From 488ab7a1ab31f7ada84a0fca1c6e36a27c81e77a Mon Sep 17 00:00:00 2001
From: smasher164 <aindurti@gmail.com>
Date: Tue, 11 Aug 2020 19:32:23 -0400
Subject: [PATCH] lambda: check if error type is InvokeResponse_Error

Currently, we cannot set the errorType field without creating a custom
named error type. This causes a proliferation of dummy named error types
whose only purpose is to set a text field, and limits the errorType
field to what can be expressed as an identifier.

This change checks that the panicked or returned error is if type
InvokeResponse_Error, and if so, uses it directly in the invoker's
response. InvokeResponse_Error is now updated to implement error.

Note: This is fully backwards compatible, since InvokeResponse_Error
previously did not implement the error interface.

Fixes #308.
---
 lambda/errors.go            | 6 ++++++
 lambda/handler_test.go      | 8 ++++++++
 lambda/messages/messages.go | 6 ++++++
 lambda/panic_test.go        | 6 ++++++
 4 files changed, 26 insertions(+)

diff --git a/lambda/errors.go b/lambda/errors.go
index 619f976c..5d482d04 100644
--- a/lambda/errors.go
+++ b/lambda/errors.go
@@ -17,6 +17,9 @@ func getErrorType(err interface{}) string {
 }
 
 func lambdaErrorResponse(invokeError error) *messages.InvokeResponse_Error {
+	if ive, ok := invokeError.(messages.InvokeResponse_Error); ok {
+		return &ive
+	}
 	var errorName string
 	if errorType := reflect.TypeOf(invokeError); errorType.Kind() == reflect.Ptr {
 		errorName = errorType.Elem().Name()
@@ -30,6 +33,9 @@ func lambdaErrorResponse(invokeError error) *messages.InvokeResponse_Error {
 }
 
 func lambdaPanicResponse(err interface{}) *messages.InvokeResponse_Error {
+	if ive, ok := err.(messages.InvokeResponse_Error); ok {
+		return &ive
+	}
 	panicInfo := getPanicInfo(err)
 	return &messages.InvokeResponse_Error{
 		Message:    panicInfo.Message,
diff --git a/lambda/handler_test.go b/lambda/handler_test.go
index b76e73e8..476dc18a 100644
--- a/lambda/handler_test.go
+++ b/lambda/handler_test.go
@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"github.com/aws/aws-lambda-go/lambda/handlertrace"
+	"github.com/aws/aws-lambda-go/lambda/messages"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -187,6 +188,13 @@ func TestInvokes(t *testing.T) {
 				return struct{ Number int }{event}, nil
 			},
 		},
+		{
+			input:    `"Lambda"`,
+			expected: expected{"", messages.InvokeResponse_Error{Message: "message", Type: "type"}},
+			handler: func(e interface{}) (interface{}, error) {
+				return nil, messages.InvokeResponse_Error{Message: "message", Type: "type"}
+			},
+		},
 	}
 	for i, testCase := range testCases {
 		testCase := testCase
diff --git a/lambda/messages/messages.go b/lambda/messages/messages.go
index 7f7f1093..9f8b3575 100644
--- a/lambda/messages/messages.go
+++ b/lambda/messages/messages.go
@@ -2,6 +2,8 @@
 
 package messages
 
+import "fmt"
+
 type PingRequest struct {
 }
 
@@ -36,6 +38,10 @@ type InvokeResponse_Error struct {
 	ShouldExit bool                               `json:"-"`
 }
 
+func (e InvokeResponse_Error) Error() string {
+	return fmt.Sprintf("%#v", e)
+}
+
 type InvokeResponse_Error_StackFrame struct {
 	Path  string `json:"path"`
 	Line  int32  `json:"line"`
diff --git a/lambda/panic_test.go b/lambda/panic_test.go
index 92db8fd7..b2135ecd 100644
--- a/lambda/panic_test.go
+++ b/lambda/panic_test.go
@@ -6,6 +6,7 @@ import (
 	"strings"
 	"testing"
 
+	"github.com/aws/aws-lambda-go/lambda/messages"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -37,6 +38,11 @@ func TestPanicFormattingCustomError(t *testing.T) {
 	assertPanicMessage(t, func() { panic(customError) }, customError.Error())
 }
 
+func TestPanicFormattingInvokeResponse_Error(t *testing.T) {
+	ive := &messages.InvokeResponse_Error{Message: "message", Type: "type"}
+	assertPanicMessage(t, func() { panic(ive) }, ive.Error())
+}
+
 func TestFormatFrame(t *testing.T) {
 	var tests = []struct {
 		inputPath     string