Rest Client sets own User-Agent header even if user specifies a different one

[andreas-eberle]

Describe the bug

This issue is based on the Zulip chat: https://quarkusio.zulipchat.com/#narrow/stream/187030-users/topic/io.2Evertx.2Ecore.2Ehttp.2Eimpl.2ENoStackTraceTimeoutException

We have a reactive rest client where we set a custom User-Agent header. The user agent needs to be this specific value for the API to accept our request.

@RegisterRestClient(configKey = "xxxxx")
@Produces(MediaType.APPLICATION_JSON)
interface GatewayApi {
    @GET
    @Path("zzzzz")
    suspend fun getUser(
        @HeaderParam("Accept-Language") acceptLanguage: String,
        @HeaderParam("x-request-tracing-id") traceId: String,
        @HeaderParam("x-api-key") apiKey: String,
        @HeaderParam("User-Agent") userAgent: String
    ): Response
}

Unfortunately, it seems that Quarkus versions >= 2.7.0 add an own User-Agent header value with the value: Resteasy Reactive Client. This value is always added, no matter if we set our own User-Agent. So when we make a request the User-Agent header has the values: [Resteasy Reactive Client, Our_Custom_Header_Value] compared to versions <= 2.6.3 where the User-Agent values is [Our_Custom_Header_Value].

A workaround is to add a custom ClientHeadersFactory and register it to above interface. For example:

class GatewayHeadersFactory: ClientHeadersFactory {
    override fun update(incomingHeaders: MultivaluedMap<String, String>?, clientOutgoingHeaders: MultivaluedMap<String, String>?): MultivaluedMap<String, String> {
        val clientHeaders = MultivaluedHashMap<String, String>()
        "Our_Custom_Header_Value".addHeader("User-Agent", clientHeaders)
        return clientHeaders
    }
}

Expected behavior

The rest client should only add its own User-Agent header when we do not specify our own header. This should apply when the header is set with the @HeaderParam annotation in the method as well as when using @ClientHeaderParam to set a User-Agent header.

Actual behavior

The rest client always adds it's own User-Agent header.

How to Reproduce?

No response

Output of uname -a or ver

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Output of java -version

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GraalVM version (if different from Java)

No response

Quarkus version or git rev

No response

Build tool (ie. output of mvnw --version or gradlew --version)

No response

Additional information

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[quarkus-bot]

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[quarkus-bot]

/cc @michalszynkiewicz

[michalszynkiewicz]

@stuartwdouglas I'll change it so that only if the User-Agent is not set, the default value is set.