// Copyright 2015 The Bazel Authors. All rights reserved.
//
// 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.

#include "src/main/tools/process-tools.h"

#include <errno.h>
#include <fcntl.h>
#include <math.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include <memory>

#include "src/main/protobuf/execution_statistics.pb.h"
#include "src/main/tools/logging.h"

static volatile sig_atomic_t child_pid_for_signal = 0;

int SwitchToEuid() {
  int uid = getuid();
  int euid = geteuid();
  if (uid != euid) {
    if (setreuid(euid, euid) < 0) {
      DIE("setreuid");
    }
  }
  return euid;
}

int SwitchToEgid() {
  int gid = getgid();
  int egid = getegid();
  if (gid != egid) {
    if (setregid(egid, egid) < 0) {
      DIE("setregid");
    }
  }
  return egid;
}

void Redirect(const std::string &target_path, int fd) {
  if (!target_path.empty() && target_path != "-") {
    const int flags = O_WRONLY | O_CREAT | O_TRUNC | O_APPEND;
    int fd_out = open(target_path.c_str(), flags, 0666);
    if (fd_out < 0) {
      DIE("open(%s)", target_path.c_str());
    }
    // If we were launched with less than 3 fds (stdin, stdout, stderr) open,
    // but redirection is still requested via a command-line flag, something is
    // wacky and the following code would not do what we intend to do, so let's
    // bail.
    if (fd_out < 3) {
      DIE("open(%s) returned a handle that is reserved for stdin / stdout / "
          "stderr",
          target_path.c_str());
    }
    if (dup2(fd_out, fd) < 0) {
      DIE("dup2");
    }
    if (close(fd_out) < 0) {
      DIE("close");
    }
  }
}

static void ForciblyKillEverything(int signo) {
  // We don't update the last_signal field tracked in process-wrapper-legacy.cc,
  // which is used to report the signal back to the user, because we want to
  // know (from the caller side) the original signal that caused us to stop.
  kill(-child_pid_for_signal, SIGKILL);
}

void KillEverything(pid_t pgrp, bool gracefully, double graceful_kill_delay) {
  if (gracefully) {
    // TODO(jmmv): If we truly want to offer graceful termination, we should
    // probably only send SIGTERM to the process group leader and allow it to
    // decide what to do. Terminating its subprocesses out of its control might
    // not have the right effect.
    kill(-pgrp, SIGTERM);

    // Previous versions of this code used to loop testing if the process had
    // already died by sending it a 0 signal... but that loop would never
    // terminate early because sending a signal to a zombie process succeeds
    // (and we cannot collect the child's exit status here).
    child_pid_for_signal = pgrp;
    InstallSignalHandler(SIGALRM, ForciblyKillEverything);
    SetTimeout(graceful_kill_delay);
  } else {
    kill(-pgrp, SIGKILL);
  }
}

void InstallSignalHandler(int signum, void (*handler)(int)) {
  struct sigaction sa = {};
  sa.sa_handler = handler;
  if (handler == SIG_IGN || handler == SIG_DFL) {
    // No point in blocking signals when using the default handler or ignoring
    // the signal.
    if (sigemptyset(&sa.sa_mask) < 0) {
      DIE("sigemptyset");
    }
  } else {
    // When using a custom handler, block all signals from firing while the
    // handler is running.
    if (sigfillset(&sa.sa_mask) < 0) {
      DIE("sigfillset");
    }
  }
  // sigaction may fail for certain reserved signals. Ignore failure in this
  // case, but report it in debug mode, just in case.
  if (sigaction(signum, &sa, nullptr) < 0) {
    PRINT_DEBUG("sigaction(%d, &sa, nullptr) failed", signum);
  }
}

void IgnoreSignal(int signum) {
  // These signals can't be handled, so we'll just not do anything for these.
  if (signum != SIGSTOP && signum != SIGKILL) {
    InstallSignalHandler(signum, SIG_IGN);
  }
}

void InstallDefaultSignalHandler(int signum) {
  // These signals can't be handled, so we'll just not do anything for these.
  if (signum != SIGSTOP && signum != SIGKILL) {
    InstallSignalHandler(signum, SIG_DFL);
  }
}

void ClearSignalMask() {
  // Use an empty signal mask for the process.
  sigset_t empty_sset;
  if (sigemptyset(&empty_sset) < 0) {
    DIE("sigemptyset");
  }
  if (sigprocmask(SIG_SETMASK, &empty_sset, nullptr) < 0) {
    DIE("sigprocmask");
  }

  // Set the default signal handler for all signals.
  for (int i = 1; i < NSIG; ++i) {
    if (i == SIGKILL || i == SIGSTOP) {
      continue;
    }
    struct sigaction sa = {};
    sa.sa_handler = SIG_DFL;
    if (sigemptyset(&sa.sa_mask) < 0) {
      DIE("sigemptyset");
    }
    // Ignore possible errors, because we might not be allowed to set the
    // handler for certain signals, but we still want to try.
    sigaction(i, &sa, nullptr);
  }
}

void SetTimeout(double timeout_secs) {
  double int_val, fraction_val;
  fraction_val = modf(timeout_secs, &int_val);

  struct itimerval timer;
  timer.it_interval.tv_sec = 0;
  timer.it_interval.tv_usec = 0;
  timer.it_value.tv_sec = static_cast<time_t>(int_val),
  timer.it_value.tv_usec = static_cast<suseconds_t>(fraction_val * 1e6);

  if (setitimer(ITIMER_REAL, &timer, nullptr) < 0) {
    DIE("setitimer");
  }
}

int WaitChild(pid_t pid, bool child_subreaper_enabled) {
  int err, status;

  if (child_subreaper_enabled) {
    // Discard any zombies that we may get when the child subreaper feature is
    // enabled.
    do {
      err = wait(&status);
    } while (err != pid || (err == -1 && errno == EINTR));
  } else {
    do {
      err = waitpid(pid, &status, 0);
    } while (err == -1 && errno == EINTR);
  }

  if (err == -1) {
    DIE("waitpid");
  }

  return status;
}

int WaitChildWithRusage(pid_t pid, struct rusage *rusage,
                        bool child_subreaper_enabled) {
  int err, status;

  if (child_subreaper_enabled) {
    // Discard any zombies that we may get when the child subreaper feature is
    // enabled.
    do {
      err = wait3(&status, 0, rusage);
    } while (err != pid || (err == -1 && errno == EINTR));
  } else {
    do {
      err = wait4(pid, &status, 0, rusage);
    } while (err == -1 && errno == EINTR);
  }

  if (err == -1) {
    DIE("wait4");
  }

  return status;
}

static std::unique_ptr<tools::protos::ExecutionStatistics>
CreateExecutionStatisticsProto(struct rusage *rusage) {
  std::unique_ptr<tools::protos::ExecutionStatistics> execution_statistics(
      new tools::protos::ExecutionStatistics);

  tools::protos::ResourceUsage *resource_usage =
      execution_statistics->mutable_resource_usage();

  resource_usage->set_utime_sec(rusage->ru_utime.tv_sec);
  resource_usage->set_utime_usec(rusage->ru_utime.tv_usec);
  resource_usage->set_stime_sec(rusage->ru_stime.tv_sec);
  resource_usage->set_stime_usec(rusage->ru_stime.tv_usec);
  resource_usage->set_maxrss(rusage->ru_maxrss);
  resource_usage->set_ixrss(rusage->ru_ixrss);
  resource_usage->set_idrss(rusage->ru_idrss);
  resource_usage->set_isrss(rusage->ru_isrss);
  resource_usage->set_minflt(rusage->ru_minflt);
  resource_usage->set_majflt(rusage->ru_majflt);
  resource_usage->set_nswap(rusage->ru_nswap);
  resource_usage->set_inblock(rusage->ru_inblock);
  resource_usage->set_oublock(rusage->ru_oublock);
  resource_usage->set_msgsnd(rusage->ru_msgsnd);
  resource_usage->set_msgrcv(rusage->ru_msgrcv);
  resource_usage->set_nsignals(rusage->ru_nsignals);
  resource_usage->set_nvcsw(rusage->ru_nvcsw);
  resource_usage->set_nivcsw(rusage->ru_nivcsw);

  return execution_statistics;
}

// Write execution statistics (e.g. resource usage) to a file.
void WriteStatsToFile(struct rusage *rusage, const std::string &stats_path) {
  const int flags = O_WRONLY | O_CREAT | O_TRUNC | O_APPEND;
  int fd_out = open(stats_path.c_str(), flags, 0666);
  if (fd_out < 0) {
    DIE("open(%s)", stats_path.c_str());
  }

  std::unique_ptr<tools::protos::ExecutionStatistics> execution_statistics =
      CreateExecutionStatisticsProto(rusage);
  std::string serialized = execution_statistics->SerializeAsString();

  if (serialized.empty()) {
    DIE("invalid execution statistics message");
  }

  const char *remaining = serialized.c_str();
  ssize_t remaining_size = serialized.size();

  while (remaining_size > 0) {
    ssize_t written = write(fd_out, remaining, remaining_size);
    if (written < 0 && errno != EINTR && errno != EAGAIN) {
      DIE("could not write resource usage to file '%s': %s",
          stats_path.c_str(), strerror(errno));
    }

    remaining_size -= written;
    remaining += written;
  }

  close(fd_out);
}