bitmessage-js/lib/structs.js
Kagami Hiiragi daf18762c8 Tune docs
2015-01-03 18:58:41 +03:00

175 lines
5.2 KiB
JavaScript

/**
* Implements common structures.
* @see {@link https://bitmessage.org/wiki/Protocol_specification#Common_structures}
* @module bitmessage/structs
*/
"use strict";
var assert = require("assert");
/**
* var_int.
* @see {@link https://bitmessage.org/wiki/Protocol_specification#Variable_length_integer}
* @namespace
* @static
*/
var var_int = exports.var_int = {
/**
* Decode var_int.
* @param {Buffer} buf - A buffer that starts with encoded var_int
* @return {{value: number, length: number, rest: Buffer}}
* Decoded var_int structure.
*/
decode: function(buf) {
var value, length;
assert(buf.length > 0, "Empty buffer");
switch (buf[0]) {
case 253:
value = buf.readUInt16BE(1);
assert(value >= 253, "Impractical var_int");
length = 3;
break;
case 254:
value = buf.readUInt32BE(1);
assert(value >= 65536, "Impractical var_int");
length = 5;
break;
case 255:
var hi = buf.readUInt32BE(1);
assert(hi !== 0, "Impractical var_int");
// Max safe number = 2^53 - 1 =
// 0b0000000000011111111111111111111111111111111111111111111111111111
// = 2097151*(2^32) + (2^32 - 1).
// So it's safe until hi <= 2097151. See
// <http://mdn.io/issafeinteger>,
// <https://stackoverflow.com/q/307179> for details.
// TODO(Kagami): We may want to return raw Buffer for
// 2^53 <= value <= 2^64 - 1 range. Possibly using the optional
// argument because most of the code expect to get a number when
// calling `var_int.decode`.
assert(hi <= 2097151, "Unsafe integer");
var lo = buf.readUInt32BE(5);
value = hi * 4294967296 + lo;
length = 9;
break;
default:
value = buf[0];
length = 1;
}
var rest = buf.slice(length);
return {value: value, length: length, rest: rest};
},
/**
* Encode number into var_int.
* @param {(number|Buffer)} value - Input number
* @return {Buffer} Encoded var_int.
*/
encode: function(value) {
var buf, targetStart;
if (typeof value === "number") {
assert(value >= 0, "Value cannot be less than zero");
if (value < 253) {
buf = new Buffer([value]);
} else if (value < 65536) {
buf = new Buffer(3);
buf[0] = 253;
buf.writeUInt16BE(value, 1, true);
} else if (value < 4294967296) {
buf = new Buffer(5);
buf[0] = 254;
buf.writeUInt32BE(value, 1, true);
} else {
assert(value <= 9007199254740991, "Unsafe integer");
buf = new Buffer(9);
buf[0] = 255;
buf.writeUInt32BE(Math.floor(value / 4294967296), 1, true); // high32
buf.writeUInt32BE(value % 4294967296, 5, true); // low32
}
} else if (Buffer.isBuffer(value)) {
assert(value.length <= 8, "Buffer is too big");
buf = new Buffer(9);
buf.fill(0);
buf[0] = 255;
targetStart = 1 + (8 - value.length);
value.copy(buf, targetStart);
} else {
throw new Error("Value encode error");
}
return buf;
},
};
/**
* var_str.
* @see {@link https://bitmessage.org/wiki/Protocol_specification#Variable_length_string}
* @namespace
*/
exports.var_str = {
/**
* Decode var_str.
* @param {Buffer} buf - A buffer that starts with encoded var_str
* @return {{str: string, length: number, rest: Buffer}}
* Decoded var_str structure.
*/
decode: function(buf) {
var decoded = var_int.decode(buf);
var strLength = decoded.value;
// XXX(Kagami): Spec doesn't mention encoding, using UTF-8.
var str = decoded.rest.slice(0, strLength).toString();
var rest = decoded.rest.slice(strLength);
return {str: str, length: decoded.length + strLength, rest: rest};
},
/**
* Encode string into var_str.
* @param {string} str - A string
* @return {Buffer} Encoded var_str.
*/
encode: function(str) {
// XXX(Kagami): Spec doesn't mention encoding, using UTF-8.
var strBuf = new Buffer(str);
return Buffer.concat([var_int.encode(strBuf.length), strBuf]);
},
};
/**
* var_int_list.
* @see {@link https://bitmessage.org/wiki/Protocol_specification#Variable_length_list_of_integers}
* @namespace
*/
exports.var_int_list = {
/**
* Decode var_int_list.
* @param {Buffer} buf - A buffer that starts with encoded
* var_int_list
* @return {{list: number[], length: number, rest: Buffer}}
* Decoded var_int_list structure.
*/
decode: function(buf) {
var decoded = var_int.decode(buf);
var listLength = decoded.value;
var list = new Array(listLength);
var rest = decoded.rest;
var sumLength = decoded.length;
for (var i = 0; i < listLength; i++) {
decoded = var_int.decode(rest);
list[i] = decoded.value;
rest = decoded.rest;
sumLength += decoded.length;
}
return {list: list, length: sumLength, rest: rest};
},
/**
* Encode list of numbers into var_int_list.
* @param {number[]} list - A number list
* @return {Buffer} Encoded var_int_list.
*/
encode: function(list) {
var listBuf = Buffer.concat(list.map(var_int.encode));
return Buffer.concat([var_int.encode(list.length), listBuf]);
},
};