124 lines
3.6 KiB
Go
124 lines
3.6 KiB
Go
// Copyright 2017 Amazon.com, Inc. or its affiliates. All Rights Reserved.
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package lambda
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import (
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"context"
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"encoding/json"
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"fmt"
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"reflect"
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)
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// lambdaHandler is the generic function type
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type lambdaHandler func(context.Context, []byte) (interface{}, error)
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// Invoke calls the handler, and serializes the response.
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// If the underlying handler returned an error, or an error occurs during serialization, error is returned.
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func (handler lambdaHandler) Invoke(ctx context.Context, payload []byte) ([]byte, error) {
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response, err := handler(ctx, payload)
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if err != nil {
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return nil, err
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}
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responseBytes, err := json.Marshal(response)
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if err != nil {
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return nil, err
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}
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return responseBytes, nil
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}
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func errorHandler(e error) lambdaHandler {
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return func(ctx context.Context, event []byte) (interface{}, error) {
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return nil, e
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}
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}
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func validateArguments(handler reflect.Type) (bool, error) {
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handlerTakesContext := false
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if handler.NumIn() > 2 {
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return false, fmt.Errorf("handlers may not take more than two arguments, but handler takes %d", handler.NumIn())
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} else if handler.NumIn() > 0 {
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contextType := reflect.TypeOf((*context.Context)(nil)).Elem()
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argumentType := handler.In(0)
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handlerTakesContext = argumentType.Implements(contextType)
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if handler.NumIn() > 1 && !handlerTakesContext {
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return false, fmt.Errorf("handler takes two arguments, but the first is not Context. got %s", argumentType.Kind())
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}
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}
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return handlerTakesContext, nil
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}
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func validateReturns(handler reflect.Type) error {
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errorType := reflect.TypeOf((*error)(nil)).Elem()
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if handler.NumOut() > 2 {
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return fmt.Errorf("handler may not return more than two values")
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} else if handler.NumOut() > 1 {
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if !handler.Out(1).Implements(errorType) {
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return fmt.Errorf("handler returns two values, but the second does not implement error")
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}
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} else if handler.NumOut() == 1 {
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if !handler.Out(0).Implements(errorType) {
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return fmt.Errorf("handler returns a single value, but it does not implement error")
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}
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}
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return nil
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}
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// newHandler Creates the base lambda handler, which will do basic payload unmarshaling before defering to handlerSymbol.
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// If handlerSymbol is not a valid handler, the returned function will be a handler that just reports the validation error.
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func newHandler(handlerSymbol interface{}) lambdaHandler {
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if handlerSymbol == nil {
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return errorHandler(fmt.Errorf("handler is nil"))
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}
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handler := reflect.ValueOf(handlerSymbol)
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handlerType := reflect.TypeOf(handlerSymbol)
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if handlerType.Kind() != reflect.Func {
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return errorHandler(fmt.Errorf("handler kind %s is not %s", handlerType.Kind(), reflect.Func))
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}
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takesContext, err := validateArguments(handlerType)
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if err != nil {
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return errorHandler(err)
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}
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if err := validateReturns(handlerType); err != nil {
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return errorHandler(err)
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}
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return func(ctx context.Context, payload []byte) (interface{}, error) {
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// construct arguments
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var args []reflect.Value
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if takesContext {
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args = append(args, reflect.ValueOf(ctx))
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}
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if (handlerType.NumIn() == 1 && !takesContext) || handlerType.NumIn() == 2 {
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eventType := handlerType.In(handlerType.NumIn() - 1)
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event := reflect.New(eventType)
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if err := json.Unmarshal(payload, event.Interface()); err != nil {
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return nil, err
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}
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args = append(args, event.Elem())
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}
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response := handler.Call(args)
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// convert return values into (interface{}, error)
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var err error
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if len(response) > 0 {
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if errVal, ok := response[len(response)-1].Interface().(error); ok {
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err = errVal
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}
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}
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var val interface{}
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if len(response) > 1 {
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val = response[0].Interface()
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}
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return val, err
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}
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}
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