Hi , I am finding it really hard to make `transfor...

# ktor

[Prateek Kumar]

Hi , I am finding it really hard to make transformResponseBody{ } , work using createClientPlugin
It works if put before ContentNegotiation plugin, but any plugin with transformResponseBody put after ContentNegotiation dosen’t get called at all.

And in my other projects , so far i have been unsuccessful in making transformResponseBody work.

Every other method provided by createClientPlugin works without problem.
Is there something i am missing or there is some extra step needed to make it work?

[Aleksei Tirman [JB]]

Can you please describe the effect you're trying to achieve?

[Prateek Kumar]

I basically need to decrypt the content before sending it to ContentNegotiation

So was trying to achieve it with transformResponseBody , but i don’t get any callback in this method

[Prateek Kumar]

So far from what i have tried , onResponse get’s called for every single installed Custom plugin , but not the case with transformResponseBody ,This should not be the case , Right? Or am i missing something

[Aleksei Tirman [JB]]

The transformResponseBody 's block is called only when the response body is still the ByteReadChannel (it isn't transformed to the specified type). The order of the plugins determines which transformation come first since both use the same pipeline phase. You can insert the phase before the HttpResponsePipeline.Transform phase to make your transformation executed first. Here is an example:

fun main(): Unit = runBlocking {
    val client = HttpClient(CIO) {
        install(ContentNegotiation) {
            json(Json {
                ignoreUnknownKeys = true
            })
        }
    }

    val beforeTransform = PipelinePhase("BeforeTransform")
    client.responsePipeline.insertPhaseBefore(HttpResponsePipeline.Transform, beforeTransform)
    client.responsePipeline.intercept(beforeTransform) { (typeInfo, body)->
        // Decrypt the body here and then pass it to proceedWith(...)
        println(body)
        proceedWith(HttpResponseContainer(typeInfo, body))
    }

    val response = client.get("<https://httpbin.org/get>")
    println(response.body<HttpBin>())
}

@Serializable
data class HttpBin(val origin: String)

[Prateek Kumar]

I tested it a bit more , even if i put this plugin at the very top , I still do not get callback for transformResponseBody , But at the same time i am able to read content using onResponse very easily.


What can be the reason for that,i tried to print
it.content.toString inside onResponse, Output is ByteBufferChannel(92329252, IDLE(with buffer))


I will use the implementation provided by you to make it work , Still wondering why transformResponseBody
didn’t work

[Aleksei Tirman [JB]]

The reason is that onResponse is executed before the HttpResponse.body method is called.

[adam-mcneilly]

Hi! I found this while searching because I'm trying to do something similar. I found an api that returns everything in jsonp, which basically means it's wrapped in parenthesis. ({ myJson })

I was hoping the easiest way to serialize this properly was to intercept it, look if it started and ended with parens, and remove them from the string. This solution seems pretty close, but I'm unclear how to manipulate the byte array here:

// Decrypt the body here and then pass it to proceedWith(...)
println(body)

Do you have any examples of this?

[Aleksei Tirman [JB]]

You can use the following method to remove JSONP characters from the response body:

@OptIn(DelicateCoroutinesApi::class)
suspend fun ByteReadChannel.transform(): ByteReadChannel {
    val body = this

    val first = body.readByte()
    val second = body.readByte()

    if (first != '('.code.toByte() || second != '{'.code.toByte()) {
        return GlobalScope.writer {
            channel.writeByte(first)
            channel.writeByte(second)
            body.copyTo(channel)
        }.channel
    }

    return GlobalScope.writer {
        while (!body.isClosedForRead) {
            val arr = body.readRemaining(8 * 1024).readByteArray()

            if (body.isClosedForRead && arr.size >= 2) {
                val first = arr[arr.size - 2]
                val second = arr[arr.size - 1]

                if (first == '}'.code.toByte() && second == ')'.code.toByte()) {
                    channel.writeFully(arr, 0, arr.size - 2)
                    break
                } else {
                    channel.writeFully(arr)
                    continue
                }
            }

            channel.writeFully(arr)
        }
    }.channel
}

Here is a usage example:

client.responsePipeline.intercept(beforeTransform) { (typeInfo, body)->
    when (body) {
        is ByteReadChannel -> {
            proceedWith(HttpResponseContainer(typeInfo, body.transform()))
        }
        else -> TODO()
    }
}

[adam-mcneilly]

Amazing, thank you a ton! That worked out great.