gecko/testing/mochitest/tests/SimpleTest/MozillaFileLogger.js

/**
 * MozillaFileLogger, a log listener that can write to a local file.
 */
try {
  netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
  const Cc = Components.classes;
  const Ci = Components.interfaces;
  const FOSTREAM_CID = "@mozilla.org/network/file-output-stream;1";
  const LF_CID = "@mozilla.org/file/local;1";
  
  // File status flags. It is a bitwise OR of the following bit flags.
  // Only one of the first three flags below may be used.
  const PR_READ_ONLY    = 0x01; // Open for reading only.
  const PR_WRITE_ONLY   = 0x02; // Open for writing only.
  const PR_READ_WRITE   = 0x04; // Open for reading and writing.
  
  // If the file does not exist, the file is created.
  // If the file exists, this flag has no effect.
  const PR_CREATE_FILE  = 0x08;
  
  // The file pointer is set to the end of the file prior to each write.
  const PR_APPEND       = 0x10;
  
  // If the file exists, its length is truncated to 0.
  const PR_TRUNCATE     = 0x20;
  
  // If set, each write will wait for both the file data
  // and file status to be physically updated.
  const PR_SYNC         = 0x40;
  
  // If the file does not exist, the file is created. If the file already
  // exists, no action and NULL is returned.
  const PR_EXCL         = 0x80;
} catch (ex) {
  // probably not running in the test harness
}

/** Init the file logger with the absolute path to the file.
    It will create and append if the file already exists **/
var MozillaFileLogger = {}

MozillaFileLogger.init = function(path) {
  netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
  MozillaFileLogger._file = Cc[LF_CID].createInstance(Ci.nsILocalFile);
  MozillaFileLogger._file.initWithPath(path);
  MozillaFileLogger._foStream = Cc[FOSTREAM_CID].createInstance(Ci.nsIFileOutputStream);
  MozillaFileLogger._foStream.init(this._file, PR_WRITE_ONLY | PR_CREATE_FILE | PR_APPEND,
                                   0664, 0);
}

MozillaFileLogger.getLogCallback = function() {
  return function (msg) {
    netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
    var data = msg.num + " " + msg.level + " " + msg.info.join(' ') + "\n";
    MozillaFileLogger._foStream.write(data, data.length);
    if (data.indexOf("SimpleTest FINISH") >= 0) {
      MozillaFileLogger.close();
    }
  }
}

MozillaFileLogger.close = function() {
  netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
  MozillaFileLogger._foStream.close();
  MozillaFileLogger._foStream = null;
  MozillaFileLogger._file = null;
}