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187 lines
5.2 KiB
187 lines
5.2 KiB
// String encode/decode helpers
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'use strict';
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var utils = require('./common');
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// Quick check if we can use fast array to bin string conversion
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//
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// - apply(Array) can fail on Android 2.2
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// - apply(Uint8Array) can fail on iOS 5.1 Safari
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//
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var STR_APPLY_OK = true;
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var STR_APPLY_UIA_OK = true;
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try { String.fromCharCode.apply(null, [ 0 ]); } catch (__) { STR_APPLY_OK = false; }
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try { String.fromCharCode.apply(null, new Uint8Array(1)); } catch (__) { STR_APPLY_UIA_OK = false; }
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// Table with utf8 lengths (calculated by first byte of sequence)
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// Note, that 5 & 6-byte values and some 4-byte values can not be represented in JS,
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// because max possible codepoint is 0x10ffff
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var _utf8len = new utils.Buf8(256);
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for (var q = 0; q < 256; q++) {
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_utf8len[q] = (q >= 252 ? 6 : q >= 248 ? 5 : q >= 240 ? 4 : q >= 224 ? 3 : q >= 192 ? 2 : 1);
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}
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_utf8len[254] = _utf8len[254] = 1; // Invalid sequence start
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// convert string to array (typed, when possible)
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exports.string2buf = function (str) {
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var buf, c, c2, m_pos, i, str_len = str.length, buf_len = 0;
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// count binary size
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for (m_pos = 0; m_pos < str_len; m_pos++) {
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c = str.charCodeAt(m_pos);
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if ((c & 0xfc00) === 0xd800 && (m_pos + 1 < str_len)) {
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c2 = str.charCodeAt(m_pos + 1);
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if ((c2 & 0xfc00) === 0xdc00) {
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c = 0x10000 + ((c - 0xd800) << 10) + (c2 - 0xdc00);
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m_pos++;
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}
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}
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buf_len += c < 0x80 ? 1 : c < 0x800 ? 2 : c < 0x10000 ? 3 : 4;
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}
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// allocate buffer
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buf = new utils.Buf8(buf_len);
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// convert
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for (i = 0, m_pos = 0; i < buf_len; m_pos++) {
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c = str.charCodeAt(m_pos);
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if ((c & 0xfc00) === 0xd800 && (m_pos + 1 < str_len)) {
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c2 = str.charCodeAt(m_pos + 1);
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if ((c2 & 0xfc00) === 0xdc00) {
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c = 0x10000 + ((c - 0xd800) << 10) + (c2 - 0xdc00);
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m_pos++;
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}
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}
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if (c < 0x80) {
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/* one byte */
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buf[i++] = c;
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} else if (c < 0x800) {
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/* two bytes */
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buf[i++] = 0xC0 | (c >>> 6);
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buf[i++] = 0x80 | (c & 0x3f);
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} else if (c < 0x10000) {
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/* three bytes */
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buf[i++] = 0xE0 | (c >>> 12);
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buf[i++] = 0x80 | (c >>> 6 & 0x3f);
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buf[i++] = 0x80 | (c & 0x3f);
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} else {
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/* four bytes */
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buf[i++] = 0xf0 | (c >>> 18);
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buf[i++] = 0x80 | (c >>> 12 & 0x3f);
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buf[i++] = 0x80 | (c >>> 6 & 0x3f);
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buf[i++] = 0x80 | (c & 0x3f);
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}
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}
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return buf;
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};
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// Helper (used in 2 places)
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function buf2binstring(buf, len) {
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// On Chrome, the arguments in a function call that are allowed is `65534`.
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// If the length of the buffer is smaller than that, we can use this optimization,
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// otherwise we will take a slower path.
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if (len < 65534) {
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if ((buf.subarray && STR_APPLY_UIA_OK) || (!buf.subarray && STR_APPLY_OK)) {
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return String.fromCharCode.apply(null, utils.shrinkBuf(buf, len));
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}
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}
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var result = '';
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for (var i = 0; i < len; i++) {
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result += String.fromCharCode(buf[i]);
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}
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return result;
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}
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// Convert byte array to binary string
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exports.buf2binstring = function (buf) {
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return buf2binstring(buf, buf.length);
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};
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// Convert binary string (typed, when possible)
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exports.binstring2buf = function (str) {
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var buf = new utils.Buf8(str.length);
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for (var i = 0, len = buf.length; i < len; i++) {
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buf[i] = str.charCodeAt(i);
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}
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return buf;
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};
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// convert array to string
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exports.buf2string = function (buf, max) {
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var i, out, c, c_len;
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var len = max || buf.length;
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// Reserve max possible length (2 words per char)
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// NB: by unknown reasons, Array is significantly faster for
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// String.fromCharCode.apply than Uint16Array.
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var utf16buf = new Array(len * 2);
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for (out = 0, i = 0; i < len;) {
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c = buf[i++];
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// quick process ascii
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if (c < 0x80) { utf16buf[out++] = c; continue; }
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c_len = _utf8len[c];
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// skip 5 & 6 byte codes
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if (c_len > 4) { utf16buf[out++] = 0xfffd; i += c_len - 1; continue; }
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// apply mask on first byte
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c &= c_len === 2 ? 0x1f : c_len === 3 ? 0x0f : 0x07;
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// join the rest
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while (c_len > 1 && i < len) {
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c = (c << 6) | (buf[i++] & 0x3f);
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c_len--;
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}
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// terminated by end of string?
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if (c_len > 1) { utf16buf[out++] = 0xfffd; continue; }
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if (c < 0x10000) {
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utf16buf[out++] = c;
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} else {
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c -= 0x10000;
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utf16buf[out++] = 0xd800 | ((c >> 10) & 0x3ff);
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utf16buf[out++] = 0xdc00 | (c & 0x3ff);
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}
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}
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return buf2binstring(utf16buf, out);
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};
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// Calculate max possible position in utf8 buffer,
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// that will not break sequence. If that's not possible
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// - (very small limits) return max size as is.
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//
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// buf[] - utf8 bytes array
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// max - length limit (mandatory);
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exports.utf8border = function (buf, max) {
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var pos;
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max = max || buf.length;
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if (max > buf.length) { max = buf.length; }
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// go back from last position, until start of sequence found
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pos = max - 1;
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while (pos >= 0 && (buf[pos] & 0xC0) === 0x80) { pos--; }
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// Very small and broken sequence,
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// return max, because we should return something anyway.
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if (pos < 0) { return max; }
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// If we came to start of buffer - that means buffer is too small,
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// return max too.
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if (pos === 0) { return max; }
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return (pos + _utf8len[buf[pos]] > max) ? pos : max;
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};
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