fix: set request ID in tracing context key (#17602)

Since `addCustomerHeaders` middleware was after the `httpTracer`
middleware, the request ID was not set in the http tracing context. By
reordering these middleware functions, the request ID header becomes
available. We also avoid setting the tracing context key again in
`newContext`.

Bonus: All middleware functions are renamed with a "Middleware" suffix
to avoid confusion with http Handler functions.

cmd/generic-handlers.go

@@ -100,7 +100,7 @@ func isHTTPHeaderSizeTooLarge(header http.Header) bool {
 }
 
 // Limits body and header to specific allowed maximum limits as per S3/MinIO API requirements.
-func setRequestLimitHandler(h http.Handler) http.Handler {
+func setRequestLimitMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tc, ok := r.Context().Value(mcontext.ContextTraceKey).(*mcontext.TraceCtxt)
 
@@ -147,7 +147,7 @@ func guessIsBrowserReq(r *http.Request) bool {
 		globalBrowserEnabled && aType == authTypeAnonymous
 }
 
-func setBrowserRedirectHandler(h http.Handler) http.Handler {
+func setBrowserRedirectMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		read := r.Method == http.MethodGet || r.Method == http.MethodHead
 		// Re-direction is handled specifically for browser requests.
@@ -325,7 +325,7 @@ func hasMultipleAuth(r *http.Request) bool {
 
 // requestValidityHandler validates all the incoming paths for
 // any malicious requests.
-func setRequestValidityHandler(h http.Handler) http.Handler {
+func setRequestValidityMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		tc, ok := r.Context().Value(mcontext.ContextTraceKey).(*mcontext.TraceCtxt)
 
@@ -425,10 +425,10 @@ func setRequestValidityHandler(h http.Handler) http.Handler {
 	})
 }
 
-// setBucketForwardingHandler middleware forwards the path style requests
+// setBucketForwardingMiddleware middleware forwards the path style requests
 // on a bucket to the right bucket location, bucket to IP configuration
 // is obtained from centralized etcd configuration service.
-func setBucketForwardingHandler(h http.Handler) http.Handler {
+func setBucketForwardingMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if globalDNSConfig == nil || !globalBucketFederation ||
 			guessIsHealthCheckReq(r) || guessIsMetricsReq(r) ||
@@ -493,9 +493,9 @@ func setBucketForwardingHandler(h http.Handler) http.Handler {
 	})
 }
 
-// addCustomHeaders adds various HTTP(S) response headers.
+// addCustomHeadersMiddleware adds various HTTP(S) response headers.
 // Security Headers enable various security protections behaviors in the client's browser.
-func addCustomHeaders(h http.Handler) http.Handler {
+func addCustomHeadersMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		header := w.Header()
 		header.Set("X-XSS-Protection", "1; mode=block")                                // Prevents against XSS attacks
@@ -539,9 +539,9 @@ func setCriticalErrorHandler(h http.Handler) http.Handler {
 	})
 }
 
-// setUploadForwardingHandler middleware forwards multiparts requests
+// setUploadForwardingMiddleware middleware forwards multiparts requests
 // in a site replication setup to peer that initiated the upload
-func setUploadForwardingHandler(h http.Handler) http.Handler {
+func setUploadForwardingMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if !globalSiteReplicationSys.isEnabled() ||
 			guessIsHealthCheckReq(r) || guessIsMetricsReq(r) ||