@lapo/z85
Version:
Z85 encoding/decoding
175 lines (169 loc) • 6.82 kB
JavaScript
/*
* Copyright (c) 2018-2020 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
;
(((root, factory) => {
if (typeof exports === 'object') {
// CommonJS.
module.exports = factory();
} else if (typeof define === 'function' && define.amd) {
// AMD.
define([], factory);
} else {
// Globals.
root.org = root.org || {};
root.org.cometd = root.org.cometd || {};
root.org.cometd.Z85 = factory();
}
})(this, () => {
const _z85EncodeTable = [
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j',
'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D',
'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N',
'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', '.', '-', ':', '+', '=', '^', '!', '/',
'*', '?', '&', '<', '>', '(', ')', '[', ']', '{',
'}', '@', '%', '$', '#'
];
const _z85DecodeTable = [
-1, 0x44, -1, 0x54, 0x53, 0x52, 0x48, -1,
0x4B, 0x4C, 0x46, 0x41, -1, 0x3F, 0x3E, 0x45,
0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
0x08, 0x09, 0x40, -1, 0x49, 0x42, 0x4A, 0x47,
0x51, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A,
0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32,
0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A,
0x3B, 0x3C, 0x3D, 0x4D, -1, 0x4E, 0x43, -1,
-1, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10,
0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20,
0x21, 0x22, 0x23, 0x4F, -1, 0x50, -1, -1
];
return {
/**
* Z85 encodes the given bytes into printable text.
*
* The given bytes can be stored in:
* - an `ArrayBuffer`
* - any `TypedArray` (such as `Uint8Array`) or any object whose `buffer` property is an `ArrayBuffer`
* - an `Array` (which will be wrapped into an `Uint8Array`)
*
* The bytes count does not need to be a multiple of 4, as
* this function will automatically pad to a multiple of 4.
*
* @example
* const Z85 = require('cometd-Z85');
*
* // The source bytes (e.g. from an image).
* const imageBytes = [0xC, 0x0, 0xF, 0xF, 0xE];
*
* // Z85-encode the bytes into a string.
* const string = Z85.encode(imageBytes);
*
* // The encoded image bytes can be stored in a JSON field.
* const json = {
* image: string
* };
*
* @param {ArrayBuffer | Array} bytes the bytes to encode
* @return {string} the text result of the encoding
*/
encode: bytes => {
let buffer = null;
if (bytes instanceof ArrayBuffer) {
buffer = bytes;
} else if (bytes.buffer instanceof ArrayBuffer && 'byteOffset' in bytes) {
buffer = bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + bytes.byteLength);
} else if (Array.isArray(bytes)) {
buffer = new Uint8Array(bytes).buffer;
}
if (buffer == null) {
throw 'Cannot Z85 encode ' + bytes;
}
const length = buffer.byteLength;
const remainder = length % 4;
const padding = 4 - (remainder === 0 ? 4 : remainder);
const view = new DataView(buffer);
let result = '';
let value = 0;
for (let i = 0; i < length + padding; ++i) {
const isPadding = i >= length;
value = value * 256 + (isPadding ? 0 : view.getUint8(i));
if ((i + 1) % 4 === 0) {
let divisor = 85 * 85 * 85 * 85;
for (let j = 5; j > 0; --j) {
if (!isPadding || j > padding) {
const code = Math.floor(value / divisor) % 85;
result += _z85EncodeTable[code];
}
divisor /= 85;
}
value = 0;
}
}
return result;
},
/**
* Z85 decodes the given input string into an `ArrayBuffer`.
*
* @example
* const Z85 = require('cometd-Z85');
*
* // A Z85-encoded image in a JSON field.
* const string = json.image;
*
* // Z85-decode into bytes.
* const buffer = Z85.decode(string);
*
* // Use the bytes in a Blob.
* const blob = new Blob([buffer], { type: 'image/png' });
*
* @param {string} string
* @return {ArrayBuffer}
*/
decode: string => {
const remainder = string.length % 5;
const padding = 5 - (remainder === 0 ? 5 : remainder);
for (let p = 0; p < padding; ++p) {
string += _z85EncodeTable[_z85EncodeTable.length - 1];
}
const length = string.length;
const buffer = new ArrayBuffer((length * 4 / 5) - padding);
const view = new DataView(buffer);
let value = 0;
let charIdx = 0;
let byteIdx = 0;
for (let i = 0; i < length; ++i) {
const code = _z85DecodeTable[string.charCodeAt(charIdx++) - 32];
if (!(code >= 0)) // also manages undefined values
throw new Error("Character '" + string.charAt(i) + "' in position " + charIdx + " is not valid Z85");
value = value * 85 + code;
if (charIdx % 5 === 0) {
let divisor = 256 * 256 * 256;
while (divisor >= 1) {
if (byteIdx < view.byteLength) {
view.setUint8(byteIdx++, Math.floor(value / divisor) % 256);
}
divisor /= 256;
}
value = 0;
}
}
return buffer;
}
};
}));