metrics/metrics_library.cc

// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/*
 * metrics_library.cc
 *
 *  Created on: Dec 1, 2009
 *      Author: sosa
 */

#include "metrics_library.h"

#include <errno.h>
#include <sys/file.h>

#include <cstdarg>
#include <cstdio>
#include <cstring>

#define READ_WRITE_ALL_FILE_FLAGS \
  (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)

static const char kAutotestPath[] =
    "/var/log/metrics/autotest-events";
static const char kChromePath[] =
    "/var/log/metrics/uma-events";
static const int32_t kBufferSize = 1024;

using namespace std;

// TODO(sosa@chromium.org) - use Chromium logger instead of stderr
static void PrintError(const char *message, const char *file,
                       int code) {
  const char *kProgramName = "metrics_library";
  if (code == 0) {
    fprintf(stderr, "%s: %s\n", kProgramName, message);
  } else if (file == NULL) {
    fprintf(stderr, "%s: ", kProgramName);
    perror(message);
  } else {
    fprintf(stderr, "%s: %s: ", kProgramName, file);
    perror(message);
  }
}

// Sends message of size |length| to Chrome and returns true on success.
static bool SendMessageToChrome(int32_t length, const char *message) {
  int chrome_fd = open(kChromePath,
                       O_WRONLY | O_APPEND | O_CREAT,
                       READ_WRITE_ALL_FILE_FLAGS);
  // If we failed to open it, return.
  if (chrome_fd < 0) {
    PrintError("open", kChromePath, errno);
    return false;
  }

  // Need to chmod because open flags are anded with umask. Ignore the
  // exit code -- a chronos process may fail chmoding because the file
  // has been created by a root process but that should be OK.
  fchmod(chrome_fd, READ_WRITE_ALL_FILE_FLAGS);

  // Grab an exclusive lock to protect Chrome from truncating
  // underneath us. Keep the file locked as briefly as possible.
  if (flock(chrome_fd, LOCK_EX) < 0) {
    PrintError("flock", kChromePath, errno);
    close(chrome_fd);
    return false;
  }

  bool success = true;
  if (write(chrome_fd, message, length) != length) {
    PrintError("write", kChromePath, errno);
    success = false;
  }

  // Release the file lock and close file.
  if (flock(chrome_fd, LOCK_UN) < 0) {
    PrintError("unlock", kChromePath, errno);
    success = false;
  }
  close(chrome_fd);
  return success;
}

// Formats a name/value message for Chrome in |buffer| and returns the
// length of the message or a negative value on error.
//
// Message format is: | LENGTH(binary) | NAME | \0 | VALUE | \0 |
//
// The arbitrary |format| argument covers the non-LENGTH portion of the
// message. The caller is responsible to store the \0 character
// between NAME and VALUE (e.g. "%s%c%d", name, '\0', value).
static int32_t FormatChromeMessage(int32_t buffer_size, char *buffer,
                                   const char *format, ...) {
  int32_t message_length;
  size_t len_size = sizeof(message_length);

  // Format the non-LENGTH contents in the buffer by leaving space for
  // LENGTH at the start of the buffer.
  va_list args;
  va_start(args, format);
  message_length = vsnprintf(&buffer[len_size], buffer_size - len_size,
                             format, args);
  va_end(args);

  if (message_length < 0) {
    PrintError("chrome message format error", NULL, 0);
    return -1;
  }

  // +1 to account for the trailing \0.
  message_length += len_size + 1;
  if (message_length > buffer_size) {
    PrintError("chrome message too long", NULL, 0);
    return -1;
  }

  // Prepend LENGTH to the message.
  memcpy(buffer, &message_length, len_size);
  return message_length;
}

// static
bool MetricsLibrary::SendToAutotest(const string& name, int value) {
  FILE *autotest_file = fopen(kAutotestPath, "a+");
  if (autotest_file == NULL) {
    PrintError("fopen", kAutotestPath, errno);
    return false;
  }

  fprintf(autotest_file, "%s=%d\n", name.c_str(), value);
  fclose(autotest_file);
  return true;
}

// static
bool MetricsLibrary::SendToChrome(const string& name, int sample,
                                  int min, int max, int nbuckets) {
  // Format the message.
  char message[kBufferSize];
  int32_t message_length =
      FormatChromeMessage(kBufferSize, message,
                          "histogram%c%s %d %d %d %d", '\0',
                          name.c_str(), sample, min, max, nbuckets);

  if (message_length < 0)
    return false;

  // Send the message.
  return SendMessageToChrome(message_length, message);
}

//static
bool MetricsLibrary::SendEnumToChrome(const std::string& name, int sample,
                                      int max) {
  // Format the message.
  char message[kBufferSize];
  int32_t message_length =
      FormatChromeMessage(kBufferSize, message,
                          "linearhistogram%c%s %d %d", '\0',
                          name.c_str(), sample, max);

  if (message_length < 0)
    return false;

  // Send the message.
  return SendMessageToChrome(message_length, message);
}