mirror of https://github.com/gchq/CyberChef.git
Completed GZIP extraction
This commit is contained in:
n1474335
parent
c077b22410
commit
4e57b4be88
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@ -1384,6 +1384,7 @@ export function extractRTF(bytes, offset) {
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export function extractGZIP(bytes, offset) {
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const stream = new Stream(bytes.slice(offset));
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/* HEADER */
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// Skip over signature and compression method
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@ -1396,7 +1397,7 @@ export function extractGZIP(bytes, offset) {
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stream.moveForwardsBy(4);
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// Read compression flags
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const compressionFlags = stream.readInt(1);
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stream.readInt(1);
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// Skip over OS
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stream.moveForwardsBy(1);
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@ -1406,34 +1407,63 @@ export function extractGZIP(bytes, offset) {
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// Extra fields
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if (flags & 0x4) {
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console.log("Extra fields");
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const extraFieldsSize = stream.readInt(2, "le");
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stream.moveForwardsby(extraFieldsSize);
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}
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// Original filename
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if (flags & 0x8) {
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console.log("Filename");
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stream.continueUntil(0x00);
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stream.moveForwardsBy(1);
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}
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// Comment
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if (flags & 0x10) {
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console.log("Comment");
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stream.continueUntil(0x00);
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stream.moveForwardsBy(1);
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}
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// Checksum
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if (flags & 0x2) {
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console.log("Checksum");
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stream.moveForwardsBy(2);
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}
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/* DEFLATE DATA */
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parseDEFLATE(stream);
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/* FOOTER */
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// Skip over checksum and size of original uncompressed input
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stream.moveForwardsBy(8);
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return stream.carve();
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}
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/**
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* Steps through a DEFLATE stream
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*
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* @param {Stream} stream
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*/
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function parseDEFLATE(stream) {
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// Construct required Huffman Tables
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const fixedLiteralTableLengths = new Uint8Array(288);
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for (let i = 0; i < fixedLiteralTableLengths.length; i++) {
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fixedLiteralTableLengths[i] =
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(i <= 143) ? 8 :
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(i <= 255) ? 9 :
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(i <= 279) ? 7 :
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8;
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}
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const fixedLiteralTable = buildHuffmanTable(fixedLiteralTableLengths);
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const fixedDistanceTableLengths = new Uint8Array(30).fill(5);
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const fixedDistanceTable = buildHuffmanTable(fixedDistanceTableLengths);
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const huffmanOrder = new Uint8Array([16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15]);
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// Parse DEFLATE data
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let finalBlock = 0;
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while (!finalBlock) {
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@ -1442,30 +1472,175 @@ export function extractGZIP(bytes, offset) {
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const blockType = stream.readBits(2);
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if (blockType === 0) {
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// No compression
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/* No compression */
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// Consume the rest of the current byte
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stream.moveForwardsBy(1);
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// Read the block length value
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const blockLength = stream.readInt(2, "le");
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console.log("No compression. Length: " + blockLength);
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// Move to the end of this block
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stream.moveForwardsBy(2 + blockLength);
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} else if (blockType === 1) {
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// Fixed Huffman
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console.log("Fixed Huffman");
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/* Fixed Huffman */
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parseHuffmanBlock(stream, fixedLiteralTable, fixedDistanceTable);
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} else if (blockType === 2) {
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// Dynamic Huffman
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console.log("Dynamic Huffman");
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/* Dynamic Huffman */
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// Read the number of liternal and length codes
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const hlit = stream.readBits(5) + 257;
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// Read the number of distance codes
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const hdist = stream.readBits(5) + 1;
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// Read the number of code lengths
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const hclen = stream.readBits(4) + 4;
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// Parse code lengths
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const codeLengths = new Uint8Array(huffmanOrder.length);
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for (let i = 0; i < hclen; i++) {
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codeLengths[huffmanOrder[i]] = stream.readBits(3);
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}
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// Parse length table
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const codeLengthsTable = buildHuffmanTable(codeLengths);
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const lengthTable = new Uint8Array(hlit + hdist);
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let code, repeat, prev;
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for (let i = 0; i < hlit + hdist;) {
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code = readHuffmanCode(stream, codeLengthsTable);
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switch (code) {
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case 16:
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repeat = 3 + stream.readBits(2);
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while (repeat--) lengthTable[i++] = prev;
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break;
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case 17:
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repeat = 3 + stream.readBits(3);
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while (repeat--) lengthTable[i++] = 0;
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prev = 0;
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break;
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case 18:
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repeat = 11 + stream.readBits(7);
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while (repeat--) lengthTable[i++] = 0;
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prev = 0;
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break;
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default:
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lengthTable[i++] = code;
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prev = code;
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break;
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}
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}
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const dynamicLiteralTable = buildHuffmanTable(lengthTable.subarray(0, hlit));
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const dynamicDistanceTable = buildHuffmanTable(lengthTable.subarray(hlit));
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parseHuffmanBlock(stream, dynamicLiteralTable, dynamicDistanceTable);
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} else {
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throw new Error("Invalid block type");
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break;
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}
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}
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/* FOOTER */
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// Skip over checksum and size of original uncompressed input
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stream.moveForwardsBy(8);
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console.log("Ending at " + stream.position);
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return stream.carve();
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// Consume final byte if it has not been fully consumed yet
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if (stream.bitPos > 0)
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stream.moveForwardsBy(1);
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}
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/**
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* Parses a Huffman Block given the literal and distance tables
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*
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* @param {Stream} stream
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* @param {Uint32Array} litTab
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* @param {Uint32Array} distTab
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*/
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function parseHuffmanBlock(stream, litTab, distTab) {
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const lengthExtraTable = new Uint8Array([
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0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0, 0, 0
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]);
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const distanceExtraTable = new Uint8Array([
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0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13
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]);
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let code;
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while ((code = readHuffmanCode(stream, litTab))) {
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// console.log("Code: " + code + " (" + Utils.chr(code) + ") " + Utils.bin(code));
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// End of block
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if (code === 256) break;
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// Literal
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if (code < 256) continue;
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// Length code
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stream.readBits(lengthExtraTable[code - 257]);
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// Dist code
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code = readHuffmanCode(stream, distTab);
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stream.readBits(distanceExtraTable[code]);
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}
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}
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/**
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* Builds a Huffman table given the relevant code lengths
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*
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* @param {Uint8Array} lengths
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* @returns {Array} result
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* @returns {Uint32Array} result.table
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* @returns {number} result.maxCodeLength
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* @returns {number} result.minCodeLength
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*/
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function buildHuffmanTable(lengths) {
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const maxCodeLength = Math.max.apply(Math, lengths);
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const minCodeLength = Math.min.apply(Math, lengths);
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const size = 1 << maxCodeLength;
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const table = new Uint32Array(size);
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for (let bitLength = 1, code = 0, skip = 2; bitLength <= maxCodeLength;) {
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for (let i = 0; i < lengths.length; i++) {
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if (lengths[i] === bitLength) {
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let reversed, rtemp, j;
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for (reversed = 0, rtemp = code, j = 0; j < bitLength; j++) {
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reversed = (reversed << 1) | (rtemp & 1);
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rtemp >>= 1;
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}
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const value = (bitLength << 16) | i;
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for (let j = reversed; j < size; j += skip) {
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table[j] = value;
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}
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code++;
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}
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}
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bitLength++;
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code <<= 1;
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skip <<= 1;
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}
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return [table, maxCodeLength, minCodeLength];
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}
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/**
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* Reads the next Huffman code from the stream, given the relevant code table
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*
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* @param {Stream} stream
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* @param {Uint32Array} table
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* @returns {number}
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*/
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function readHuffmanCode(stream, table) {
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const [codeTable, maxCodeLength] = table;
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// Read max length
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const bitsBuf = stream.readBits(maxCodeLength);
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const codeWithLength = codeTable[bitsBuf & ((1 << maxCodeLength) - 1)];
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const codeLength = codeWithLength >>> 16;
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if (codeLength > maxCodeLength) {
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throw new Error("Invalid code length: " + codeLength);
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}
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stream.moveBackwardsByBits(maxCodeLength - codeLength);
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return codeWithLength & 0xffff;
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}
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@ -90,7 +90,6 @@ export default class Stream {
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return val;
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}
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/**
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* Reads a number of bits from the buffer.
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*
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@ -194,7 +193,6 @@ export default class Stream {
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this.bitPos = 0;
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}
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/**
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* Move backwards through the stream by the specified number of bytes.
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*
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@ -208,6 +206,29 @@ export default class Stream {
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this.bitPos = 0;
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}
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/**
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* Move backwards through the strem by the specified number of bits.
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*
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* @param {number} numBits
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*/
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moveBackwardsByBits(numBits) {
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if (numBits <= this.bitPos) {
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this.bitPos -= numBits;
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} else {
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if (this.bitPos > 0) {
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numBits -= this.bitPos;
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this.bitPos = 0;
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}
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while (numBits > 0) {
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this.moveBackwardsBy(1);
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this.bitPos = 8;
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this.moveBackwardsByBits(numBits);
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numBits -= 8;
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}
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}
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}
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/**
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* Move to a specified position in the stream.
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*
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@ -46,7 +46,10 @@ class ExtractFiles extends Operation {
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detectedFiles.forEach(detectedFile => {
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try {
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files.push(extractFile(bytes, detectedFile.fileDetails, detectedFile.offset));
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} catch (err) {}
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} catch (err) {
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if (err.message.indexOf("No extraction algorithm available") < 0)
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throw err;
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}
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});
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return files;
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