obuf/index.js

Byte buffer specialized for data in chunks with special cases for dropping bytes in the front, merging bytes in to various integer types and abandoning buffer without penalty for previous chunk merges.

var Buffer = require('buffer').Buffer;

function OffsetBuffer() {
  this.offset = 0;
  this.size = 0;
  this.buffers = [];
}
module.exports = OffsetBuffer;

OffsetBuffer.prototype.isEmpty = function isEmpty() {
  return this.size === 0;
};

OffsetBuffer.prototype.clone = function clone(size) {
  var r = new OffsetBuffer();
  r.offset = this.offset;
  r.size = size;
  r.buffers = this.buffers.slice();
  return r;
};

OffsetBuffer.prototype.toChunks = function toChunks() {
  if (this.size === 0)
    return [];

  // We are going to slice it anyway
  if (this.offset !== 0) {
    this.buffers[0] = this.buffers[0].slice(this.offset);
    this.offset = 0;
  }

  var chunks = [ ];
  var off = 0;
  for (var i = 0; off <= this.size && i < this.buffers.length; i++) {
    var buf = this.buffers[i];
    off += buf.length;

    // Slice off last buffer
    if (off > this.size) {
      buf = buf.slice(0, buf.length - (off - this.size));
      this.buffers[i] = buf;
    }

    chunks.push(buf);
  }

  // If some buffers were skipped - trim length
  if (i < this.buffers.length)
    this.buffers.length = i;

  return chunks;
};

OffsetBuffer.prototype.toString = function toString(enc) {
  return this.toChunks().map(function(c) {
    return c.toString(enc);
  }).join('');
};

OffsetBuffer.prototype.use = function use(buf, off, n) {
  this.buffers = [ buf ];
  this.offset = off;
  this.size = n;
};

OffsetBuffer.prototype.push = function push(data) {
  // Ignore empty writes
  if (data.length === 0)
    return;

  this.size += data.length;
  this.buffers.push(data);
};

OffsetBuffer.prototype.has = function has(n) {
  return this.size >= n;
};

OffsetBuffer.prototype.skip = function skip(n) {
  if (this.size === 0)
    return;

  this.size -= n;

  // Fast case, skip bytes in a first buffer
  if (this.offset + n < this.buffers[0].length) {
    this.offset += n;
    return;
  }

  var left = n - (this.buffers[0].length - this.offset);
  this.offset = 0;

  for (var shift = 1; left > 0 && shift < this.buffers.length; shift++) {
    var buf = this.buffers[shift];
    if (buf.length > left) {
      this.offset = left;
      break;
    }
    left -= buf.length;
  }
  this.buffers = this.buffers.slice(shift);
};

OffsetBuffer.prototype.copy = function copy(target, targetOff, off, n) {
  if (this.size === 0)
    return;
  if (off !== 0)
    throw new Error('Unsupported offset in .copy()');

  var toff = targetOff;
  var first = this.buffers[0];
  var toCopy = Math.min(n, first.length - this.offset);
  first.copy(target, toff, this.offset, this.offset + toCopy);

  toff += toCopy;
  var left = n - toCopy;
  for (var i = 1; left > 0 && i < this.buffers.length; i++) {
    var buf = this.buffers[i];
    var toCopy = Math.min(left, buf.length);

    buf.copy(target, toff, 0, toCopy);

    toff += toCopy;
    left -= toCopy;
  }
};

OffsetBuffer.prototype.take = function take(n) {
  if (n === 0)
    return new Buffer(0);

  this.size -= n;

  // Fast cases
  var first = this.buffers[0].length - this.offset;
  if (first === n) {
    var r = this.buffers.shift();
    if (this.offset !== 0) {
      r = r.slice(this.offset);
      this.offset = 0;
    }
    return r;
  } else if (first > n) {
    var r = this.buffers[0].slice(this.offset, this.offset + n);
    this.offset += n;
    return r;
  }

  // Allocate and fill buffer
  var out = new Buffer(n);
  var toOff = 0;
  var startOff = this.offset;
  for (var i = 0; toOff !== n && i < this.buffers.length; i++) {
    var buf = this.buffers[i];
    var toCopy = Math.min(buf.length - startOff, n - toOff);

    buf.copy(out, toOff, startOff, startOff + toCopy);
    if (startOff + toCopy < buf.length) {
      this.offset = startOff + toCopy;
      break;
    } else {
      toOff += toCopy;
      startOff = 0;
    }
  }

  this.buffers = this.buffers.slice(i);
  if (this.buffers.length === 0)
    this.offset = 0;

  return out;
};

OffsetBuffer.prototype.peekUInt8 = function peekUInt8() {
  return this.buffers[0][this.offset];
};

OffsetBuffer.prototype.readUInt8 = function readUInt8() {
  this.size -= 1;
  var first = this.buffers[0];
  var r = first[this.offset];
  if (++this.offset === first.length) {
    this.offset = 0;
    this.buffers.shift();
  }

  return r;
};

OffsetBuffer.prototype.readUInt16LE = function readUInt16LE() {
  var first = this.buffers[0];
  this.size -= 2;

  var r;
  var shift;

  // Fast case - first buffer has all bytes
  if (first.length - this.offset >= 2) {
    r = first.readUInt16LE(this.offset);
    shift = 0;
    this.offset += 2;

  // One byte here - one byte there
  } else {
    r = first[this.offset] | (this.buffers[1][0] << 8);
    shift = 1;
    this.offset = 1;
  }

  if (this.offset === this.buffers[shift].length) {
    this.offset = 0;
    shift++;
  }
  if (shift !== 0)
    this.buffers = this.buffers.slice(shift);

  return r;
};

OffsetBuffer.prototype.readUInt24LE = function readUInt24LE() {
  var first = this.buffers[0];

  var r;
  var shift;
  var firstHas = first.length - this.offset;

  // Fast case - first buffer has all bytes
  if (firstHas >= 3) {
    r = first.readUInt16LE(this.offset) | (first[this.offset + 2] << 16);
    shift = 0;
    this.offset += 3;

  // First buffer has 2 of 3 bytes
  } else if (firstHas >= 2) {
    r = first.readUInt16LE(this.offset) | (this.buffers[1][0] << 16);
    shift = 1;
    this.offset = 1;

  // Slow case: First buffer has 1 of 3 bytes
  } else {
    r = first[this.offset];
    this.offset = 0;
    this.buffers.shift();
    this.size -= 1;

    r |= this.readUInt16LE() << 8;
    return r;
  }

  this.size -= 3;
  if (this.offset === this.buffers[shift].length) {
    this.offset = 0;
    shift++;
  }
  if (shift !== 0)
    this.buffers = this.buffers.slice(shift);

  return r;
};

OffsetBuffer.prototype.readUInt32LE = function readUInt32LE() {
  var first = this.buffers[0];

  var r;
  var shift;
  var firstHas = first.length - this.offset;

  // Fast case - first buffer has all bytes
  if (firstHas >= 4) {
    r = first.readUInt32LE(this.offset);
    shift = 0;
    this.offset += 4;

  // First buffer has 3 of 4 bytes
  } else if (firstHas >= 3) {
    r = (first.readUInt16LE(this.offset) |
         (first[this.offset + 2] << 16)) +
        (this.buffers[1][0] * 0x1000000);
    shift = 1;
    this.offset = 1;

  // Slow case: First buffer has 2 of 4 bytes
  } else if (firstHas >= 2) {
    r = first.readUInt16LE(this.offset);
    this.offset = 0;
    this.buffers.shift();
    this.size -= 2;

    r += this.readUInt16LE() * 0x10000;
    return r;

  // Slow case: First buffer has 1 of 4 bytes
  } else {
    r = first[this.offset];
    this.offset = 0;
    this.buffers.shift();
    this.size -= 1;

    r += this.readUInt24LE() * 0x100;
    return r;
  }

  this.size -= 4;
  if (this.offset === this.buffers[shift].length) {
    this.offset = 0;
    shift++;
  }
  if (shift !== 0)
    this.buffers = this.buffers.slice(shift);

  return r;
};

OffsetBuffer.prototype.readUInt16BE = function readUInt16BE() {
  var r = this.readUInt16LE();

  return ((r & 0xff) << 8) | (r >> 8);
};

OffsetBuffer.prototype.readUInt24BE = function readUInt24BE() {
  var r = this.readUInt24LE();

  return ((r & 0xff) << 16) | (((r >> 8) & 0xff) << 8) | (r >> 16);
};

OffsetBuffer.prototype.readUInt32BE = function readUInt32BE() {
  var r = this.readUInt32LE();

  return (((r & 0xff) << 24) |
          (((r >>> 8) & 0xff) << 16) |
          (((r >>> 16) & 0xff) << 8) |
          (r >>> 24)) >>> 0;
};

// Signed number APIs

function signedInt8(num) {
  if (num >= 0x80)
    return -(0xff ^ num) - 1;
  else
    return num;
}

OffsetBuffer.prototype.peekInt8 = function peekInt8() {
  return signedInt8(this.peekUInt8());
};

OffsetBuffer.prototype.readInt8 = function readInt8() {
  return signedInt8(this.readUInt8());
};

function signedInt16(num) {
  if (num >= 0x8000)
    return -(0xffff ^ num) - 1;
  else
    return num;
}

OffsetBuffer.prototype.readInt16BE = function readInt16BE() {
  return signedInt16(this.readUInt16BE());
};

OffsetBuffer.prototype.readInt16LE = function readInt16LE() {
  return signedInt16(this.readUInt16LE());
};

function signedInt24(num) {
  if (num >= 0x800000)
    return -(0xffffff ^ num) - 1;
  else
    return num;
}

OffsetBuffer.prototype.readInt24BE = function readInt24BE() {
  return signedInt24(this.readUInt24BE());
};

OffsetBuffer.prototype.readInt24LE = function readInt24LE() {
  return signedInt24(this.readUInt24LE());
};

function signedInt32(num) {
  if (num >= 0x80000000)
    return -(0xffffffff ^ num) - 1;
  else
    return num;
}

OffsetBuffer.prototype.readInt32BE = function readInt32BE() {
  return signedInt32(this.readUInt32BE());
};

OffsetBuffer.prototype.readInt32LE = function readInt32LE() {
  return signedInt32(this.readUInt32LE());
};