React Native throws exception on ws.send(null)

[microsoft]

React Native throws exception on ws.send(null)

[grootendorste]

Here is the precise line of code: sub = Observable.interval(timeout).subscribe(_ => ws.send(null));

Is there a reason why it's sending null?

[tschnoelzer]

Hi Team,

same here... just a simple test:

componentDidMount() {

   let directLine = new DirectLine({
     token: "_sdWTnasdasdasd...."
   });

   console.log("mounted");

   directLine.postActivity({
     from: { id: 'myUserId', name: 'Timo' }, // required (from.name is optional)
     type: 'message',
     text: '123'
   }).subscribe(
     id => console.log("Posted activity, assigned ID ", id),
     error => console.log("Error posting activity", error)
     );

   directLine.activity$
     .filter(activity => activity.type === 'message')
     .subscribe(
     message => console.log("received message ", message)
     );

 }

error is Unsupported data type in WebSocket.send 124:10

[grootendorste]

I'm surprised no other people are having this issue.

[tschnoelzer]

Perhaps its because of npm / node version ?!? I am using node 8.2.1 and npm 5.3.0 ....

[grootendorste]

I'm using v8.3.0. It also gave a problem with 6.9.1. I'm having an issue changing node versions now, I actually had to uninstall it completely because something broke. But according the comments of that Observable.interval(timeout).subscribe(_ => ws.send(null));, it's there because of some chrome issue. So I'm having this issue on iOS and Android, not in web.

[billba]

I don't see any reason it couldn't send {} instead of null, would that fix the problem with React Native?

@dandriscoll periodically DirectLineJS sends empty messages up the WebSocket as a way of helping Chrome notice if the connection is broken so that we can reconnect. Right now we send null but are contemplating changing this to {} because React Native's WebSocket implementation doesn't allow us to send null. I assume you don't check the incoming messages on your end, but I want to be careful not to break anything.

[billba]

Another alternative is to make this behavior optional. But I think it might be generally useful for any WebSocket implementation that, like Chrome's, is a little sleepy about noticing WebSocket disconnections.

[dandriscoll]

Can you send an empty string? That's what the service is expecting.

[billba]

I think so. Out of curiosity, does the service do anything with non-empty strings?

React Native people, can you try changing that null to "" and see if it works?

[dandriscoll]

Right now nothing, but "" and null are protected from future changes in a way that other values aren't.

[billba]

Got it. Okay, let's wait to hear from the React Native people and then I'll make the change.

[billba]

@grootendorste @tschnoelzer we are waiting for your feedback on his one.

[grootendorste]

Hi I'll try tonight, sorry I wasn't at my laptop for a while.

[billba]

@grootendorste @tschnoelzer any news for us, React Native folks?

[grootendorste]

Hi all, sorry I've been on my other github account. A while ago I forked the repo and removed the .send(null) part and since then I haven't had any issues on any browser (on React) or any device (on React-Native). I apologize, I have not sent in an empty string (.send('')) yet to see if it works. But up until now removing the send completely has worked for me. I realize it's a cheap fix, but at the time I was in a rush.

[billba]

@grootendorste Thank you for the response. Unfortunately this doesn't help us evaluate the solution on the table.

[grootendorste]

@billba Sending {} instead of null also does fix the solution. I'm not a fan of quick fixes that I can't really motivate, can anyone explain why this is a good idea?

[billba]

@grootendorste we're looking to see if send("") fixes the solution.

This is not a quick fix.

We periodically ping the server to see if the connection is still good. We can't send just any message, but
our server specifically ignores null and "" as messages, so those are safe as pings. We had been sending null, which works in the browser, but breaks React Native. So since none of us here use React Native, we are trying to find out if send("") works on React Native.

[colewinans]

@billba send("") does indeed work. Confirming on React Native 0.50.

[billba]

Hooray, thank you @colewinans!