hi, regarding the otel ktor server plugin, i notic...

# ktor

[RJ Garcia]

hi, regarding the otel ktor server plugin, i noticed the default span names / http.route attribute generated include route nodes with transparent selectors, so things like (authentication: jwt) show up within the generated span name which gets really noisy. Here's an example span name / http.route value:

GET /(authenticate auth-x-forwarded-client-certs)/MTLSRouteVisibilitySelector(visibility=Private)/MTLSRouteVisibilitySelector(visibility=Public)/api/v1/users

ideally, this would be just /api/v1/users.

the ktor otel server plugin just simply transforms the route into a string which includes all route nodes regardless if that node doesn't actually change the route path itself.

application.monitor.subscribe(RoutingRoot.RoutingCallStarted) { call ->
    HttpServerRoute.update(Context.current(), HttpServerRouteSource.SERVER, { _, arg -> arg!!.route.parent.toString() }, call)
  }

After digging in a bit, I think some logic that filtered out routes where the selector wasn't apart of RoutePathComponent would do the trick.

Would a PR be accepted that would:
1. change the default implementation of the http.route lambda to filter out routing nodes with non RoutePathComponent selectors
2. and support a new configuration item in the plugin that accepts a lambda of (Call) -> String to get the http.route from the call to allow overriding in case people want different behavior?

[RJ Garcia]

claude came up with something like this which seems to work in my limited testing:

private fun Route.filteredPath(): String {
    val parentPath = parent?.filteredPath()

    if (selector !is RoutePathComponent) {
        return parentPath ?: ""
    }

    return when (parentPath) {
        null -> when (selector) {
            is TrailingSlashRouteSelector -> "/"
            else -> "/$selector"
        }

        else -> when (selector) {
            is TrailingSlashRouteSelector -> if (parentPath.endsWith('/')) parentPath else "$parentPath/"
            else -> if (parentPath.endsWith('/')) "$parentPath$selector" else "$parentPath/$selector"
        }
    }
}

I don't love the duplication of the existing Route.toString(), this feels like this could be an extension function just shipped within ktor itself which could be used in the otel instrumentation

[Bruce Hamilton]

We already have a utility function for this:

/**
 * String representation of the path matched by this route.
 *
 * [Report a problem](<https://ktor.io/feedback/?fqname=io.ktor.server.routing.path>)
 */
public val Route.path: String
    get() = path()

/**
 * Constructs the full path of the routing node by combining the path of the parent node
 * and the formatted path of this node's selector, using the provided format.
 *
 * [Report a problem](<https://ktor.io/feedback/?fqname=io.ktor.server.routing.path>)
 *
 * @param format formats each selector in the node's lineage. Defaults to [RoutePathFormat.Default].
 * @return the full path of the routing node as a string.
 */
public fun Route.path(format: RoutePathFormat = RoutePathFormat.Default): String {
    val parentPath = parent?.path(format)
    val pathComponent = selector as? RoutePathComponent ?: return parentPath.orEmpty()
    val formattedPath = format.format(pathComponent)
    return when {
        parentPath == null -> formattedPath
        formattedPath.isEmpty() -> parentPath
        parentPath.endsWith('/') || formattedPath.startsWith('/') -> "$parentPath$formattedPath"
        else -> "$parentPath/$formattedPath"
    }
}

It would make sense to use this instead of toString() in the otel plugin

[RJ Garcia]

Lmao, amazing. Ya I think just using that would be simplest fix for sure

[Bruce Hamilton]

it was only introduced in 3.3.0 I think... so maybe if they're supporting back to 3.0 it won't be possible

[RJ Garcia]

Got it, so maybe we'll have to do some duplication for now.

This also would be a potential breaking change because it would shift the http route name. So we'd need to feature flag/opt into it if we release for ktor2/3

[RJ Garcia]

just deployed an internal fix on our side which to use route.path and works like a charm.

@Bruce Hamilton is this something ktor would be willing to accept a pr for?

[Bruce Hamilton]

nice. yeah, fire away 👍