refactor: plugin functions can be defined in any format

plugin/shared/utils.go

@@ -0,0 +1,50 @@
+package shared
+
+import (
+	"fmt"
+	"reflect"
+)
+
+// CallFunc calls function with arguments
+// it is used when calling go plugin or builtin functions
+func CallFunc(fn reflect.Value, args ...interface{}) (interface{}, error) {
+	fnArgsNum := fn.Type().NumIn()
+	if fnArgsNum > 0 && fn.Type().In(fnArgsNum-1).Kind() == reflect.Slice {
+		// last argument is slice, do not check arguments number
+		// e.g. ...interface{}
+		// e.g. a, b string, c ...interface{}
+	} else if fnArgsNum != len(args) {
+		// function arguments not match
+		return nil, fmt.Errorf("function arguments number not match, expect %d, got %d", fnArgsNum, len(args))
+	}
+	// arguments do not have slice, and arguments number matched
+
+	argumentsValue := make([]reflect.Value, len(args))
+	for index, argument := range args {
+		if argument == nil {
+			argumentsValue[index] = reflect.Zero(fn.Type().In(index))
+		} else {
+			argumentsValue[index] = reflect.ValueOf(args[index])
+		}
+	}
+
+	resultValues := fn.Call(argumentsValue)
+	if resultValues == nil {
+		// no returns
+		return nil, nil
+	} else if len(resultValues) == 2 {
+		// return two arguments: interface{}, error
+		if resultValues[1].Interface() != nil {
+			return resultValues[0].Interface(), resultValues[1].Interface().(error)
+		} else {
+			return resultValues[0].Interface(), nil
+		}
+	} else if len(resultValues) == 1 {
+		// return one arguments: interface{}
+		return resultValues[0].Interface(), nil
+	} else {
+		// return more than 2 arguments, unexpected
+		err := fmt.Errorf("function should return at most 2 arguments")
+		return nil, err
+	}
+}