feat(middleware): add request id to response header in RequestIDMiddleware

CHANGELOG.md

@@ -4,6 +4,9 @@ How to release a new version:
 - Manually release new version.
 
 ## [Unreleased]
+### Changed
+- In `http.RequestIDMiddleware`, the `request_id` is now always set in the response header.
+
 
 ## [0.8.0] - 2024-11-14
 ### Added

go.mod

@@ -2,7 +2,7 @@ module go.strv.io/net
 
 go 1.23.0
 
-toolchain go1.25.4
+toolchain go1.25.6
 
 require (
 	github.com/99designs/gqlgen v0.17.78

http/middleware.go

@@ -16,13 +16,14 @@ const (
 // RequestIDFunc is used for obtaining a request ID from the HTTP header.
 type RequestIDFunc func(h http.Header) string
 
-// RequestIDMiddleware saves request ID into the request context.
+// RequestIDMiddleware saves request ID into the request context and response header.
 // If context already contains request ID, next handler is called.
 // If the user provided function returns empty request ID, a new one is generated.
 func RequestIDMiddleware(f RequestIDFunc) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			if requestID := net.RequestIDFromCtx(r.Context()); requestID != "" {
+				w.Header().Set(Header.XRequestID, requestID)
 				next.ServeHTTP(w, r)
 				return
 			}
@@ -34,6 +35,8 @@ func RequestIDMiddleware(f RequestIDFunc) func(http.Handler) http.Handler {
 				requestID = net.NewRequestID()
 			}
 
+			w.Header().Set(Header.XRequestID, requestID)
+
 			ctx := net.WithRequestID(r.Context(), requestID)
 			next.ServeHTTP(w, r.WithContext(ctx))
 		})