Streaming a file from server to client with socket.io-stream - node.js

Question

I've managed to upload files in chunk from a client to a server, but now i want to achieve the opposite way. Unfortunately the documentation on the offical module page lacks for this part.
I want to do the following:
emit a stream and 'download'-event with the filename to the server
the server should create a readstream and pipe it to the stream emitted from the client
when the client reaches the stream, a download-popup should appear and ask where to save the file
The reason why i don't wanna use simple file-hyperlinks is obfuscating: the files on the server are encrpted and renamed, so i have to decrypt and rename them for each download request.
Any code snippets around to get me started with this?

Answer 1

This is a working example I'm using. But somehow (maybe only in my case) this can be very slow.
//== Server Side
ss(socket).on('filedownload', function (stream, name, callback) {
//== Do stuff to find your file
callback({
name : "filename",
size : 500
});
var MyFileStream = fs.createReadStream(name);
MyFileStream.pipe(stream);
});
//== Client Side
/** Download a file from the object store
* #param {string} name Name of the file to download
* #param {string} originalFilename Overrules the file's originalFilename
* #returns {$.Deferred}
*/
function downloadFile(name, originalFilename) {
var deferred = $.Deferred();
//== Create stream for file to be streamed to and buffer to save chunks
var stream = ss.createStream(),
fileBuffer = [],
fileLength = 0;
//== Emit/Request
ss(mysocket).emit('filedownload', stream, name, function (fileError, fileInfo) {
if (fileError) {
deferred.reject(fileError);
} else {
console.log(['File Found!', fileInfo]);
//== Receive data
stream.on('data', function (chunk) {
fileLength += chunk.length;
var progress = Math.floor((fileLength / fileInfo.size) * 100);
progress = Math.max(progress - 2, 1);
deferred.notify(progress);
fileBuffer.push(chunk);
});
stream.on('end', function () {
var filedata = new Uint8Array(fileLength),
i = 0;
//== Loop to fill the final array
fileBuffer.forEach(function (buff) {
for (var j = 0; j < buff.length; j++) {
filedata[i] = buff[j];
i++;
}
});
deferred.notify(100);
//== Download file in browser
downloadFileFromBlob([filedata], originalFilename);
deferred.resolve();
});
}
});
//== Return
return deferred;
}
var downloadFileFromBlob = (function () {
var a = document.createElement("a");
document.body.appendChild(a);
a.style = "display: none";
return function (data, fileName) {
var blob = new Blob(data, {
type : "octet/stream"
}),
url = window.URL.createObjectURL(blob);
a.href = url;
a.download = fileName;
a.click();
window.URL.revokeObjectURL(url);
};
}());

Answer 2

Answer My dear friend Jeffrey van Norden That's right. it worked for me. But there was a small bug so I changed the server side code this way:
//== Server Side
ss(socket).on('filedownload', function (stream, name, callback) {
//== Do stuff to find your file
try {
let stats = fs.statSync(name);
let size = stats.size;
callback(false,{
name: name,
size: size
});
let MyFileStream = fs.createReadStream(name);
MyFileStream.pipe(stream);
}
catch (e){
callback(true,{});
}
});
//== Client Side
/** Download a file from the object store
* #param {string} name Name of the file to download
* #param {string} originalFilename Overrules the file's originalFilename
* #returns {$.Deferred}
*/
function downloadFile(name, originalFilename) {
var deferred = $.Deferred();
//== Create stream for file to be streamed to and buffer to save chunks
var stream = ss.createStream(),
fileBuffer = [],
fileLength = 0;
//== Emit/Request
ss(mysocket).emit('filedownload', stream, name, function (fileError, fileInfo) {
if (fileError) {
deferred.reject(fileError);
} else {
console.log(['File Found!', fileInfo]);
//== Receive data
stream.on('data', function (chunk) {
fileLength += chunk.length;
var progress = Math.floor((fileLength / fileInfo.size) * 100);
progress = Math.max(progress - 2, 1);
deferred.notify(progress);
fileBuffer.push(chunk);
});
stream.on('end', function () {
var filedata = new Uint8Array(fileLength),
i = 0;
//== Loop to fill the final array
fileBuffer.forEach(function (buff) {
for (var j = 0; j < buff.length; j++) {
filedata[i] = buff[j];
i++;
}
});
deferred.notify(100);
//== Download file in browser
downloadFileFromBlob([filedata], originalFilename);
deferred.resolve();
});
}
});
//== Return
return deferred;
}
var downloadFileFromBlob = (function () {
var a = document.createElement("a");
document.body.appendChild(a);
a.style = "display: none";
return function (data, fileName) {
var blob = new Blob(data, {
type : "octet/stream"
}),
url = window.URL.createObjectURL(blob);
a.href = url;
a.download = fileName;
a.click();
window.URL.revokeObjectURL(url);
};
}());