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var BIT_16 = Math.pow(2, 16);
var BIT_24 = Math.pow(2, 24);
var BUFFER_ALLOC_SIZE = Math.pow(2, 8);
// The maximum precision JS Numbers can hold precisely
// Don't panic: Good enough to represent byte values up to 8192 TB
var IEEE_754_BINARY_64_PRECISION = Math.pow(2, 53);
var MAX_PACKET_LENGTH = Math.pow(2, 24) - 1;
var Buffer = require('safe-buffer').Buffer;
module.exports = PacketWriter;
function PacketWriter() {
this._buffer = null;
this._offset = 0;
}
PacketWriter.prototype.toBuffer = function toBuffer(parser) {
if (!this._buffer) {
this._buffer = Buffer.alloc(0);
this._offset = 0;
}
var buffer = this._buffer;
var length = this._offset;
var packets = Math.floor(length / MAX_PACKET_LENGTH) + 1;
this._buffer = Buffer.allocUnsafe(length + packets * 4);
this._offset = 0;
for (var packet = 0; packet < packets; packet++) {
var isLast = (packet + 1 === packets);
var packetLength = (isLast)
? length % MAX_PACKET_LENGTH
: MAX_PACKET_LENGTH;
var packetNumber = parser.incrementPacketNumber();
this.writeUnsignedNumber(3, packetLength);
this.writeUnsignedNumber(1, packetNumber);
var start = packet * MAX_PACKET_LENGTH;
var end = start + packetLength;
this.writeBuffer(buffer.slice(start, end));
}
return this._buffer;
};
PacketWriter.prototype.writeUnsignedNumber = function(bytes, value) {
this._allocate(bytes);
for (var i = 0; i < bytes; i++) {
this._buffer[this._offset++] = (value >> (i * 8)) & 0xff;
}
};
PacketWriter.prototype.writeFiller = function(bytes) {
this._allocate(bytes);
for (var i = 0; i < bytes; i++) {
this._buffer[this._offset++] = 0x00;
}
};
PacketWriter.prototype.writeNullTerminatedString = function(value, encoding) {
// Typecast undefined into '' and numbers into strings
value = value || '';
value = value + '';
var bytes = Buffer.byteLength(value, encoding || 'utf-8') + 1;
this._allocate(bytes);
this._buffer.write(value, this._offset, encoding);
this._buffer[this._offset + bytes - 1] = 0x00;
this._offset += bytes;
};
PacketWriter.prototype.writeString = function(value) {
// Typecast undefined into '' and numbers into strings
value = value || '';
value = value + '';
var bytes = Buffer.byteLength(value, 'utf-8');
this._allocate(bytes);
this._buffer.write(value, this._offset, 'utf-8');
this._offset += bytes;
};
PacketWriter.prototype.writeBuffer = function(value) {
var bytes = value.length;
this._allocate(bytes);
value.copy(this._buffer, this._offset);
this._offset += bytes;
};
PacketWriter.prototype.writeLengthCodedNumber = function(value) {
if (value === null) {
this._allocate(1);
this._buffer[this._offset++] = 251;
return;
}
if (value <= 250) {
this._allocate(1);
this._buffer[this._offset++] = value;
return;
}
if (value > IEEE_754_BINARY_64_PRECISION) {
throw new Error(
'writeLengthCodedNumber: JS precision range exceeded, your ' +
'number is > 53 bit: "' + value + '"'
);
}
if (value < BIT_16) {
this._allocate(3);
this._buffer[this._offset++] = 252;
} else if (value < BIT_24) {
this._allocate(4);
this._buffer[this._offset++] = 253;
} else {
this._allocate(9);
this._buffer[this._offset++] = 254;
}
// 16 Bit
this._buffer[this._offset++] = value & 0xff;
this._buffer[this._offset++] = (value >> 8) & 0xff;
if (value < BIT_16) {
return;
}
// 24 Bit
this._buffer[this._offset++] = (value >> 16) & 0xff;
if (value < BIT_24) {
return;
}
this._buffer[this._offset++] = (value >> 24) & 0xff;
// Hack: Get the most significant 32 bit (JS bitwise operators are 32 bit)
value = value.toString(2);
value = value.substr(0, value.length - 32);
value = parseInt(value, 2);
this._buffer[this._offset++] = value & 0xff;
this._buffer[this._offset++] = (value >> 8) & 0xff;
this._buffer[this._offset++] = (value >> 16) & 0xff;
// Set last byte to 0, as we can only support 53 bits in JS (see above)
this._buffer[this._offset++] = 0;
};
PacketWriter.prototype.writeLengthCodedBuffer = function(value) {
var bytes = value.length;
this.writeLengthCodedNumber(bytes);
this.writeBuffer(value);
};
PacketWriter.prototype.writeNullTerminatedBuffer = function(value) {
this.writeBuffer(value);
this.writeFiller(1); // 0x00 terminator
};
PacketWriter.prototype.writeLengthCodedString = function(value) {
if (value === null) {
this.writeLengthCodedNumber(null);
return;
}
value = (value === undefined)
? ''
: String(value);
var bytes = Buffer.byteLength(value, 'utf-8');
this.writeLengthCodedNumber(bytes);
if (!bytes) {
return;
}
this._allocate(bytes);
this._buffer.write(value, this._offset, 'utf-8');
this._offset += bytes;
};
PacketWriter.prototype._allocate = function _allocate(bytes) {
if (!this._buffer) {
this._buffer = Buffer.alloc(Math.max(BUFFER_ALLOC_SIZE, bytes));
this._offset = 0;
return;
}
var bytesRemaining = this._buffer.length - this._offset;
if (bytesRemaining >= bytes) {
return;
}
var newSize = this._buffer.length + Math.max(BUFFER_ALLOC_SIZE, bytes);
var oldBuffer = this._buffer;
this._buffer = Buffer.alloc(newSize);
oldBuffer.copy(this._buffer);
};