rc: add NeedsResponse for rc calls

fs/rc/params.go

@@ -91,7 +91,7 @@ func (p Params) Get(key string) (interface{}, error) {
 	return value, nil
 }
 
-// GetHTTPRequest gets a http.Request parameter associated with the request with the key "HttpRequest"
+// GetHTTPRequest gets a http.Request parameter associated with the request with the key "_request"
 //
 // If the parameter isn't found then error will be of type
 // ErrParamNotFound and the returned value will be nil.
@@ -108,6 +108,23 @@ func (p Params) GetHTTPRequest() (*http.Request, error) {
 	return request, nil
 }
 
+// GetHTTPResponseWriter gets a http.ResponseWriter parameter associated with the request with the key "_response"
+//
+// If the parameter isn't found then error will be of type
+// ErrParamNotFound and the returned value will be nil.
+func (p Params) GetHTTPResponseWriter() (*http.ResponseWriter, error) {
+	key := "_response"
+	value, err := p.Get(key)
+	if err != nil {
+		return nil, err
+	}
+	request, ok := value.(*http.ResponseWriter)
+	if !ok {
+		return nil, ErrParamInvalid{errors.Errorf("expecting http.ResponseWriter value for key %q (was %T)", key, value)}
+	}
+	return request, nil
+}
+
 // GetString gets a string parameter from the input
 //
 // If the parameter isn't found then error will be of type

fs/rc/rcserver/rcserver.go

@@ -265,6 +265,10 @@ func (s *Server) handlePost(w http.ResponseWriter, r *http.Request, path string)
 		in["_request"] = r
 	}
 
+	if call.NeedsResponse {
+		in["_response"] = &w
+	}
+
 	// Check to see if it is async or not
 	isAsync, err := in.GetBool("_async")
 	if rc.NotErrParamNotFound(err) {

fs/rc/registry.go

@@ -17,12 +17,13 @@ type Func func(ctx context.Context, in Params) (out Params, err error)
 // Call defines info about a remote control function and is used in
 // the Add function to create new entry points.
 type Call struct {
-	Path         string // path to activate this RC
-	Fn           Func   `json:"-"` // function to call
-	Title        string // help for the function
-	AuthRequired bool   // if set then this call requires authorisation to be set
-	Help         string // multi-line markdown formatted help
-	NeedsRequest bool   // if set then this call will be passed the original request object as _request
+	Path          string // path to activate this RC
+	Fn            Func   `json:"-"` // function to call
+	Title         string // help for the function
+	AuthRequired  bool   // if set then this call requires authorisation to be set
+	Help          string // multi-line markdown formatted help
+	NeedsRequest  bool   // if set then this call will be passed the original request object as _request
+	NeedsResponse bool   // if set then this call will be passed the original response object as _response
 }
 
 // Registry holds the list of all the registered remote control functions