90 lines
2.7 KiB
JavaScript
90 lines
2.7 KiB
JavaScript
(function (exports) {
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'use strict';
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// unpack labels with 0x20 compression pointer support
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// ui8 is the ArrayBuffer of the entire packet
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// ptr is the current index of the packet
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// q = { byteLength: 0, cpcount: 0, labels: [], name: '' }
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//
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// NOTE:
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// "NAME"s are terminated with 0x00
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// "RDATA" is terminated by its length
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exports.DNS_UNPACK_LABELS = function (ui8, ptr, q) {
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if (q.cpcount > 25) {
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throw new Error("compression pointer loop detected (over 25 pointers seems like a loop)");
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}
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var total = ptr;
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var i;
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var len;
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var label = [];
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do {
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label.length = 0;
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len = ui8[total];
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if (len === undefined){
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// RDATA is terminated by undefined, not len === 0
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q.trunc = true;
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break;
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}
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// Handle message compression pointers. See 4.1.4 of RFC1035 for details.
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// 0xc0 // 192 // parseInt('11000000', 2).toString(16)
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if (len >= 0xc0) {
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// Only the two highest bits are used to signify the pointer.
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// The remaining bits may be used to specify the address of the pointer
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// (it would seem that only 1 extra bit is actually used since the message size is 512 bytes)
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var cpptr = ((ui8[total] & 0x3f) << 8) | ui8[total + 1];
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// We're not coming back, so if this is the first time we're following one of
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// these pointers we up the byteLength to mark the pointer as part of the label
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if (!q.cpcount) {
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q.byteLength += 2; // cp and len
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}
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q.cpcount += 1;
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// recursion
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return exports.DNS_UNPACK_LABELS(ui8, cpptr, q);
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}
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//str.length = 0; // fast empty array
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if (ui8.byteLength - total < len) {
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//console.error('-1', ui8[total - 1]);
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//console.error(' 0', ui8[total]);
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//console.error(' 1', ui8[total + 1]);
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//console.error(' 1', ui8[total + 2]);
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throw new Error(
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"Expected a string of length " + len
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+ " but packet itself has " + (ui8.byteLength - total) + " bytes remaining"
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);
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}
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// Advance the pointer to after the length indicator, then read the string in.
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total += 1;
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for (i = 0; i < len; i += 1) {
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// TODO check url-allowable characters
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label.push(String.fromCharCode(ui8[total]));
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total += 1;
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}
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if (label.length) {
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q.labels.push(label.join(''));
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}
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// It is important this be done every time, so that if we run into a message compression
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// pointer later we still have a record of what was consumed before that.
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if (0 === q.cpcount) {
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q.byteLength = total - ptr;
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}
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} while (0 !== len && undefined !== len);
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//str.pop(); // remove trailing '.'
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q.name = q.labels.join('.');
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return q;
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};
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}('undefined' !== typeof window ? window : exports));
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