CloudFormation wrapper panics are reported as failures (closes #172) (#174)

Panics are not recovered, as this would cause the stacktrace to be lost by
handlers higher in the stack that are yet to be unwound.

Author: aidansteele

cfn/wrap.go

@@ -21,7 +21,19 @@ type CustomResourceFunction func(context.Context, Event) (physicalResourceID str
 func lambdaWrapWithClient(lambdaFunction CustomResourceFunction, client httpClient) (fn CustomResourceLambdaFunction) {
 	fn = func(ctx context.Context, event Event) (reason string, err error) {
 		r := NewResponse(&event)
+
+		funcDidPanic := true
+		defer func() {
+			if funcDidPanic {
+				r.Status = StatusFailed
+				r.Reason = "Function panicked, see log stream for details"
+				r.sendWith(client)
+			}
+		}()
+
 		r.PhysicalResourceID, r.Data, err = lambdaFunction(ctx, event)
+		funcDidPanic = false
+
 		if r.PhysicalResourceID == "" {
 			log.Println("PhysicalResourceID must exist, copying Log Stream name")
 			r.PhysicalResourceID = lambdacontext.LogStreamName

cfn/wrap_test.go

@@ -50,6 +50,34 @@ func TestCopyLambdaLogStream(t *testing.T) {
 	lambdacontext.LogStreamName = lgs
 }
 
+func TestPanicSendsFailure(t *testing.T) {
+	didSendStatus := false
+
+	client := &mockClient{
+		DoFunc: func(req *http.Request) (*http.Response, error) {
+			response := extractResponseBody(t, req)
+			assert.Equal(t, StatusFailed, response.Status)
+			didSendStatus = response.Status == StatusFailed
+
+			return &http.Response{
+				StatusCode: http.StatusOK,
+				Body:       nopCloser{bytes.NewBufferString("")},
+			}, nil
+		},
+	}
+
+	fn := func(ctx context.Context, event Event) (physicalResourceID string, data map[string]interface{}, err error) {
+		err = errors.New("some panic that shouldn't be caught")
+		panic(err)
+	}
+
+	assert.Panics(t, func() {
+		lambdaWrapWithClient(fn, client)(context.TODO(), *testEvent)
+	})
+
+	assert.True(t, didSendStatus, "FAILED should be sent to CloudFormation service")
+}
+
 func TestDontCopyLogicalResourceId(t *testing.T) {
 	client := &mockClient{
 		DoFunc: func(req *http.Request) (*http.Response, error) {