How can I implement refresh token mechanism in an GRPC android client?

[OhhhThatVarun]

First of all, there are already two questions on the StackOverflow with this same kinda issue this and this which is kinda workaround, not an actual solution.

So there is a ClientInterceptor that is intercepting and attaching the header to the request so if the access token expired the server will respond with an UNAUTHENTICATED status but then how to recall the same method with new access token attached to it.
It is something like an authenticator which is used in retrofit here is the link.

[creamsoup]

you may find this thread useful.

[OhhhThatVarun]

Hey, @creamsoup thanks for your response it really means a lot. Actually, when I'm trying to convert the class from the answer to kotlin I'm getting this error. Can you help me with this?

Type inference failed. Expected type mismatch: inferred type is (ClientCall<(ReqT#2 (type parameter of com.app.android.app.services.Interceptor.interceptCall)..ReqT#2?), (RespT#2 (type parameter of com.app.android.app.services.Interceptor.interceptCall)..RespT#2?)>..ClientCall<ReqT#2!, RespT#2!>?) but ClientCall<ReqT#1 (type parameter of com.app.android.app.services.Interceptor.interceptCall.RetryingUnaryRequestClientCall), RespT#1 (type parameter of com.app.android.app.services.Interceptor.interceptCall.RetryingUnaryRequestClientCall)>? was expected

class Interceptor(private val app: App) : ClientInterceptor {

    override fun <ReqT : Any?, RespT : Any?> interceptCall(method: MethodDescriptor<ReqT, RespT>?, callOptions: CallOptions?, next: Channel?): ClientCall<ReqT, RespT> {

        class RetryingUnaryRequestClientCall<ReqT, RespT> : ClientCall<ReqT, RespT>() {

            var listener: Listener<RespT>? = null
            var metadata: Metadata? = null
            var message: ReqT? = null
            var request = 0
            var call: ClientCall<ReqT, RespT>? = null

            override fun sendMessage(message: ReqT) {
                assert(this.message == null)
                this.message = message
            }

            override fun halfClose() {
                startCall(CheckingListener())
            }

            override fun start(responseListener: Listener<RespT>?, headers: Metadata?) {
                this.listener = responseListener
                this.metadata = headers
            }

            override fun cancel(message: String?, cause: Throwable?) {
                if (call != null) {
                    call?.cancel(message, cause)
                }
                listener?.onClose(Status.CANCELLED.withDescription(message).withCause(cause), Metadata())
            }

            override fun request(numMessages: Int) {
                request += numMessages
                assert(this.message == null)
            }

            private fun startCall(listener: Listener<RespT>?) {
                call = next?.newCall(method,callOptions)  <---- This line
                val headers = Metadata()
                headers.merge(metadata)
                call?.start(listener, headers)
                assert(this.message != null)
                call?.request(request)
                call?.sendMessage(message)
                call?.halfClose()
            }

            inner class CheckingListener : ForwardingClientCallListener<RespT>() {

                var delegate: Listener<RespT>? = null

                override fun delegate(): Listener<RespT> {
                    if (delegate == null) {
                        throw IllegalStateException()
                    }
                    return delegate!!
                }

                override fun onHeaders(headers: Metadata?) {
                    delegate = listener
                    super.onHeaders(headers)
                }

                override fun onClose(status: Status?, trailers: Metadata?) {
                    if (delegate == null) {
                        super.onClose(status, trailers)
                        return
                    }
                    if (!needToRetry(status, trailers)) {
                        delegate = listener
                        super.onClose(status, trailers)
                        return
                    }
                    startCall(listener) // Only retry once
                }

                private fun needToRetry(status: Status?, trailers: Metadata?): Boolean {
                    if (status?.code?.toStatus() == UNAUTHENTICATED) {
                        Log.e("code", status?.code.toString())
                        return true
                    }
                    return false
                }
            }
        }
        return RetryingUnaryRequestClientCall()
    }
}

[creamsoup]

i am not familiar with kotlin. it looks like the last return statement is missing generic types (not sure kotlin fills it for you or not), do you need to specify types?

[OhhhThatVarun]

No, it doesn't require to specify generic types!

[creamsoup]

yeah like I said i am not familiar with kotlin. the error message is related to the type inferring, is there a way to provide hint or solid type?

[OhhhThatVarun]

Yeah, I understand.
I think I know the issue but I don't know how to fix it.
If you look at the java code in the class RetryingUnaryRequestClientCall it has a member ClientCall call; but in kotlin, if I do this var call: ClientCall (i.e declaring the member same as given in the java code) it gives this error
2 type arguments expected for class ClientCall<ReqT : Any!, RespT : Any!> but it fixes the old error.

[OhhhThatVarun]

Hey, @creamsoup thanks for your replies I have fixed it. I forgot about the best thing in kotlin which is using objects. So instead of using class I created the object of that class and passed it directly. Now it is showing no errors and this method is not calling up in kotlin

override fun onHeaders(headers: Metadata?) {
    delegate = listener
     super.onHeaders(headers)
}

So it was throwing the IllegalStateException so to assign the delegate I used the onReady method and now it looks fine!

Thanks again.

[creamsoup]

np! glad that it worked. if can you close this issue if no further issues?