Develop (#250)

lib/binding/function.go

@@ -0,0 +1,165 @@
+package binding
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"runtime"
+
+	"github.com/wailsapp/wails/lib/logger"
+)
+
+type boundFunction struct {
+	fullName           string
+	function           reflect.Value
+	functionType       reflect.Type
+	inputs             []reflect.Type
+	returnTypes        []reflect.Type
+	log                *logger.CustomLogger
+	hasErrorReturnType bool
+}
+
+// Creates a new bound function based on the given method + type
+func newBoundFunction(object interface{}) (*boundFunction, error) {
+
+	objectValue := reflect.ValueOf(object)
+	objectType := reflect.TypeOf(object)
+
+	name := runtime.FuncForPC(objectValue.Pointer()).Name()
+
+	result := &boundFunction{
+		fullName:     name,
+		function:     objectValue,
+		functionType: objectType,
+		log:          logger.NewCustomLogger(name),
+	}
+
+	err := result.processParameters()
+
+	return result, err
+}
+
+func (b *boundFunction) processParameters() error {
+
+	// Param processing
+	functionType := b.functionType
+
+	// Input parameters
+	inputParamCount := functionType.NumIn()
+	if inputParamCount > 0 {
+		b.inputs = make([]reflect.Type, inputParamCount)
+		// We start at 1 as the first param is the struct
+		for index := 0; index < inputParamCount; index++ {
+			param := functionType.In(index)
+			name := param.Name()
+			kind := param.Kind()
+			b.inputs[index] = param
+			typ := param
+			index := index
+			b.log.DebugFields("Input param", logger.Fields{
+				"index": index,
+				"name":  name,
+				"kind":  kind,
+				"typ":   typ,
+			})
+		}
+	}
+
+	// Process return/output declarations
+	returnParamsCount := functionType.NumOut()
+	// Guard against bad number of return types
+	switch returnParamsCount {
+	case 0:
+	case 1:
+		// Check if it's an error type
+		param := functionType.Out(0)
+		paramName := param.Name()
+		if paramName == "error" {
+			b.hasErrorReturnType = true
+		}
+		// Save return type
+		b.returnTypes = append(b.returnTypes, param)
+	case 2:
+		// Check the second return type is an error
+		secondParam := functionType.Out(1)
+		secondParamName := secondParam.Name()
+		if secondParamName != "error" {
+			return fmt.Errorf("last return type of method '%s' must be an error (got %s)", b.fullName, secondParamName)
+		}
+
+		// Check the second return type is an error
+		firstParam := functionType.Out(0)
+		firstParamName := firstParam.Name()
+		if firstParamName == "error" {
+			return fmt.Errorf("first return type of method '%s' must not be an error", b.fullName)
+		}
+		b.hasErrorReturnType = true
+
+		// Save return types
+		b.returnTypes = append(b.returnTypes, firstParam)
+		b.returnTypes = append(b.returnTypes, secondParam)
+
+	default:
+		return fmt.Errorf("cannot register method '%s' with %d return parameters. Please use up to 2", b.fullName, returnParamsCount)
+	}
+
+	return nil
+}
+
+// call the method with the given data
+func (b *boundFunction) call(data string) ([]reflect.Value, error) {
+
+	// The data will be an array of values so we will decode the
+	// input data into
+	var jsArgs []interface{}
+	d := json.NewDecoder(bytes.NewBufferString(data))
+	// d.UseNumber()
+	err := d.Decode(&jsArgs)
+	if err != nil {
+		return nil, fmt.Errorf("Invalid data passed to method call: %s", err.Error())
+	}
+
+	// Check correct number of inputs
+	if len(jsArgs) != len(b.inputs) {
+		return nil, fmt.Errorf("Invalid number of parameters given to %s. Expected %d but got %d", b.fullName, len(b.inputs), len(jsArgs))
+	}
+
+	// Set up call
+	args := make([]reflect.Value, len(b.inputs))
+	for index := 0; index < len(b.inputs); index++ {
+
+		// Set the input values
+		value, err := b.setInputValue(index, b.inputs[index], jsArgs[index])
+		if err != nil {
+			return nil, err
+		}
+		args[index] = value
+	}
+	b.log.Debugf("Unmarshalled Args: %+v\n", jsArgs)
+	b.log.Debugf("Converted Args: %+v\n", args)
+	results := b.function.Call(args)
+
+	b.log.Debugf("results = %+v", results)
+	return results, nil
+}
+
+// Attempts to set the method input <typ> for parameter <index> with the given value <val>
+func (b *boundFunction) setInputValue(index int, typ reflect.Type, val interface{}) (result reflect.Value, err error) {
+
+	// Catch type conversion panics thrown by convert
+	defer func() {
+		if r := recover(); r != nil {
+			// Modify error
+			err = fmt.Errorf("%s for parameter %d of function %s", r.(string)[23:], index+1, b.fullName)
+		}
+	}()
+
+	// Translate javascript null values
+	if val == nil {
+		result = reflect.Zero(typ)
+	} else {
+		result = reflect.ValueOf(val).Convert(typ)
+	}
+	return result, err
+}