net/http/httputil: docs about X-Forwarded-For in ReverseProxy

src/net/http/httputil/reverseproxy.go

@@ -24,6 +24,13 @@ import (
 // ReverseProxy is an HTTP Handler that takes an incoming request and
 // sends it to another server, proxying the response back to the
 // client.
+// ReverseProxy automatically sets the client IP as value of the
+// X-Forwarded-For header.
+// If a X-Forwarded-For header already exists, the client IP is
+// appended to existing values.
+// To prevent IP spoofing, be sure to delete any pre-existing
+// X-Forwarded-For header comming from the client or
+// an untrusted proxy.
 type ReverseProxy struct {
 	// Director must be a function which modifies
 	// the request into a new request to be sent