Reduce kept state in JPEG decoder
We don't have to keep track of this much data between rects, so restructure things to make it more simple. This allows the JPEG parsing code to be a pure function which only depends on the input.
This commit is contained in:
Pierre Ossman
parent
eb0ad829d2
commit
87143b361e
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@ -11,131 +11,136 @@ export default class JPEGDecoder {
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constructor() {
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// RealVNC will reuse the quantization tables
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// and Huffman tables, so we need to cache them.
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this._quantTables = [];
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this._huffmanTables = [];
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this._cachedQuantTables = [];
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this._cachedHuffmanTables = [];
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this._jpegLength = 0;
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this._segments = [];
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}
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decodeRect(x, y, width, height, sock, display, depth) {
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// A rect of JPEG encodings is simply a JPEG file
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if (!this._parseJPEG(sock.rQslice(0))) {
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return false;
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}
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const data = sock.rQshiftBytes(this._jpegLength);
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if (this._quantTables.length != 0 && this._huffmanTables.length != 0) {
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// If there are quantization tables and Huffman tables in the JPEG
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// image, we can directly render it.
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display.imageRect(x, y, width, height, "image/jpeg", data);
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return true;
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} else {
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// Otherwise we need to insert cached tables.
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const sofIndex = this._segments.findIndex(
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x => x[1] == 0xC0 || x[1] == 0xC2
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);
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if (sofIndex == -1) {
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throw new Error("Illegal JPEG image without SOF");
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}
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let segments = this._segments.slice(0, sofIndex);
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segments = segments.concat(this._quantTables.length ?
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this._quantTables :
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this._cachedQuantTables);
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segments.push(this._segments[sofIndex]);
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segments = segments.concat(this._huffmanTables.length ?
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this._huffmanTables :
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this._cachedHuffmanTables,
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this._segments.slice(sofIndex + 1));
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let length = 0;
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for (let i = 0; i < segments.length; i++) {
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length += segments[i].length;
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}
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const data = new Uint8Array(length);
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length = 0;
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for (let i = 0; i < segments.length; i++) {
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data.set(segments[i], length);
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length += segments[i].length;
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}
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display.imageRect(x, y, width, height, "image/jpeg", data);
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return true;
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}
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}
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_parseJPEG(buffer) {
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if (this._quantTables.length != 0) {
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this._cachedQuantTables = this._quantTables;
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}
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if (this._huffmanTables.length != 0) {
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this._cachedHuffmanTables = this._huffmanTables;
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}
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this._quantTables = [];
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this._huffmanTables = [];
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this._segments = [];
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let i = 0;
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let bufferLength = buffer.length;
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while (true) {
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let j = i;
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if (j + 2 > bufferLength) {
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let segment = this._readSegment(sock);
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if (segment === null) {
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return false;
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}
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if (buffer[j] != 0xFF) {
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throw new Error("Illegal JPEG marker received (byte: " +
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buffer[j] + ")");
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}
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const type = buffer[j+1];
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j += 2;
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if (type == 0xD9) {
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this._jpegLength = j;
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this._segments.push(buffer.slice(i, j));
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return true;
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} else if (type == 0xDA) {
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// start of scan
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let hasFoundEndOfScan = false;
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for (let k = j + 3; k + 1 < bufferLength; k++) {
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if (buffer[k] == 0xFF && buffer[k+1] != 0x00 &&
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!(buffer[k+1] >= 0xD0 && buffer[k+1] <= 0xD7)) {
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j = k;
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hasFoundEndOfScan = true;
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break;
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}
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}
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if (!hasFoundEndOfScan) {
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return false;
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}
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this._segments.push(buffer.slice(i, j));
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i = j;
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continue;
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} else if (type >= 0xD0 && type < 0xD9 || type == 0x01) {
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// No length after marker
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this._segments.push(buffer.slice(i, j));
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i = j;
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continue;
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}
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if (j + 2 > bufferLength) {
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return false;
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}
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const length = (buffer[j] << 8) + buffer[j+1] - 2;
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if (length < 0) {
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throw new Error("Illegal JPEG length received (length: " +
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length + ")");
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}
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j += 2;
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if (j + length > bufferLength) {
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return false;
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}
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j += length;
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const segment = buffer.slice(i, j);
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if (type == 0xC4) {
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// Huffman tables
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this._huffmanTables.push(segment);
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} else if (type == 0xDB) {
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// Quantization tables
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this._quantTables.push(segment);
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}
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this._segments.push(segment);
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i = j;
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// End of image?
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if (segment[1] === 0xD9) {
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break;
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}
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}
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let huffmanTables = [];
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let quantTables = [];
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for (let segment of this._segments) {
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let type = segment[1];
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if (type === 0xC4) {
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// Huffman tables
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huffmanTables.push(segment);
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} else if (type === 0xDB) {
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// Quantization tables
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quantTables.push(segment);
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}
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}
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const sofIndex = this._segments.findIndex(
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x => x[1] == 0xC0 || x[1] == 0xC2
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);
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if (sofIndex == -1) {
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throw new Error("Illegal JPEG image without SOF");
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}
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if (quantTables.length === 0) {
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this._segments.splice(sofIndex+1, 0,
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...this._cachedQuantTables);
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}
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if (huffmanTables.length === 0) {
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this._segments.splice(sofIndex+1, 0,
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...this._cachedHuffmanTables);
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}
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let length = 0;
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for (let segment of this._segments) {
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length += segment.length;
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}
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let data = new Uint8Array(length);
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length = 0;
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for (let segment of this._segments) {
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data.set(segment, length);
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length += segment.length;
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}
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display.imageRect(x, y, width, height, "image/jpeg", data);
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if (huffmanTables.length !== 0) {
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this._cachedHuffmanTables = huffmanTables;
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}
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if (quantTables.length !== 0) {
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this._cachedQuantTables = quantTables;
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}
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this._segments = [];
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return true;
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}
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_readSegment(sock) {
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if (sock.rQwait("JPEG", 2)) {
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return null;
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}
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let marker = sock.rQshift8();
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if (marker != 0xFF) {
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throw new Error("Illegal JPEG marker received (byte: " +
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marker + ")");
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}
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let type = sock.rQshift8();
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if (type >= 0xD0 && type <= 0xD9 || type == 0x01) {
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// No length after marker
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return new Uint8Array([marker, type]);
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}
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if (sock.rQwait("JPEG", 2, 2)) {
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return null;
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}
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let length = sock.rQshift16();
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if (length < 2) {
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throw new Error("Illegal JPEG length received (length: " +
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length + ")");
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}
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if (sock.rQwait("JPEG", length-2, 4)) {
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return null;
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}
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let extra = 0;
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if (type === 0xDA) {
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// start of scan
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extra += 2;
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while (true) {
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if (sock.rQwait("JPEG", length-2+extra, 4)) {
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return null;
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}
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let data = sock.rQslice(0, length-2+extra);
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if (data.at(-2) === 0xFF && data.at(-1) !== 0x00 &&
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!(data.at(-1) >= 0xD0 && data.at(-1) <= 0xD7)) {
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extra -= 2;
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break;
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}
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extra++;
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}
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}
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let segment = new Uint8Array(2 + length + extra);
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segment[0] = marker;
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segment[1] = type;
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segment[2] = length >> 8;
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segment[3] = length;
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segment.set(sock.rQshiftBytes(length-2+extra), 4);
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return segment;
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}
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}
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