279 lines
9.6 KiB
JavaScript
279 lines
9.6 KiB
JavaScript
// 浏览器端读取照片的 EXIF（拍摄时间 + GPS），只读文件头附近的一小段，
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// 不把整张照片传到服务器——几十张手机照片动辄几百 MB，上传既慢又占磁盘。
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//
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// 支持的容器：JPEG（APP1 段）与 HEIC/HEIF（ISO BMFF 的 meta box）。
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// 算法与 internal/exif 的 Go 实现一致，但这里必须分片读取：
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// JPEG 的 APP1 在最前面，通常 < 64KB；
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// HEIC 的 Exif item 位置由 iloc 指定（绝对偏移），可能落在文件靠后，
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// 所以先读 64KB 解析出偏移，必要时再按需读那一小段。
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(function () {
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'use strict';
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var HEAD_BYTES = 64 * 1024;
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function readRange(file, start, end) {
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var blob = file.slice(start, Math.min(end, file.size));
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return blob.arrayBuffer().then(function (buf) {
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return new Uint8Array(buf);
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});
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}
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function str(u8, off, len) {
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var s = '';
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for (var i = 0; i < len && off + i < u8.length; i++) s += String.fromCharCode(u8[off + i]);
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return s;
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}
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// ---------- TIFF（JPEG 与 HEIC 共用，HEIC 里是 Exif item 的负载） ----------
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function readIFD(dv, u8, base, off, le) {
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var out = {};
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if (off < 0 || base + off + 2 > u8.length) return out;
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var n = dv.getUint16(base + off, le);
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var p0 = base + off + 2;
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if (p0 + n * 12 > u8.length) n = Math.max(0, Math.floor((u8.length - p0) / 12));
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for (var i = 0; i < n; i++) {
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var p = p0 + i * 12;
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out[dv.getUint16(p, le)] = {
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type: dv.getUint16(p + 2, le),
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count: dv.getUint32(p + 4, le),
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valOff: p + 8
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};
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}
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return out;
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}
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function typeSize(t) {
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switch (t) {
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case 1: case 2: case 6: case 7: return 1;
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case 3: case 8: return 2;
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case 4: case 9: case 11: return 4;
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case 5: case 10: case 12: return 8;
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}
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return 1;
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}
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// ascii 读 ASCII 值：总长 ≤ 4 字节时内联在条目里，否则 valOff 是偏移
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function ascii(dv, u8, base, e, le) {
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var total = e.count;
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if (total <= 0) return '';
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var start;
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if (total <= 4) {
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start = e.valOff;
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} else {
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start = base + dv.getUint32(e.valOff, le);
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}
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var out = '';
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for (var i = 0; i < total && start + i < u8.length; i++) {
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var c = u8[start + i];
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if (c === 0) break;
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out += String.fromCharCode(c);
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}
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return out;
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}
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function rationals(dv, u8, base, e, le, n) {
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var off = base + dv.getUint32(e.valOff, le);
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if (off < 0 || off + n * 8 > u8.length) return null;
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var out = [];
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for (var i = 0; i < n; i++) {
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var num = dv.getUint32(off + i * 8, le);
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var den = dv.getUint32(off + i * 8 + 4, le);
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if (den === 0) return null;
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out.push(num / den);
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}
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return out;
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}
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// gpsCoord 把「度分秒 + 半球」拼成十进制度
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function gpsCoord(dv, u8, base, le, gps, refTag, valTag) {
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var refE = gps[refTag], valE = gps[valTag];
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if (!refE || !valE) return null;
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var parts = rationals(dv, u8, base, valE, le, 3);
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if (!parts) return null;
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var v = parts[0] + parts[1] / 60 + parts[2] / 3600;
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var ref = ascii(dv, u8, base, refE, le).toUpperCase();
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if (ref === 'S' || ref === 'W') v = -v;
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return v;
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}
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function parseTIFF(u8, base) {
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var dv = new DataView(u8.buffer, u8.byteOffset, u8.byteLength);
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if (base + 8 > u8.length) throw new Error('EXIF 数据不完整');
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var mark = str(u8, base, 2);
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if (mark !== 'II' && mark !== 'MM') throw new Error('EXIF 标识不对');
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var le = mark === 'II';
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if (dv.getUint16(base + 2, le) !== 0x002A) throw new Error('EXIF 标识不对');
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var res = { hasGPS: false, hasTime: false, lat: 0, lon: 0, shot: null };
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var ifd0 = readIFD(dv, u8, base, dv.getUint32(base + 4, le), le);
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if (ifd0[0x8769]) {
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var sub = readIFD(dv, u8, base, dv.getUint32(ifd0[0x8769].valOff, le), le);
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if (sub[0x9003]) {
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var m = /^(\d{4}):(\d{2}):(\d{2})[ T](\d{2}):(\d{2}):(\d{2})/.exec(ascii(dv, u8, base, sub[0x9003], le).trim());
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if (m) {
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res.shot = new Date(+m[1], +m[2] - 1, +m[3], +m[4], +m[5], +m[6]);
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res.hasTime = true;
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}
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}
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}
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if (ifd0[0x8825]) {
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var gps = readIFD(dv, u8, base, dv.getUint32(ifd0[0x8825].valOff, le), le);
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var la = gpsCoord(dv, u8, base, le, gps, 1, 2);
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var lo = gpsCoord(dv, u8, base, le, gps, 3, 4);
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if (la !== null && lo !== null && (la !== 0 || lo !== 0)) {
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res.lat = la; res.lon = lo; res.hasGPS = true;
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}
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}
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return res;
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}
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// ---------- JPEG ----------
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function parseJPEG(u8) {
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var dv = new DataView(u8.buffer, u8.byteOffset, u8.byteLength);
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var i = 2;
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while (i + 4 <= u8.length) {
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if (u8[i] !== 0xFF) { i++; continue; }
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var marker = u8[i + 1];
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if (marker === 0xD8 || marker === 0x01 || (marker >= 0xD0 && marker <= 0xD7)) { i += 2; continue; }
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if (marker === 0xDA || marker === 0xD9) break; // 图像数据开始
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var size = (u8[i + 2] << 8) | u8[i + 3];
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if (size < 2 || i + 2 + size > u8.length) break;
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if (marker === 0xE1 && size > 8 && str(u8, i + 4, 6) === 'Exif\x00\x00') {
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return parseTIFF(u8, i + 10);
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}
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i += 2 + size;
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}
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throw new Error('这张 JPEG 里没有 EXIF 信息');
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}
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// ---------- HEIC / HEIF ----------
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function boxHeader(dv, u8, off) {
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if (off + 8 > u8.length) return null;
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var size = dv.getUint32(off);
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var hdr = 8;
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if (size === 1) {
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if (off + 16 > u8.length) return null;
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size = Number(dv.getBigUint64(off + 8));
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hdr = 16;
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} else if (size === 0) {
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size = u8.length - off;
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}
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if (size < hdr) return null;
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// next 允许超出已读范围：大文件的 meta 往往只读到头部，后面的数据按需再取
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return { typ: str(u8, off + 4, 4), payload: off + hdr, next: off + size };
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}
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function findExifItemID(dv, u8, start, end) {
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if (start + 4 > u8.length) return 0;
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var ver = u8[start];
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var p = start + 4;
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var count = ver === 0 ? dv.getUint16(p) : dv.getUint32(p);
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p += ver === 0 ? 2 : 4;
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for (var i = 0; i < count; i++) {
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var b = boxHeader(dv, u8, p);
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if (!b) break;
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if (b.typ === 'infe' && b.payload < u8.length && u8[b.payload] >= 2 && b.payload + 12 <= u8.length) {
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if (str(u8, b.payload + 8, 4) === 'Exif') return dv.getUint16(b.payload + 4);
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}
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p = b.next;
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}
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return 0;
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}
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function findItemExtent(dv, u8, start, wantID) {
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if (start + 8 > u8.length) return null;
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var ver = u8[start];
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var p = start + 4;
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var offsetSize = u8[p] >> 4, lengthSize = u8[p] & 0x0F;
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p++;
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var baseSize = u8[p] >> 4, indexSize = ver >= 1 ? (u8[p] & 0x0F) : 0;
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p++;
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if (!offsetSize || !lengthSize) return null;
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var count = dv.getUint16(p);
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p += 2;
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function readN(n) {
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if (n < 0 || p + n > u8.length) return null;
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var v = 0;
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for (var i = 0; i < n; i++) v = v * 256 + u8[p + i];
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p += n;
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return v;
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}
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for (var i = 0; i < count; i++) {
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var id = ver === 0 ? readN(2) : readN(4);
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if (id === null) return null;
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if (ver >= 1 && readN(2) === null) return null;
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if (readN(2) === null) return null; // data_reference_index
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var base = readN(baseSize);
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if (base === null) return null;
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var extents = readN(2);
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if (extents === null) return null;
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for (var e = 0; e < extents; e++) {
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if (ver >= 1 && indexSize > 0 && readN(indexSize) === null) return null;
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var off = readN(offsetSize), len = readN(lengthSize);
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if (off === null || len === null) return null;
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if (id === wantID) return { offset: base + off, length: len };
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}
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}
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return null;
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}
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function parseHEIF(file, u8) {
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var dv = new DataView(u8.buffer, u8.byteOffset, u8.byteLength);
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var meta = null;
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for (var off = 0; off + 8 <= u8.length;) {
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var b = boxHeader(dv, u8, off);
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if (!b) break;
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if (b.typ === 'meta') { meta = b; break; }
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off = b.next;
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}
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if (!meta) throw new Error('HEIC 文件里没有找到 meta');
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var start = meta.payload + 4; // meta 是 FullBox
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var iinf = null, iloc = null;
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for (var o = start; o + 8 <= u8.length && o < meta.next;) {
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var sb = boxHeader(dv, u8, o);
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if (!sb) break;
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if (sb.typ === 'iinf') iinf = sb;
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if (sb.typ === 'iloc') iloc = sb;
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o = sb.next;
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}
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if (!iinf || !iloc) throw new Error('HEIC 里缺少 iinf/iloc');
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var itemID = findExifItemID(dv, u8, iinf.payload, iinf.next);
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if (!itemID) throw new Error('这张 HEIC 里没有 EXIF');
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var ext = findItemExtent(dv, u8, iloc.payload, itemID);
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if (!ext || ext.length <= 8) throw new Error('HEIC 的 EXIF 位置无效');
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function finish(bytes) {
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var tiff = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength).getUint32(0);
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if (tiff + 8 > bytes.length) tiff = 4;
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return parseTIFF(bytes, tiff);
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}
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// Exif item 已经读进来了就直接解析，否则按偏移再取那一小段
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if (ext.offset >= 0 && ext.offset + ext.length <= u8.length) {
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return finish(u8.subarray(ext.offset, ext.offset + ext.length));
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}
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return readRange(file, ext.offset, ext.offset + ext.length).then(finish);
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}
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// ---------- 对外入口 ----------
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function read(file) {
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return readRange(file, 0, HEAD_BYTES).then(function (head) {
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if (head.length >= 2 && head[0] === 0xFF && head[1] === 0xD8) {
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return Promise.resolve(parseJPEG(head));
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}
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if (head.length >= 12 && str(head, 4, 4) === 'ftyp') {
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return parseHEIF(file, head);
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}
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return Promise.reject(new Error('不认识的图片格式（支持 JPEG 与 HEIC/HEIF）'));
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});
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}
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window.rondExif = { read: read };
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})();
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