81 lines
2.5 KiB
JavaScript
81 lines
2.5 KiB
JavaScript
const BASE64_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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/**
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* 把 SVG 文本编码成 UTF-8 字节。
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* 说明：
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* 1. 小程序运行时没有稳定可用的 Buffer，因此这里使用纯 JS 编码；
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* 2. 需要显式处理代理对，避免非 ASCII 字符在 data URI 中损坏；
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* 3. 非法代理项统一替换成 U+FFFD，保证输出始终可编码。
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*/
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function encodeUtf8Bytes(input) {
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const source = String(input || "");
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const bytes = [];
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for (let index = 0; index < source.length; index += 1) {
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const first = source.charCodeAt(index);
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if (first < 0x80) {
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bytes.push(first);
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continue;
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}
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if (first < 0x800) {
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bytes.push(0xc0 | (first >> 6), 0x80 | (first & 0x3f));
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continue;
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}
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let codePoint = first;
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if (first >= 0xd800 && first <= 0xdbff) {
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const second = source.charCodeAt(index + 1);
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if (second >= 0xdc00 && second <= 0xdfff) {
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codePoint = ((first - 0xd800) << 10) + (second - 0xdc00) + 0x10000;
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index += 1;
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} else {
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codePoint = 0xfffd;
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}
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} else if (first >= 0xdc00 && first <= 0xdfff) {
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codePoint = 0xfffd;
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}
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if (codePoint < 0x10000) {
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bytes.push(0xe0 | (codePoint >> 12), 0x80 | ((codePoint >> 6) & 0x3f), 0x80 | (codePoint & 0x3f));
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continue;
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}
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bytes.push(
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0xf0 | (codePoint >> 18),
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0x80 | ((codePoint >> 12) & 0x3f),
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0x80 | ((codePoint >> 6) & 0x3f),
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0x80 | (codePoint & 0x3f)
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);
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}
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return bytes;
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}
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/**
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* 把 UTF-8 字节数组转成 base64。
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* 这样生成的 data URI 可以避开开发者工具对 `utf8,...` 形式 SVG URI 的兼容问题。
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*/
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function encodeBase64FromBytes(bytes) {
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const output = [];
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for (let index = 0; index < bytes.length; index += 3) {
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const first = bytes[index];
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const second = index + 1 < bytes.length ? bytes[index + 1] : null;
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const third = index + 2 < bytes.length ? bytes[index + 2] : null;
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const triplet = (first << 16) | ((second || 0) << 8) | (third || 0);
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output.push(
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BASE64_ALPHABET[(triplet >> 18) & 0x3f],
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BASE64_ALPHABET[(triplet >> 12) & 0x3f],
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second === null ? "=" : BASE64_ALPHABET[(triplet >> 6) & 0x3f],
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third === null ? "=" : BASE64_ALPHABET[triplet & 0x3f]
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);
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}
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return output.join("");
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}
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function toSvgDataUri(svg) {
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const base64 = encodeBase64FromBytes(encodeUtf8Bytes(svg));
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return `data:image/svg+xml;base64,${base64}`;
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}
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module.exports = {
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toSvgDataUri
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};
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