src/main/cpp/blaze_util_windows.cc

// Copyright 2014 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 <fcntl.h>
#include <stdarg.h>  // va_start, va_end, va_list

#ifndef COMPILER_MSVC
#include <errno.h>
#include <limits.h>
#include <sys/cygwin.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/statfs.h>
#include <unistd.h>
#endif  // not COMPILER_MSVC

#include <windows.h>
#include <lmcons.h>  // UNLEN

#ifdef COMPILER_MSVC
#include <io.h>  // _open
#endif  // COMPILER_MSVC

#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <sstream>
#include <thread>  // NOLINT (to slience Google-internal linter)
#include <type_traits>  // static_assert
#include <vector>

#include "src/main/cpp/blaze_util.h"
#include "src/main/cpp/blaze_util_platform.h"
#include "src/main/cpp/global_variables.h"
#include "src/main/cpp/startup_options.h"
#include "src/main/cpp/util/errors.h"
#include "src/main/cpp/util/exit_code.h"
#include "src/main/cpp/util/file.h"
#include "src/main/cpp/util/file_platform.h"
#include "src/main/cpp/util/md5.h"
#include "src/main/cpp/util/numbers.h"
#include "src/main/cpp/util/strings.h"
#include "src/main/native/windows_file_operations.h"
#include "src/main/native/windows_util.h"

namespace blaze {

// Ensure we can safely cast (const) wchar_t* to LP(C)WSTR.
// This is true with MSVC but usually not with GCC.
static_assert(sizeof(wchar_t) == sizeof(WCHAR),
              "wchar_t and WCHAR should be the same size");

// When using widechar Win32 API functions the maximum path length is 32K.
// Add 4 characters for potential UNC prefix and a couple more for safety.
static const size_t kWindowsPathBufferSize = 0x8010;

// TODO(bazel-team): get rid of die/pdie, handle errors on the caller side.
// die/pdie are exit points in the code and they make it difficult to follow the
// control flow, plus it's not clear whether they call destructors on local
// variables in the call stack.
using blaze_util::die;
using blaze_util::pdie;

using std::string;
using std::unique_ptr;
using std::wstring;

SignalHandler SignalHandler::INSTANCE;

class WindowsClock {
 public:
  uint64_t GetMilliseconds() const;
  uint64_t GetProcessMilliseconds() const;

  static const WindowsClock INSTANCE;

 private:
  // Clock frequency per seconds.
  // It's safe to cache this because (from QueryPerformanceFrequency on MSDN):
  // "The frequency of the performance counter is fixed at system boot and is
  // consistent across all processors. Therefore, the frequency need only be
  // queried upon application initialization, and the result can be cached."
  const LARGE_INTEGER kFrequency;

  // Time (in milliseconds) at process start.
  const LARGE_INTEGER kStart;

  WindowsClock();

  static LARGE_INTEGER GetFrequency();
  static LARGE_INTEGER GetMillisecondsAsLargeInt(const LARGE_INTEGER& freq);
};

#ifdef COMPILER_MSVC

void SignalHandler::Install(GlobalVariables* globals,
                            SignalHandler::Callback cancel_server) {
  // TODO(bazel-team): implement this.
}

ATTRIBUTE_NORETURN void SignalHandler::PropagateSignalOrExit(int exit_code) {
  // TODO(bazel-team): implement this.
}

#else  // not COMPILER_MSVC

// The number of the last received signal that should cause the client
// to shutdown.  This is saved so that the client's WTERMSIG can be set
// correctly.  (Currently only SIGPIPE uses this mechanism.)
static volatile sig_atomic_t signal_handler_received_signal = 0;

// Signal handler.
static void handler(int signum) {
  int saved_errno = errno;

  static volatile sig_atomic_t sigint_count = 0;

  switch (signum) {
    case SIGINT:
      if (++sigint_count >= 3) {
        SigPrintf(
            "\n%s caught third interrupt signal; killed.\n\n",
            SignalHandler::Get().GetGlobals()->options->product_name.c_str());
        if (SignalHandler::Get().GetGlobals()->server_pid != -1) {
          KillServerProcess(SignalHandler::Get().GetGlobals()->server_pid);
        }
        _exit(1);
      }
      SigPrintf(
          "\n%s caught interrupt signal; shutting down.\n\n",
          SignalHandler::Get().GetGlobals()->options->product_name.c_str());
      SignalHandler::Get().CancelServer();
      break;
    case SIGTERM:
      SigPrintf(
          "\n%s caught terminate signal; shutting down.\n\n",
          SignalHandler::Get().GetGlobals()->options->product_name.c_str());
      SignalHandler::Get().CancelServer();
      break;
    case SIGPIPE:
      signal_handler_received_signal = SIGPIPE;
      break;
    case SIGQUIT:
      SigPrintf("\nSending SIGQUIT to JVM process %d (see %s).\n\n",
                SignalHandler::Get().GetGlobals()->server_pid,
                SignalHandler::Get().GetGlobals()->jvm_log_file.c_str());
      kill(SignalHandler::Get().GetGlobals()->server_pid, SIGQUIT);
      break;
  }

  errno = saved_errno;
}

void SignalHandler::Install(GlobalVariables* globals,
                            SignalHandler::Callback cancel_server) {
  _globals = globals;
  _cancel_server = cancel_server;

  // Unblock all signals.
  sigset_t sigset;
  sigemptyset(&sigset);
  sigprocmask(SIG_SETMASK, &sigset, NULL);

  signal(SIGINT, handler);
  signal(SIGTERM, handler);
  signal(SIGPIPE, handler);
  signal(SIGQUIT, handler);
}

ATTRIBUTE_NORETURN void SignalHandler::PropagateSignalOrExit(int exit_code) {
  if (signal_handler_received_signal) {
    // Kill ourselves with the same signal, so that callers see the
    // right WTERMSIG value.
    signal(signal_handler_received_signal, SIG_DFL);
    raise(signal_handler_received_signal);
    exit(1);  // (in case raise didn't kill us for some reason)
  } else {
    exit(exit_code);
  }
}

#endif  // COMPILER_MSVC

// A signal-safe version of fprintf(stderr, ...).
//
// WARNING: any output from the blaze client may be interleaved
// with output from the blaze server.  In --curses mode,
// the Blaze server often erases the previous line of output.
// So, be sure to end each such message with TWO newlines,
// otherwise it may be erased by the next message from the
// Blaze server.
// Also, it's a good idea to start each message with a newline,
// in case the Blaze server has written a partial line.
void SigPrintf(const char *format, ...) {
#ifdef COMPILER_MSVC
  // TODO(bazel-team): implement this.
#else  // not COMPILER_MSVC
  char buf[1024];
  va_list ap;
  va_start(ap, format);
  int r = vsnprintf(buf, sizeof buf, format, ap);
  va_end(ap);
  if (write(STDERR_FILENO, buf, r) <= 0) {
    // We don't care, just placate the compiler.
  }
#endif  // COMPILER_MSVC
}

static void PrintError(const string& op) {
    DWORD last_error = ::GetLastError();
    if (last_error == 0) {
        return;
    }

    char* message_buffer;
    size_t size = FormatMessageA(
        FORMAT_MESSAGE_ALLOCATE_BUFFER
            | FORMAT_MESSAGE_FROM_SYSTEM
            | FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        last_error,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPSTR) &message_buffer,
        0,
        NULL);

    fprintf(stderr, "ERROR: %s: %s (%d)\n",
            op.c_str(), message_buffer, last_error);
    LocalFree(message_buffer);
}

static void PrintErrorW(const wstring& op) {
  DWORD last_error = ::GetLastError();
  if (last_error == 0) {
    return;
  }

  WCHAR* message_buffer;
  FormatMessageW(
      /* dwFlags */ FORMAT_MESSAGE_ALLOCATE_BUFFER |
          FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
      /* lpSource */ nullptr,
      /* dwMessageId */ last_error,
      /* dwLanguageId */ MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
      /* lpBuffer */ message_buffer,
      /* nSize */ 0,
      /* Arguments */ nullptr);

  fwprintf(stderr, L"ERROR: %s: %s (%d)\n", op.c_str(), message_buffer,
           last_error);
  LocalFree(message_buffer);
}

void WarnFilesystemType(const string& output_base) {
}

string GetProcessIdAsString() {
  return ToString(GetCurrentProcessId());
}

string GetSelfPath() {
  WCHAR buffer[kWindowsPathBufferSize] = {0};
  if (!GetModuleFileNameW(0, buffer, kWindowsPathBufferSize)) {
    pdie(255, "Error %u getting executable file name\n", GetLastError());
  }
  return string(blaze_util::WstringToCstring(buffer).get());
}

string GetOutputRoot() {
  for (const char* i : {"TMPDIR", "TEMPDIR", "TMP", "TEMP"}) {
    string tmpdir(GetEnv(i));
    if (!tmpdir.empty()) {
      return tmpdir;
    }
  }
#ifdef COMPILER_MSVC
  // GetTempPathW and GetEnvironmentVariableW only work properly when Bazel
  // runs under cmd.exe, not when it's run from msys.
  // The reason is that MSYS consumes all environment variables and sets its own
  // ones. The symptom of this is that GetEnvironmentVariableW returns nothing
  // for TEMP under MSYS, though it can retrieve WINDIR.

  WCHAR buffer[kWindowsPathBufferSize] = {0};
  if (!::GetTempPathW(kWindowsPathBufferSize, buffer)) {
    PrintErrorW(L"GetTempPathW");
    pdie(255, "Could not retrieve the temp directory path");
  }
  return string(blaze_util::WstringToCstring(buffer).get());
#else  // not COMPILER_MSVC
  return "/var/tmp";
#endif  // COMPILER_MSVC
}

string FindSystemWideBlazerc() {
#ifdef COMPILER_MSVC
  // TODO(bazel-team): implement this.
  return "";
#else   // not COMPILER_MSVC
  string path = "/etc/bazel.bazelrc";
  if (blaze_util::CanReadFile(path)) {
    return path;
  }
  return "";
#endif  // COMPILER_MSVC
}

string GetJavaBinaryUnderJavabase() { return "bin/java.exe"; }

uint64_t GetMillisecondsMonotonic() {
  return WindowsClock::INSTANCE.GetMilliseconds();
}

uint64_t GetMillisecondsSinceProcessStart() {
  return WindowsClock::INSTANCE.GetProcessMilliseconds();
}

void SetScheduling(bool batch_cpu_scheduling, int io_nice_level) {
  // TODO(bazel-team): There should be a similar function on Windows.
}

string GetProcessCWD(int pid) {
#ifdef COMPILER_MSVC
  // TODO(bazel-team) 2016-11-18: decide whether we need this on Windows and
  // implement or delete.
  return "";
#else   // not COMPILER_MSVC
  char server_cwd[PATH_MAX] = {};
  if (readlink(
          ("/proc/" + ToString(pid) + "/cwd").c_str(),
          server_cwd, sizeof(server_cwd)) < 0) {
    return "";
  }

  return string(server_cwd);
#endif  // COMPILER_MSVC
}

bool IsSharedLibrary(const string &filename) {
  return blaze_util::ends_with(filename, ".dll");
}

string GetDefaultHostJavabase() {
  string javahome(GetEnv("JAVA_HOME"));
  if (javahome.empty()) {
    die(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
        "Error: JAVA_HOME not set.");
  }
  return javahome;
}

namespace {

// Max command line length is per CreateProcess documentation
// (https://msdn.microsoft.com/en-us/library/ms682425(VS.85).aspx)
//
// Quoting rules are described here:
// https://blogs.msdn.microsoft.com/twistylittlepassagesallalike/2011/04/23/everyone-quotes-command-line-arguments-the-wrong-way/

static const int MAX_CMDLINE_LENGTH = 32768;

struct CmdLine {
  char cmdline[MAX_CMDLINE_LENGTH];
};
static void CreateCommandLine(CmdLine* result, const string& exe,
                              const std::vector<string>& args_vector) {
  std::ostringstream cmdline;
  string short_exe;
  if (!blaze_util::AsShortWindowsPath(exe, &short_exe)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "CreateCommandLine: AsShortWindowsPath(%s) failed, err=%d",
         exe.c_str(), GetLastError());
  }
  bool first = true;
  for (const auto& s : args_vector) {
    if (first) {
      first = false;
      // Skip first argument, instead use quoted executable name.
      cmdline << '\"' << short_exe << '\"';
      continue;
    } else {
      cmdline << ' ';
    }

    bool has_space = s.find(" ") != string::npos;

    if (has_space) {
      cmdline << '\"';
    }

    // TODO(bazel-team): get rid of the code to append character by character,
    // because each time a new buffer is allocated and the old one copied, so
    // this means N allocations (of O(N) size each) and N copies.
    // If possible, get rid of the whole CreateCommandLine method and do the
    // logic on the caller side.
    std::string::const_iterator it = s.begin();
    while (it != s.end()) {
      char ch = *it++;
      switch (ch) {
        case '"':
          // Escape double quotes
          cmdline << "\\\"";
          break;

        case '\\':
          if (it == s.end()) {
            // Backslashes at the end of the string are quoted if we add quotes
            cmdline << (has_space ? "\\\\" : "\\");
          } else {
            // Backslashes everywhere else are quoted if they are followed by a
            // quote or a backslash
            cmdline << (*it == '"' || *it == '\\' ? "\\\\" : "\\");
          }
          break;

        default:
          cmdline << ch;
      }
    }

    if (has_space) {
      cmdline << '\"';
    }
  }

  string cmdline_str = cmdline.str();
  if (cmdline_str.size() >= MAX_CMDLINE_LENGTH) {
    pdie(blaze_exit_code::INTERNAL_ERROR, "Command line too long: %s",
         cmdline_str.c_str());
  }

  // Copy command line into a mutable buffer.
  // CreateProcess is allowed to mutate its command line argument.
  strncpy(result->cmdline, cmdline_str.c_str(), MAX_CMDLINE_LENGTH - 1);
  result->cmdline[MAX_CMDLINE_LENGTH - 1] = 0;
}

}  // namespace

string GetJvmVersion(const string& java_exe) {
  // TODO(bazel-team): implement IPipe for Windows and use that here.
  HANDLE pipe_read, pipe_write;

  SECURITY_ATTRIBUTES sa = {sizeof(SECURITY_ATTRIBUTES), NULL, TRUE};
  if (!CreatePipe(&pipe_read, &pipe_write, &sa, 0)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "CreatePipe");
  }

  if (!SetHandleInformation(pipe_read, HANDLE_FLAG_INHERIT, 0)) {
    CloseHandle(pipe_read);
    CloseHandle(pipe_write);
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "SetHandleInformation");
  }

  PROCESS_INFORMATION processInfo = {0};
  STARTUPINFOA startupInfo = {0};
  startupInfo.hStdError = pipe_write;
  startupInfo.hStdOutput = pipe_write;
  startupInfo.dwFlags |= STARTF_USESTDHANDLES;

  string win_java_exe;
  if (!blaze_util::AsShortWindowsPath(java_exe, &win_java_exe)) {
    CloseHandle(pipe_read);
    CloseHandle(pipe_write);
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "GetJvmVersion: AsShortWindowsPath(%s)", java_exe.c_str());
  }
  win_java_exe = string("\"") + win_java_exe + "\" -version";

  char cmdline[MAX_CMDLINE_LENGTH];
  strncpy(cmdline, win_java_exe.c_str(), win_java_exe.size() + 1);
  BOOL ok = CreateProcessA(
      /* lpApplicationName */ NULL,
      /* lpCommandLine */ cmdline,
      /* lpProcessAttributes */ NULL,
      /* lpThreadAttributes */ NULL,
      /* bInheritHandles */ TRUE,
      /* dwCreationFlags */ 0,
      /* lpEnvironment */ NULL,
      /* lpCurrentDirectory */ NULL,
      /* lpStartupInfo */ &startupInfo,
      /* lpProcessInformation */ &processInfo);

  if (!ok) {
    CloseHandle(pipe_read);
    CloseHandle(pipe_write);
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "RunProgram/CreateProcess: Error %d while retrieving java version",
         GetLastError());
  }

  CloseHandle(pipe_write);
  std::string result = "";
  DWORD bytes_read;
  CHAR buf[1024];

  for (;;) {
    ok = ::ReadFile(pipe_read, buf, 1023, &bytes_read, NULL);
    if (!ok || bytes_read == 0) {
      break;
    }
    buf[bytes_read] = 0;
    result = result + buf;
  }

  CloseHandle(pipe_read);
  CloseHandle(processInfo.hProcess);
  CloseHandle(processInfo.hThread);
  return ReadJvmVersion(result);
}

#ifndef COMPILER_MSVC
// If we pass DETACHED_PROCESS to CreateProcess(), cmd.exe appropriately
// returns the command prompt when the client terminates. msys2, however, in
// its infinite wisdom, waits until the *server* terminates and cannot be
// convinced otherwise.
//
// So, we first pretend to be a POSIX daemon so that msys2 knows about our
// intentions and *then* we call CreateProcess(). Life ain't easy.
static bool DaemonizeOnWindows() {
  if (fork() > 0) {
    // We are the original client process.
    return true;
  }

  if (fork() > 0) {
    // We are the child of the original client process. Terminate so that the
    // actual server is not a child process of the client.
    exit(0);
  }

  setsid();
  // Contrary to the POSIX version, we are not closing the three standard file
  // descriptors here. CreateProcess() will take care of that and it's useful
  // to see the error messages in ExecuteDaemon() on the console of the client.
  return false;
}
#endif  // not COMPILER_MSVC

// Keeping an eye on the server process on Windows is not implemented yet.
// TODO(lberki): Implement this, because otherwise if we can't start up a server
// process, the client will hang until it times out.
class DummyBlazeServerStartup : public BlazeServerStartup {
 public:
  DummyBlazeServerStartup() {}
  virtual ~DummyBlazeServerStartup() {}
  virtual bool IsStillAlive() { return true; }
};

void ExecuteDaemon(const string& exe, const std::vector<string>& args_vector,
                   const string& daemon_output, const string& server_dir,
                   BlazeServerStartup** server_startup) {
#ifdef COMPILER_MSVC
  *server_startup = new DummyBlazeServerStartup();
#else   // not COMPILER_MSVC
  if (DaemonizeOnWindows()) {
    // We are the client process
    *server_startup = new DummyBlazeServerStartup();
    return;
  }
#endif  // COMPILER_MSVC

  wstring wdaemon_output;
  if (!blaze_util::AsWindowsPathWithUncPrefix(daemon_output, &wdaemon_output)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "AsWindowsPathWithUncPrefix");
  }

  SECURITY_ATTRIBUTES sa;
  sa.nLength = sizeof(SECURITY_ATTRIBUTES);
  // We redirect stdout and stderr by telling CreateProcess to use a file handle
  // we open below and these handles must be inheriatable
  sa.bInheritHandle = TRUE;
  sa.lpSecurityDescriptor = NULL;

  HANDLE output_file = ::CreateFileW(
      /* lpFileName */ wdaemon_output.c_str(),
      /* dwDesiredAccess */ GENERIC_READ | GENERIC_WRITE,
      // TODO(laszlocsomor): add FILE_SHARE_DELETE, that allows deleting jvm.out
      // and maybe fixes https://github.com/bazelbuild/bazel/issues/2326 .
      // Unfortunately however if a file that we opened with FILE_SHARE_DELETE
      // is deleted while its still open, write operations will still succeed
      // but have no effect, the file won't be recreated. (I haven't tried what
      // happens with read operations.)
      //
      // FILE_SHARE_READ: So that the file can be read while the server is
      // running
      /* dwShareMode */ FILE_SHARE_READ,
      /* lpSecurityAttributes */ &sa,
      /* dwCreationDisposition */ CREATE_ALWAYS,
      /* dwFlagsAndAttributes */ FILE_ATTRIBUTE_NORMAL,
      /* hTemplateFile */ NULL);

  if (output_file == INVALID_HANDLE_VALUE) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "CreateFile");
  }

  HANDLE pipe_read, pipe_write;
  if (!CreatePipe(&pipe_read, &pipe_write, &sa, 0)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "CreatePipe");
  }

  if (!SetHandleInformation(pipe_write, HANDLE_FLAG_INHERIT, 0)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "SetHandleInformation");
  }

  PROCESS_INFORMATION processInfo = {0};
  STARTUPINFOA startupInfo = {0};

  startupInfo.hStdInput = pipe_read;
  startupInfo.hStdError = output_file;
  startupInfo.hStdOutput = output_file;
  startupInfo.dwFlags |= STARTF_USESTDHANDLES;
  CmdLine cmdline;
  CreateCommandLine(&cmdline, exe, args_vector);

  // Propagate BAZEL_SH environment variable to a sub-process.
  // todo(dslomov): More principled approach to propagating
  // environment variables.
  SetEnvironmentVariableA("BAZEL_SH", getenv("BAZEL_SH"));

  BOOL ok = CreateProcessA(
      /* lpApplicationName */ NULL,
      /* lpCommandLine */ cmdline.cmdline,
      /* lpProcessAttributes */ NULL,
      /* lpThreadAttributes */ NULL,
      /* bInheritHandles */ TRUE,
      /* dwCreationFlags */ DETACHED_PROCESS | CREATE_NEW_PROCESS_GROUP,
      /* lpEnvironment */ NULL,
      /* lpCurrentDirectory */ NULL,
      /* lpStartupInfo */ &startupInfo,
      /* lpProcessInformation */ &processInfo);

  if (!ok) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "ExecuteDaemon/CreateProcess: error %u executing: %s\n",
         GetLastError(), cmdline.cmdline);
  }

  CloseHandle(output_file);
  CloseHandle(pipe_write);
  CloseHandle(pipe_read);

  string pid_string = ToString(processInfo.dwProcessId);
  string pid_file = blaze_util::JoinPath(server_dir, kServerPidFile);
  if (!blaze_util::WriteFile(pid_string, pid_file)) {
    // Not a lot we can do if this fails
    fprintf(stderr, "Cannot write PID file %s\n", pid_file.c_str());
  }

  CloseHandle(processInfo.hProcess);
  CloseHandle(processInfo.hThread);

#ifndef COMPILER_MSVC
  exit(0);
#endif  // COMPILER_MSVC
}

void BatchWaiterThread(HANDLE java_handle) {
  WaitForSingleObject(java_handle, INFINITE);
}

#ifdef COMPILER_MSVC
  // TODO(bazel-team): implement signal handling.
#else  // not COMPILER_MSVC
static void MingwSignalHandler(int signum) {
  // Java process will be terminated because we set the job to terminate if its
  // handle is closed.
  //
  // Note that this is different how interruption is handled on Unix, where the
  // Java process sets up a signal handler for SIGINT itself. That cannot be
  // done on Windows without using native code, and it's better to have as
  // little JNI as possible. The most important part of the cleanup after
  // termination (killing all child processes) happens automatically on Windows
  // anyway, since we put the batch Java process in its own job which does not
  // allow breakaway processes.
  exit(blaze_exit_code::ExitCode::INTERRUPTED);
}
#endif  // COMPILER_MSVC

// Returns whether assigning the given process to a job failed because nested
// jobs are not available on the current system.
static bool IsFailureDueToNestedJobsNotSupported(HANDLE process) {
  BOOL is_in_job;
  if (!IsProcessInJob(process, NULL, &is_in_job)) {
    PrintError("IsProcessInJob()");
    return false;
  }

  if (!is_in_job) {
    // Not in a job.
    return false;
  }

  OSVERSIONINFOEX version_info;
  version_info.dwOSVersionInfoSize = sizeof(version_info);
  if (!GetVersionEx(reinterpret_cast<OSVERSIONINFO*>(&version_info))) {
    PrintError("GetVersionEx()");
    return false;
  }

  return version_info.dwMajorVersion < 6
      || version_info.dwMajorVersion == 6 && version_info.dwMinorVersion <= 1;
}

// Run the given program in the current working directory, using the given
// argument vector, wait for it to finish, then exit ourselves with the exitcode
// of that program.
void ExecuteProgram(const string& exe, const std::vector<string>& args_vector) {
  CmdLine cmdline;
  CreateCommandLine(&cmdline, exe, args_vector);

  STARTUPINFOA startupInfo = {0};
  startupInfo.cb = sizeof(STARTUPINFOA);

  PROCESS_INFORMATION processInfo = {0};

  // Propagate BAZEL_SH environment variable to a sub-process.
  // todo(dslomov): More principled approach to propagating
  // environment variables.
  SetEnvironmentVariableA("BAZEL_SH", getenv("BAZEL_SH"));

  HANDLE job = CreateJobObject(NULL, NULL);
  if (job == NULL) {
    pdie(255, "ExecuteProgram/CreateJobObject: error %u\n", GetLastError());
  }

  JOBOBJECT_EXTENDED_LIMIT_INFORMATION job_info = {0};
  job_info.BasicLimitInformation.LimitFlags =
      JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;

  if (!SetInformationJobObject(job, JobObjectExtendedLimitInformation,
                               &job_info, sizeof(job_info))) {
    pdie(255, "ExecuteProgram/SetInformationJobObject: error %u\n",
         GetLastError());
  }

  BOOL success = CreateProcessA(
      /* lpApplicationName */ NULL,
      /* lpCommandLine */ cmdline.cmdline,
      /* lpProcessAttributes */ NULL,
      /* lpThreadAttributes */ NULL,
      /* bInheritHandles */ TRUE,
      /* dwCreationFlags */ CREATE_SUSPENDED,
      /* lpEnvironment */ NULL,
      /* lpCurrentDirectory */ NULL,
      /* lpStartupInfo */ &startupInfo,
      /* lpProcessInformation */ &processInfo);

  if (!success) {
    pdie(255, "ExecuteProgram/CreateProcess: error %u executing: %s\n",
         GetLastError(), cmdline.cmdline);
  }

  // We will try to put the launched process into a Job object. This will make
  // Windows reliably kill all child processes that the process itself may
  // launch once the process exits. On Windows systems that don't support nested
  // jobs, this may fail if we are already running inside a job ourselves. In
  // this case, we'll continue anyway, because we assume that our parent is
  // handling process management for us.
  if (!AssignProcessToJobObject(job, processInfo.hProcess) &&
      !IsFailureDueToNestedJobsNotSupported(processInfo.hProcess)) {
    pdie(255, "ExecuteProgram/AssignProcessToJobObject: error %u\n",
         GetLastError());
  }

  // Now that we potentially put the process into a new job object, we can start
  // running it.
  if (ResumeThread(processInfo.hThread) == -1) {
    pdie(255, "ExecuteProgram/ResumeThread: error %u\n", GetLastError());
  }

  // msys doesn't deliver signals while a Win32 call is pending so we need to
  // do the blocking call in another thread

#ifdef COMPILER_MSVC
  // TODO(bazel-team): implement signal handling.
#else  // not COMPILER_MSVC
  signal(SIGINT, MingwSignalHandler);
#endif  // COMPILER_MSVC
  std::thread batch_waiter_thread([=]() {
    BatchWaiterThread(processInfo.hProcess);
  });

  // The output base lock is held while waiting
  batch_waiter_thread.join();
  DWORD exit_code;
  GetExitCodeProcess(processInfo.hProcess, &exit_code);
  CloseHandle(processInfo.hProcess);
  CloseHandle(processInfo.hThread);
  exit(exit_code);
}

string ListSeparator() { return ";"; }

string PathAsJvmFlag(const string& path) {
  string spath;
  if (!blaze_util::AsShortWindowsPath(path, &spath)) {
    pdie(255, "PathAsJvmFlag(%s): AsShortWindowsPath failed", path.c_str());
  }
  // Convert backslashes to forward slashes, in order to avoid the JVM parsing
  // Windows paths as if they contained escaped characters.
  // See https://github.com/bazelbuild/bazel/issues/2576
  std::replace(spath.begin(), spath.end(), '\\', '/');
  return spath;
}

string ConvertPath(const string& path) {
#ifdef COMPILER_MSVC
  // This isn't needed when the binary isn't linked against msys-2.0.dll (when
  // we build with MSVC): MSYS converts all Unix paths to Windows paths for such
  // binaries.
  return path;
#else  // not COMPILER_MSVC
  // If the path looks like %USERPROFILE%/foo/bar, don't convert.
  if (path.empty() || path[0] == '%') {
    return path;
  }
  char* wpath = static_cast<char*>(cygwin_create_path(
      CCP_POSIX_TO_WIN_A, static_cast<const void*>(path.c_str())));
  string result(wpath);
  free(wpath);
  return result;
#endif  // COMPILER_MSVC
}

// Convert a Unix path list to Windows path list
string ConvertPathList(const string& path_list) {
#ifdef COMPILER_MSVC
  // In the MSVC version we use the actual %PATH% value which is separated by
  // ";" and contains Windows paths.
  return path_list;
#else   // not COMPILER_MSVC
  string w_list = "";
  int start = 0;
  int pos;
  while ((pos = path_list.find(":", start)) != string::npos) {
    w_list += ConvertPath(path_list.substr(start, pos - start)) + ";";
    start = pos + 1;
  }
  if (start < path_list.size()) {
    w_list += ConvertPath(path_list.substr(start));
  }
  return w_list;
#endif  // COMPILER_MSVC
}

static string ConvertPathToPosix(const string& win_path) {
#ifdef COMPILER_MSVC
  // TODO(bazel-team) 2016-11-18: verify that this function is not needed on
  // Windows.
  return win_path;
#else   // not COMPILER_MSVC
  char* posix_path = static_cast<char*>(cygwin_create_path(
      CCP_WIN_A_TO_POSIX, static_cast<const void*>(win_path.c_str())));
  string result(posix_path);
  free(posix_path);
  return result;
#endif  // COMPILER_MSVC
}

// Cribbed from ntifs.h, not present in windows.h

#define REPARSE_MOUNTPOINT_HEADER_SIZE   8

typedef struct {
  DWORD ReparseTag;
  WORD ReparseDataLength;
  WORD Reserved;
  WORD SubstituteNameOffset;
  WORD SubstituteNameLength;
  WORD PrintNameOffset;
  WORD PrintNameLength;
  WCHAR PathBuffer[ANYSIZE_ARRAY];
} REPARSE_MOUNTPOINT_DATA_BUFFER, *PREPARSE_MOUNTPOINT_DATA_BUFFER;

bool SymlinkDirectories(const string &posix_target, const string &posix_name) {
  wstring name;
  wstring target;
  if (!blaze_util::AsWindowsPathWithUncPrefix(posix_name, &name)) {
    PrintError("SymlinkDirectories: AsWindowsPathWithUncPrefix(" + posix_name +
               ")");
    return false;
  }
  if (!blaze_util::AsWindowsPathWithUncPrefix(posix_target, &target)) {
    PrintError("SymlinkDirectories: AsWindowsPathWithUncPrefix(" +
               posix_target + ")");
    return false;
  }
  string error(windows_util::CreateJunction(name, target));
  if (!error.empty()) {
    PrintError("SymlinkDirectories(name=" + posix_name +
               ", target=" + posix_target + "): " + error);
    return false;
  }
  return true;
}

// TODO(laszlocsomor): use JunctionResolver in file_windows.cc
bool ReadDirectorySymlink(const string &posix_name, string* result) {
  string name = ConvertPath(posix_name);
  wstring wname;

  if (!blaze_util::AsWindowsPathWithUncPrefix(name, &wname)) {
    PrintError("ReadDirectorySymlink: AsWindowsPathWithUncPrefix(" + name +
               ")");
    return false;
  }

  HANDLE directory = windows_util::OpenDirectory(wname.c_str(), false);
  if (directory == INVALID_HANDLE_VALUE) {
    return false;
  }

  char reparse_buffer_bytes[MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
  REPARSE_MOUNTPOINT_DATA_BUFFER* reparse_buffer =
      reinterpret_cast<REPARSE_MOUNTPOINT_DATA_BUFFER *>(reparse_buffer_bytes);
  memset(reparse_buffer_bytes, 0, MAXIMUM_REPARSE_DATA_BUFFER_SIZE);

  reparse_buffer->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
  DWORD bytes_returned;
  bool ok = ::DeviceIoControl(
      directory,
      FSCTL_GET_REPARSE_POINT,
      NULL,
      0,
      reparse_buffer,
      MAXIMUM_REPARSE_DATA_BUFFER_SIZE,
      &bytes_returned,
      NULL);
  if (!ok) {
    PrintError("DeviceIoControl(FSCTL_GET_REPARSE_POINT, " + name + ")");
  }

  CloseHandle(directory);
  if (!ok) {
    return false;
  }

  std::vector<char> print_name(reparse_buffer->PrintNameLength * sizeof(WCHAR) +
                               1);
  int count = ::WideCharToMultiByte(
      CP_UTF8,
      0,
      reparse_buffer->PathBuffer +
         (reparse_buffer->PrintNameOffset / sizeof(WCHAR)),
      reparse_buffer->PrintNameLength,
      &print_name[0],
      print_name.size(),
      NULL,
      NULL);
  if (count == 0) {
    PrintError("WideCharToMultiByte()");
    *result = "";
    return false;
  } else {
    *result = ConvertPathToPosix(&print_name[0]);
    return true;
  }
}

bool CompareAbsolutePaths(const string& a, const string& b) {
  // `a` and `b` may not be Windows-style and may not be normalized, so convert
  // them both before comparing them.
  wstring a_real, b_real;
  if (!blaze_util::AsWindowsPathWithUncPrefix(a, &a_real)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "CompareAbsolutePaths(a=%s, b=%s)", a.c_str(), b.c_str());
  }
  if (!blaze_util::AsWindowsPathWithUncPrefix(b, &b_real)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "CompareAbsolutePaths(a=%s, b=%s)", a.c_str(), b.c_str());
  }
  return a_real == b_real;
}

bool VerifyServerProcess(
    int pid, const string& output_base, const string& install_base) {
  // TODO(lberki): This might accidentally kill an unrelated process if the
  // server died and the PID got reused.
  return true;
}

bool KillServerProcess(int pid) {
  HANDLE process = OpenProcess(PROCESS_TERMINATE, FALSE, pid);
  if (process == NULL) {
    // Cannot find the server process. Can happen if the PID file is stale.
    return false;
  }

  BOOL result = TerminateProcess(process, /*uExitCode*/ 0);
  if (!result) {
    blaze_util::PrintError("Cannot terminate server process with PID %d", pid);
  }

  CloseHandle(process);
  return result;
}

// Not supported.
void ExcludePathFromBackup(const string &path) {
}

string GetHashedBaseDir(const string& root, const string& hashable) {
  // Builds a shorter output base dir name for Windows.
  // This algorithm only uses 1/3 of the bits to get 8-char alphanumeric
  // file name.

  static const char* alphabet
      // Exactly 64 characters.
      = "abcdefghigklmnopqrstuvwxyzABCDEFGHIGKLMNOPQRSTUVWXYZ0123456789_-";

  // The length of the resulting filename (8 characters).
  static const int filename_length = blaze_util::Md5Digest::kDigestLength / 2;
  unsigned char buf[blaze_util::Md5Digest::kDigestLength];
  char coded_name[filename_length + 1];
  blaze_util::Md5Digest digest;
  digest.Update(hashable.data(), hashable.size());
  digest.Finish(buf);
  for (int i = 0; i < filename_length; i++) {
    coded_name[i] = alphabet[buf[i] & 0x3F];
  }
  coded_name[filename_length] = '\0';
  return blaze_util::JoinPath(root, string(coded_name));
}

void CreateSecureOutputRoot(const string& path) {
  // TODO(bazel-team): implement this properly, by mimicing whatever the POSIX
  // implementation does.
  const char* root = path.c_str();
  if (!blaze_util::MakeDirectories(path, 0755)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "MakeDirectories(%s) failed: %s", root,
         blaze_util::GetLastErrorString());
  }

#ifndef COMPILER_MSVC
  struct stat fileinfo = {};

  // The path already exists.
  // Check ownership and mode, and verify that it is a directory.

  if (lstat(root, &fileinfo) < 0) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "lstat('%s')", root);
  }

  if (fileinfo.st_uid != geteuid()) {
    die(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "'%s' is not owned by me",
        root);
  }

  // Ensure the permission mask is indeed 0755 (rwxr-xr-x).
  if ((fileinfo.st_mode & 022) != 0) {
    int new_mode = fileinfo.st_mode & (~022);
    if (chmod(root, new_mode) < 0) {
      die(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
          "'%s' has mode %o, chmod to %o failed", root,
          fileinfo.st_mode & 07777, new_mode);
    }
  }
#endif  // not COMPILER_MSVC

  if (!blaze_util::IsDirectory(path)) {
    die(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR, "'%s' is not a directory",
        root);
  }

  ExcludePathFromBackup(root);
}

string GetEnv(const string& name) {
  DWORD size = ::GetEnvironmentVariableA(name.c_str(), NULL, 0);
  if (size == 0) {
#ifdef COMPILER_MSVC
    return string();  // unset or empty envvar
#else  // not COMPILER_MSVC
    char* result = getenv(name.c_str());
    return result != NULL ? string(result) : string();
#endif  // COMPILER_MSVC
  }

  unique_ptr<char[]> value(new char[size]);
  ::GetEnvironmentVariableA(name.c_str(), value.get(), size);
  return string(value.get());
}

void SetEnv(const string& name, const string& value) {
  if (value.empty()) {
    ::SetEnvironmentVariableA(name.c_str(), NULL);
#ifndef COMPILER_MSVC
    unsetenv(name.c_str());
#endif  // not COMPILER_MSVC
  } else {
    ::SetEnvironmentVariableA(name.c_str(), value.c_str());
#ifndef COMPILER_MSVC
    setenv(name.c_str(), value.c_str(), 1);
#endif  // not COMPILER_MSVC
  }
}

void UnsetEnv(const string& name) { SetEnv(name, ""); }

void SetupStdStreams() {
#ifdef COMPILER_MSVC
  static const DWORD stdhandles[] = {STD_INPUT_HANDLE, STD_OUTPUT_HANDLE,
                                     STD_ERROR_HANDLE};
  for (int i = 0; i < 2; ++i) {
    HANDLE handle = ::GetStdHandle(stdhandles[i]);
    if (handle == INVALID_HANDLE_VALUE || handle == NULL) {
      // Ensure we have open fds to each std* stream. Otherwise we can end up
      // with bizarre things like stdout going to the lock file, etc.
      _open("NUL", (i == 0) ? _O_RDONLY : _O_WRONLY);
    }
  }
#else  // not COMPILER_MSVC
  // Set non-buffered output mode for stderr/stdout. The server already
  // line-buffers messages where it makes sense, so there's no need to do set
  // line-buffering here. On the other hand the server sometimes sends binary
  // output (when for example a query returns results as proto), in which case
  // we must not perform line buffering on the client side. So turn off
  // buffering here completely.
  setvbuf(stdout, NULL, _IONBF, 0);
  setvbuf(stderr, NULL, _IONBF, 0);

  // Ensure we have three open fds.  Otherwise we can end up with
  // bizarre things like stdout going to the lock file, etc.
  if (fcntl(STDIN_FILENO, F_GETFL) == -1) open("/dev/null", O_RDONLY);
  if (fcntl(STDOUT_FILENO, F_GETFL) == -1) open("/dev/null", O_WRONLY);
  if (fcntl(STDERR_FILENO, F_GETFL) == -1) open("/dev/null", O_WRONLY);
#endif  // COMPILER_MSVC
}

LARGE_INTEGER WindowsClock::GetFrequency() {
  LARGE_INTEGER result;
  if (!QueryPerformanceFrequency(&result)) {
    PrintError("QueryPerformanceFrequency");
    pdie(255, "Error getting time resolution\n");
  }

  // On ancient Windows versions (pre-XP) and specific hardware the result may
  // be 0. Since this is pre-XP, we don't handle that, just error out.
  if (result.QuadPart <= 0) {
    pdie(255, "QueryPerformanceFrequency returned invalid result (%llu)\n",
         result.QuadPart);
  }

  return result;
}

LARGE_INTEGER WindowsClock::GetMillisecondsAsLargeInt(
    const LARGE_INTEGER& freq) {
  LARGE_INTEGER counter;
  if (!QueryPerformanceCounter(&counter)) {
    PrintError("QueryPerformanceCounter");
    pdie(255, "Error getting performance counter\n");
  }

  LARGE_INTEGER result;
  result.QuadPart =
      // seconds
      (counter.QuadPart / freq.QuadPart) * 1000LL +
      // milliseconds
      (((counter.QuadPart % freq.QuadPart) * 1000LL) / freq.QuadPart);

  return result;
}

const WindowsClock WindowsClock::INSTANCE;

WindowsClock::WindowsClock()
    : kFrequency(GetFrequency()),
      kStart(GetMillisecondsAsLargeInt(kFrequency)) {}

uint64_t WindowsClock::GetMilliseconds() const {
  return GetMillisecondsAsLargeInt(kFrequency).QuadPart;
}

uint64_t WindowsClock::GetProcessMilliseconds() const {
  return GetMilliseconds() - kStart.QuadPart;
}

uint64_t AcquireLock(const string& output_base, bool batch_mode, bool block,
                     BlazeLock* blaze_lock) {
#ifdef COMPILER_MSVC
  // TODO(bazel-team): implement this.
  return 0;
#else  // not COMPILER_MSVC
  string lockfile = blaze_util::JoinPath(output_base, "lock");
  int lockfd = open(lockfile.c_str(), O_CREAT|O_RDWR, 0644);

  if (lockfd < 0) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "cannot open lockfile '%s' for writing", lockfile.c_str());
  }

  // Keep server from inheriting a useless fd if we are not in batch mode
  if (!batch_mode) {
    if (fcntl(lockfd, F_SETFD, FD_CLOEXEC) == -1) {
      pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
           "fcntl(F_SETFD) failed for lockfile");
    }
  }

  struct flock lock;
  lock.l_type = F_WRLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start = 0;
  // This doesn't really matter now, but allows us to subdivide the lock
  // later if that becomes meaningful.  (Ranges beyond EOF can be locked.)
  lock.l_len = 4096;

  uint64_t wait_time = 0;
  // Try to take the lock, without blocking.
  if (fcntl(lockfd, F_SETLK, &lock) == -1) {
    if (errno != EACCES && errno != EAGAIN) {
      pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
           "unexpected result from F_SETLK");
    }

    // We didn't get the lock.  Find out who has it.
    struct flock probe = lock;
    probe.l_pid = 0;
    if (fcntl(lockfd, F_GETLK, &probe) == -1) {
      pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
           "unexpected result from F_GETLK");
    }
    if (!block) {
      die(blaze_exit_code::BAD_ARGV,
          "Another command is running (pid=%d). Exiting immediately.",
          probe.l_pid);
    }
    fprintf(stderr, "Another command is running (pid = %d).  "
            "Waiting for it to complete...", probe.l_pid);
    fflush(stderr);

    // Take a clock sample for that start of the waiting time
    uint64_t st = GetMillisecondsMonotonic();
    // Try to take the lock again (blocking).
    int r;
    do {
      r = fcntl(lockfd, F_SETLKW, &lock);
    } while (r == -1 && errno == EINTR);
    fprintf(stderr, "\n");
    if (r == -1) {
      pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
           "couldn't acquire file lock");
    }
    // Take another clock sample, calculate elapsed
    uint64_t et = GetMillisecondsMonotonic();
    wait_time = et - st;
  }

  // Identify ourselves in the lockfile.
  (void) ftruncate(lockfd, 0);
  const char *tty = ttyname(STDIN_FILENO);  // NOLINT (single-threaded)
  string msg = "owner=launcher\npid="
      + ToString(getpid()) + "\ntty=" + (tty ? tty : "") + "\n";
  // The contents are currently meant only for debugging.
  (void) write(lockfd, msg.data(), msg.size());
  blaze_lock->lockfd = lockfd;
  return wait_time;
#endif  // COMPILER_MSVC
}

void ReleaseLock(BlazeLock* blaze_lock) {
#ifdef COMPILER_MSVC
  // TODO(bazel-team): implement this.
#else  // not COMPILER_MSVC
  close(blaze_lock->lockfd);
#endif  // COMPILER_MSVC
}

#ifdef GetUserName
// By including <windows.h>, we have GetUserName defined either as
// GetUserNameA or GetUserNameW.
#undef GetUserName
#endif

string GetUserName() {
  WCHAR buffer[UNLEN + 1];
  DWORD len = UNLEN + 1;
  if (!GetUserNameW(buffer, &len)) {
    pdie(blaze_exit_code::LOCAL_ENVIRONMENTAL_ERROR,
         "ERROR: GetUserNameW failed, err=%d\n", GetLastError());
  }
  return string(blaze_util::WstringToCstring(buffer).get());
}

bool IsEmacsTerminal() {
  string emacs = GetEnv("EMACS");
  string inside_emacs = GetEnv("INSIDE_EMACS");
  // GNU Emacs <25.1 (and ~all non-GNU emacsen) set EMACS=t, but >=25.1 doesn't
  // do that and instead sets INSIDE_EMACS=<stuff> (where <stuff> can look like
  // e.g. "25.1.1,comint").  So we check both variables for maximum
  // compatibility.
  return emacs == "t" || !inside_emacs.empty();
}

// Returns true iff both stdout and stderr are connected to a
// terminal, and it can support color and cursor movement
// (this is computed heuristically based on the values of
// environment variables).
bool IsStandardTerminal() {
#ifdef COMPILER_MSVC
  // TODO(bazel-team): Implement this method properly. We may return true if
  // stdout and stderr are not redirected.
  return false;
#else  // not COMPILER_MSVC
  string term = GetEnv("TERM");
  if (term.empty() || term == "dumb" || term == "emacs" ||
      term == "xterm-mono" || term == "symbolics" || term == "9term" ||
      IsEmacsTerminal()) {
    return false;
  }
  return isatty(STDOUT_FILENO) && isatty(STDERR_FILENO);
#endif  // COMPILER_MSVC
}

// Returns the number of columns of the terminal to which stdout is
// connected, or $COLUMNS (default 80) if there is no such terminal.
int GetTerminalColumns() {
#ifndef COMPILER_MSVC
  struct winsize ws;
  if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) != -1) {
    return ws.ws_col;
  }
#endif  // not COMPILER_MSVC

  string columns_env = GetEnv("COLUMNS");
  if (!columns_env.empty()) {
    char* endptr;
    int columns = blaze_util::strto32(columns_env.c_str(), &endptr, 10);
    if (*endptr == '\0') {  // $COLUMNS is a valid number
      return columns;
    }
  }

#ifdef COMPILER_MSVC
  // This code path is MSVC-only because when running under MSYS there's no
  // Windows console attached so GetConsoleScreenBufferInfo fails.
  windows_util::AutoHandle stdout_handle(::GetStdHandle(STD_OUTPUT_HANDLE));
  CONSOLE_SCREEN_BUFFER_INFO screen_info;
  if (GetConsoleScreenBufferInfo(stdout_handle, &screen_info)) {
    int width = 1 + screen_info.srWindow.Right - screen_info.srWindow.Left;
    if (width > 1) {
      return width;
    }
  }
#endif  // COMPILER_MSVC

  return 80;  // default if not a terminal.
}

}  // namespace blaze