Content-Type set in interceptor is overwritten, maybe by ConverterFactory default

• Bug report.

I think its a bug, maybe not, we will see 😉 If I set the Content-Type header with chain interceptor, it will be overwritten to a default. I guess it is the ConverterFactory, but i’m not sure.

I wrote a test to show whats happening. In interceptor I set .addHeader("Content-Type", "application/vnd.x.api.v1+json") which is also logged by HttPLoggingInterceptor, but the request received by the MockServer has Content-Type: application/json; charset=UTF-8

If anything is unclear fell free to ask.

open class RetrofitBug {
    internal interface Service {
        @POST("/path")
        fun post(@Body body:PostBody): Call<ResponseBody?>
    }

    data class PostBody(val value: String)

    @Test
    @Throws(Exception::class)
    fun test() {
        val server = MockWebServer()
        val retrofit = Retrofit.Builder()
            .addConverterFactory(
                GsonConverterFactory.create(
                    GsonBuilder()
                        .create()
                )
            )
            .client(
                OkHttpClient().newBuilder()
                    .addInterceptor { chain ->
                        val newRequest = chain.request().newBuilder()
                            .header("Content-Type", "application/vnd.x.api.v1+json")
                            .build()
                        chain.proceed(newRequest)
                    }
                    .addInterceptor(HttpLoggingInterceptor { message -> println(message) }.apply {
                        level = HttpLoggingInterceptor.Level.BODY
                    })
                    .build()
            )
            .baseUrl(server.url("/"))
            .build()
        val example = retrofit.create(
            Service::class.java
        )
        server.enqueue(
            MockResponse()
                .addHeader("Content-Type", "text/plain")
                .setBody("Hi")
        )
        val call = example.post(PostBody("Test"))
        val response = call.execute()
        val recordedRequest = server.takeRequest()
        println(recordedRequest.headers) // does not show my header, but **Content-Type: application/json; charset=UTF-8**
        assertEquals("application/vnd.x.api.v1+json", recordedRequest.getHeader("Content-Type"));
        server.shutdown()
    }
}

[JakeWharton]

That’s right. Also if you use getHeaders on the MockWebServer validation you’ll get a list with two values for both headers which also would have helped indicate the problem.

[matecode]

@waqasakram117 thank you for pointing out that!