StreamHelper.js

'use strict';

var utils = require('../utils');
var ConvertWorker = require('./ConvertWorker');
var GenericWorker = require('./GenericWorker');
var base64 = require('../base64');
var support = require("../support");
var external = require("../external");

var NodejsStreamOutputAdapter = null;
if (support.nodestream) {
    try {
        NodejsStreamOutputAdapter = require('../nodejs/NodejsStreamOutputAdapter');
    } catch(e) {}
}

/**
 * Apply the final transformation of the data. If the user wants a Blob for
 * example, it's easier to work with an U8intArray and finally do the
 * ArrayBuffer/Blob conversion.
 * @param {String} type the name of the final type
 * @param {String|Uint8Array|Buffer} content the content to transform
 * @param {String} mimeType the mime type of the content, if applicable.
 * @return {String|Uint8Array|ArrayBuffer|Buffer|Blob} the content in the right format.
 */
function transformZipOutput(type, content, mimeType) {
    switch(type) {
        case "blob" :
            return utils.newBlob(utils.transformTo("arraybuffer", content), mimeType);
        case "base64" :
            return base64.encode(content);
        default :
            return utils.transformTo(type, content);
    }
}

/**
 * Concatenate an array of data of the given type.
 * @param {String} type the type of the data in the given array.
 * @param {Array} dataArray the array containing the data chunks to concatenate
 * @return {String|Uint8Array|Buffer} the concatenated data
 * @throws Error if the asked type is unsupported
 */
function concat (type, dataArray) {
    var i, index = 0, res = null, totalLength = 0;
    for(i = 0; i < dataArray.length; i++) {
        totalLength += dataArray[i].length;
    }
    switch(type) {
        case "string":
            return dataArray.join("");
          case "array":
            return Array.prototype.concat.apply([], dataArray);
        case "uint8array":
            res = new Uint8Array(totalLength);
            for(i = 0; i < dataArray.length; i++) {
                res.set(dataArray[i], index);
                index += dataArray[i].length;
            }
            return res;
        case "nodebuffer":
            return Buffer.concat(dataArray);
        default:
            throw new Error("concat : unsupported type '"  + type + "'");
    }
}

/**
 * Listen a StreamHelper, accumulate its content and concatenate it into a
 * complete block.
 * @param {StreamHelper} helper the helper to use.
 * @param {Function} updateCallback a callback called on each update. Called
 * with one arg :
 * - the metadata linked to the update received.
 * @return Promise the promise for the accumulation.
 */
function accumulate(helper, updateCallback) {
    return new external.Promise(function (resolve, reject){
        var dataArray = [];
        var chunkType = helper._internalType,
            resultType = helper._outputType,
            mimeType = helper._mimeType;
        helper
        .on('data', function (data, meta) {
            dataArray.push(data);
            if(updateCallback) {
                updateCallback(meta);
            }
        })
        .on('error', function(err) {
            dataArray = [];
            reject(err);
        })
        .on('end', function (){
            try {
                var result = transformZipOutput(resultType, concat(chunkType, dataArray), mimeType);
                resolve(result);
            } catch (e) {
                reject(e);
            }
            dataArray = [];
        })
        .resume();
    });
}

/**
 * An helper to easily use workers outside of JSZip.
 * @constructor
 * @param {Worker} worker the worker to wrap
 * @param {String} outputType the type of data expected by the use
 * @param {String} mimeType the mime type of the content, if applicable.
 */
function StreamHelper(worker, outputType, mimeType) {
    var internalType = outputType;
    switch(outputType) {
        case "blob":
        case "arraybuffer":
            internalType = "uint8array";
        break;
        case "base64":
            internalType = "string";
        break;
    }

    try {
        // the type used internally
        this._internalType = internalType;
        // the type used to output results
        this._outputType = outputType;
        // the mime type
        this._mimeType = mimeType;
        utils.checkSupport(internalType);
        this._worker = worker.pipe(new ConvertWorker(internalType));
        // the last workers can be rewired without issues but we need to
        // prevent any updates on previous workers.
        worker.lock();
    } catch(e) {
        this._worker = new GenericWorker("error");
        this._worker.error(e);
    }
}

StreamHelper.prototype = {
    /**
     * Listen a StreamHelper, accumulate its content and concatenate it into a
     * complete block.
     * @param {Function} updateCb the update callback.
     * @return Promise the promise for the accumulation.
     */
    accumulate : function (updateCb) {
        return accumulate(this, updateCb);
    },
    /**
     * Add a listener on an event triggered on a stream.
     * @param {String} evt the name of the event
     * @param {Function} fn the listener
     * @return {StreamHelper} the current helper.
     */
    on : function (evt, fn) {
        var self = this;

        if(evt === "data") {
            this._worker.on(evt, function (chunk) {
                fn.call(self, chunk.data, chunk.meta);
            });
        } else {
            this._worker.on(evt, function () {
                utils.delay(fn, arguments, self);
            });
        }
        return this;
    },
    /**
     * Resume the flow of chunks.
     * @return {StreamHelper} the current helper.
     */
    resume : function () {
        utils.delay(this._worker.resume, [], this._worker);
        return this;
    },
    /**
     * Pause the flow of chunks.
     * @return {StreamHelper} the current helper.
     */
    pause : function () {
        this._worker.pause();
        return this;
    },
    /**
     * Return a nodejs stream for this helper.
     * @param {Function} updateCb the update callback.
     * @return {NodejsStreamOutputAdapter} the nodejs stream.
     */
    toNodejsStream : function (updateCb) {
        utils.checkSupport("nodestream");
        if (this._outputType !== "nodebuffer") {
            // an object stream containing blob/arraybuffer/uint8array/string
            // is strange and I don't know if it would be useful.
            // I you find this comment and have a good usecase, please open a
            // bug report !
            throw new Error(this._outputType + " is not supported by this method");
        }

        return new NodejsStreamOutputAdapter(this, {
            objectMode : this._outputType !== "nodebuffer"
        }, updateCb);
    }
};


module.exports = StreamHelper;