66 lines
1.5 KiB
JavaScript
66 lines
1.5 KiB
JavaScript
'use strict';
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/* eslint-disable consistent-return */
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var readUInt16BE = require('../common').readUInt16BE;
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module.exports = function (data) {
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if (data.length < 2) return;
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// first marker of the file MUST be 0xFFD8
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if (data[0] !== 0xFF || data[1] !== 0xD8) return;
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var offset = 2;
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for (;;) {
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if (data.length - offset < 2) return;
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// not a JPEG marker
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if (data[offset++] !== 0xFF) return;
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var code = data[offset++];
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var length;
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// skip padding bytes
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while (code === 0xFF) code = data[offset++];
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// standalone markers, according to JPEG 1992,
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// http://www.w3.org/Graphics/JPEG/itu-t81.pdf, see Table B.1
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if ((0xD0 <= code && code <= 0xD9) || code === 0x01) {
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length = 0;
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} else if (0xC0 <= code && code <= 0xFE) {
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// the rest of the unreserved markers
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if (data.length - offset < 2) return;
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length = readUInt16BE(data, offset) - 2;
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offset += 2;
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} else {
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// unknown markers
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return;
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}
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if (code === 0xD9 /* EOI */ || code === 0xDA /* SOS */) {
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// end of the datastream
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return;
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}
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if (length >= 5 &&
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(0xC0 <= code && code <= 0xCF) &&
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code !== 0xC4 && code !== 0xC8 && code !== 0xCC) {
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if (data.length - offset < length) return;
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return {
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width: readUInt16BE(data, offset + 3),
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height: readUInt16BE(data, offset + 1),
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type: 'jpg',
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mime: 'image/jpeg',
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wUnits: 'px',
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hUnits: 'px'
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};
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}
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offset += length;
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}
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};
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