Hi, we used `ktor-client-cio` to shake hands with an external APIs, but the APIs does not expose a c...

# ktor

[hantsy]

Hi, we used ktor-client-cio to shake hands with an external APIs, but the APIs does not expose a correct ContentType header(application/octet-stream) as expected, the content is JSON.

I tried to add a default content type to the response via the built-in HttpSend plugin like the following, but it did not work.

var client = HttpClient(CIO){
            install(ContentNegotiation) {
                register(ContentType.Application.Json, JacksonConverter(objectMapper))
            }
}        
client.plugin(HttpSend).intercept { builder ->
            val originalCall = execute(builder)
//            if (!originalCall.response.headers.contains(HttpHeaders.ContentType) ||
//                originalCall.response.headers[HttpHeaders.ContentType] == ContentType.Application.OctetStream.contentType
//            ) {
                originalCall.response.apply {
                    headers {
                        set(HttpHeaders.ContentType, ContentType.Application.Json.contentType)
                    }
                }
           // }
            originalCall
        }

I have tried the Apache 5 engine, it is more flexible for the engine config and I configured customizeClient

customizeClient {
                    addResponseInterceptorLast(
                        HttpResponseInterceptor { response, _, _ ->
                            response.setHeader(HttpHeaders.ContentType, ContentType.Application.Json)
                        }
                    )
                }

to add an interceptor there, it worked well.

But some of our team members are stick on the CIO engine.

[Aleksei Tirman [JB]]

Why registering a converter for the application/octet-stream content type doesn't work for you?

[hantsy]

I want to know what is wrong in usage of HttpSend plugin.

[hantsy]

treat application/octet-stream content with a json converter is ugly.

[Aleksei Tirman [JB]]

You can try this workaround to override the Content-Type header.

[hantsy]

We can not modify the response headers via the HttpSendIntercepter directly?

[Aleksei Tirman [JB]]

No, because they are immutable there

[hantsy]

If the HttpSendIntecepter can not modify request/response, what is the purpose of using it?

[hantsy]

And it the response is immutable there, it should not accept a apply{} block.

[hantsy]

And headers builder has set to modify the headers.

[Aleksei Tirman [JB]]

If the HttpSendIntecepter can not modify request/response, what is the purpose of using it?

The purpose is to intercept the network calls to implement, for example, redirection, request retrying and so on. You can modify the request through the HttpRequestBuilder parameter (the builder parameter in your example).

And it the response is immutable there, it should not accept a apply{} block.

The following code just returns a new instance of Headers .

headers {
    set(HttpHeaders.ContentType, ContentType.Application.Json.contentType)
}

In your example, there is no code that tries to modify the response.