shaka-player
Version:
DASH/EME video player library
262 lines (232 loc) • 8.7 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.util.StringUtils');
goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.util.BufferUtils');
goog.require('shaka.util.Error');
goog.require('shaka.util.Iterables');
goog.require('shaka.util.Lazy');
/**
* @namespace shaka.util.StringUtils
* @summary A set of string utility functions.
* @export
*/
shaka.util.StringUtils = class {
/**
* Creates a string from the given buffer as UTF-8 encoding.
*
* @param {?BufferSource} data
* @return {string}
* @export
*/
static fromUTF8(data) {
if (!data) {
return '';
}
let uint8 = shaka.util.BufferUtils.toUint8(data);
// If present, strip off the UTF-8 BOM.
if (uint8[0] == 0xef && uint8[1] == 0xbb && uint8[2] == 0xbf) {
uint8 = uint8.subarray(3);
}
// http://stackoverflow.com/a/13691499
const utf8 = shaka.util.StringUtils.fromCharCode(uint8);
// This converts each character in the string to an escape sequence. If the
// character is in the ASCII range, it is not converted; otherwise it is
// converted to a URI escape sequence.
// Example: '\x67\x35\xe3\x82\xac' -> 'g#%E3%82%AC'
const escaped = escape(utf8);
// Decode the escaped sequence. This will interpret UTF-8 sequences into
// the correct character.
// Example: 'g#%E3%82%AC' -> 'g#€'
try {
return decodeURIComponent(escaped);
} catch (e) {
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL, shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.BAD_ENCODING);
}
}
/**
* Creates a string from the given buffer as UTF-16 encoding.
*
* @param {?BufferSource} data
* @param {boolean} littleEndian
true to read little endian, false to read big.
* @param {boolean=} noThrow true to avoid throwing in cases where we may
* expect invalid input. If noThrow is true and the data has an odd
* length,it will be truncated.
* @return {string}
* @export
*/
static fromUTF16(data, littleEndian, noThrow) {
if (!data) {
return '';
}
if (!noThrow && data.byteLength % 2 != 0) {
shaka.log.error('Data has an incorrect length, must be even.');
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL, shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.BAD_ENCODING);
}
// Use a DataView to ensure correct endianness.
const length = Math.floor(data.byteLength / 2);
const arr = new Uint16Array(length);
const dataView = shaka.util.BufferUtils.toDataView(data);
for (const i of shaka.util.Iterables.range(length)) {
arr[i] = dataView.getUint16(i * 2, littleEndian);
}
return shaka.util.StringUtils.fromCharCode(arr);
}
/**
* Creates a string from the given buffer, auto-detecting the encoding that is
* being used. If it cannot detect the encoding, it will throw an exception.
*
* @param {?BufferSource} data
* @return {string}
* @export
*/
static fromBytesAutoDetect(data) {
const StringUtils = shaka.util.StringUtils;
if (!data) {
return '';
}
const uint8 = shaka.util.BufferUtils.toUint8(data);
if (uint8[0] == 0xef && uint8[1] == 0xbb && uint8[2] == 0xbf) {
return StringUtils.fromUTF8(uint8);
} else if (uint8[0] == 0xfe && uint8[1] == 0xff) {
return StringUtils.fromUTF16(
uint8.subarray(2), /* littleEndian= */ false);
} else if (uint8[0] == 0xff && uint8[1] == 0xfe) {
return StringUtils.fromUTF16(uint8.subarray(2), /* littleEndian= */ true);
}
const isAscii = (i) => {
// arr[i] >= ' ' && arr[i] <= '~';
return uint8.byteLength <= i || (uint8[i] >= 0x20 && uint8[i] <= 0x7e);
};
shaka.log.debug(
'Unable to find byte-order-mark, making an educated guess.');
if (uint8[0] == 0 && uint8[2] == 0) {
return StringUtils.fromUTF16(data, /* littleEndian= */ false);
} else if (uint8[1] == 0 && uint8[3] == 0) {
return StringUtils.fromUTF16(data, /* littleEndian= */ true);
} else if (isAscii(0) && isAscii(1) && isAscii(2) && isAscii(3)) {
return StringUtils.fromUTF8(data);
}
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.UNABLE_TO_DETECT_ENCODING);
}
/**
* Creates a ArrayBuffer from the given string, converting to UTF-8 encoding.
*
* @param {string} str
* @return {!ArrayBuffer}
* @export
*/
static toUTF8(str) {
// http://stackoverflow.com/a/13691499
// Converts the given string to a URI encoded string. If a character falls
// in the ASCII range, it is not converted; otherwise it will be converted
// to a series of URI escape sequences according to UTF-8.
// Example: 'g#€' -> 'g#%E3%82%AC'
const encoded = encodeURIComponent(str);
// Convert each escape sequence individually into a character. Each escape
// sequence is interpreted as a code-point, so if an escape sequence happens
// to be part of a multi-byte sequence, each byte will be converted to a
// single character.
// Example: 'g#%E3%82%AC' -> '\x67\x35\xe3\x82\xac'
const utf8 = unescape(encoded);
const result = new Uint8Array(utf8.length);
const enumerate = (it) => shaka.util.Iterables.enumerate(it);
for (const {i, item} of enumerate(utf8)) {
result[i] = item.charCodeAt(0);
}
return shaka.util.BufferUtils.toArrayBuffer(result);
}
/**
* Creates a ArrayBuffer from the given string, converting to UTF-16 encoding.
*
* @param {string} str
* @param {boolean} littleEndian
* @return {!ArrayBuffer}
* @export
*/
static toUTF16(str, littleEndian) {
const result = new ArrayBuffer(str.length * 2);
const view = new DataView(result);
const enumerate = (it) => shaka.util.Iterables.enumerate(it);
for (const {i, item} of enumerate(str)) {
const value = item.charCodeAt(0);
view.setUint16(/* position= */ i * 2, value, littleEndian);
}
return result;
}
/**
* Creates a new string from the given array of char codes.
*
* Using String.fromCharCode.apply is risky because you can trigger stack
* errors on very large arrays. This breaks up the array into several pieces
* to avoid this.
*
* @param {!TypedArray} array
* @return {string}
*/
static fromCharCode(array) {
return shaka.util.StringUtils.fromCharCodeImpl_.value()(array);
}
/**
* Resets the fromCharCode method's implementation.
* For debug use.
* @export
*/
static resetFromCharCode() {
shaka.util.StringUtils.fromCharCodeImpl_.reset();
}
};
/** @private {!shaka.util.Lazy.<function(!TypedArray):string>} */
shaka.util.StringUtils.fromCharCodeImpl_ = new shaka.util.Lazy(() => {
/** @param {number} size @return {boolean} */
const supportsChunkSize = (size) => {
try {
// The compiler will complain about suspicious value if this isn't
// stored in a variable and used.
const buffer = new Uint8Array(size);
// This can't use the spread operator, or it blows up on Xbox One.
// So we use apply() instead, which is normally not allowed.
// See issue #2186 for more details.
// eslint-disable-next-line no-restricted-syntax
const foo = String.fromCharCode.apply(null, buffer);
goog.asserts.assert(foo, 'Should get value');
return foo.length > 0; // Actually use "foo", so it's not compiled out.
} catch (error) {
return false;
}
};
// Different browsers support different chunk sizes; find out the largest
// this browser supports so we can use larger chunks on supported browsers
// but still support lower-end devices that require small chunks.
// 64k is supported on all major desktop browsers.
for (let size = 64 * 1024; size > 0; size /= 2) {
if (supportsChunkSize(size)) {
return (buffer) => {
let ret = '';
for (let i = 0; i < buffer.length; i += size) {
const subArray = buffer.subarray(i, i + size);
// This can't use the spread operator, or it blows up on Xbox One.
// So we use apply() instead, which is normally not allowed.
// See issue #2186 for more details.
// eslint-disable-next-line no-restricted-syntax
ret += String.fromCharCode.apply(null, subArray); // Issue #2186
}
return ret;
};
}
}
goog.asserts.assert(false, 'Unable to create a fromCharCode method');
return null;
});