dns-suite.js/dns.unpack-labels.js

79 lines
1.7 KiB
JavaScript

(function (exports) {
'use strict';
// unpack labels with 0x20 compression pointer support
// ui8 is the ArrayBuffer of the entire packet
// ptr is the current index of the packet
// q = { byteLength: 0, cpcount: 0, labels: [], name: '' }
//
// NOTE:
// "NAME"s are terminated with 0x00
// "RDATA" is terminated by its length
exports.DNS_UNPACK_LABELS = function (ui8, ptr, q) {
if (q.cpcount > 25) {
throw new Error("compression pointer loop detected (over 25 pointers seems like a loop)");
}
var total = ptr;
var i;
var len;
var label = [];
do {
label.length = 0;
len = ui8[total];
if (len === undefined){
// RDATA is terminated by undefined, not len === 0
break;
}
if (0xc0 === len) {
var cpptr = ui8[total + 1];
// we're not coming back!
ptr = cpptr;
if (!q.cpcount) {
q.byteLength += 2; // cp and len
}
q.cpcount += 1;
// recursion
return exports.DNS_UNPACK_LABELS(ui8, ptr, q);
}
//str.length = 0; // fast empty array
if (ui8.byteLength - total < len) {
throw new Error(
"Expected a string of length " + len
+ " but packet itself has " + (ui8.byteLength - total) + " bytes remaining"
);
}
for (i = 0; i < len; i += 1) {
total += 1;
// TODO check url-allowable characters
label.push(String.fromCharCode(ui8[total]));
}
if (label.length) {
q.labels.push(label.join(''));
}
total += 1;
} while (0 !== len && undefined !== len);
//str.pop(); // remove trailing '.'
q.name = q.labels.join('.');
if (0 === q.cpcount) {
q.byteLength = total - ptr;
}
return q;
};
}('undefined' !== typeof window ? window : exports));