code: function processFile(file, opts, stylize, callback) {
      var stream = fs.createReadStream(file);
      if (/\.gz$/.test(file)) {
          stream = stream.pipe(require('zlib').createGunzip());
      }
      // Manually decode streams - lazy load here as per node/lib/fs.js
      var decoder = new (require('string_decoder')
        .StringDecoder)('utf8');
  
      streams[file].stream = stream;
  
      stream.on('error', function (err) {
          streams[file].done = true;
          callback(err);
      });
  
      var leftover = '';  // Left-over partial line from last chunk.
      stream.on('data', function (data) {
          var chunk = decoder.write(data);
          if (!chunk.length) {
              return;
          }
          var lines = chunk.split(/\r\n|\n/);
          var length = lines.length;
          if (length === 1) {
              leftover += lines[0];
              return;
          }
  
          if (length > 1) {
              handleLogLine(file, leftover + lines[0], opts, stylize);
          }
          leftover = lines.pop();
          length -= 1;
          for (var i = 1; i < length; i++) {
              handleLogLine(file, lines[i], opts, stylize);
          }
      });
  
      stream.on('end', function () {
          streams[file].done = true;
          if (leftover) {
              handleLogLine(file, leftover, opts, stylize);
              leftover = '';
          } else {
              emitNextRecord(opts, stylize);
          }
          callback();
      });
  }
docs: Process all input from the given log file.
  
  @param file {String} Log file path to process.
  @params opts {Object} Bunyan options object.
  @param stylize {Function} Output stylize function to use.
  @param callback {Function} `function ()`