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/routers.go

@@ -41,32 +41,34 @@ func registerDistErasureRouters(router *mux.Router, endpointServerPools Endpoint
 	registerLockRESTHandlers(router)
 }
 
-// List of some generic handlers which are applied for all incoming requests.
-var globalHandlers = []mux.MiddlewareFunc{
-	// The generic tracer needs to be the first handler
-	// to catch all requests returned early by any other handler
-	httpTracer,
-	// Auth handler verifies incoming authorization headers and
-	// routes them accordingly. Client receives a HTTP error for
-	// invalid/unsupported signatures.
+// List of some generic middlewares which are applied for all incoming requests.
+var globalMiddlewares = []mux.MiddlewareFunc{
+	// set x-amz-request-id header and others
+	addCustomHeadersMiddleware,
+	// The generic tracer needs to be the first middleware to catch all requests
+	// returned early by any other middleware (but after the middleware that
+	// sets the amz request id).
+	httpTracerMiddleware,
+	// Auth middleware verifies incoming authorization headers and routes them
+	// accordingly. Client receives a HTTP error for invalid/unsupported
+	// signatures.
 	//
 	// Validates all incoming requests to have a valid date header.
-	setAuthHandler,
-	// Redirect some pre-defined browser request paths to a static location prefix.
-	setBrowserRedirectHandler,
-	// Adds 'crossdomain.xml' policy handler to serve legacy flash clients.
-	setCrossDomainPolicy,
+	setAuthMiddleware,
+	// Redirect some pre-defined browser request paths to a static location
+	// prefix.
+	setBrowserRedirectMiddleware,
+	// Adds 'crossdomain.xml' policy middleware to serve legacy flash clients.
+	setCrossDomainPolicyMiddleware,
 	// Limits all body and header sizes to a maximum fixed limit
-	setRequestLimitHandler,
+	setRequestLimitMiddleware,
 	// Validate all the incoming requests.
-	setRequestValidityHandler,
-	// set x-amz-request-id header.
-	addCustomHeaders,
-	// Add upload forwarding handler for site replication
-	setUploadForwardingHandler,
-	// Add bucket forwarding handler
-	setBucketForwardingHandler,
-	// Add new handlers here.
+	setRequestValidityMiddleware,
+	// Add upload forwarding middleware for site replication
+	setUploadForwardingMiddleware,
+	// Add bucket forwarding middleware
+	setBucketForwardingMiddleware,
+	// Add new middlewares here.
 }
 
 // configureServer handler returns final handler for the http server.
@@ -98,7 +100,7 @@ func configureServerHandler(endpointServerPools EndpointServerPools) (http.Handl
 	// Add API router
 	registerAPIRouter(router)
 
-	router.Use(globalHandlers...)
+	router.Use(globalMiddlewares...)
 
 	return router, nil
 }