Hi, I’d like to custom my Ktor response pipeline to add 2 headers, one for the time it takes for the app to process the request and send the response and another one to handle etag response header transparently. I tried to create a Feature, try some interceptors, ... but I failed to find a phase where the response is processed but I am still able to add headers to the response. Often I get this error :

java.lang.UnsupportedOperationException: Headers can no longer be set because response was already completed

. I suppose it’s too late. So I was wandering if it is possible to have a phase where the Request is processed, the response is ready but I’m still able to modify the response to add some headers.

You could find the phase which is responsible for actually sending the request, then add your own just before it and do your thing on your own added phase

One usually should add headers to a response object, not to response itself

After some work, I found a solution for my problem. I used a Feature to register my code to Ktor. In this Feature, I registered 2 phases : • pipeline.intercept(ApplicationCallPipeline.Setup) • pipeline.sendPipeline.intercept(ApplicationSendPipeline.After) In the first phase, I take the start time. In the second phase, I take the stop time and compute the elapse time between start and stop and I add it to the Headers using the method `

responseHeaders.append(XMyAppLatency, start.durationToNow().toString())

` I will put the code in Github in a while.