hello channel a quick question about websockets in ktor for

Question

hello channel a quick question about websockets in ktor for example in node js we can do something like this socket emit event name JSON stringify data the event name can be used to differentiate between event types on client side how to do something like this in ktor all I can see in ktor examples is that you send message as socket send Frame data Is there a neat way to send the event type along with the data

Aleksei Tirman [JB] · Answer

You can encode an event in a frame itself and write methods that hide this detail Also there is a to support interface out of the box

Hamza Maqsood · Answer

just for clarification so you mean that I can have a base class that ll hold the event value and the generic data value and based on the event value I parse the data value right or is there a better way

Aleksei Tirman [JB] · Answer

I mean to have an extension function for a `SendChannel lt Frame gt ` object that internally encodes event in a `Frame` Here is an example ```suspend fun SendChannel lt Frame gt emit event String frame Frame val packet = BytePacketBuilder apply append event writeFully frame data build send Frame Binary true packet readBytes ``` And the calling side will look like this ```client webSocket <ws 0 0 0 0 4444 socket> outgoing emit event Frame Text hello ```

Hamza Maqsood · Answer

thanks alot man I ll give it a try

Hamza Maqsood · Answer

It works on the server side I have tried connecting to the websocket from android using the socketio java client library but it s not connecting working through postman but not from the app I have enabled the internet permissions in manifest file and also allowed clear text traffic still not connecting from android so I am assuming that ktor websockets aren t compatible with socketio clients is that so also if I use ktor client on android to connect to the websockets how can I extract the event using ktor websocket client

Aleksei Tirman [JB] · Answer

They should be compatible but I m not sure I suggest using a network protocol analyzer like WireShark to determine if the Websockets frames are actually sent or not To extract an event from the frame you need to understand how <http Socket IO|Socket IO> encodes it by analyzing frames

Hamza Maqsood · Answer

I am trying ktor client now on Android but I am not sure how can I extract the event when I receive the frames on Android side from this ``` val packet = BytePacketBuilder apply append event writeFully frame data build ```

Hamza Maqsood · Answer

on android I can do something like ```socket incoming receiveAsFlow filter it is Frame Binary ``` now how to separate data and event from this stream because the length will be different for the event string

Aleksei Tirman [JB] · Answer

This was just an example slightly smiling face You need to encode events in a way to deterministically read them on the other side

Hamza Maqsood · Answer

Oh I see pardon for my ignorance I am a sort of a newbie here undergrad student still what if I make each event string of length of 32 and for shorter strings I append some character like to fulfill the length and on android side when I get the event string of length 32 I can do something like event replace or is there a neater way

Aleksei Tirman [JB] · Answer

I would encode the length of an event string in the first byte like in Pascal strings so you could have events with up to 255 characters

Hamza Maqsood · Answer

I see that s neat I ll give it shot thanks