Fully end to end encrypted anonymous chat program. Server only stores public key lookup for users and the encrypted messages. No credentials are transfered to the server, but kept in local browser storage. This allows 100% safe chatting. https://safechat.ch
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var BIT_16 = Math.pow(2, 16);
var BIT_24 = Math.pow(2, 24);
// 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;
module.exports = PacketWriter;
function PacketWriter() {
this._buffer = new Buffer(0);
this._offset = 0;
}
PacketWriter.prototype.toBuffer = function(parser) {
var packets = Math.floor(this._buffer.length / MAX_PACKET_LENGTH) + 1;
var buffer = this._buffer;
this._buffer = new Buffer(this._buffer.length + packets * 4);
for (var packet = 0; packet < packets; packet++) {
this._offset = packet * (MAX_PACKET_LENGTH + 4);
var isLast = (packet + 1 === packets);
var packetLength = (isLast)
? buffer.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(bytes) {
if (!this._buffer) {
this._buffer = new Buffer(bytes);
return;
}
var bytesRemaining = this._buffer.length - this._offset;
if (bytesRemaining >= bytes) {
return;
}
var oldBuffer = this._buffer;
this._buffer = new Buffer(oldBuffer.length + bytes);
oldBuffer.copy(this._buffer);
};