Add errors to actions to allow for custom handling

action.go

@@ -3,6 +3,8 @@ package spanner
 import "context"
 
 type Action interface {
+	HasError
+
 	Type() string
 	Data() interface{}
 }

api.go

@@ -51,6 +51,7 @@ type SlashCommand interface {
 // It can be used to create blocks and handle submission or closing of the modal.
 type Modal interface {
 	BlockUI
+
 	SubmitButton(title string) ModalSubmission
 	CloseButton(title string) bool
 }
@@ -75,6 +76,14 @@ type EphemeralSender interface {
 // Messages are constructed using BlockUI commands.
 type Message interface {
 	BlockUI
+	HasError
+
+	Channel(channelID string)
+}
+
+type NonInteractiveMessage interface {
+	NonInteractiveBlockUI
+	HasError
 
 	Channel(channelID string)
 }

blocks.go

@@ -2,9 +2,17 @@ package spanner
 
 // BlockUI allows the creation of Slack blocks in a message or modal.
 type BlockUI interface {
+	NonInteractiveBlockUI
+	InteractiveBlockUI
+}
+
+type NonInteractiveBlockUI interface {
 	Header(message string)
 	PlainText(text string)
 	Markdown(text string)
+}
+
+type InteractiveBlockUI interface {
 	TextInput(label string, hint string, placeholder string) string
 	MultilineTextInput(label string, hint string, placeholder string) string
 	Divider()

error.go

@@ -0,0 +1,18 @@
+package spanner
+
+import "context"
+
+type HasError interface {
+	ErrorFunc(ErrorFunc)
+}
+
+type ErrorFunc func(ctx context.Context, ev ErrorEvent)
+
+type ErrorEvent interface {
+	SendMessage(channelID string) ErrorMessage
+	ReceiveError() error
+}
+
+type ErrorMessage interface {
+	NonInteractiveMessage
+}

examples/error/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"log"
 	"os"
 
@@ -63,12 +64,22 @@ func main() {
 
 			replyGood := ev.SendMessage(msg.Channel().ID())
 			replyGood.PlainText("This message should succeed")
+			replyGood.ErrorFunc(func(ctx context.Context, ev spanner.ErrorEvent) {
+				panic("did not expect this message to fail")
+			})
 
 			replyBad := ev.SendMessage("invalid_channel")
 			replyBad.PlainText("This message will always fail to post")
+			replyBad.ErrorFunc(func(ctx context.Context, ev spanner.ErrorEvent) {
+				errorNotice := ev.SendMessage(msg.Channel().ID())
+				errorNotice.PlainText(fmt.Sprintf("There was an error sending a message: %v", ev.ReceiveError()))
+			})
 
 			replySkipped := ev.SendMessage(msg.Channel().ID())
 			replySkipped.PlainText("This message should be skipped because of the previous error")
+			replySkipped.ErrorFunc(func(ctx context.Context, ev spanner.ErrorEvent) {
+				panic("did not expect this message to fail")
+			})
 		}
 		return nil
 	})

slack/action.go

@@ -11,6 +11,8 @@ type action interface {
 
 	// exec performs and action and returns a payload to acknowledge the request as appropriate
 	exec(ctx context.Context, req request) (interface{}, error)
+
+	getErrorFunc() spanner.ErrorFunc
 }
 
 type actionQueue struct {

slack/app_test.go

@@ -10,7 +10,7 @@ import (
 )
 
 func TestHandlerIsCalledForEachEvent(t *testing.T) {
-	client := newTestClient()
+	client := newTestClient([]string{"ABC123"})
 	testApp := client.CreateApp()
 
 	results := make(chan struct{}, 2)

slack/channel.go

@@ -46,6 +46,15 @@ var _ action = &joinChannelAction{}
 
 type joinChannelAction struct {
 	channelID string
+	errFunc   spanner.ErrorFunc
+}
+
+func (j *joinChannelAction) ErrorFunc(ef spanner.ErrorFunc) {
+	j.errFunc = ef
+}
+
+func (j *joinChannelAction) getErrorFunc() spanner.ErrorFunc {
+	return j.errFunc
 }
 
 // Data implements action.

slack/ephemeral.go

@@ -30,6 +30,16 @@ var _ action = &sendEphemeralMessageAction{}
 
 type sendEphemeralMessageAction struct {
 	text string
+
+	errFunc spanner.ErrorFunc
+}
+
+func (e *sendEphemeralMessageAction) ErrorFunc(ef spanner.ErrorFunc) {
+	e.errFunc = ef
+}
+
+func (e *sendEphemeralMessageAction) getErrorFunc() spanner.ErrorFunc {
+	return e.errFunc
 }
 
 // Data implements action.

slack/error_test.go

@@ -0,0 +1,73 @@
+package slack
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/slack-go/slack/slackevents"
+	"github.com/theothertomelliott/spanner"
+)
+
+// TestErrorHandling verifies that error handlers are called appropriately
+func TestErrorHandling(t *testing.T) {
+	client := newTestClient([]string{"ABC123"})
+	testApp := client.CreateApp()
+
+	go func() {
+		err := testApp.Run(handlerTestErrors)
+		if err != nil {
+			t.Errorf("error running app: %v", err)
+		}
+	}()
+
+	// Send hello message
+	client.SendEventToApp(messageEvent(
+		slackevents.MessageEvent{
+			Text:    "hello",
+			Channel: "ABC123",
+			User:    "DEF456",
+		},
+	))
+
+	// Expect a single message and clear the message list
+	if len(client.messagesSent) != 2 {
+		t.Errorf("expected two messages to be sent, got %d", len(client.messagesSent))
+	}
+
+	firstBlocks, _ := json.MarshalIndent(client.messagesSent[0].blocks, "", "  ")
+	if !strings.Contains(string(firstBlocks), `This message should succeed`) {
+		t.Errorf("first message content was not as expected, got: %v", string(firstBlocks))
+	}
+
+	secondBlocks, _ := json.MarshalIndent(client.messagesSent[1].blocks, "", "  ")
+	if !strings.Contains(string(secondBlocks), `There was an error sending a message`) {
+		t.Errorf("first message content was not as expected, got: %v", string(secondBlocks))
+	}
+}
+
+func handlerTestErrors(ctx context.Context, ev spanner.Event) error {
+	if msg := ev.ReceiveMessage(); msg != nil && msg.Text() == "hello" {
+		replyGood := ev.SendMessage(msg.Channel().ID())
+		replyGood.PlainText("This message should succeed")
+		replyGood.ErrorFunc(func(ctx context.Context, ev spanner.ErrorEvent) {
+			panic("did not expect this message to fail")
+		})
+
+		replyBad := ev.SendMessage("invalid_channel")
+		replyBad.PlainText("This message will always fail to post")
+		replyBad.ErrorFunc(func(ctx context.Context, ev spanner.ErrorEvent) {
+			errorNotice := ev.SendMessage(msg.Channel().ID())
+			errorNotice.PlainText(fmt.Sprintf("There was an error sending a message: %v", ev.ReceiveError()))
+		})
+
+		replySkipped := ev.SendMessage(msg.Channel().ID())
+		replySkipped.PlainText("This message should be skipped because of the previous error")
+		replySkipped.ErrorFunc(func(ctx context.Context, ev spanner.ErrorEvent) {
+			panic("did not expect this message to fail")
+		})
+	}
+	return nil
+}

slack/errors.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/slack-go/slack"
+	"github.com/theothertomelliott/spanner"
 )
 
 func renderSlackError(err error) error {
@@ -16,3 +17,32 @@ func renderSlackError(err error) error {
 	}
 	return err
 }
+
+var _ spanner.ErrorEvent = &errorEvent{}
+
+func newErrorEvent(err error) *errorEvent {
+	q := &actionQueue{}
+	return &errorEvent{
+		actionQueue: q,
+		sender: &MessageSender{
+			actionQueue: q,
+		},
+		err: err,
+	}
+}
+
+type errorEvent struct {
+	actionQueue *actionQueue
+	sender      *MessageSender
+
+	err error
+}
+
+func (e *errorEvent) SendMessage(channelID string) spanner.ErrorMessage {
+	return e.sender.SendMessage(channelID)
+}
+
+// ReceiveError implements spanner.ErrorEvent.
+func (e *errorEvent) ReceiveError() error {
+	return e.err
+}

slack/event.go

@@ -18,6 +18,19 @@ type eventPopulator interface {
 
 var _ spanner.Event = &event{}
 
+func newEvent() *event {
+	q := &actionQueue{}
+	return &event{
+		eventType: "unknown",
+		state: eventState{
+			actionQueue: q,
+			MessageSender: &MessageSender{
+				actionQueue: q,
+			},
+		},
+	}
+}
+
 type event struct {
 	hash      string
 	eventType string
@@ -92,9 +105,19 @@ func (e *event) finishEvent(
 	ctx context.Context,
 	actionInterceptor spanner.ActionInterceptor,
 	req request,
+) error {
+	return finishEvent(ctx, actionInterceptor, req, e.state.actionQueue, true)
+}
+
+func finishEvent(
+	ctx context.Context,
+	actionInterceptor spanner.ActionInterceptor,
+	req request,
+	actionQueue *actionQueue,
+	shouldAck bool,
 ) error {
 	var payload interface{}
-	for _, a := range e.state.actionQueue.actions {
+	for _, a := range actionQueue.actions {
 		var (
 			newPayload interface{}
 			execFunc   = func(ctx context.Context) error {
@@ -105,9 +128,23 @@ func (e *event) finishEvent(
 		)
 
 		err := actionInterceptor(ctx, a, execFunc)
+
 		if err != nil {
+			if ef := a.getErrorFunc(); ef != nil {
+				// Set up and run handler for error
+				errorEvent := newErrorEvent(err)
+				ef(ctx, errorEvent)
+
+				// Process actions from error event
+				err := finishEvent(ctx, actionInterceptor, req, errorEvent.actionQueue, false)
+				if err != nil {
+					return fmt.Errorf("executing error event: %w", err)
+				}
+			}
+
 			return fmt.Errorf("executing action: %w", err)
 		}
+
 		if newPayload != nil {
 			if payload != nil {
 				// TODO: Make this log configurable
@@ -117,11 +154,14 @@ func (e *event) finishEvent(
 		}
 	}
 
-	// Acknowledge the event
 	if payload == nil {
 		payload = map[string]interface{}{}
 	}
-	req.client.Ack(req.req, payload)
+
+	if shouldAck {
+		// Acknowledge the event
+		req.client.Ack(req.req, payload)
+	}
 
 	return nil
 }
@@ -136,16 +176,7 @@ type eventPopulation struct {
 }
 
 func parseCombinedEvent(ctx context.Context, client socketClient, ce combinedEvent) *event {
-	q := &actionQueue{}
-	out := &event{
-		eventType: "unknown",
-		state: eventState{
-			actionQueue: q,
-			MessageSender: &MessageSender{
-				actionQueue: q,
-			},
-		},
-	}
+	out := newEvent()
 
 	defer func() {
 		// Set clients in metadata

slack/examples_test.go

@@ -15,7 +15,7 @@ import (
 // TestGettingStarted verifies that the code in examples/gettingstarted
 // interacts with Slack in the expected way
 func TestGettingStarted(t *testing.T) {
-	client := newTestClient()
+	client := newTestClient([]string{"ABC123"})
 	testApp := client.CreateApp()
 
 	go func() {

slack/message.go

@@ -36,6 +36,16 @@ type message struct {
 	currentEventDepth   int
 	actionMessageTS     string
 	unsent              bool
+
+	errFunc spanner.ErrorFunc
+}
+
+func (m *message) ErrorFunc(ef spanner.ErrorFunc) {
+	m.errFunc = ef
+}
+
+func (m *message) getErrorFunc() spanner.ErrorFunc {
+	return m.errFunc
 }
 
 func (m *message) Type() string {