flex-buffer.js

// flex-buffer.js

exports.FlexDecoder = FlexDecoder;
exports.FlexEncoder = FlexEncoder;

var Bufferish = require("./bufferish");

var MIN_BUFFER_SIZE = 2048;
var MAX_BUFFER_SIZE = 65536;
var BUFFER_SHORTAGE = "BUFFER_SHORTAGE";

function FlexDecoder() {
  if (!(this instanceof FlexDecoder)) return new FlexDecoder();
}

function FlexEncoder() {
  if (!(this instanceof FlexEncoder)) return new FlexEncoder();
}

FlexDecoder.mixin = mixinFactory(getDecoderMethods());
FlexDecoder.mixin(FlexDecoder.prototype);

FlexEncoder.mixin = mixinFactory(getEncoderMethods());
FlexEncoder.mixin(FlexEncoder.prototype);

function getDecoderMethods() {
  return {
    bufferish: Bufferish,
    write: write,
    fetch: fetch,
    flush: flush,
    push: push,
    pull: pull,
    read: read,
    reserve: reserve,
    offset: 0
  };

  function write(chunk) {
    var prev = this.offset ? Bufferish.prototype.slice.call(this.buffer, this.offset) : this.buffer;
    this.buffer = prev ? (chunk ? this.bufferish.concat([prev, chunk]) : prev) : chunk;
    this.offset = 0;
  }

  function flush() {
    while (this.offset < this.buffer.length) {
      var start = this.offset;
      var value;
      try {
        value = this.fetch();
      } catch (e) {
        if (e && e.message != BUFFER_SHORTAGE) throw e;
        // rollback
        this.offset = start;
        break;
      }
      this.push(value);
    }
  }

  function reserve(length) {
    var start = this.offset;
    var end = start + length;
    if (end > this.buffer.length) throw new Error(BUFFER_SHORTAGE);
    this.offset = end;
    return start;
  }
}

function getEncoderMethods() {
  return {
    bufferish: Bufferish,
    write: write,
    fetch: fetch,
    flush: flush,
    push: push,
    pull: pull,
    read: read,
    reserve: reserve,
    send: send,
    maxBufferSize: MAX_BUFFER_SIZE,
    minBufferSize: MIN_BUFFER_SIZE,
    offset: 0,
    start: 0
  };

  function fetch() {
    var start = this.start;
    if (start < this.offset) {
      var end = this.start = this.offset;
      return Bufferish.prototype.slice.call(this.buffer, start, end);
    }
  }

  function flush() {
    while (this.start < this.offset) {
      var value = this.fetch();
      if (value) this.push(value);
    }
  }

  function pull() {
    var buffers = this.buffers || (this.buffers = []);
    var chunk = buffers.length > 1 ? this.bufferish.concat(buffers) : buffers[0];
    buffers.length = 0; // buffer exhausted
    return chunk;
  }

  function reserve(length) {
    var req = length | 0;

    if (this.buffer) {
      var size = this.buffer.length;
      var start = this.offset | 0;
      var end = start + req;

      // is it long enough?
      if (end < size) {
        this.offset = end;
        return start;
      }

      // flush current buffer
      this.flush();

      // resize it to 2x current length
      length = Math.max(length, Math.min(size * 2, this.maxBufferSize));
    }

    // minimum buffer size
    length = Math.max(length, this.minBufferSize);

    // allocate new buffer
    this.buffer = this.bufferish.alloc(length);
    this.start = 0;
    this.offset = req;
    return 0;
  }

  function send(buffer) {
    var length = buffer.length;
    if (length > this.minBufferSize) {
      this.flush();
      this.push(buffer);
    } else {
      var offset = this.reserve(length);
      Bufferish.prototype.copy.call(buffer, this.buffer, offset);
    }
  }
}

// common methods

function write() {
  throw new Error("method not implemented: write()");
}

function fetch() {
  throw new Error("method not implemented: fetch()");
}

function read() {
  var length = this.buffers && this.buffers.length;

  // fetch the first result
  if (!length) return this.fetch();

  // flush current buffer
  this.flush();

  // read from the results
  return this.pull();
}

function push(chunk) {
  var buffers = this.buffers || (this.buffers = []);
  buffers.push(chunk);
}

function pull() {
  var buffers = this.buffers || (this.buffers = []);
  return buffers.shift();
}

function mixinFactory(source) {
  return mixin;

  function mixin(target) {
    for (var key in source) {
      target[key] = source[key];
    }
    return target;
  }
}