How can I listen the changes occurred in the Gun server database :
My server is listening like below
var Gun = require('gun');
var server = http.createServer();
var gun = Gun({web: server});
server.listen(port, function () {
console.log('Server listening on ...')
})
While puting the data from Gun client my data.json file updated. Now I need to get the listern the whole changes happening in the db. I think on a perticuler node I can listern using gun.on method. Can we able to Listern the whole changes/ change request coming from the client?
#ajmal-m-a yes, via the "wire spec" (you'll need to understand the graph format, here is a tech talk where I explain it in 30min on stage):
gun.on('in', function(msg){}) where gun is the root.
Note: You'll need to understand how to handle the middleware event hook system - your listener will need to remember to call this.to.next(msg).
A good and simple resource to look at is this:
https://github.com/zrrrzzt/bullet-catcher
Does this help?
(Sorry for the delay in answering the question, we were headed into a conference at that time, and it got buried under a bunch of emails)
Related
I want to make a route in express js to send some content after 1000 ms.
Note: I cant use res.sendFile, it has to be a plain route.
This is the code for the route:
app.get('/r', (req,res)=>{
res.send("a")
setTimeout(()=>{
res.send("fter")
}, 1000)
}
app.listen(8080)
But I get the error: ERR_HTTP_HEADERS_SENT, I assume because the page has already been loaded.
I need my node program to send it after it has already been loaded, so I cant like send a html,js,css script to do it. Is it possible? I cant seem to find how.
Well, if that is not possible, what I am really trying to do is after the page has loaded, execute js or send a message that the page can receive from the node program, like if there was res.execute_js('postMessage(1)')
EDIT based on your edit: So as I understand you want a way to send different values from a node app endpoint without using socketio. I've managed to replicate a similar experimental behavior using readable streams. Starting off, instead of returning response to the request with res.send() you should be using res.write() In my case I did something like this:
app.post('/api', (req, res) => {
res.write("First");
setTimeout(() => {
res.write("Second");
res.end();
}, 1000);
});
This will write to a stream "First" then after 1000ms it'll write another "Second" chunk then end the stream, thus completing the POST request.
Now in the client, you'll make the fetch response callback async, get the ReadableStream from the request like so
const reader = response.body.getReader();
now we should be reading this stream, we'll first initialize an array to collect all what we're reading,
const output = [];
now to actually read the stream,
let finished, current;
while (!finished) {
({ current, finished} = await reader.read());
if (finished) break;
output.push(current);
}
if you read current in the loop, it'll contain each value we passed from res.write() and it should read twice, "First" and after 1000ms "Second".
EDIT: This is very experimental however, and I wouldn't recommend this in a production codebase. I'd suggest trying out socketio or a publish/subscribe mechanism instead.
Old answer: You're already sending "a" back, you should remove the first res.send() invocation at the top of the callback.
So, this is for all the people wondering. No you cannot do this with pure express (there is a workaround, so keep reading).
The reason you cant do this is because, when the user requests to the url, it sends them a response, and the browser renders it. You cant then tell it to change the response, as the browser has already received a response. Even if you send multiple, like with res.write, rather then res.send, the browser will just wait until it receives all the data.
Here are two workarounds:
1. Use socket.io, cscnode, or another library to have events for updating text,
2. Send hardcoded html, that updates text (1 was probably better)
That is all I think you can do.
More clarification on the socketio one is basically have an event for changing text that you can fire from node, and the browser will understand, and change the text.
I have this use case:
- I'm working on a game with a webapp for user management and chat, which is on MERN, and a unity game, with socket.io as the real time messaging layer for the multiplayer game.
- User may register to webapp by either providing a pair of email/password, or getting authenticated on FB/Gamil/etc. as usual, in which case the user's email is obtained and saved to MongoDB and this is done by passport.
- There is no session in express side, and socket.io is on a redis. There is no cookie but JWT is used.
My problem is that I don't know what's the best practices in this. I read this
article
and this
one
which both have content and code close to what I want to do, but in the first one:
app.use(express.cookieParser());
while I don't want to use cookie at all, and the other one also has in code:
cookie: {
secure: process.env.ENVIRONMENT !== 'development' && process.env.ENVIRONMENT !== 'test',maxAge: 2419200000}...
Also, I found this on
github
which suggests for the client side (unity):
var socket = io.connect('http://localhost:9000');
socket.on('connect', function (socket) {
socket.on('authenticated', function () {
//do other things
})
.emit('authenticate', {token: jwt}); //send the jwt
});
meaning that:
1. socket is created
2. authentication is requested
but I think that the approach I found in the other article is better, where the socket is not created at all if the JWT for auth is not provided at the first ever connection request sent to "io", so if I'd do it I'd issue:
var socket = io.connect('http://localhost:9000', {query: {"JWT":"myjwt"}});
and in my server side where I have:
io.on("connection", function(socket){...});
I'd like to first get the JWT:
var jwt = socket.handshake.query["JWT"];
and then if auth will be unsuccessful, simply return socket.disconnect('reason') and do not open any connection at all (here maybe I just didn't understand, say, that the approach the Author took in the github source is using a middle ware technique and it is maybe also done before anything else).
I still could not find out what is the best practice that Gurus use, please help me get clear.
I want to use breezejs api for storing data in local storage (indexdb or websql) and also want to sync local data with sql server.
But I am failed to achieve this and also not able to find sample app of this type of application using breezejs, knockout and mvc api.
My requirement is:
1) If internet is available, the data will come from sql server by using mvc web api.
2) If internet is shutdown, the application will retrieve data from cached local storage (indexdb or websql).
3) As soon as internet is on, the local data will sync to sql server.
Please let me know Can I achieve this requirement by using breezejs api or not?
If yes, please provide me some and links and sample.
If no, what other can we use for achieving this type of requirement?
Thanks.
Please help me to meet this requirement.
You can do this, but I would suggest simply using localstorage. Basically, every time you read from the server or save to the server, you export the entities and save that to local storage. THen, when you need to read in the data, if the server is unreachable, you read the data from localstorage and use importentities to get it into the manager and then query locally.
function getData() {
var query = breeze.EntityQuery
.from("{YourAPI}");
manager.executeQuery.then(saveLocallyAndReturnPromise)
.fail(tryLocalRestoreAndReturnPromise)
// If query was successful remotely, then save the data in case connection
// is lost
function saveLocallyAndReturnPromise(data) {
// Should add error handling here. This code
// assumes tis local processing will be successful.
var cacheData = manager.exportEntities()
window.localStorage.setItem('savedCache',cacheData);
// return queried data as a promise so that this detour is
// transparent to viewmodel
return Q(data);
}
function tryLocalRestoreAndReturnPromise(error) {
// Assume any error just means the server is inaccessible.
// Simplified for example, but more robust error handling is
// warranted
var cacheData = window.localStorage.getItem('savedCache');
// NOTE: should handle empty saved cache here by throwing error;
manager.importEntities(cacheData); // restore saved cache
var query = query.using(breeze.FetchStrategy.FromLocalCache);
return manager.executeQuery(query); // this is a promise
}
}
This is a code skeleton for simplicity. You should check catch and handle errors, add an isConnected function to determine connectivity, etc.
If you are doing editing locally, there are a few more hoops to jump through. Every time you make a change to the cache, you will need to export either the whole cache or the changes (probably depending on the size of the cache). When there is a connection, you will need to test for local changes first and, if found, save them to the server before requerying the server. In addition, any schema changes made while offline complicate matters tremendously, so be aware of that.
Hope this helps. A robust implementation is a bit more complex, but this should give you a starting point.
I am working on webrtc Peer to Peer Calling and successfully running the AppRTCDemo available on WEBRTC site . I have gone through the code and stuck on few points :
1 : When I enter the URL it hit the server and I got response like :
response return from server{"meta_viewport":"","pc_constraints":"{\"optional\": [{\"googImprovedWifiBwe\": true}]}","opusfec":"true","include_vr_js":"","vsbr":"","audio_receive_codec":"opus\/48000","arbr":"","vrbr":"","vsibr":"","token":"AHRlWroqCeuFFBWs4dLJRahxtwho2ldeH_94M_ZipRkK7aIH3nAiSFfScjb_Opz2LwC9xVeWeQrJkRWQAeTsK5sxdJEPoC3jP8uQXkE23QnSANqoBwsHOM4","initiator":1,"ssr":"","room_key":"95505311","pc_config":"{\"iceServers\": [{\"urls\": \"stun:stun.l.google.com:19302\"}]}","stereo":"false","audio_send_codec":"","turn_url":"https:\/\/computeengineondemand.appspot.com\/turn?username=77294535&key=4080218913","me":"77294535","room_link":"https:\/\/apprtc.appspot.com\/?r=95505311&t=json","error_messages":[],"offer_constraints":"{\"optional\": [], \"mandatory\": {}}","asbr":"","media_constraints":"{\"audio\": true, \"video\": true}"}
Here , I just want to know where exactly they are creating iceServer ? On their Server or is there any code inside their channel.html file.
Is there any way to generate iceServer on application without server ? or IceServer is our stun/turn URL sent from server ?
I also have few question on Channel.html :
how exactly channel.html file helping this demo to run ? I have gone through this also and it is calling the onOpen() and which is calling the GAECLIENT class method .
Thanks,
Whichever ice server is going to be used is passed through to the RTCPeerConnection constructor when it is constructed(the object is called pc for the apprtc example). You can see the servers specifically by looking at the pcConfig object.
Once the connection is created(it is not done until a call starts in this example), the localDescription(a RTCSessionDescription object) is set. Once it is set, the WebRTC api will start automatically gathering IceCandidates against the ice servers first introduced when the peer connection was created. Once a new candidate is created, the onicecandidate event is fired(you can see the function used to transfer the candidates if you look at that callback after the pc object is created).
So the general steps are as follows:
Set what iceServers you want to gather candidates against when you create your RTCPPeerConnection object
Set your localDescription to your local RTCSessionDescription object you create(usually created via the success callback you set in the createOffer or createAnswer functions from the peerconnection).
It will start gathering candidates automatically against the servers you set when the peerconnection was constructed and with each candidate the onicecandidate event is fired.
Now, specifically for the apprtc demo page, it uses an open stun server stun:stun.l.google.com:19302 and an array of closed turn servers(that are hosted on Google's cloud) with dynamic credentials that are gathered at page load.
I have a very frustrating problem with a client's network environment, and I'm hoping someone can lend a hand in helping me figure this out...
They have an app that for now is written entirely inside of VBA for Excel. (No laughing.)
Part of my helping them improve their product and user experience involved converting their UI from VBA form elements to a single WebBrowser element that houses a rich web app which communicates between Excel and their servers. It does this primarily via a socket.io server/connection.
When the user logs in, a connection is made to a room on the socket server.
Initial "owner" called:
socket.on('create', function (roomName, userName) {
socket.username = userName;
socket.join(roomName);
});
Followup "participant" called:
socket.on('adduser', function (userName, roomName){
socket.username = userName;
socket.join(roomName);
servletparam = roomName;
var request = require('request');
request(bserURL + servletparam, function (error, response, body) {
io.sockets.to(roomName).emit('messages', body);
});
servletparam = roomName + '|' + userName;
request( baseURL + servletparam, function (error, response, body) {
io.sockets.to(roomName).emit('participantList', body);
});
});
This all worked beautifully well until we got to the point where their VBA code would lock everything up causing the socket connection to get lost. When the client surfaces form it's forced VBA induced pause (that lasts anywhere from 20 seconds to 3 minutes), I try to join the room again by passing an onclick to an HTML element that triggers a script to rejoin. Oddly, that doesn't work. However if I wait a few seconds and click the object by hand, it does rejoin the room. Yes, the click is getting received from the Excel file... we see the message to the socket server, but it doesn't allow that call to rejoin the room.
Here's what makes this really hard to debug. There's no ability to see a console in VBA's WebBrowser object, so I use weinre as a remote debugger, but a) it seems to not output logs and errors to the console unless I'm triggering them to happen in the console, and b) it loses its connection when socket.io does, and I'm dead in the water.
Now, for completeness, if I remove the .join() calls and the .to() calls, it all works like we'd expect it to minus all messages being written into a big non-private room. So it's an issue with rejoining rooms.
As a long-time user of StackOverflow, I know that a long question with very little code is frowned upon, but there is absolutely nothing special about this setup (which is likely part of the problem). It's just simple emits and broadcasts (from the client). I'm happy to fill anything in based on followup questions.
To anyone that might run across this in the future...
The answer is to manage your room reconnection on the server side of things. If your client can't make reliable connections, or is getting disconnected a lot, the trick it to keep track of the rooms on the server side and join them when they do a connect.
The other piece of this that was a stumper was that the chat server and the web UI weren't on the same domain, so I couldn't share cookies to know who was connecting. In their case there wasn't a need to have them hosted in two different places, so I merged them, had Express serve the UI, and then when the client surfaced after a forced disconnect, I'd look at their user ID cookie, match them to the rooms they were in that I kept track of on the server, and rejoined them.