Add Example_crossOrigin

Closes #194

Author: nhooyr

example_test.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"log"
 	"net/http"
+	"net/url"
 	"time"
 
 	"nhooyr.io/websocket"
@@ -115,3 +116,30 @@ func Example_writeOnly() {
 	err := http.ListenAndServe("localhost:8080", fn)
 	log.Fatal(err)
 }
+
+// This example demonstrates how to safely accept cross origin WebSockets
+// from the origin example.com.
+func Example_crossOrigin() {
+	fn := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		origin := r.Header.Get("Origin")
+		if origin != "" {
+			u, err := url.Parse(origin)
+			if err != nil || u.Host != "example.com" {
+				http.Error(w, "bad origin header", http.StatusForbidden)
+				return
+			}
+		}
+
+		c, err := websocket.Accept(w, r, &websocket.AcceptOptions{
+			InsecureSkipVerify: true,
+		})
+		if err != nil {
+			log.Println(err)
+			return
+		}
+		c.Close(websocket.StatusNormalClosure, "cross origin WebSocket accepted")
+	})
+
+	err := http.ListenAndServe("localhost:8080", fn)
+	log.Fatal(err)
+}