Hi team, We are adopting `grpc` and have hit a mig...

# kotlinx-rpc

[Manuel Lilienberg]

Hi team,
We are adopting grpc and have hit a migration blocker with gRPC metadata serialization for composite headers like User-Agent.
Even when we explicitly set a header value without spaces (e.g., Android=36;Version=26.23.0), the grpc client automatically injects a space after each semicolon upon sending (Android=36; Version=26.23.0).
While RFC 9110 permits Optional White Space, this automatic injection breaks compatibility. Our existing Java, Swift, Go and JS clients do not add these spaces, and hundreds of our backend microservices rely on strict string splitting without trimming. Updating parsing logic across our entire backend architecture to handle this new whitespace is a major effort.
Could you either remove this automatic space injection to align with other gRPC platform implementations, or expose an API to disable this formatting? This would maintain backward compatibility and unblock our migration.

[Alexander Sysoev]

Hi! Is this happening on Android?

[Manuel Lilienberg]

I only got this verified for android, but i think it happens also on iOS.

[Alexander Sysoev]

Alright, I'll what's the problem migth be

[Manuel Lilienberg]

After investigating further, the root cause is different than I initially reported. The grpc client is actually overriding the User-Agent header we set via our interceptor. As far as I can tell, there is currently no API to customize or append to the header value. I have temporarily unblocked our setup by forking the repository and adding this capability.
While making that change, I also removed the configuration that excludes iOS as a server target. Running the gRPC server on localhost directly on an iOS device works perfectly for our local mock server setup.
Since the iOS server target is a somewhat niche use case, I wanted to check your stance. Would you be open to a Pull Request for either the User-Agent configuration API or enabling the iOS server target?

[Alexander Sysoev]

Sure! We are open for both

[Manuel Lilienberg]

github.com/Kotlin/kotlinx-rpc/pull/742
github.com/Kotlin/kotlinx-rpc/pull/741