exports.handler = function()

in aws-blog-lambda-map-reduce-streaming/wordcount.js [11:122]
43 lines of code
10 McCabe index (conditional complexity)

exports.handler = function(event, context) {
  var startTime = process.hrtime();
  var id = context.invokeid;
  var srcBucket = event.bucket;
  var srcKeys = event.keys;
  var doAgg = true;
  if (event.no_agg)
    doAgg = false;

  if (!srcBucket || !srcKeys){
    context.error('Invalid args.');
  }
  
  // Word counting routine
  var countWords = function(srcKey, cb){
    try {      
      var lineCount = 0;
      var totalWords = 0;
      var finished = false;
      var warning = '';

      // Create our processor that splits lines/words
      var lineSplitter = es.split();
      lineSplitter.on('data', function(line){
        lineCount++;
        totalWords += line.split(/\W/).length;
        // Check our execution time
        var timeDiff = process.hrtime(startTime);
        if (timeDiff[0] >= MAX_EXEC_TIME){
          var msg = 'Hit max execution time of ' + MAX_EXEC_TIME +
            ' seconds, sending incomplete results.';
          console.error(msg);
          warning = msg;
          this.end();
        }
      })
      .on('error', function(err){
        console.error('Error in lineSplitter: ' + err);
      })
      .on('end', function(err){
        if (finished) return;
        if (err){
          console.error(err);
          cb(err, null);
          return;
        }
        console.log('Finished ' + srcKey + ' with ' +
          totalWords + ' in ' + lineCount + ' lines');
        cb(null, [srcKey, totalWords, lineCount, warning]);
        finished = true;
      });

      console.log('Downloading key ' + srcKey);
      // Create our pipeline
      if (srcKey.match(/\.gz/)){
        s3.getObject({
          Bucket: srcBucket,
          Key: srcKey
        })
          .createReadStream()
          .pipe(zlib.createGunzip())
          .pipe(lineSplitter);
      }
      else {
        s3.getObject({
          Bucket: srcBucket,
          Key: srcKey
        })
          .createReadStream()
          .pipe(lineSplitter);
      }
    } catch (e) {
      console.error(e);
      cb(e, null);
    }
  };

  // Execute the countWords function in parallel on all given keys
  async.map(srcKeys, countWords, function (err, results) {
    if (err){
      console.error(err);
      context.fail(err);
    }
    
    var warnings = [];
    
    if (doAgg){
      var totalWords = 0;
      var totalLines = 0;
      for (var i = 0, len = results.length; i < len; i++){
        totalWords += results[i][1];
        totalLines += results[i][2];
        if (results[i][3] !== ''){
          warnings.push(results[i][3]);
        }
      }
      console.log('Final total words: ' + totalWords);
      context.succeed([totalWords, totalLines, warnings]);
    }
    else {
      var entries = [];
      for (var i = 0, len = results.length; i < len; i++){
        entries.push([results[i][0], results[i][1], results[i][2]]);
        if (results[i][3] !== ''){
          warnings.push(results[i][3]);
        }
      }
      console.log('Processed ' + results.length + ' keys.');
      context.succeed([entries, warnings]);
    }
  });
};