Add introspection functions

server/server.go

@@ -36,13 +36,10 @@ import (
 type any = interface{}
 
 var (
-	ErrInvalidType         = errors.New("type must be struct or pointer to struct")
-	ErrTooManyInputs       = errors.New("method may not have more than two inputs")
-	ErrTooManyOutputs      = errors.New("method may not have more than two return values")
-	ErrNoSuchReceiver      = errors.New("no such receiver registered")
-	ErrNoSuchMethod        = errors.New("no such method was found")
-	ErrInvalidSecondReturn = errors.New("second return value must be error")
-	ErrInvalidFirstInput   = errors.New("first input must be *Context")
+	ErrInvalidType    = errors.New("type must be struct or pointer to struct")
+	ErrNoSuchReceiver = errors.New("no such receiver registered")
+	ErrNoSuchMethod   = errors.New("no such method was found")
+	ErrInvalidMethod  = errors.New("method invalid for lrpc call")
 )
 
 // Server is an lrpc server
@@ -114,22 +111,13 @@ func (s *Server) execute(typ string, name string, arg any, c codec.Codec) (a any
 		return nil, nil, ErrNoSuchMethod
 	}
 
-	// Get method's type
+	// If method invalid, return error
+	if !mtdValid(mtd) {
+		return nil, nil, ErrInvalidMethod
+	}
+
+	// Get method type
 	mtdType := mtd.Type()
-	if mtdType.NumIn() > 2 {
-		return nil, nil, ErrTooManyInputs
-	} else if mtdType.NumIn() < 1 {
-		return nil, nil, ErrInvalidFirstInput
-	}
-
-	if mtdType.NumOut() > 2 {
-		return nil, nil, ErrTooManyOutputs
-	}
-
-	// Check to ensure first parameter is context
-	if mtdType.In(0) != reflect.TypeOf(&Context{}) {
-		return nil, nil, ErrInvalidFirstInput
-	}
 
 	//TODO: if arg not nil but fn has no arg, err
 
@@ -215,7 +203,7 @@ func (s *Server) execute(typ string, name string, arg any, c codec.Codec) (a any
 
 				// If second return value is not an error, the function is invalid
 				if !ok {
-					a, err = nil, ErrInvalidSecondReturn
+					a, err = nil, ErrInvalidMethod
 				}
 			}
 
@@ -231,7 +219,7 @@ func (s *Server) execute(typ string, name string, arg any, c codec.Codec) (a any
 				// If second return value is not an error, the function is invalid
 				err, ok = out1.(error)
 				if !ok {
-					a, err = nil, ErrInvalidSecondReturn
+					a, err = nil, ErrInvalidMethod
 				}
 			}
 
@@ -388,3 +376,108 @@ func (l lrpc) ChannelDone(_ *Context, id string) {
 	delete(l.srv.contexts, id)
 	l.srv.contextsMtx.Unlock()
 }
+
+// MethodDesc describes methods on a receiver
+type MethodDesc struct {
+	Name    string
+	Args    []string
+	Returns []string
+}
+
+// Introspect returns method descriptions for the given receiver
+func (l lrpc) Introspect(_ *Context, name string) ([]MethodDesc, error) {
+	// Attempt to get receiver
+	rcvr, ok := l.srv.rcvrs[name]
+	if !ok {
+		return nil, ErrNoSuchReceiver
+	}
+	// Get receiver type value
+	rcvrType := rcvr.Type()
+
+	// Create slice for output
+	var out []MethodDesc
+	// For every method on receiver
+	for i := 0; i < rcvr.NumMethod(); i++ {
+		// Get receiver method
+		mtd := rcvr.Method(i)
+		// If invalid, skip
+		if !mtdValid(mtd) {
+			continue
+		}
+		// Get method type
+		mtdType := mtd.Type()
+
+		// Get amount of arguments
+		numIn := mtdType.NumIn()
+		args := make([]string, numIn-1)
+		// For every argument, store type in slice
+		// Skip first argument, as it is *Context
+		for i := 1; i < numIn; i++ {
+			args[i-1] = mtdType.In(i).String()
+		}
+
+		// Get amount of returns
+		numOut := mtdType.NumOut()
+		returns := make([]string, numOut)
+		// For every return, store type in slice
+		for i := 0; i < numOut; i++ {
+			returns[i] = mtdType.Out(i).String()
+		}
+
+		out = append(out, MethodDesc{
+			Name:    rcvrType.Method(i).Name,
+			Args:    args,
+			Returns: returns,
+		})
+	}
+
+	return out, nil
+}
+
+// IntrospectAll runs Introspect on all registered receivers and returns all results
+func (l lrpc) IntrospectAll(_ *Context) (map[string][]MethodDesc, error) {
+	// Create map for output
+	out := make(map[string][]MethodDesc, len(l.srv.rcvrs))
+	// For every registered receiver
+	for name := range l.srv.rcvrs {
+		// Introspect receiver
+		descs, err := l.Introspect(nil, name)
+		if err != nil {
+			return nil, err
+		}
+
+		// Set results in map
+		out[name] = descs
+	}
+	return out, nil
+}
+
+func mtdValid(mtd reflect.Value) bool {
+	// Get method's type
+	mtdType := mtd.Type()
+
+	// If method has more than 2 or less than 1 input, it is invalid
+	if mtdType.NumIn() > 2 || mtdType.NumIn() < 1 {
+		return false
+	}
+
+	// If method has more than 2 outputs, it is invalid
+	if mtdType.NumOut() > 2 {
+		return false
+	}
+
+	// Check to ensure first parameter is context
+	if mtdType.In(0) != reflect.TypeOf((*Context)(nil)) {
+		return false
+	}
+
+	// If method has 2 outputs
+	if mtdType.NumOut() == 2 {
+		// Check to ensure the second one is an error
+		if mtdType.Out(1).Name() != "error" {
+			return false
+		}
+	}
+
+	return true
+}