Response Metadata

trpcgo injects response metadata into the context before HTTP procedure execution. Handlers and middleware can add response headers or cookies without depending on http.ResponseWriter.

Set Headers

func handler(ctx context.Context, input Input) (Output, error) {
    trpcgo.SetResponseHeader(ctx, "X-Trace-ID", traceIDFrom(ctx))
    return Output{}, nil
}

SetResponseHeader adds a header value. It is safe to call from JSONL batch handlers concurrently.

Set Cookies

func login(ctx context.Context, input LoginInput) (User, error) {
    trpcgo.SetCookie(ctx, &http.Cookie{
        Name:     "session",
        Value:    issueSession(input),
        Path:     "/",
        HttpOnly: true,
        Secure:   true,
        SameSite: http.SameSiteLaxMode,
    })

    return user, nil
}

Headers and cookies are applied before the status line is written.

No-Op Outside Metadata Context

If the context does not carry response metadata, SetResponseHeader and SetCookie are safe no-ops. The HTTP handler creates the metadata context automatically.

RawCall

RawCall injects response metadata if the context does not already have it, but callers only receive headers and cookies if they keep and inspect the context that carries metadata.

ctx := trpcgo.WithResponseMetadata(context.Background())

result, err := router.RawCall(ctx, "auth.login", rawInput)
if err != nil {
    return err
}

headers := trpcgo.GetResponseHeaders(ctx)
cookies := trpcgo.GetResponseCookies(ctx)
_ = result
_ = headers
_ = cookies

Use this when server-side procedure calls need to observe cookies or custom headers set by handlers.