Webhooks: post each new incoming message (closes #7)

Each message a contact sends in a direct chat is posted to each webhook
on that chat, as JSON holding `chat_id` and the message record of the
messages endpoint. The event handler only queues it: `api.Deliveries`
serves a queue of 100 with four goroutines, reads the chat's webhooks
there, and makes one POST per webhook, with a 10-second timeout, no
retry and no redirect followed. A full queue or a failed post is logged
by ids, never by URL or text. `bot.Run` stops it last, once the chat
client has exited. Tests cover the payload and its routing, a full
queue, failures, and a webhook that never answers; the README documents
the payload and what delivery promises.

Model: opus-5-5

internal/api/api.go

@@ -1,6 +1,7 @@
 // Package api is the bot's HTTP API, through which another program
 // reads the bot's chats, sends messages in them and registers webhooks
-// on them.
+// on them. Deliveries posts to those webhooks each message a contact
+// sends.
 //
 // Every request must carry the credential, as "Authorization: Bearer
 // {credential}"; with no credential configured, every request is
@@ -9,6 +10,8 @@
 // Handlers call the chat client on the request's own goroutine. Doing
 // so from the chat client's event handler would wait forever, since
 // that goroutine also delivers the responses (see simplex.EventHandler).
+// For the same reason, the event handler hands messages to Deliveries
+// without waiting.
 package api
 
 import (

internal/api/deliveries.go

@@ -0,0 +1,187 @@
+package api
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"sync"
+	"time"
+
+	"sneak.berlin/go/simplexcalc/internal/simplex"
+)
+
+const (
+	// queueLength is how many messages can wait to be posted, and
+	// deliveryGoroutines how many goroutines post them, each one message
+	// at a time.
+	queueLength        = 100
+	deliveryGoroutines = 4
+
+	// deliveryTimeout bounds one POST to a webhook.
+	deliveryTimeout = 10 * time.Second
+)
+
+// delivery is the body of the POST to each webhook of a chat: a message a
+// contact sent in it, as GET /api/v1/chats/{id}/messages shows it.
+type delivery struct {
+	ChatID  int64   `json:"chat_id"`
+	Message message `json:"message"`
+}
+
+// Deliveries posts each message a contact sends to each webhook of its
+// chat, once, with no retry. Add hands it a message without waiting: the
+// message joins a queue served by deliveryGoroutines goroutines, or is
+// dropped if the queue is full. What goes wrong is logged with ids only:
+// never a webhook's URL, which can hold a secret, nor a message's text.
+type Deliveries struct {
+	log      *slog.Logger
+	webhooks *Webhooks
+	client   *http.Client
+	queue    chan delivery
+
+	// stop ends the goroutines' context, abandoning the POSTs in
+	// progress; wg waits for the goroutines to return.
+	stop context.CancelFunc
+	wg   sync.WaitGroup
+}
+
+// StartDeliveries starts posting the messages Add is given, until ctx
+// ends or Stop is called.
+func StartDeliveries(
+	ctx context.Context, log *slog.Logger, webhooks *Webhooks,
+) *Deliveries {
+	ctx, stop := context.WithCancel(ctx)
+
+	d := &Deliveries{
+		log:      log,
+		webhooks: webhooks,
+		client: &http.Client{
+			Timeout: deliveryTimeout,
+			// A redirect is not followed, and so counts as a status
+			// other than 2xx: following it could turn the POST into a
+			// GET without the message.
+			CheckRedirect: func(*http.Request, []*http.Request) error {
+				return http.ErrUseLastResponse
+			},
+		},
+		queue: make(chan delivery, queueLength),
+		stop:  stop,
+	}
+
+	for range deliveryGoroutines {
+		d.wg.Go(func() { d.serve(ctx) })
+	}
+
+	return d
+}
+
+// Add queues the message in item for the webhooks of its chat, if it is a
+// message a contact sent in a direct chat: one that GET
+// /api/v1/chats/{id}/messages shows as received. The chat client's event
+// handler calls it, so it never waits: if the queue is full, the message
+// is dropped, and the log says so.
+func (d *Deliveries) Add(item simplex.AChatItem) {
+	contact := item.ChatInfo.Contact
+
+	m, ok := newMessage(item.ChatItem)
+	if !ok || m.Direction != "received" || item.ChatInfo.Type != "direct" ||
+		contact == nil {
+		return
+	}
+
+	select {
+	case d.queue <- delivery{ChatID: contact.ContactID, Message: m}:
+	default:
+		d.log.Warn("dropping a message for the webhooks: the queue is full",
+			"chat_id", contact.ContactID, "message_id", m.ID)
+	}
+}
+
+// Stop stops posting, and returns once the goroutines have: POSTs in
+// progress are abandoned, and messages still queued are not posted.
+func (d *Deliveries) Stop() {
+	d.stop()
+	d.wg.Wait()
+}
+
+// serve posts queued messages, one at a time, until ctx ends.
+func (d *Deliveries) serve(ctx context.Context) {
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case m := <-d.queue:
+			d.deliver(ctx, m)
+		}
+	}
+}
+
+// deliver posts m to each webhook of its chat, and logs each POST that
+// fails or is answered with a status other than 2xx. The webhooks are
+// read here rather than in Add, as reading them waits while the webhooks
+// file is written.
+func (d *Deliveries) deliver(ctx context.Context, m delivery) {
+	body, err := json.Marshal(m)
+	if err != nil {
+		d.log.Error("encoding a message for the webhooks",
+			"message_id", m.Message.ID, "error", err)
+
+		return
+	}
+
+	for _, hook := range d.webhooks.list(m.ChatID) {
+		// Stopped: the chat's other webhooks do not get the message.
+		if ctx.Err() != nil {
+			return
+		}
+
+		status, err := d.post(ctx, hook.URL, body)
+
+		switch {
+		case err != nil:
+			d.log.Warn("posting a message to a webhook",
+				"webhook_id", hook.ID, "message_id", m.Message.ID, "error", err)
+		case status < http.StatusOK || status >= http.StatusMultipleChoices:
+			d.log.Warn("posting a message to a webhook",
+				"webhook_id", hook.ID, "message_id", m.Message.ID, "status", status)
+		}
+	}
+}
+
+// post sends body to hookURL, once, and returns the status of the answer.
+// Its error, unlike net/http's, never holds the URL.
+func (d *Deliveries) post(
+	ctx context.Context, hookURL string, body []byte,
+) (int, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, hookURL,
+		bytes.NewReader(body))
+	if err != nil {
+		return 0, withoutURL(err)
+	}
+
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := d.client.Do(req)
+	if err != nil {
+		return 0, withoutURL(err)
+	}
+
+	_ = resp.Body.Close()
+
+	return resp.StatusCode, nil
+}
+
+// withoutURL returns the cause of a *url.Error, whose own text holds the
+// URL, and any other error as it is.
+func withoutURL(err error) error {
+	var urlErr *url.Error
+	if errors.As(err, &urlErr) {
+		return urlErr.Err
+	}
+
+	return err
+}

internal/api/deliveries_test.go

@@ -0,0 +1,328 @@
+package api_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/simplexcalc/internal/api"
+	"sneak.berlin/go/simplexcalc/internal/simplex"
+)
+
+// newChatItems is a newChatItems event, reduced to the fields the bot
+// reads. It holds, in this order, a message in a group, a message the bot
+// sent, an event the chat client records in a chat, and two messages a
+// contact sent: a text and a picture with a caption.
+const newChatItems = `{"type":"newChatItems","chatItems":[
+{"chatInfo":{"type":"group","groupInfo":{"groupId":9}},
+ "chatItem":{"chatDir":{"type":"groupRcv"},"meta":{"itemId":5},
+  "content":{"type":"rcvMsgContent","msgContent":{"type":"text","text":"1 + 1"}}}},
+{"chatInfo":{"type":"direct","contact":{"contactId":3}},
+ "chatItem":{"chatDir":{"type":"directSnd"},"meta":{"itemId":6},
+  "content":{"type":"sndMsgContent","msgContent":{"type":"text","text":"2"}}}},
+{"chatInfo":{"type":"direct","contact":{"contactId":3}},
+ "chatItem":{"chatDir":{"type":"directRcv"},"meta":{"itemId":7},
+  "content":{"type":"rcvChatFeature","feature":"calls"}}},
+{"chatInfo":{"type":"direct","contact":{"contactId":3}},
+ "chatItem":{"chatDir":{"type":"directRcv"},
+  "meta":{"itemId":9,"itemTs":"2026-09-29T03:14:34Z"},
+  "content":{"type":"rcvMsgContent","msgContent":{"type":"text","text":"2 + 2"}}}},
+{"chatInfo":{"type":"direct","contact":{"contactId":3}},
+ "chatItem":{"chatDir":{"type":"directRcv"},
+  "meta":{"itemId":11,"itemTs":"2026-09-29T03:15:02Z"},
+  "content":{"type":"rcvMsgContent","msgContent":{"type":"image",
+  "text":"a picture","image":"data:image/jpg;base64,/9j/4AAQ"}}}}]}`
+
+// textItem is the index in newChatItems of the text the contact sent.
+const textItem = 3
+
+// logBuffer is a log that the goroutines posting messages write to while
+// the test reads it.
+type logBuffer struct {
+	mu  sync.Mutex
+	buf bytes.Buffer
+}
+
+func (b *logBuffer) Write(p []byte) (int, error) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	return b.buf.Write(p)
+}
+
+func (b *logBuffer) String() string {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+
+	return b.buf.String()
+}
+
+// chatItems returns the chat items in a newChatItems record.
+func chatItems(t *testing.T, record string) []simplex.AChatItem {
+	t.Helper()
+
+	var r simplex.NewChatItems
+
+	err := json.Unmarshal([]byte(record), &r)
+	if err != nil {
+		t.Fatalf("decoding %s: %v", record, err)
+	}
+
+	return r.ChatItems
+}
+
+// receive returns the next of posts, and fails the test if none comes
+// within 5 seconds.
+func receive(t *testing.T, posts <-chan string) string {
+	t.Helper()
+
+	select {
+	case p := <-posts:
+		return p
+	case <-time.After(5 * time.Second):
+		t.Fatal("nothing more was posted")
+
+		return ""
+	}
+}
+
+// within runs f, and fails the test with complaint if f has not returned
+// within 5 seconds.
+func within(t *testing.T, complaint string, f func()) {
+	t.Helper()
+
+	done := make(chan struct{})
+
+	go func() {
+		defer close(done)
+
+		f()
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(5 * time.Second):
+		t.Fatal(complaint)
+	}
+}
+
+// TestDeliveries: each message a contact sends is posted, as JSON with
+// its chat's id, to each webhook of its chat and to no other chat's.
+// Messages in groups, the bot's own messages and the events the chat
+// client records in a chat are not posted.
+func TestDeliveries(t *testing.T) {
+	t.Parallel()
+
+	posts := make(chan string, 10)
+	receiver := httptest.NewServer(http.HandlerFunc(
+		func(_ http.ResponseWriter, r *http.Request) {
+			body, _ := io.ReadAll(r.Body)
+			posts <- r.Method + " " + r.URL.Path + " " +
+				r.Header.Get("Content-Type") + " " + string(body)
+		}))
+	t.Cleanup(receiver.Close)
+
+	webhooks := readWebhooks(t, t.TempDir())
+	srv := webhookAPI(webhooks)
+
+	// Chat 4's webhook comes between chat 3's, so a message posted to
+	// every webhook in turn would reach it before chat 3's second.
+	register(t, srv, webhooksPath, receiver.URL+"/a", http.StatusCreated)
+	register(t, srv, "/api/v1/chats/4/webhooks", receiver.URL+"/c", http.StatusCreated)
+	register(t, srv, webhooksPath, receiver.URL+"/b", http.StatusCreated)
+
+	deliveries := api.StartDeliveries(t.Context(), slog.New(slog.DiscardHandler),
+		webhooks)
+	t.Cleanup(deliveries.Stop)
+
+	for _, item := range chatItems(t, newChatItems) {
+		deliveries.Add(item)
+	}
+
+	text := `{"chat_id":3,"message":{"id":9,"direction":"received",` +
+		`"type":"text","text":"2 + 2","time":"2026-09-29T03:14:34Z"}}`
+	picture := `{"chat_id":3,"message":{"id":11,"direction":"received",` +
+		`"type":"image","text":"a picture","time":"2026-09-29T03:15:02Z"}}`
+	want := []string{
+		"POST /a application/json " + text,
+		"POST /a application/json " + picture,
+		"POST /b application/json " + text,
+		"POST /b application/json " + picture,
+	}
+	got := make([]string, 0, len(want)+1)
+
+	for range want {
+		got = append(got, receive(t, posts))
+	}
+
+	deliveries.Stop()
+
+	select {
+	case p := <-posts:
+		got = append(got, p)
+	default:
+	}
+
+	slices.Sort(want)
+	slices.Sort(got)
+
+	if !slices.Equal(got, want) {
+		t.Errorf("posted:\n%s\nwant:\n%s",
+			strings.Join(got, "\n"), strings.Join(want, "\n"))
+	}
+}
+
+// TestDeliveriesQueueFull: while a webhook holds a POST from each of the
+// goroutines, Add queues as many messages as the queue takes, then drops
+// the next rather than wait, logging it by its chat's id and its own,
+// never its text. Stop abandons the POSTs in progress rather than wait
+// for them.
+func TestDeliveriesQueueFull(t *testing.T) {
+	t.Parallel()
+
+	held := make(chan string, api.DeliveryGoroutines)
+	receiver := httptest.NewServer(http.HandlerFunc(
+		func(_ http.ResponseWriter, r *http.Request) {
+			// Read to the end: only then does the server notice when the
+			// bot abandons the POST, and end r's context.
+			body, _ := io.ReadAll(r.Body)
+			held <- string(body)
+
+			<-r.Context().Done() // never answers
+		}))
+	t.Cleanup(receiver.Close)
+
+	webhooks := readWebhooks(t, t.TempDir())
+	register(t, webhookAPI(webhooks), webhooksPath, receiver.URL, http.StatusCreated)
+
+	var logged logBuffer
+
+	deliveries := api.StartDeliveries(t.Context(),
+		slog.New(slog.NewJSONHandler(&logged, nil)), webhooks)
+	t.Cleanup(deliveries.Stop)
+
+	// A message for each goroutine, whose POST the webhook holds, then as
+	// many as the queue takes, then one more.
+	items := make([]simplex.AChatItem, api.DeliveryGoroutines+api.QueueLength+1)
+	for i := range items {
+		items[i] = chatItems(t, newChatItems)[textItem]
+		items[i].ChatItem.Meta.ItemID = int64(i + 1)
+	}
+
+	for _, item := range items[:api.DeliveryGoroutines] {
+		deliveries.Add(item)
+		receive(t, held)
+	}
+
+	within(t, "Add waited for room in the queue", func() {
+		for _, item := range items[api.DeliveryGoroutines:] {
+			deliveries.Add(item)
+		}
+	})
+
+	within(t, "Stop waited for the webhook to answer", deliveries.Stop)
+
+	log := logged.String()
+	dropped := `"level":"WARN","msg":"dropping a message for the webhooks: ` +
+		`the queue is full","chat_id":3,"message_id":`
+
+	if strings.Count(log, dropped) != 1 ||
+		!strings.Contains(log, dropped+strconv.Itoa(len(items))+"}") {
+		t.Errorf("log = %s, want message %d dropped, and no other", log, len(items))
+	}
+
+	if strings.Contains(log, "2 + 2") {
+		t.Errorf("log = %s, holding a message's text", log)
+	}
+}
+
+// TestDeliveryFailures: a POST that fails, or is answered with a status
+// other than 2xx, is logged with the webhook's id, the message's and the
+// reason or the status, and is not made again. A redirect is not
+// followed. The log holds neither the webhook's URL nor the message's
+// text.
+func TestDeliveryFailures(t *testing.T) {
+	t.Parallel()
+
+	requested := make(chan string, 10)
+	receiver := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			requested <- r.URL.Path
+
+			switch r.URL.Path {
+			case "/refuses":
+				w.WriteHeader(http.StatusServiceUnavailable)
+			case "/redirects":
+				http.Redirect(w, r, "/elsewhere", http.StatusFound)
+			case "/hangs-up":
+				conn, _, err := http.NewResponseController(w).Hijack()
+				if err == nil {
+					_ = conn.Close()
+				}
+			}
+		}))
+	t.Cleanup(receiver.Close)
+
+	webhooks := readWebhooks(t, t.TempDir())
+	paths := []string{"/hangs-up", "/redirects", "/refuses"}
+	ids := map[string]string{}
+
+	// The query stands for a secret that a webhook's URL can hold.
+	for _, path := range paths {
+		ids[path] = register(t, webhookAPI(webhooks), webhooksPath,
+			receiver.URL+path+"?key=s3cret", http.StatusCreated).ID
+	}
+
+	var logged logBuffer
+
+	deliveries := api.StartDeliveries(t.Context(),
+		slog.New(slog.NewJSONHandler(&logged, nil)), webhooks)
+	t.Cleanup(deliveries.Stop)
+
+	deliveries.Add(chatItems(t, newChatItems)[textItem])
+
+	failed := `"level":"WARN","msg":"posting a message to a webhook","webhook_id":"`
+
+	within(t, "the three failures were not logged", func() {
+		for strings.Count(logged.String(), failed) < len(paths) {
+			time.Sleep(10 * time.Millisecond)
+		}
+	})
+
+	log := logged.String()
+
+	for _, want := range []string{
+		failed + ids["/hangs-up"] + `","message_id":9,"error":"`,
+		failed + ids["/redirects"] + `","message_id":9,"status":302}`,
+		failed + ids["/refuses"] + `","message_id":9,"status":503}`,
+	} {
+		if !strings.Contains(log, want) {
+			t.Errorf("log = %s, want it to hold %s", log, want)
+		}
+	}
+
+	for _, secret := range []string{receiver.URL, "s3cret", "2 + 2"} {
+		if strings.Contains(log, secret) {
+			t.Errorf("log = %s, holding %s", log, secret)
+		}
+	}
+
+	// Each webhook was asked once, before its failure was logged, and
+	// the redirect's target never.
+	got := []string{<-requested, <-requested, <-requested}
+	slices.Sort(got)
+
+	if !slices.Equal(got, paths) || len(requested) != 0 {
+		t.Errorf("requested %v and %d more, want %v once each",
+			got, len(requested), paths)
+	}
+}

internal/api/export_test.go

@@ -0,0 +1,9 @@
+package api
+
+// DeliveryGoroutines and QueueLength are deliveryGoroutines and
+// queueLength, exported for the external test package, which fills the
+// queue.
+const (
+	DeliveryGoroutines = deliveryGoroutines
+	QueueLength        = queueLength
+)

internal/bot/bot.go

@@ -56,10 +56,10 @@ var errExited = errors.New("simplex-chat exited")
 
 // Run reads the webhooks kept in cfg.DataDir, starts the chat client with
 // its database there, serving its API on localhost at chatPort, connects
-// to it, sets up the bot's address, then answers messages and serves the
-// bot's API until ctx is cancelled — which is a clean stop and returns
-// nil — or until the chat client, the connection to it or the API's
-// listener fails, which returns the error.
+// to it, sets up the bot's address, then answers messages, posts them to
+// the webhooks and serves the bot's API until ctx is cancelled — which is
+// a clean stop and returns nil — or until the chat client, the connection
+// to it or the API's listener fails, which returns the error.
 func Run(
 	ctx context.Context, log *slog.Logger, cfg *config.Config, chatPort int,
 ) error {
@@ -75,6 +75,12 @@ func Run(
 		return err
 	}
 
+	// Posts the messages the event handler hands it to the webhooks. Its
+	// stop, deferred first, runs last, once the chat client has exited
+	// and can send no more messages; cancelling ctx does not reach it.
+	deliveries := api.StartDeliveries(context.WithoutCancel(ctx), log, webhooks)
+	defer deliveries.Stop()
+
 	// Cancelling this stops the chat client; the deferred wait makes
 	// Run return only once it has exited, whatever path Run takes.
 	// Cancelling ctx does not reach it, so that the API, stopped first,
@@ -94,7 +100,7 @@ func Run(
 		<-cli.Done()
 	}()
 
-	client, err := connect(ctx, log, cli, chatPort)
+	client, err := connect(ctx, log, cli, chatPort, handle(log, deliveries))
 	if err != nil {
 		return err
 	}
@@ -155,9 +161,10 @@ func stopAPI(ctx context.Context, log *slog.Logger, srv *http.Server) {
 }
 
 // connect waits for the chat client to open its API on chatPort and
-// connects to it.
+// connects to it, passing its events to onEvent.
 func connect(
 	ctx context.Context, log *slog.Logger, cli *simplex.CLI, chatPort int,
+	onEvent simplex.EventHandler,
 ) (*simplex.Client, error) {
 	ctx, cancel := context.WithTimeout(ctx, connectTimeout)
 	defer cancel()
@@ -165,7 +172,7 @@ func connect(
 	url := "ws://127.0.0.1:" + strconv.Itoa(chatPort)
 
 	for {
-		client, err := simplex.Dial(ctx, url, log, handle(log))
+		client, err := simplex.Dial(ctx, url, log, onEvent)
 		if err == nil {
 			return client, nil
 		}
@@ -228,8 +235,9 @@ func setUp(
 	return user, nil
 }
 
-// handle answers each text message a contact sends.
-func handle(log *slog.Logger) simplex.EventHandler {
+// handle answers each text message a contact sends, and hands every
+// message a contact sends to deliveries, for the webhooks of its chat.
+func handle(log *slog.Logger, deliveries *api.Deliveries) simplex.EventHandler {
 	return func(c *simplex.Client, ev simplex.Event) {
 		switch ev.Type {
 		case simplex.TypeNewChatItems:
@@ -243,6 +251,9 @@ func handle(log *slog.Logger) simplex.EventHandler {
 			}
 
 			for _, item := range r.ChatItems {
+				// Never waits, so no webhook holds up the replies.
+				deliveries.Add(item)
+
 				msg, ok := item.Message()
 				if !ok {
 					continue

internal/bot/run_test.go

@@ -8,6 +8,7 @@ import (
 	"log/slog"
 	"net"
 	"net/http"
+	"net/http/httptest"
 	"net/netip"
 	"os"
 	"path/filepath"
@@ -35,11 +36,28 @@ const (
 	// long enough for the test to stop the bot meanwhile, and well
 	// within the 5 seconds the API gets to finish its requests.
 	contactsDelay = time.Second
+
+	// sent starts the name of the file the stand-in writes in the data
+	// directory for each message the bot sends, holding the command.
+	sent = "sent-"
 )
 
+// twoMessages is the event the stand-in sends once the bot is set up: a
+// contact sending the bot two messages. It is reduced to the fields the
+// bot reads.
+const twoMessages = `{"type":"newChatItems","chatItems":[
+{"chatInfo":{"type":"direct","contact":{"contactId":3}},
+ "chatItem":{"chatDir":{"type":"directRcv"},
+  "meta":{"itemId":41,"itemTs":"2026-09-29T03:14:34Z"},
+  "content":{"type":"rcvMsgContent","msgContent":{"type":"text","text":"2 + 2"}}}},
+{"chatInfo":{"type":"direct","contact":{"contactId":3}},
+ "chatItem":{"chatDir":{"type":"directRcv"},
+  "meta":{"itemId":42,"itemTs":"2026-09-29T03:14:35Z"},
+  "content":{"type":"rcvMsgContent","msgContent":{"type":"text","text":"3 * 3"}}}}]}`
+
 // TestMain lets this test binary be the chat client as well: started
-// under the chat client's name, as TestStopDuringRequest arranges, it is
-// the stand-in instead of running the tests.
+// under the chat client's name, as standInPath arranges, it is the
+// stand-in instead of running the tests.
 func TestMain(m *testing.M) {
 	if filepath.Base(os.Args[0]) == simplex.Binary {
 		standIn() // never returns
@@ -58,13 +76,13 @@ func standIn() {
 		return os.Args[slices.Index(os.Args, name)+1]
 	}
 
-	marker := filepath.Join(filepath.Dir(arg("--database")), asked)
+	dir := filepath.Dir(arg("--database"))
 
 	srv := &http.Server{
 		Addr:              "127.0.0.1:" + arg("--chat-server-port"),
 		ReadHeaderTimeout: time.Second,
 		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			answer(w, r, marker)
+			answer(w, r, dir)
 		}),
 	}
 
@@ -75,9 +93,11 @@ func standIn() {
 }
 
 // answer answers the commands on one connection with records reduced to
-// the fields the bot reads. Asked for the contacts, it first creates
-// the file marker, then holds its answer for contactsDelay.
-func answer(w http.ResponseWriter, r *http.Request, marker string) {
+// the fields the bot reads. Asked for the contacts, it first creates the
+// file asked in dir, then holds its answer for contactsDelay. Once the
+// bot is set up, it sends twoMessages. Each message the bot sends, it
+// writes to a file in dir, named sent and the command's id.
+func answer(w http.ResponseWriter, r *http.Request, dir string) {
 	conn, err := (&websocket.Upgrader{}).Upgrade(w, r, nil)
 	if err != nil {
 		return
@@ -101,13 +121,20 @@ func answer(w http.ResponseWriter, r *http.Request, marker string) {
 
 		name, _, _ := strings.Cut(cmd["cmd"], " ")
 
+		if name == "/_send" {
+			_ = os.WriteFile(filepath.Join(dir, sent+cmd["corrId"]),
+				[]byte(cmd["cmd"]), 0o600)
+
+			continue
+		}
+
 		record, ok := records[name]
 		if !ok {
 			continue
 		}
 
 		if name == "/_contacts" {
-			_ = os.WriteFile(marker, nil, 0o600)
+			_ = os.WriteFile(filepath.Join(dir, asked), nil, 0o600)
 
 			time.Sleep(contactsDelay)
 		}
@@ -116,6 +143,11 @@ func answer(w http.ResponseWriter, r *http.Request, marker string) {
 			"corrId": cmd["corrId"],
 			"resp":   json.RawMessage(record),
 		})
+
+		// The last command of the bot's set-up.
+		if name == "/_address_settings" {
+			_ = conn.WriteJSON(map[string]any{"resp": json.RawMessage(twoMessages)})
+		}
 	}
 }
 
@@ -123,8 +155,129 @@ func answer(w http.ResponseWriter, r *http.Request, marker string) {
 // when the bot is told to stop still gets the chat client's answer,
 // because the chat client is stopped only once the API has stopped.
 func TestStopDuringRequest(t *testing.T) {
-	// Run starts the chat client from PATH: put this test binary there
-	// under the chat client's name.
+	t.Setenv("PATH", standInPath(t))
+
+	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t), APIToken: credential}
+	stop, done := runBot(t, cfg)
+
+	// Stop the bot once the request below is waiting on the chat client.
+	go func() {
+		for {
+			_, err := os.Stat(filepath.Join(cfg.DataDir, asked))
+			if err == nil {
+				stop()
+			}
+
+			select {
+			case <-done:
+				return
+			case <-time.After(10 * time.Millisecond):
+			}
+		}
+	}()
+
+	status, body := getChats(t, cfg.Port, done)
+
+	want := `{"chats":[{"id":3,"display_name":"tester","contact_deleted":false}]}` + "\n"
+	if status != http.StatusOK || body != want {
+		t.Errorf("GET /api/v1/chats = %d %q, want 200 %q", status, body, want)
+	}
+}
+
+// TestSlowWebhook: a webhook that takes the bot's POSTs and never answers
+// them holds up neither the bot's replies nor its stop.
+func TestSlowWebhook(t *testing.T) {
+	t.Setenv("PATH", standInPath(t))
+
+	posts := make(chan string, 2)
+	receiver := httptest.NewServer(http.HandlerFunc(
+		func(_ http.ResponseWriter, r *http.Request) {
+			body, _ := io.ReadAll(r.Body)
+			posts <- string(body)
+
+			<-r.Context().Done() // until the bot abandons the POST
+		}))
+	t.Cleanup(receiver.Close)
+
+	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t), APIToken: credential}
+
+	err := os.WriteFile(filepath.Join(cfg.DataDir, "webhooks.json"),
+		[]byte(`{"webhooks":[{"id":"00112233445566778899aabbccddeeff",`+
+			`"chat_id":3,"url":"`+receiver.URL+`"}]}`), 0o600)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	stop, done := runBot(t, cfg)
+
+	// The webhook gets both messages, and holds on to them...
+	got := []string{receive(t, posts, done), receive(t, posts, done)}
+	slices.Sort(got)
+
+	want := []string{
+		`{"chat_id":3,"message":{"id":41,"direction":"received",` +
+			`"type":"text","text":"2 + 2","time":"2026-09-29T03:14:34Z"}}`,
+		`{"chat_id":3,"message":{"id":42,"direction":"received",` +
+			`"type":"text","text":"3 * 3","time":"2026-09-29T03:14:35Z"}}`,
+	}
+	if !slices.Equal(got, want) {
+		t.Errorf("posted %q, want %q", got, want)
+	}
+
+	// ...while the bot answers both.
+	replies := []string{
+		`/_send @3 json [{"quotedItemId":41,` +
+			`"msgContent":{"type":"text","text":"4"},"mentions":{}}]`,
+		`/_send @3 json [{"quotedItemId":42,` +
+			`"msgContent":{"type":"text","text":"9"},"mentions":{}}]`,
+	}
+
+	deadline := time.Now().Add(5 * time.Second)
+
+	for !slices.Equal(sentMessages(t, cfg.DataDir), replies) {
+		if time.Now().After(deadline) {
+			t.Fatalf("sent %q, want %q", sentMessages(t, cfg.DataDir), replies)
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	// Stopping abandons the POSTs, rather than give the webhook the 10
+	// seconds it has to answer.
+	stop()
+
+	select {
+	case <-done:
+	case <-time.After(5 * time.Second):
+		t.Fatal("Run did not return while a webhook held a POST")
+	}
+}
+
+// TestUnreadableWebhooks: a webhooks file that cannot be read stops Run
+// before it starts the chat client.
+func TestUnreadableWebhooks(t *testing.T) {
+	// No chat client on PATH: starting one would fail with another error.
+	t.Setenv("PATH", t.TempDir())
+
+	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t)}
+
+	err := os.WriteFile(filepath.Join(cfg.DataDir, "webhooks.json"), []byte("{"), 0o600)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = bot.Run(t.Context(), slog.New(slog.DiscardHandler), cfg, freePort(t))
+	if err == nil || !strings.Contains(err.Error(), "webhooks.json") {
+		t.Errorf("Run = %v, want an error naming webhooks.json", err)
+	}
+}
+
+// standInPath returns a directory holding this test binary under the
+// chat client's name. Run starts the chat client from PATH, so with PATH
+// set to it, Run starts the stand-in.
+func standInPath(t *testing.T) string {
+	t.Helper()
+
 	bin := t.TempDir()
 
 	exe, err := os.Executable()
@@ -137,9 +290,15 @@ func TestStopDuringRequest(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	t.Setenv("PATH", bin)
+	return bin
+}
+
+// runBot runs the bot with cfg until stop is called or the test ends,
+// and fails the test if Run returns an error. done is closed once Run
+// has returned.
+func runBot(t *testing.T, cfg *config.Config) (context.CancelFunc, <-chan struct{}) {
+	t.Helper()
 
-	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t), APIToken: credential}
 	// Never bot.ChatPort: a real chat client may be listening there.
 	chatPort := freePort(t)
 	ctx, stop := context.WithCancel(t.Context())
@@ -162,43 +321,55 @@ func TestStopDuringRequest(t *testing.T) {
 		}
 	})
 
-	// Stop the bot once the request below is waiting on the chat client.
-	go func() {
-		for ctx.Err() == nil {
-			_, err := os.Stat(filepath.Join(cfg.DataDir, asked))
-			if err == nil {
-				stop()
-			}
-
-			time.Sleep(10 * time.Millisecond)
-		}
-	}()
-
-	status, body := getChats(t, cfg.Port, done)
-
-	want := `{"chats":[{"id":3,"display_name":"tester","contact_deleted":false}]}` + "\n"
-	if status != http.StatusOK || body != want {
-		t.Errorf("GET /api/v1/chats = %d %q, want 200 %q", status, body, want)
-	}
+	return stop, done
 }
 
-// TestUnreadableWebhooks: a webhooks file that cannot be read stops Run
-// before it starts the chat client.
-func TestUnreadableWebhooks(t *testing.T) {
-	// No chat client on PATH: starting one would fail with another error.
-	t.Setenv("PATH", t.TempDir())
+// receive returns the next of posts. It fails the test if none comes
+// within 10 seconds, or if Run returns first, which closes done.
+func receive(t *testing.T, posts <-chan string, done <-chan struct{}) string {
+	t.Helper()
 
-	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t)}
+	select {
+	case p := <-posts:
+		return p
+	case <-done:
+		t.Fatal("Run returned before the webhook got the messages")
+	case <-time.After(10 * time.Second):
+		t.Fatal("the webhook did not get the messages")
+	}
 
-	err := os.WriteFile(filepath.Join(cfg.DataDir, "webhooks.json"), []byte("{"), 0o600)
+	return ""
+}
+
+// sentMessages returns the commands of the messages the bot has sent, as
+// the stand-in wrote them in dir, sorted.
+func sentMessages(t *testing.T, dir string) []string {
+	t.Helper()
+
+	entries, err := os.ReadDir(dir)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	err = bot.Run(t.Context(), slog.New(slog.DiscardHandler), cfg, freePort(t))
-	if err == nil || !strings.Contains(err.Error(), "webhooks.json") {
-		t.Errorf("Run = %v, want an error naming webhooks.json", err)
+	var cmds []string
+
+	for _, entry := range entries {
+		if !strings.HasPrefix(entry.Name(), sent) {
+			continue
+		}
+
+		//nolint:gosec // G304: the test's own file.
+		cmd, err := os.ReadFile(filepath.Join(dir, entry.Name()))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		cmds = append(cmds, string(cmd))
 	}
+
+	slices.Sort(cmds)
+
+	return cmds
 }
 
 // freePort returns a TCP port that nothing listens on at the moment.