Crash reading trailers in Retrofit Call

[swankjesse]

We’ve observed this crash with Retrofit 3 and OkHttp 5.0.0:

java.lang.IllegalStateException: Cannot read raw response body of a converted body.
	at retrofit2.OkHttpCall$NoContentResponseBody.source(OkHttpCall.java:300)
	at okhttp3.Response.trailers(Response.kt:195)
	at misk.client.ClientMetricsInterceptorNoSummaryTest.responseCodes(ClientMetricsInterceptorNoSummaryTest.kt:107)
	at java.lang.reflect.Method.invoke(Method.java:568)

I believe the core problem is this recently-changed function in OkHttp 5:

  @Throws(IOException::class)
  fun trailers(): Headers {
    val source = body.source()
    if (source.isOpen) {
      source.skipAll()
    }
    return trailersSource.get()
  }

I think it’s fine that we exhaust the response body before attempting to read the trailers. But I also believe that behavior should be within the implementation of trailersSource and not in the code that calls that function.

Ie. we should change all of our built-in TrailersSource.get implementations to do this:

  override fun get(): Headers {
    val source = bodySource // Somehow!
    if (source.isOpen) {
      source.skipAll()
    }
  }

That way a custom ResponseBody won’t interact awkwardly with Response.

An alternative solution would be a custom function on ResponseBody to do this work. That way the custom Retrofit ResponseBody could override that function.