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117 lines
3.5 KiB
JavaScript
117 lines
3.5 KiB
JavaScript
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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"use strict";
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const { Cu } = require("chrome");
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const { Promise: promise } =
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Cu.import("resource://gre/modules/Promise.jsm", {});
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// Lazily require encoder and decoder in case only one is needed
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Object.defineProperty(this, "Encoder", {
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get: () => require("./encoder/index").Encoder
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});
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Object.defineProperty(this, "QRRSBlock", {
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get: () => require("./encoder/index").QRRSBlock
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});
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Object.defineProperty(this, "QRErrorCorrectLevel", {
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get: () => require("./encoder/index").QRErrorCorrectLevel
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});
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Object.defineProperty(this, "decoder", {
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get: () => {
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// Some applications don't ship the decoder, see moz.build
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try {
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return require("./decoder/index");
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} catch(e) {
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return null;
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}
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}
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});
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/**
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* There are many "versions" of QR codes, which describes how many dots appear
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* in the resulting image, thus limiting the amount of data that can be
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* represented.
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*
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* The encoder used here allows for versions 1 - 10 (more dots for larger
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* versions).
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*
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* It expects you to pick a version large enough to contain your message. Here
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* we search for the mimimum version based on the message length.
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* @param string message
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* Text to encode
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* @param string quality
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* Quality level: L, M, Q, H
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* @return integer
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*/
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exports.findMinimumVersion = function(message, quality) {
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let msgLength = message.length;
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let qualityLevel = QRErrorCorrectLevel[quality];
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for (let version = 1; version <= 10; version++) {
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let rsBlocks = QRRSBlock.getRSBlocks(version, qualityLevel);
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let maxLength = rsBlocks.reduce((prev, block) => {
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return prev + block.dataCount;
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}, 0);
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// Remove two bytes to fit header info
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maxLength -= 2;
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if (msgLength <= maxLength) {
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return version;
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}
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}
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throw new Error("Message too large");
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};
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/**
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* Simple wrapper around the underlying encoder's API.
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* @param string message
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* Text to encode
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* @param string quality (optional)
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Quality level: L, M, Q, H
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* @param integer version (optional)
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* QR code "version" large enough to contain the message
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* @return object with the following fields:
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* * src: an image encoded a data URI
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* * height: image height
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* * width: image width
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*/
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exports.encodeToDataURI = function(message, quality, version) {
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quality = quality || "H";
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version = version || exports.findMinimumVersion(message, quality);
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let encoder = new Encoder(version, quality);
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encoder.addData(message);
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encoder.make();
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return encoder.createImgData();
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};
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/**
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* Simple wrapper around the underlying decoder's API.
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* @param string URI
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* URI of an image of a QR code
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* @return Promise
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* The promise will be resolved with a string, which is the data inside
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* the QR code.
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*/
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exports.decodeFromURI = function(URI) {
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if (!decoder) {
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return promise.reject();
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}
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let deferred = promise.defer();
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decoder.decodeFromURI(URI, deferred.resolve, deferred.reject);
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return deferred.promise;
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};
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/**
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* Decode a QR code that has been drawn to a canvas element.
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* @param Canvas canvas
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* <canvas> element to read from
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* @return string
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* The data inside the QR code
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*/
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exports.decodeFromCanvas = function(canvas) {
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if (!decoder) {
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throw new Error("Decoder not available");
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}
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return decoder.decodeFromCanvas(canvas);
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};
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