of the same Action, the output paths
  // MUST be deduplicated and sorted lexicographically by code point (or,
  // equivalently, by UTF-8 bytes).
  //
  // Directories leading up to the output paths are created by the worker prior
  // to execution, even if they are not explicitly part of the input root.
  //
  // New in v2.1: this field supersedes the DEPRECATED `output_files` and
  // `output_directories` fields. If `output_paths` is used, `output_files` and
  // `output_directories` will be ignored!
  repeated string output_paths = 7;

  // The platform requirements for the execution environment. The server MAY
  // choose to execute the action on any worker satisfying the requirements, so
  // the client SHOULD ensure that running the action on any such worker will
  // have the same result.  A detailed lexicon for this can be found in the
  // accompanying platform.md.
  // DEPRECATED as of v2.2: platform properties are now specified directly in
  // the action. See documentation note in the
  // [Action][build.bazel.remote.execution.v2.Action] for migration.
  Platform platform = 5;

  // The working directory, relative to the input root, for the command to run
  // in. It must be a directory which exists in the input tree. If it is left
  // empty, then the action is run in the input root.
  string working_directory = 6;

  // A list of keys for node properties the client expects to retrieve for
  // output files and directories. Keys are either names of string-based
  // [NodeProperty][build.bazel.remote.execution.v2.NodeProperty] or
  // names of fields in [NodeProperties][build.bazel.remote.execution.v2.NodeProperties].
  // In order to ensure that equivalent `Action`s always hash to the same
  // value, the node properties MUST be lexicographically sorted by name.
  // Sorting of strings is done by code point, equivalently, by the UTF-8 bytes.
  //
  // The interpretation of string-based properties is server-dependent. If a
  // property is not recognized by the server, the server will return an
  // `INVALID_ARGUMENT`.
  repeated string output_node_properties = 8;
}

// A `Platform` is a set of requirements, such as hardware, operating system, or
// compiler toolchain, for an
// [Action][build.bazel.remote.execution.v2.Action]'s execution
// environment. A `Platform` is represented as a series of key-value pairs
// representing the properties that are required of the platform.
message Platform {
  // A single property for the environment. The server is responsible for
  // specifying the property `name`s that it accepts. If an unknown `name` is
  // provided in the requirements for an
  // [Action][build.bazel.remote.execution.v2.Action], the server SHOULD
  // reject the execution request. If permitted by the server, the same `name`
  // may occur multiple times.
  //
  // The server is also responsible for specifying the interpretation of
  // property `value`s. For instance, a property describing how much RAM must be
  // available may be interpreted as allowing a worker with 16GB to fulfill a
  // request for 8GB, while a property describing the OS environment on which
  // the action must be performed may require an exact match with the worker's
  // OS.
  //
  // The server MAY use the `value` of one or more properties to determine how
  // it sets up the execution environment, such as by making specific system
  // files available to the worker.
  //
  // Both names and values are typically case-sensitive. Note that the platform
  // is implicitly part of the action digest, so even tiny changes in the names
  // or values (like changing case) may result in different action cache
  // entries.
  message Property {
    // The property name.
    string name = 1;

    // The property value.
    string value = 2;
  }

  // The properties that make up this platform. In order to ensure that
  // equivalent `Platform`s always hash to the same value, the properties MUST
  // be lexicographically sorted by name, and then by value. Sorting of strings
  // is done by code point, equivalently, by the UTF-8 bytes.
  repeated Property properties = 1;
}

// A `Directory` represents a directory node in a file tree, containing zero or
// more children [FileNodes][build.bazel.remote.execution.v2.FileNode],
// [DirectoryNodes][build.bazel.remote.execution.v2.DirectoryNode] and
// [SymlinkNodes][build.bazel.remote.execution.v2.SymlinkNode].
// Each `Node` contains its name in the directory, either the digest of its
// content (either a file blob or a `Directory` proto) or a symlink target, as
// well as possibly some metadata about the file or directory.
//
// In order to ensure that two equivalent directory trees hash to the same
// value, the following restrictions MUST be obeyed when constructing a
// a `Directory`:
//
// * Every child in the directory must have a path of exactly one segment.
//   Multiple levels of directory hierarchy may not be collapsed.
// * Each child in the directory must have a unique path segment (file name).
//   Note that while the API itself is case-sensitive, the environment where
//   the Action is executed may or may not be case-sensitive. That is, it is
//   legal to call the API with a Directory that has both "Foo" and "foo" as
//   children, but the Action may be rejected by the remote system upon
//   execution.
// * The files, directories and symlinks in the directory must each be sorted
//   in lexicographical order by path. The path strings must be sorted by code
//   point, equivalently, by UTF-8 bytes.
// * The [NodeProperties][build.bazel.remote.execution.v2.NodeProperty] of files,
//   directories, and symlinks must be sorted in lexicographical order by
//   property name.
//
// A `Directory` that obeys the restrictions is said to be in canonical form.
//
// As an example, the following could be used for a file named `bar` and a
// directory named `foo` with an executable file named `baz` (hashes shortened
// for readability):
//
// ```json
// // (Directory proto)
// {
//   files: [
//     {
//       name: "bar",
//       digest: {
//         hash: "4a73bc9d03...",
//         size: 65534
//       },
//       node_properties: [
//         {
//           "name": "MTime",
//           "value": "2017-01-15T01:30:15.01Z"
//         }
//       ]
//     }
//   ],
//   directories: [
//     {
//       name: "foo",
//       digest: {
//         hash: "4cf2eda940...",
//         size: 43
//       }
//     }
//   ]
// }
//
// // (Directory proto with hash "4cf2eda940..." and size 43)
// {
//   files: [
//     {
//       name: "baz",
//       digest: {
//         hash: "b2c941073e...",
//         size: 1294,
//       },
//       is_executable: true
//     }
//   ]
// }
// ```
message Directory {
  // The files in the directory.
  repeated FileNode files = 1;

  // The subdirectories in the directory.
  repeated DirectoryNode directories = 2;

  // The symlinks in the directory.
  repeated SymlinkNode symlinks = 3;

  // The node properties of the Directory.
  reserved 4;
  NodeProperties node_properties = 5;
}

// A single property for [FileNodes][build.bazel.remote.execution.v2.FileNode],
// [DirectoryNodes][build.bazel.remote.execution.v2.DirectoryNode], and
// [SymlinkNodes][build.bazel.remote.execution.v2.SymlinkNode]. The server is
// responsible for specifying the property `name`s that it accepts. If
// permitted by the server, the same `name` may occur multiple times.
message NodeProperty {
    // The property name.
    string name = 1;

    // The property value.
    string value = 2;
}

// Node properties for [FileNodes][build.bazel.remote.execution.v2.FileNode],
// [DirectoryNodes][build.bazel.remote.execution.v2.DirectoryNode], and
// [SymlinkNodes][build.bazel.remote.execution.v2.SymlinkNode]. The server is
// responsible for specifying the properties that it accepts.
//
message NodeProperties {
  // A list of string-based
  // [NodeProperties][build.bazel.remote.execution.v2.NodeProperty].
  repeated NodeProperty properties = 1;

  // The file's last modification timestamp.
  google.protobuf.Timestamp mtime = 2;

  // The UNIX file mode, e.g., 0755.
  google.protobuf.UInt32Value unix_mode = 3;
}

// A `FileNode` represents a single file and associated metadata.
message FileNode {
  // The name of the file.
  string name = 1;

  // The digest of the file's content.
  Digest digest = 2;

  reserved 3; // Reserved to ensure wire-compatibility with `OutputFile`.

  // True if file is executable, false otherwise.
  bool is_executable = 4;

  // The node properties of the FileNode.
  reserved 5;
  NodeProperties node_properties = 6;
}

// A `DirectoryNode` represents a child of a
// [Directory][build.bazel.remote.execution.v2.Directory] which is itself
// a `Directory` and its associated metadata.
message DirectoryNode {
  // The name of the directory.
  string name = 1;

  // The digest of the
  // [Directory][build.bazel.remote.execution.v2.Directory] object
  // represented. See [Digest][build.bazel.remote.execution.v2.Digest]
  // for information about how to take the digest of a proto message.
  Digest digest = 2;
}

// A `SymlinkNode` represents a symbolic link.
message SymlinkNode {
  // The name of the symlink.
  string name = 1;

  // The target path of the symlink. The path separator is a forward slash `/`.
  // The target path can be relative to the parent directory of the symlink or
  // it can be an absolute path starting with `/`. Support for absolute paths
  // can be checked using the [Capabilities][build.bazel.remote.execution.v2.Capabilities]
  // API. `..` components are allowed anywhere in the target path as logical
  // canonicalization may lead to different behavior in the presence of
  // directory symlinks (e.g. `foo/../bar` may not be the same as `bar`).
  // To reduce potential cache misses, canonicalization is still recommended
  // where this is possible without impacting correctness.
  string target = 2;

  // The node properties of the SymlinkNode.
  reserved 3;
  NodeProperties node_properties = 4;
}

// A content digest. A digest for a given blob consists of the size of the blob
// and its hash. The hash algorithm to use is defined by the server.
//
// The size is considered to be an integral part of the digest and cannot be
// separated. That is, even if the `hash` field is correctly specified but
// `size_bytes` is not, the server MUST reject the request.
//
// The reason for including the size in the digest is as follows: in a great
// many cases, the server needs to know the size of the blob it is about to work
// with prior to starting an operation with it, such as flattening Merkle tree
// structures or streaming it to a worker. Technically, the server could
// implement a separate metadata store, but this results in a significantly more
// complicated implementation as opposed to having the client specify the size
// up-front (or storing the size along with the digest in every message where
// digests are embedded). This does mean that the API leaks some implementation
// details of (what we consider to be) a reasonable server implementation, but
// we consider this to be a worthwhile tradeoff.
//
// When a `Digest` is used to refer to a proto message, it always refers to the
// message in binary encoded form. To ensure consistent hashing, clients and
// servers MUST ensure that they serialize messages according to the following
// rules, even if there are alternate valid encodings for the same message:
//
// * Fields are serialized in tag order.
// * There are no unknown fields.
// * There are no duplicate fields.
// * Fields are serialized according to the default semantics for their type.
//
// Most protocol buffer implementations will always follow these rules when
// serializing, but care should be taken to avoid shortcuts. For instance,
// concatenating two messages to merge them may produce duplicate fields.
message Digest {
  // The hash. In the case of SHA-256, it will always be a lowercase hex string
  // exactly 64 characters long.
  string hash = 1;

  // The size of the blob, in bytes.
  int64 size_bytes = 2;
}

// ExecutedActionMetadata contains details about a completed execution.
message ExecutedActionMetadata {
  // The name of the worker which ran the execution.
  string worker = 1;

  // When was the action added to the queue.
  google.protobuf.Timestamp queued_timestamp = 2;

  // When the worker received the action.
  google.protobuf.Timestamp worker_start_timestamp = 3;

  // When the worker completed the action, including all stages.
  google.protobuf.Timestamp worker_completed_timestamp = 4;

  // When the worker started fetching action inputs.
  google.protobuf.Timestamp input_fetch_start_timestamp = 5;

  // When the worker finished fetching action inputs.
  google.protobuf.Timestamp input_fetch_completed_timestamp = 6;

  // When the worker started executing the action command.
  google.protobuf.Timestamp execution_start_timestamp = 7;

  // When the worker completed executing the action command.
  google.protobuf.Timestamp execution_completed_timestamp = 8;

  // New in v2.3: the amount of time the worker spent executing the action
  // command, potentially computed using a worker-specific virtual clock.
  //
  // The virtual execution duration is only intended to cover the "execution" of
  // the specified action and not time in queue nor any overheads before or
  // after execution such as marshalling inputs/outputs. The server SHOULD avoid
  // including time spent the client doesn't have control over, and MAY extend
  // or reduce the execution duration to account for delays or speedups that
  // occur during execution itself (e.g., lazily loading data from the Content
  // Addressable Storage, live migration of virtual machines, emulation
  // overhead).
  //
  // The method of timekeeping used to compute the virtual execution duration
  // MUST be consistent with what is used to enforce the
  // [Action][[build.bazel.remote.execution.v2.Action]'s `timeout`. There is no
  // relationship between the virtual execution duration and the values of
  // `execution_start_timestamp` and `execution_completed_timestamp`.
  google.protobuf.Duration virtual_execution_duration = 12;

  // When the worker started uploading action outputs.
  google.protobuf.Timestamp output_upload_start_timestamp = 9;

  // When the worker finished uploading action outputs.
  google.protobuf.Timestamp output_upload_completed_timestamp = 10;

  // Details that are specific to the kind of worker used. For example,
  // on POSIX-like systems this could contain a message with
  // getrusage(2) statistics.
  repeated google.protobuf.Any auxiliary_metadata = 11;
}

// An ActionResult represents the result of an
// [Action][build.bazel.remote.execution.v2.Action] being run.
//
// It is advised that at least one field (for example
// `ActionResult.execution_metadata.Worker`) have a non-default value, to
// ensure that the serialized value is non-empty, which can then be used
// as a basic data sanity check.
message ActionResult {
  reserved 1; // Reserved for use as the resource name.

  // The output files of the action. For each output file requested in the
  // `output_files` or `output_paths` field of the Action, if the corresponding
  // file existed after the action completed, a single entry will be present
  // either in this field, or the `output_file_symlinks` field if the file was
  // a symbolic link to another file (`output_symlinks` field after v2.1).
  //
  // If an output listed in `output_files` was found, but was a directory rather
  // than a regular file, the server will return a FAILED_PRECONDITION.
  // If the action does not produce the requested output, then that output
  // will be omitted from the list. The server is free to arrange the output
  // list as desired; clients MUST NOT assume that the output list is sorted.
  repeated OutputFile output_files = 2;

  // The output files of the action that are symbolic links to other files. Those
  // may be links to other output files, or input files, or even absolute paths
  // outside of the working directory, if the server supports
  // [SymlinkAbsolutePathStrategy.ALLOWED][build.bazel.remote.execution.v2.CacheCapabilities.SymlinkAbsolutePathStrategy].
  // For each output file requested in the `output_files` or `output_paths`
  // field of the Action, if the corresponding file existed after
  // the action completed, a single entry will be present either in this field,
  // or in the `output_files` field, if the file was not a symbolic link.
  //
  // If an output symbolic link of the same name as listed in `output_files` of
  // the Command was found, but its target type was not a regular file, the
  // server will return a FAILED_PRECONDITION.
  // If the action does not produce the requested output, then that output
  // will be omitted from the list. The server is free to arrange the output
  // list as desired; clients MUST NOT assume that the output list is sorted.
  //
  // DEPRECATED as of v2.1. Servers that wish to be compatible with v2.0 API
  // should still populate this field in addition to `output_symlinks`.
  repeated OutputSymlink output_file_symlinks = 10;

  // New in v2.1: this field will only be populated if the command
  // `output_paths` field was used, and not the pre v2.1 `output_files` or
  // `output_directories` fields.
  // The output paths of the action that are symbolic links to other paths. Those
  // may be links to other outputs, or inputs, or even absolute paths
  // outside of the working directory, if the server supports
  // [SymlinkAbsolutePathStrategy.ALLOWED][build.bazel.remote.execution.v2.CacheCapabilities.SymlinkAbsolutePathStrategy].
  // A single entry for each output requested in `output_paths`
  // field of the Action, if the corresponding path existed after
  // the action completed and was a symbolic link.
  //
  // If the action does not produce a requested output, then that output
  // will be omitted from the list. The server is free to arrange the output
  // list as desired; clients MUST NOT assume that the output list is sorted.
  repeated OutputSymlink output_symlinks = 12;

  // The output directories of the action. For each output directory requested
  // in the `output_directories` or `output_paths` field of the Action, if the
  // corresponding directory existed after the action completed, a single entry
  // will be present in the output list, which will contain the digest of a
  // [Tree][build.bazel.remote.execution.v2.Tree] message containing the
  // directory tree, and the path equal exactly to the corresponding Action
  // output_directories member.
  //
  // As an example, suppose the Action had an output directory `a/b/dir` and the
  // execution produced the following contents in `a/b/dir`: a file named `bar`
  // and a directory named `foo` with an executable file named `baz`. Then,
  // output_directory will contain (hashes shortened for readability):
  //
  // ```json
  // // OutputDirectory proto:
  // {
  //   path: "a/b/dir"
  //   tree_digest: {
  //     hash: "4a73bc9d03...",
  //     size: 55
  //   }
  // }
  // // Tree proto with hash "4a73bc9d03..." and size 55:
  // {
  //   root: {
  //     files: [
  //       {
  //         name: "bar",
  //         digest: {
  //           hash: "4a73bc9d03...",
  //           size: 65534
  //         }
  //       }
  //     ],
  //     directories: [
  //       {
  //         name: "foo",
  //         digest: {
  //           hash: "4cf2eda940...",
  //           size: 43
  //         }
  //       }
  //     ]
  //   }
  //   children : {
  //     // (Directory proto with hash "4cf2eda940..." and size 43)
  //     files: [
  //       {
  //         name: "baz",
  //         digest: {
  //           hash: "b2c941073e...",
  //           size: 1294,
  //         },
  //         is_executable: true
  //       }
  //     ]
  //   }
  // }
  // ```
  // If an output of the same name as listed in `output_files` of
  // the Command was found in `output_directories`, but was not a directory, the
  // server will return a FAILED_PRECONDITION.
  repeated OutputDirectory output_directories = 3;

  // The output directories of the action that are symbolic links to other
  // directories. Those may be links to other output directories, or input
  // directories, or even absolute paths outside of the working directory,
  // if the server supports
  // [SymlinkAbsolutePathStrategy.ALLOWED][build.bazel.remote.execution.v2.CacheCapabilities.SymlinkAbsolutePathStrategy].
  // For each output directory requested in the `output_directories` field of
  // the Action, if the directory existed after the action completed, a
  // single entry will be present either in this field, or in the
  // `output_directories` field, if the directory was not a symbolic link.
  //
  // If an output of the same name was found, but was a symbolic link to a file
  // instead of a directory, the server will return a FAILED_PRECONDITION.
  // If the action does not produce the requested output, then that output
  // will be omitted from the list. The server is free to arrange the output
  // list as desired; clients MUST NOT assume that the output list is sorted.
  //
  // DEPRECATED as of v2.1. Servers that wish to be compatible with v2.0 API
  // should still populate this field in addition to `output_symlinks`.
  repeated OutputSymlink output_directory_symlinks = 11;

  // The exit code of the command.
  int32 exit_code = 4;

  // The standard output buffer of the action. The server SHOULD NOT inline
  // stdout unless requested by the client in the
  // [GetActionResultRequest][build.bazel.remote.execution.v2.GetActionResultRequest]
  // message. The server MAY omit inlining, even if requested, and MUST do so if inlining
  // would cause the response to exceed message size limits.
  // Clients SHOULD NOT populate this field when uploading to the cache.
  bytes stdout_raw = 5;

  // The digest for a blob containing the standard output of the action, which
  // can be retrieved from the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage].
  Digest stdout_digest = 6;

  // The standard error buffer of the action. The server SHOULD NOT inline
  // stderr unless requested by the client in the
  // [GetActionResultRequest][build.bazel.remote.execution.v2.GetActionResultRequest]
  // message. The server MAY omit inlining, even if requested, and MUST do so if inlining
  // would cause the response to exceed message size limits.
  // Clients SHOULD NOT populate this field when uploading to the cache.
  bytes stderr_raw = 7;

  // The digest for a blob containing the standard error of the action, which
  // can be retrieved from the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage].
  Digest stderr_digest = 8;

  // The details of the execution that originally produced this result.
  ExecutedActionMetadata execution_metadata = 9;
}

// An `OutputFile` is similar to a
// [FileNode][build.bazel.remote.execution.v2.FileNode], but it is used as an
// output in an `ActionResult`. It allows a full file path rather than
// only a name.
message OutputFile {
  // The full path of the file relative to the working directory, including the
  // filename. The path separator is a forward slash `/`. Since this is a
  // relative path, it MUST NOT begin with a leading forward slash.
  string path = 1;

  // The digest of the file's content.
  Digest digest = 2;

  reserved 3; // Used for a removed field in an earlier version of the API.

  // True if file is executable, false otherwise.
  bool is_executable = 4;

  // The contents of the file if inlining was requested. The server SHOULD NOT inline
  // file contents unless requested by the client in the
  // [GetActionResultRequest][build.bazel.remote.execution.v2.GetActionResultRequest]
  // message. The server MAY omit inlining, even if requested, and MUST do so if inlining
  // would cause the response to exceed message size limits.
  // Clients SHOULD NOT populate this field when uploading to the cache.
  bytes contents = 5;

  // The supported node properties of the OutputFile, if requested by the Action.
  reserved 6;
  NodeProperties node_properties = 7;
}

// A `Tree` contains all the
// [Directory][build.bazel.remote.execution.v2.Directory] protos in a
// single directory Merkle tree, compressed into one message.
message Tree {
  // The root directory in the tree.
  Directory root = 1;

  // All the child directories: the directories referred to by the root and,
  // recursively, all its children. In order to reconstruct the directory tree,
  // the client must take the digests of each of the child directories and then
  // build up a tree starting from the `root`.
  // Servers SHOULD ensure that these are ordered consistently such that two
  // actions producing equivalent output directories on the same server
  // implementation also produce Tree messages with matching digests.
  repeated Directory children = 2;
}

// An `OutputDirectory` is the output in an `ActionResult` corresponding to a
// directory's full contents rather than a single file.
message OutputDirectory {
  // The full path of the directory relative to the working directory. The path
  // separator is a forward slash `/`. Since this is a relative path, it MUST
  // NOT begin with a leading forward slash. The empty string value is allowed,
  // and it denotes the entire working directory.
  string path = 1;

  reserved 2; // Used for a removed field in an earlier version of the API.

  // The digest of the encoded
  // [Tree][build.bazel.remote.execution.v2.Tree] proto containing the
  // directory's contents.
  Digest tree_digest = 3;

  // If set, consumers MAY make the following assumptions about the
  // directories contained in the the Tree, so that it may be
  // instantiated on a local file system by scanning through it
  // sequentially:
  //
  // - All directories with the same binary representation are stored
  //   exactly once.
  // - All directories, apart from the root directory, are referenced by
  //   at least one parent directory.
  // - Directories are stored in topological order, with parents being
  //   stored before the child. The root directory is thus the first to
  //   be stored.
  //
  // Additionally, the Tree MUST be encoded as a stream of records,
  // where each record has the following format:
  //
  // - A tag byte, having one of the following two values:
  //   - (1 << 3) | 2 == 0x0a: First record (the root directory).
  //   - (2 << 3) | 2 == 0x12: Any subsequent records (child directories).
  // - The size of the directory, encoded as a base 128 varint.
  // - The contents of the directory, encoded as a binary serialized
  //   Protobuf message.
  //
  // This encoding is a subset of the Protobuf wire format of the Tree
  // message. As it is only permitted to store data associated with
  // field numbers 1 and 2, the tag MUST be encoded as a single byte.
  // More details on the Protobuf wire format can be found here:
  // https://developers.google.com/protocol-buffers/docs/encoding
  //
  // It is recommended that implementations using this feature construct
  // Tree objects manually using the specification given above, as
  // opposed to using a Protobuf library to marshal a full Tree message.
  // As individual Directory messages already need to be marshaled to
  // compute their digests, constructing the Tree object manually avoids
  // redundant marshaling.
  bool is_topologically_sorted = 4;
}

// An `OutputSymlink` is similar to a
// [Symlink][build.bazel.remote.execution.v2.SymlinkNode], but it is used as an
// output in an `ActionResult`.
//
// `OutputSymlink` is binary-compatible with `SymlinkNode`.
message OutputSymlink {
  // The full path of the symlink relative to the working directory, including the
  // filename. The path separator is a forward slash `/`. Since this is a
  // relative path, it MUST NOT begin with a leading forward slash.
  string path = 1;

  // The target path of the symlink. The path separator is a forward slash `/`.
  // The target path can be relative to the parent directory of the symlink or
  // it can be an absolute path starting with `/`. Support for absolute paths
  // can be checked using the [Capabilities][build.bazel.remote.execution.v2.Capabilities]
  // API. `..` components are allowed anywhere in the target path.
  string target = 2;

  // The supported node properties of the OutputSymlink, if requested by the
  // Action.
  reserved 3;
  NodeProperties node_properties = 4;
}

// An `ExecutionPolicy` can be used to control the scheduling of the action.
message ExecutionPolicy {
  // The priority (relative importance) of this action. Generally, a lower value
  // means that the action should be run sooner than actions having a greater
  // priority value, but the interpretation of a given value is server-
  // dependent. A priority of 0 means the *default* priority. Priorities may be
  // positive or negative, and such actions should run later or sooner than
  // actions having the default priority, respectively. The particular semantics
  // of this field is up to the server. In particular, every server will have
  // their own supported range of priorities, and will decide how these map into
  // scheduling policy.
  int32 priority = 1;
}

// A `ResultsCachePolicy` is used for fine-grained control over how action
// outputs are stored in the CAS and Action Cache.
message ResultsCachePolicy {
  // The priority (relative importance) of this content in the overall cache.
  // Generally, a lower value means a longer retention time or other advantage,
  // but the interpretation of a given value is server-dependent. A priority of
  // 0 means a *default* value, decided by the server.
  //
  // The particular semantics of this field is up to the server. In particular,
  // every server will have their own supported range of priorities, and will
  // decide how these map into retention/eviction policy.
  int32 priority = 1;
}

// A request message for
// [Execution.Execute][build.bazel.remote.execution.v2.Execution.Execute].
message ExecuteRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // If true, the action will be executed even if its result is already
  // present in the [ActionCache][build.bazel.remote.execution.v2.ActionCache].
  // The execution is still allowed to be merged with other in-flight executions
  // of the same action, however - semantically, the service MUST only guarantee
  // that the results of an execution with this field set were not visible
  // before the corresponding execution request was sent.
  // Note that actions from execution requests setting this field set are still
  // eligible to be entered into the action cache upon completion, and services
  // SHOULD overwrite any existing entries that may exist. This allows
  // skip_cache_lookup requests to be used as a mechanism for replacing action
  // cache entries that reference outputs no longer available or that are
  // poisoned in any way.
  // If false, the result may be served from the action cache.
  bool skip_cache_lookup = 3;

  reserved 2, 4, 5; // Used for removed fields in an earlier version of the API.

  // The digest of the [Action][build.bazel.remote.execution.v2.Action] to
  // execute.
  Digest action_digest = 6;

  // An optional policy for execution of the action.
  // The server will have a default policy if this is not provided.
  ExecutionPolicy execution_policy = 7;

  // An optional policy for the results of this execution in the remote cache.
  // The server will have a default policy if this is not provided.
  // This may be applied to both the ActionResult and the associated blobs.
  ResultsCachePolicy results_cache_policy = 8;

  // The digest function that was used to compute the action digest.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the action digest hash and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 9;
}

// A `LogFile` is a log stored in the CAS.
message LogFile {
  // The digest of the log contents.
  Digest digest = 1;

  // This is a hint as to the purpose of the log, and is set to true if the log
  // is human-readable text that can be usefully displayed to a user, and false
  // otherwise. For instance, if a command-line client wishes to print the
  // server logs to the terminal for a failed action, this allows it to avoid
  // displaying a binary file.
  bool human_readable = 2;
}

// The response message for
// [Execution.Execute][build.bazel.remote.execution.v2.Execution.Execute],
// which will be contained in the [response
// field][google.longrunning.Operation.response] of the
// [Operation][google.longrunning.Operation].
message ExecuteResponse {
  // The result of the action.
  ActionResult result = 1;

  // True if the result was served from cache, false if it was executed.
  bool cached_result = 2;

  // If the status has a code other than `OK`, it indicates that the action did
  // not finish execution. For example, if the operation times out during
  // execution, the status will have a `DEADLINE_EXCEEDED` code. Servers MUST
  // use this field for errors in execution, rather than the error field on the
  // `Operation` object.
  //
  // If the status code is other than `OK`, then the result MUST NOT be cached.
  // For an error status, the `result` field is optional; the server may
  // populate the output-, stdout-, and stderr-related fields if it has any
  // information available, such as the stdout and stderr of a timed-out action.
  google.rpc.Status status = 3;

  // An optional list of additional log outputs the server wishes to provide. A
  // server can use this to return execution-specific logs however it wishes.
  // This is intended primarily to make it easier for users to debug issues that
  // may be outside of the actual job execution, such as by identifying the
  // worker executing the action or by providing logs from the worker's setup
  // phase. The keys SHOULD be human readable so that a client can display them
  // to a user.
  map<string, LogFile> server_logs = 4;

  // Freeform informational message with details on the execution of the action
  // that may be displayed to the user upon failure or when requested explicitly.
  string message = 5;
}

// The current stage of action execution.
//
// Even though these stages are numbered according to the order in which
// they generally occur, there is no requirement that the remote
// execution system reports events along this order. For example, an
// operation MAY transition from the EXECUTING stage back to QUEUED
// in case the hardware on which the operation executes fails.
//
// If and only if the remote execution system reports that an operation
// has reached the COMPLETED stage, it MUST set the [done
// field][google.longrunning.Operation.done] of the
// [Operation][google.longrunning.Operation] and terminate the stream.
message ExecutionStage {
  enum Value {
    // Invalid value.
    UNKNOWN = 0;

    // Checking the result against the cache.
    CACHE_CHECK = 1;

    // Currently idle, awaiting a free machine to execute.
    QUEUED = 2;

    // Currently being executed by a worker.
    EXECUTING = 3;

    // Finished execution.
    COMPLETED = 4;
  }
}

// Metadata about an ongoing
// [execution][build.bazel.remote.execution.v2.Execution.Execute], which
// will be contained in the [metadata
// field][google.longrunning.Operation.response] of the
// [Operation][google.longrunning.Operation].
message ExecuteOperationMetadata {
  // The current stage of execution.
  ExecutionStage.Value stage = 1;

  // The digest of the [Action][build.bazel.remote.execution.v2.Action]
  // being executed.
  Digest action_digest = 2;

  // If set, the client can use this resource name with
  // [ByteStream.Read][google.bytestream.ByteStream.Read] to stream the
  // standard output from the endpoint hosting streamed responses.
  string stdout_stream_name = 3;

  // If set, the client can use this resource name with
  // [ByteStream.Read][google.bytestream.ByteStream.Read] to stream the
  // standard error from the endpoint hosting streamed responses.
  string stderr_stream_name = 4;

  // The client can read this field to view details about the ongoing
  // execution.
  ExecutedActionMetadata partial_execution_metadata = 5;
}

// A request message for
// [WaitExecution][build.bazel.remote.execution.v2.Execution.WaitExecution].
message WaitExecutionRequest {
  // The name of the [Operation][google.longrunning.Operation]
  // returned by [Execute][build.bazel.remote.execution.v2.Execution.Execute].
  string name = 1;
}

// A request message for
// [ActionCache.GetActionResult][build.bazel.remote.execution.v2.ActionCache.GetActionResult].
message GetActionResultRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // The digest of the [Action][build.bazel.remote.execution.v2.Action]
  // whose result is requested.
  Digest action_digest = 2;

  // A hint to the server to request inlining stdout in the
  // [ActionResult][build.bazel.remote.execution.v2.ActionResult] message.
  bool inline_stdout = 3;

  // A hint to the server to request inlining stderr in the
  // [ActionResult][build.bazel.remote.execution.v2.ActionResult] message.
  bool inline_stderr = 4;

  // A hint to the server to inline the contents of the listed output files.
  // Each path needs to exactly match one file path in either `output_paths` or
  // `output_files` (DEPRECATED since v2.1) in the
  // [Command][build.bazel.remote.execution.v2.Command] message.
  repeated string inline_output_files = 5;

  // The digest function that was used to compute the action digest.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the action digest hash and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 6;
}

// A request message for
// [ActionCache.UpdateActionResult][build.bazel.remote.execution.v2.ActionCache.UpdateActionResult].
message UpdateActionResultRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // The digest of the [Action][build.bazel.remote.execution.v2.Action]
  // whose result is being uploaded.
  Digest action_digest = 2;

  // The [ActionResult][build.bazel.remote.execution.v2.ActionResult]
  // to store in the cache.
  ActionResult action_result = 3;

  // An optional policy for the results of this execution in the remote cache.
  // The server will have a default policy if this is not provided.
  // This may be applied to both the ActionResult and the associated blobs.
  ResultsCachePolicy results_cache_policy = 4;

  // The digest function that was used to compute the action digest.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the action digest hash and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 5;
}

// A request message for
// [ContentAddressableStorage.FindMissingBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.FindMissingBlobs].
message FindMissingBlobsRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // A list of the blobs to check. All digests MUST use the same digest
  // function.
  repeated Digest blob_digests = 2;

  // The digest function of the blobs whose existence is checked.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the blob digest hashes and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 3;
}

// A response message for
// [ContentAddressableStorage.FindMissingBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.FindMissingBlobs].
message FindMissingBlobsResponse {
  // A list of the blobs requested *not* present in the storage.
  repeated Digest missing_blob_digests = 2;
}

// A request message for
// [ContentAddressableStorage.BatchUpdateBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchUpdateBlobs].
message BatchUpdateBlobsRequest {
  // A request corresponding to a single blob that the client wants to upload.
  message Request {
    // The digest of the blob. This MUST be the digest of `data`. All
    // digests MUST use the same digest function.
    Digest digest = 1;

    // The raw binary data.
    bytes data = 2;

    // The format of `data`. Must be `IDENTITY`/unspecified, or one of the
    // compressors advertised by the 
    // [CacheCapabilities.supported_batch_compressors][build.bazel.remote.execution.v2.CacheCapabilities.supported_batch_compressors]
    // field.
    Compressor.Value compressor = 3;
  }

  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // The individual upload requests.
  repeated Request requests = 2;

  // The digest function that was used to compute the digests of the
  // blobs being uploaded.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the blob digest hashes and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 5;
}

// A response message for
// [ContentAddressableStorage.BatchUpdateBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchUpdateBlobs].
message BatchUpdateBlobsResponse {
  // A response corresponding to a single blob that the client tried to upload.
  message Response {
    // The blob digest to which this response corresponds.
    Digest digest = 1;

    // The result of attempting to upload that blob.
    google.rpc.Status status = 2;
  }

  // The responses to the requests.
  repeated Response responses = 1;
}

// A request message for
// [ContentAddressableStorage.BatchReadBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchReadBlobs].
message BatchReadBlobsRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // The individual blob digests. All digests MUST use the same digest
  // function.
  repeated Digest digests = 2;

  // A list of acceptable encodings for the returned inlined data, in no
  // particular order. `IDENTITY` is always allowed even if not specified here.
  repeated Compressor.Value acceptable_compressors = 3;

  // The digest function of the blobs being requested.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the blob digest hashes and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 4;
}

// A response message for
// [ContentAddressableStorage.BatchReadBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchReadBlobs].
message BatchReadBlobsResponse {
  // A response corresponding to a single blob that the client tried to download.
  message Response {
    // The digest to which this response corresponds.
    Digest digest = 1;

    // The raw binary data.
    bytes data = 2;

    // The format the data is encoded in. MUST be `IDENTITY`/unspecified,
    // or one of the acceptable compressors specified in the `BatchReadBlobsRequest`.
    Compressor.Value compressor = 4;

    // The result of attempting to download that blob.
    google.rpc.Status status = 3;
  }

  // The responses to the requests.
  repeated Response responses = 1;
}

// A request message for
// [ContentAddressableStorage.GetTree][build.bazel.remote.execution.v2.ContentAddressableStorage.GetTree].
message GetTreeRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;

  // The digest of the root, which must be an encoded
  // [Directory][build.bazel.remote.execution.v2.Directory] message
  // stored in the
  // [ContentAddressableStorage][build.bazel.remote.execution.v2.ContentAddressableStorage].
  Digest root_digest = 2;

  // A maximum page size to request. If present, the server will request no more
  // than this many items. Regardless of whether a page size is specified, the
  // server may place its own limit on the number of items to be returned and
  // require the client to retrieve more items using a subsequent request.
  int32 page_size = 3;

  // A page token, which must be a value received in a previous
  // [GetTreeResponse][build.bazel.remote.execution.v2.GetTreeResponse].
  // If present, the server will use that token as an offset, returning only
  // that page and the ones that succeed it.
  string page_token = 4;

  // The digest function that was used to compute the digest of the root
  // directory.
  //
  // If the digest function used is one of MD5, MURMUR3, SHA1, SHA256,
  // SHA384, SHA512, or VSO, the client MAY leave this field unset. In
  // that case the server SHOULD infer the digest function using the
  // length of the root digest hash and the digest functions announced
  // in the server's capabilities.
  DigestFunction.Value digest_function = 5;
}

// A response message for
// [ContentAddressableStorage.GetTree][build.bazel.remote.execution.v2.ContentAddressableStorage.GetTree].
message GetTreeResponse {
  // The directories descended from the requested root.
  repeated Directory directories = 1;

  // If present, signifies that there are more results which the client can
  // retrieve by passing this as the page_token in a subsequent
  // [request][build.bazel.remote.execution.v2.GetTreeRequest].
  // If empty, signifies that this is the last page of results.
  string next_page_token = 2;
}

// A request message for
// [Capabilities.GetCapabilities][build.bazel.remote.execution.v2.Capabilities.GetCapabilities].
message GetCapabilitiesRequest {
  // The instance of the execution system to operate against. A server may
  // support multiple instances of the execution system (with their own workers,
  // storage, caches, etc.). The server MAY require use of this field to select
  // between them in an implementation-defined fashion, otherwise it can be
  // omitted.
  string instance_name = 1;
}

// A response message for
// [Capabilities.GetCapabilities][build.bazel.remote.execution.v2.Capabilities.GetCapabilities].
message ServerCapabilities {
  // Capabilities of the remote cache system.
  CacheCapabilities cache_capabilities = 1;

  // Capabilities of the remote execution system.
  ExecutionCapabilities execution_capabilities = 2;

  // Earliest RE API version supported, including deprecated versions.
  build.bazel.semver.SemVer deprecated_api_version = 3;

  // Earliest non-deprecated RE API version supported.
  build.bazel.semver.SemVer low_api_version = 4;

  // Latest RE API version supported.
  build.bazel.semver.SemVer high_api_version = 5;
}

// The digest function used for converting values into keys for CAS and Action
// Cache.
message DigestFunction {
  enum Value {
    // It is an error for the server to return this value.
    UNKNOWN = 0;

    // The SHA-256 digest function.
    SHA256 = 1;

    // The SHA-1 digest function.
    SHA1 = 2;

    // The MD5 digest function.
    MD5 = 3;

    // The Microsoft "VSO-Hash" paged SHA256 digest function.
    // See https://github.com/microsoft/BuildXL/blob/master/Documentation/Specs/PagedHash.md .
    VSO = 4;

    // The SHA-384 digest function.
    SHA384 = 5;

    // The SHA-512 digest function.
    SHA512 = 6;

    // Murmur3 128-bit digest function, x64 variant. Note that this is not a
    // cryptographic hash function and its collision properties are not strongly guaranteed.
    // See https://github.com/aappleby/smhasher/wiki/MurmurHash3 .
    MURMUR3 = 7;

    // The SHA-256 digest function, modified to use a Merkle tree for
    // large objects. This permits implementations to store large blobs
    // as a decomposed sequence of 2^j sized chunks, where j >= 10,
    // while being able to validate integrity at the chunk level.
    //
    // Furthermore, on systems that do not offer dedicated instructions
    // for computing SHA-256 hashes (e.g., the Intel SHA and ARMv8
    // cryptographic extensions), SHA256TREE hashes can be computed more
    // efficiently than plain SHA-256 hashes by using generic SIMD
    // extensions, such as Intel AVX2 or ARM NEON.
    //
    // SHA256TREE hashes are computed as follows:
    //
    // - For blobs that are 1024 bytes or smaller, the hash is computed
    //   using the regular SHA-256 digest function.
    //
    // - For blobs that are more than 1024 bytes in size, the hash is
    //   computed as follows:
    //
    //   1. The blob is partitioned into a left (leading) and right
    //      (trailing) blob. These blobs have lengths m and n
    //      respectively, where m = 2^k and 0 < n <= m.
    //
    //   2. Hashes of the left and right blob, Hash(left) and
    //      Hash(right) respectively, are computed by recursively
    //      applying the SHA256TREE algorithm.
    //
    //   3. A single invocation is made to the SHA-256 block cipher with
    //      the following parameters:
    //
    //          M = Hash(left) || Hash(right)
    //          H = {
    //              0xcbbb9d5d, 0x629a292a, 0x9159015a, 0x152fecd8,
    //              0x67332667, 0x8eb44a87, 0xdb0c2e0d, 0x47b5481d,
    //          }
    //
    //      The values of H are the leading fractional parts of the
    //      square roots of the 9th to the 16th prime number (23 to 53).
    //      This differs from plain SHA-256, where the first eight prime
    //      numbers (2 to 19) are used, thereby preventing trivial hash
    //      collisions between small and large objects.
    //
    //   4. The hash of the full blob can then be obtained by
    //      concatenating the outputs of the block cipher:
    //
    //          Hash(blob) = a || b || c || d || e || f || g || h
    //
    //      Addition of the original values of H, as normally done
    //      through the use of the Davies-Meyer structure, is not
    //      performed. This isn't necessary, as the block cipher is only
    //      invoked once.
    //
    // Test vectors of this digest function can be found in the
    // accompanying sha256tree_test_vectors.txt file.
    SHA256TREE = 8;

    // The BLAKE3 hash function.
    // See https://github.com/BLAKE3-team/BLAKE3.
    BLAKE3 = 9;
  }
}

// Describes the server/instance capabilities for updating the action cache.
message ActionCacheUpdateCapabilities {
  bool update_enabled = 1;
}

// Allowed values for priority in
// [ResultsCachePolicy][build.bazel.remoteexecution.v2.ResultsCachePolicy] and
// [ExecutionPolicy][build.bazel.remoteexecution.v2.ResultsCachePolicy]
// Used for querying both cache and execution valid priority ranges.
message PriorityCapabilities {
  // Supported range of priorities, including boundaries.
  message PriorityRange {
    // The minimum numeric value for this priority range, which represents the
    // most urgent task or longest retained item.
    int32 min_priority = 1;
    // The maximum numeric value for this priority range, which represents the
    // least urgent task or shortest retained item.
    int32 max_priority = 2;
  }
  repeated PriorityRange priorities = 1;
}

// Describes how the server treats absolute symlink targets.
message SymlinkAbsolutePathStrategy {
  enum Value {
    // Invalid value.
    UNKNOWN = 0;

    // Server will return an `INVALID_ARGUMENT` on input symlinks with absolute
    // targets.
    // If an action tries to create an output symlink with an absolute target, a
    // `FAILED_PRECONDITION` will be returned.
    DISALLOWED = 1;

    // Server will allow symlink targets to escape the input root tree, possibly
    // resulting in non-hermetic builds.
    ALLOWED = 2;
  }
}

// Compression formats which may be supported.
message Compressor {
  enum Value {
    // No compression. Servers and clients MUST always support this, and do
    // not need to advertise it.
    IDENTITY = 0;

    // Zstandard compression.
    ZSTD = 1;

    // RFC 1951 Deflate. This format is identical to what is used by ZIP
    // files. Headers such as the one generated by gzip are not
    // included.
    //
    // It is advised to use algorithms such as Zstandard instead, as
    // those are faster and/or provide a better compression ratio.
    DEFLATE = 2;

    // Brotli compression.
    BROTLI = 3;
  }
}

// Capabilities of the remote cache system.
message CacheCapabilities {
  // All the digest functions supported by the remote cache.
  // Remote cache may support multiple digest functions simultaneously.
  repeated DigestFunction.Value digest_functions = 1;

  // Capabilities for updating the action cache.
  ActionCacheUpdateCapabilities action_cache_update_capabilities = 2;

  // Supported cache priority range for both CAS and ActionCache.
  PriorityCapabilities cache_priority_capabilities = 3;

  // Maximum total size of blobs to be uploaded/downloaded using
  // batch methods. A value of 0 means no limit is set, although
  // in practice there will always be a message size limitation
  // of the protocol in use, e.g. GRPC.
  int64 max_batch_total_size_bytes = 4;

  // Whether absolute symlink targets are supported.
  SymlinkAbsolutePathStrategy.Value symlink_absolute_path_strategy = 5;

  // Compressors supported by the "compressed-blobs" bytestream resources.
  // Servers MUST support identity/no-compression, even if it is not listed
  // here.
  //
  // Note that this does not imply which if any compressors are supported by
  // the server at the gRPC level.
  repeated Compressor.Value supported_compressors = 6;

  // Compressors supported for inlined data in
  // [BatchUpdateBlobs][build.bazel.remote.execution.v2.ContentAddressableStorage.BatchUpdateBlobs]
  // requests.
  repeated Compressor.Value supported_batch_update_compressors = 7;
}

// Capabilities of the remote execution system.
message ExecutionCapabilities {
  // Legacy field for indicating which digest function is supported by the
  // remote execution system. It MUST be set to a value other than UNKNOWN.
  // Implementations should consider the repeated digest_functions field
  // first, falling back to this singular field if digest_functions is unset.
  DigestFunction.Value digest_function = 1;

  // Whether remote execution is enabled for the particular server/instance.
  bool exec_enabled = 2;

  // Supported execution priority range.
  PriorityCapabilities execution_priority_capabilities = 3;

  // Supported node properties.
  repeated string supported_node_properties = 4;

  // All the digest functions supported by the remote execution system.
  // If this field is set, it MUST also contain digest_function.
  //
  // Even if the remote execution system announces support for multiple
  // digest functions, individual execution requests may only reference
  // CAS objects using a single digest function. For example, it is not
  // permitted to execute actions having both MD5 and SHA-256 hashed
  // files in their input root.
  //
  // The CAS objects referenced by action results generated by the
  // remote execution system MUST use the same digest function as the
  // one used to construct the action.
  repeated DigestFunction.Value digest_functions = 5;
}

// Details for the tool used to call the API.
message ToolDetails {
  // Name of the tool, e.g. bazel.
  string tool_name = 1;

  // Version of the tool used for the request, e.g. 5.0.3.
  string tool_version = 2;
}

// An optional Metadata to attach to any RPC request to tell the server about an
// external context of the request. The server may use this for logging or other
// purposes. To use it, the client attaches the header to the call using the
// canonical proto serialization:
//
// * name: `build.bazel.remote.execution.v2.requestmetadata-bin`
// * contents: the base64 encoded binary `RequestMetadata` message.
// Note: the gRPC library serializes binary headers encoded in base 64 by
// default (https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests).
// Therefore, if the gRPC library is used to pass/retrieve this
// metadata, the user may ignore the base64 encoding and assume it is simply
// serialized as a binary message.
message RequestMetadata {
  // The details for the tool invoking the requests.
  ToolDetails tool_details = 1;

  // An identifier that ties multiple requests to the same action.
  // For example, multiple requests to the CAS, Action Cache, and Execution
  // API are used in order to compile foo.cc.
  string action_id = 2;

  // An identifier that ties multiple actions together to a final result.
  // For example, multiple actions are required to build and run foo_test.
  string tool_invocation_id = 3;

  // An identifier to tie multiple tool invocations together. For example,
  // runs of foo_test, bar_test and baz_test on a post-submit of a given patch.
  string correlated_invocations_id = 4;

  // A brief description of the kind of action, for example, CppCompile or GoLink.
  // There is no standard agreed set of values for this, and they are expected to vary between different client tools.
  string action_mnemonic = 5;

  // An identifier for the target which produced this action.
  // No guarantees are made around how many actions may relate to a single target.
  string target_id = 6;

  // An identifier for the configuration in which the target was built,
  // e.g. for differentiating building host tools or different target platforms.
  // There is no expectation that this value will have any particular structure,
  // or equality across invocations, though some client tools may offer these guarantees.
  string configuration_id = 7;
}