baucis-json/index.js

Baucis uses this to parse and format streams of JSON.

// __Dependencies__
var es = require('event-stream');

// __Module Definition__
var plugin = module.exports = function () {
  var baucis = this;

  // __Private Methods__
  // Default formatter — emit a single JSON object or an array of them.
  function singleOrArray (alwaysArray) {
    var first = false;
    var multiple = false;

    return es.through(
      function (doc) {
        // Start building the output.  If this is the first document,
        // store it for a moment.
        if (!first) {
          first = doc;
          return;
        }
        // If this is the second document, output array opening and the two documents
        // separated by a comma.
        if (!multiple) {
          multiple = true;
          this.emit('data', '[');
          this.emit('data', JSON.stringify(first));
          this.emit('data', ',\n')
          this.emit('data', JSON.stringify(doc));
          return;
        }
        // For all documents after the second, emit a comma preceding the document.
        this.emit('data', ',\n');
        this.emit('data', JSON.stringify(doc));
      },
      function () {
        // If no documents, simply end the stream.
        if (!first) return this.emit('end');
        // If only one document emit it unwrapped, unless always returning an array.
        if (!multiple && alwaysArray) this.emit('data', '[');
        if (!multiple) this.emit('data', JSON.stringify(first));
        // For greater than one document, emit the closing array.
        else this.emit('data', ']');
        if (!multiple && alwaysArray) this.emit('data', ']');
        // Done.  End the stream.
        this.emit('end');
      }
    );
  };

  // Default parser.  Parses incoming JSON string into an object or objects.
  // Works whether an array or single object is sent as the request body.  It's
  // very lenient with input outside of first-level braces.  This means that
  // a collection of JSON objects can be sent in different ways e.g. separated
  // by whitespace or in a fully JSON-compatible array with objects split by 
  // commas.
  function JSONParser () {
    var depth = 0;
    var buffer = '';

    return es.through(function (chunk) {
      var match;
      var head;
      var brace;
      var tail;
      var emission;
      var remaining = chunk.toString();
      while (remaining !== '') {
        match = remaining.match(/[\}\{]/);
        // The head of the string is all characters up to the first brace, if any.
        head = match ? remaining.substr(0, match.index) : remaining;
        // The first brace in the string, if any.
        brace = match ? match[0] : '';
        // The rest of the string, following the brace.
        tail = match ? remaining.substr(match.index + 1) : '';

        if (depth === 0) {
          // The parser is outside an object.
          // Ignore the head of the string.
          // Add brace if it's an open brace.
          if (brace === '{') {
            depth += 1;
            buffer += brace;
          }
        }
        else {
          // The parser is inside an object.
          // Add the head of the string to the buffer.
          buffer += head;
          // Increase or decrease depth if a brace was found.
          if (brace === '{') depth += 1;
          else if (brace === '}') depth -= 1;
          // Add the brace to the buffer.
          buffer += brace;
          // If the object ended, emit it.
          if (depth === 0) {
            try {
              emission = JSON.parse(buffer);
            }
            catch (error) {
              this.emit('error', baucis.Error.BadSyntax('The body of this request was invalid and could not be parsed. "%s"', error.message));
            }

            this.emit('data', emission);
            buffer = '';
          }
        }
        // Move on to the unprocessed remainder of the string.
        remaining = tail;
      }
    });
  }

  // Add a JSON formatter and parser.
  baucis.setFormatter('application/json', singleOrArray);
  baucis.setParser('application/json', JSONParser);
};