What would be the easiest way to add a header to every request with a value that can change when spe...

# ktor

[MJegorovas]

What would be the easiest way to add a header to every request with a value that can change when specific action is taken? (example: user logs in I get the value from server, user sends specific request, I get new value)

[Big Chungus]

Have some http client provider that checks for your condition each time a client is requested and injects relevant headers on defaultRequest{} config block

[Aleksei Tirman [JB]]

Could you please describe your example in terms of HTTP requests/responses?

[Rustam Siniukov]

Have you tried using DefaultRequest plugin?

[MJegorovas]

@Big Chungus you mean I should create new client for every header value change? Because as I understand you can't change the client config after it's been set up.

[Big Chungus]

Well HTTPClient is meant to be disposable - so yes

[MJegorovas]

@Aleksei Tirman [JB] Lets say user logs in and gets his id as response, now I need to send a specific header with his id as a value with every subsequent request. Now if user changes account I have new user id which I need to send as a header value.

[MJegorovas]

@Rustam Siniukov I did try naive approach, having value as a variable in my httpclient class and using it in defaultRequest, but then I get InvalidMutabilityException on init.

[Big Chungus]

To be clear, both, me and @Aleksei Tirman [JB] are talking about the same thing.

[Big Chungus]

As for immutability exception, defaultRequest{} lambda is meant to be pure and immutable withing the same instance of an HTTPClient

[Aleksei Tirman [JB]]

Can you define some variable to refer to some storage on the file level to read the ID of a user and then send it as a header value?

private val map = mutableMapOf<String, Int>()

fun main(): Unit = runBlocking {
    val client = HttpClient(Curl)
    map["John"] = 1

    var r = client.get<String>("<https://httpbin.org/get>") {
        header("user", map["John"].toString())
    }

    println(r)

    map["John"] = 2

    r = client.get<String>("<https://httpbin.org/get>") {
        header("user", map["John"].toString())
    }

    println(r)
}

[MJegorovas]

@Aleksei Tirman [JB] I tested something like this:

private var activeEnvironmentId = 0
private val client = createClient {
    ...
    defaultRequest {
        header("active-environment", activeEnvironmentId)
    }
}

but with this I got InvalidMutabilityException as I said before. I'll try @Big Chungus variant to clone the client every time and change its defaultRequest values, because I didn't knew that clients were easily disposable and their creation is lightweight.

[Rustam Siniukov]

You can use private val activeEnvironmentId = atomic(0) to fix InvalidMutabilityException