Implement api/server/cors (#1294)

api/server/cors/cors.go

@@ -0,0 +1,43 @@
+package cors
+
+import (
+	"net/http"
+)
+
+// CombinedCORSHandler wraps a server and provides CORS headers
+func CombinedCORSHandler(h http.Handler) http.Handler {
+	return corsHandler{h}
+}
+
+type corsHandler struct {
+	handler http.Handler
+}
+
+func (c corsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	SetHeaders(w, r)
+
+	if r.Method == "OPTIONS" {
+		return
+	}
+
+	c.handler.ServeHTTP(w, r)
+}
+
+// SetHeaders sets the CORS headers
+func SetHeaders(w http.ResponseWriter, r *http.Request) {
+	set := func(w http.ResponseWriter, k, v string) {
+		if v := w.Header().Get(k); len(v) > 0 {
+			return
+		}
+		w.Header().Set(k, v)
+	}
+
+	if origin := r.Header.Get("Origin"); len(origin) > 0 {
+		set(w, "Access-Control-Allow-Origin", origin)
+	} else {
+		set(w, "Access-Control-Allow-Origin", "*")
+	}
+
+	set(w, "Access-Control-Allow-Methods", "POST, PATCH, GET, OPTIONS, PUT, DELETE")
+	set(w, "Access-Control-Allow-Headers", "Accept, Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token, Authorization")
+}

api/server/http/http.go

@@ -10,6 +10,7 @@ import (
 
 	"github.com/gorilla/handlers"
 	"github.com/micro/go-micro/v2/api/server"
+	"github.com/micro/go-micro/v2/api/server/cors"
 	log "github.com/micro/go-micro/v2/logger"
 )
 
@@ -45,7 +46,13 @@ func (s *httpServer) Init(opts ...server.Option) error {
 }
 
 func (s *httpServer) Handle(path string, handler http.Handler) {
-	s.mux.Handle(path, handlers.CombinedLoggingHandler(os.Stdout, handler))
+	h := handlers.CombinedLoggingHandler(os.Stdout, handler)
+
+	if s.opts.EnableCORS {
+		h = cors.CombinedCORSHandler(h)
+	}
+
+	s.mux.Handle(path, h)
 }
 
 func (s *httpServer) Start() error {

api/server/options.go

@@ -10,12 +10,19 @@ type Option func(o *Options)
 
 type Options struct {
 	EnableACME   bool
+	EnableCORS   bool
 	ACMEProvider acme.Provider
 	EnableTLS    bool
 	ACMEHosts    []string
 	TLSConfig    *tls.Config
 }
 
+func EnableCORS(b bool) Option {
+	return func(o *Options) {
+		o.EnableCORS = b
+	}
+}
+
 func EnableACME(b bool) Option {
 	return func(o *Options) {
 		o.EnableACME = b