select-stream.js

var { Transform } = require('stream');
var sysUtil = require('util');
var util = require('./util');

function SelectStream(options) {
  if (!(this instanceof SelectStream)) return new SelectStream(options);
  Transform.call(this, options);
  Object.assign(this, {
    totalLength: 0, // current message block's total length
    headerLength: 0, // current message block's header length
    payloadRestLength: 0, // current message block's rest payload length
    header: null, // current message block's header
    chunk: Buffer.alloc(0), // the data chunk being parsed
    callback: null, // current _transform function's callback
  });
}
SelectStream.prototype = {
  /**
   * process data chunk
   * concat the last chunk and current chunk
   * try to parse current message block's totalLength and headerLength
   * try to parse current message block's header
   * try to parse current message block's payload
   */
  processChunk(chunk, encoding, callback) {
    Object.assign(this, {
      chunk: Buffer.concat([this.chunk, chunk], this.chunk.length + chunk.length),
      encoding,
      callback,
    });

    this.parseLength();
    this.parseHeader();
    this.parsePayload();
  },

  /**
   * try to parse current message block's totalLength and headerLength
   */
  parseLength() {
    if (!this.callback) {
      return;
    }

    if (this.totalLength && this.headerLength) {
      return;
    }

    if (this.chunk.length >= 12) {
      this.totalLength = this.chunk.readInt32BE(0);
      this.headerLength = this.chunk.readInt32BE(4);
      this.payloadRestLength = this.totalLength - this.headerLength - 16;
      this.chunk = this.chunk.slice(12);
    } else {
      this.callback();
      this.callback = null;
    }
  },

  /**
   * try to parse current message block's header
   * if header[':message-type'] is error, callback the error, emit error to next stream
   */
  parseHeader() {
    if (!this.callback) {
      return;
    }

    if (!this.headerLength || this.header) {
      return;
    }

    if (this.chunk.length >= this.headerLength) {
      var header = {};
      var offset = 0;
      while (offset < this.headerLength) {
        var headerNameLength = this.chunk[offset] * 1;
        var headerName = this.chunk.toString('ascii', offset + 1, offset + 1 + headerNameLength);
        var headerValueLength = this.chunk.readInt16BE(offset + headerNameLength + 2);
        var headerValue = this.chunk.toString(
          'ascii',
          offset + headerNameLength + 4,
          offset + headerNameLength + 4 + headerValueLength
        );
        header[headerName] = headerValue;
        offset += headerNameLength + 4 + headerValueLength;
      }
      this.header = header;
      this.chunk = this.chunk.slice(this.headerLength);
      this.checkErrorHeader();
    } else {
      this.callback();
      this.callback = null;
    }
  },

  /**
   * try to parse current message block's payload
   */
  parsePayload() {
    var self = this;
    if (!this.callback) {
      return;
    }

    if (this.chunk.length <= this.payloadRestLength) {
      this.payloadRestLength -= this.chunk.length;
      this.pushData(this.chunk);
      this.chunk = Buffer.alloc(0);
    } else if (this.chunk.length < this.payloadRestLength + 4) {
      this.pushData(this.chunk.slice(0, this.payloadRestLength));
      this.chunk = this.chunk.slice(this.payloadRestLength);
      this.payloadRestLength = 0;
    } else {
      this.pushData(this.chunk.slice(0, this.payloadRestLength));
      this.chunk = this.chunk.slice(this.payloadRestLength + 4);
      this.totalLength = 0;
      this.headerLength = 0;
      this.payloadRestLength = 0;
      this.header = null;
    }

    if (this.chunk.length && !(this.payloadRestLength === 0 && this.chunk.length < 4)) {
      process.nextTick(function () {
        self.processChunk(Buffer.alloc(0), self.encoding, self.callback);
      });
    } else {
      this.callback();
      this.callback = null;
    }
  },

  /**
   * if header[':event-type'] is Records, pipe payload to next stream
   */
  pushData(content) {
    if (this.header[':event-type'] === 'Records') {
      this.push(content);
      this.emit('message:records', content);
    } else if (this.header[':event-type'] === 'Progress') {
      var progress = util.xml2json(content.toString()).Progress;
      this.emit('message:progress', progress);
    } else if (this.header[':event-type'] === 'Stats') {
      var stats = util.xml2json(content.toString()).Stats;
      this.emit('message:stats', stats);
    } else if (this.header[':event-type'] === 'error') {
      var errCode = this.header[':error-code'];
      var errMessage = this.header[':error-message'];
      var err = new Error(errMessage);
      err.message = errMessage;
      err.name = err.code = errCode;
      this.emit('message:error', err);
    } else {
      // 'Continuation', 'End'
      this.emit('message:' + this.header[':event-type'].toLowerCase());
    }
  },

  /**
   * if header[':message-type'] is error, callback the error, emit error to next stream
   */
  checkErrorHeader() {
    if (this.header[':message-type'] === 'error') {
      this.callback(this.header);
      this.callback = null;
    }
  },

  /**
   * Transform Stream's implementations
   */
  _transform(chunk, encoding, callback) {
    this.processChunk(chunk, encoding, callback);
  },
  _flush(callback) {
    this.processChunk(Buffer.alloc(0), this.encoding, callback);
  },
};
sysUtil.inherits(SelectStream, Transform);

module.exports = SelectStream;