Ktor plugin does not capture kotlinx rpc (and perhaps even websocket) traces.

[jobinlawrance]

Describe the bug

When adding opentelemetry plugin to ktor server, only the http request are captured in the traces. KotlinX RPC (krpc) is added to Ktor via a plugin.

Unlike gRPC, kotlinx RPC does not use Http 2 and instead relies on websockets as is evident from the logs and it's plugin implementation which also leads me to believe that websocket traces are missing as well.

// It's installed on the server like 

install(RPC)

// internal implementation

public val RPC: ApplicationPlugin<RPCConfigBuilder.Server> = createApplicationPlugin(
    name = "RPC",
    createConfiguration = { RPCConfigBuilder.Server() },
) {
    application.install(WebSockets)           // < -----------------------------  Websockets
    application.attributes.put(RPCServerPluginAttributesKey, pluginConfig)
}

// And on the client

installRPC {
            waitForServices = true
}

// implementation

public fun HttpClientConfig<*>.installRPC(
    configure: RPCConfigBuilder.Client.() -> Unit = {}
) {
    install(WebSockets)                      // < -----------------------------  Websockets
    install(RPC, configure)
}

Steps to reproduce

In order to add OpenTelemetry plugin to Ktor server and client i've followed the offical ktor examples and implemented here

Expected behavior

The Ktor server has a bi-directional stream like

routing {
        rpc("/stream") {
            rpcConfig {
                serialization {
                    json{
                        ignoreUnknownKeys = true
                    }
                }
            }
        
            registerService<DeviceStream> { ctx -> DeviceStreamImpl(ctx) }
        }
    }

and a http GET request like

routing {
        get("/") {
            call.respondText("Hello World!")
        }
    }

Actual behavior

Only the http requests are automatically captured on the server

In client if the initial RPC call fails I do get the trace for it but otherwise there are no traces related to rpc & websockets

Javaagent or library instrumentation version

opentelemetry-ktor-3.0 v2.10.0-alpha

Environment

JDK:
Temurin 21
OS:
MacOS Sequoia version 15.1

Additional context

No response

[laurit]

We'd welcome a contribution for this.