Add per-delivery replay to the event log (closes #203)

A delivery that exhausted max_retries was failed forever. The event
body is durably stored, so the only way to get it delivered was to
download it and re-POST by hand.

The event log now offers a Replay action on any finished delivery.
Replay creates a NEW pending delivery for the same event and target
and hands it to the delivery engine through the same Notifier the
receiver uses, so it is retried, SSRF-guarded and circuit-broken
exactly as a first attempt. The original delivery's status,
timestamps and recorded attempts are never touched, and what is
re-sent is the stored event body, not the response the original
attempt received.

The target is read as it stands now, including soft-deleted rows so
that a deleted target refuses the replay with a message on the page
instead of erroring or delivering from stale configuration. A
deactivated target and a target id that names nothing refuse the same
way, as does a replay of a delivery the engine has not finished.

Two bounds on replay storms: the route carries a per-client POST rate
limit of 30 per minute, and the handler refuses a replay while an
earlier one for the same event and target is still pending or
retrying.

One new metric, webhooker_delivery_replays_total, on the existing
target_type label. A replay is a real delivery and moves the attempt,
outcome and duration series like any other; this counter is what
separates it from ordinary traffic without adding a dimension to
every existing series.

The delivery row is written with associations omitted and with
neither Event nor Target populated, so no target row reaches the
per-webhook event database.

README.md

@@ -904,6 +904,23 @@ DeliveryResults.
   succeeded).
 - **`failed`** — All retry attempts exhausted without success.
 
+**Replay.** A `delivered` or `failed` delivery is finished as far as
+the engine is concerned, but the event is still stored, so the event
+log offers a per-delivery **Replay** action for it. Replay creates a
+NEW `pending` delivery for the same event and target and hands it to
+the engine on the ordinary path — same retries, same SSRF guard, same
+circuit breaker as a first attempt. It never touches the delivery it
+repeats: that row's status, timestamps and recorded attempts stand as
+the record of what happened.
+
+What is re-sent is the stored event body, against the target's
+configuration **as it stands now** — the point of a replay is to
+deliver where the destination has since been fixed. A target that has
+been deleted or deactivated therefore refuses the replay with a
+message on the event log rather than delivering from stale
+configuration, and a replay is refused while an earlier one for the
+same event and target is still pending or retrying.
+
 #### DeliveryResult
 
 The result of a single delivery attempt. Every attempt (including
@@ -1231,6 +1248,7 @@ arriving and being stored, they are just not getting anywhere.
 | `webhooker_deliveries_succeeded_total` | counter | Deliveries that reached `delivered` |
 | `webhooker_deliveries_failed_total` | counter | Deliveries that failed terminally and will not be retried |
 | `webhooker_delivery_retries_total` | counter | Deliveries put back into `retrying` |
+| `webhooker_delivery_replays_total` | counter | Deliveries an operator replayed from the event log. A replay runs the ordinary engine path, so it also moves the attempt, outcome and duration series; this is the only one that separates it from ordinary traffic |
 | `webhooker_delivery_duration_seconds` | histogram | Wall time of a single dispatched delivery attempt, the same duration the attempt's `DeliveryResult` records |
 | `webhooker_deliveries_pending` | gauge | Deliveries currently in `pending` |
 | `webhooker_deliveries_retrying` | gauge | Deliveries currently in `retrying` |
@@ -1828,6 +1846,7 @@ abuse limit later; they are tracked as future work.
 | `POST` | `/source/{id}/edit`      | Edit webhook submission |
 | `POST` | `/source/{id}/delete`    | Delete webhook |
 | `GET`  | `/source/{id}/logs`      | Webhook event logs |
+| `POST` | `/source/{id}/deliveries/{deliveryID}/replay` | Replay a finished delivery: creates a new delivery for the same event against the target's current configuration (30 per minute per bucket, then `429`) |
 | `POST` | `/source/{id}/entrypoints` | Add entrypoint to webhook |
 | `POST` | `/source/{id}/entrypoints/{entrypointID}/delete` | Delete an entrypoint |
 | `POST` | `/source/{id}/entrypoints/{entrypointID}/toggle` | Enable or disable an entrypoint |
@@ -1912,6 +1931,7 @@ webhooker/
 │   ├── handlers/
 │   │   ├── handlers.go        # Base handler struct, JSON helpers, template rendering
 │   │   ├── auth.go            # Login, logout handlers
+│   │   ├── delivery_replay.go # Per-delivery replay: new delivery, current target config
 │   │   ├── event_log_view.go  # Event log projection, byte-capped in SQL
 │   │   ├── healthcheck.go     # Health check handler
 │   │   ├── index.go           # Index page handler

internal/database/model_delivery.go

@@ -11,6 +11,23 @@ const (
 	DeliveryStatusRetrying  DeliveryStatus = "retrying"
 )
 
+// Terminal reports whether a delivery in this status has finished, so
+// the delivery engine will make no further attempt of its own.
+//
+// It is what decides which deliveries the event log offers to replay:
+// a pending or retrying delivery is still the engine's, and replaying
+// one would race it.
+func (s DeliveryStatus) Terminal() bool {
+	switch s {
+	case DeliveryStatusDelivered, DeliveryStatusFailed:
+		return true
+	case DeliveryStatusPending, DeliveryStatusRetrying:
+		return false
+	default:
+		return false
+	}
+}
+
 // Delivery represents a delivery attempt for an event to a target
 type Delivery struct {
 	BaseModel

internal/handlers/delivery_replay.go

@@ -0,0 +1,378 @@
+package handlers
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/go-chi/chi"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+)
+
+// replayOutcomeParam is the query parameter the replay POST redirects
+// with and the event log page reads its banner from.
+const replayOutcomeParam = "replay"
+
+// replayOutcomeCode is the outcome of a replay POST. The redirect
+// carries one of these fixed codes rather than a message, so nothing a
+// client submits can reach the rendered page through it.
+type replayOutcomeCode string
+
+const (
+	// replayQueued reports that a new delivery was created and handed
+	// to the delivery engine.
+	replayQueued replayOutcomeCode = "queued"
+
+	// replayTargetDeleted reports a target that once existed and has
+	// since been deleted. Deletes are soft and deliveries carry no
+	// foreign key to the target row, so the history survives its
+	// target and this is the ordinary case for an old event.
+	replayTargetDeleted replayOutcomeCode = "target-deleted"
+
+	// replayTargetMissing reports a target id that names no row at
+	// all, deleted or otherwise.
+	replayTargetMissing replayOutcomeCode = "target-missing"
+
+	// replayTargetInactive reports a target the operator has
+	// deactivated. A deactivated target receives no new deliveries, so
+	// a replay to it would be a delivery they switched off.
+	replayTargetInactive replayOutcomeCode = "target-inactive"
+
+	// replayNotTerminal reports a delivery the engine has not finished
+	// with.
+	replayNotTerminal replayOutcomeCode = "not-terminal"
+
+	// replayInFlight reports that an earlier replay of this event to
+	// this target is still running.
+	replayInFlight replayOutcomeCode = "in-flight"
+)
+
+// replayOutcome returns the banner the event log page shows for an
+// outcome code, and whether the replay was queued. An unrecognised
+// code yields no banner.
+func replayOutcome(code string) (string, bool) {
+	switch replayOutcomeCode(code) {
+	case replayQueued:
+		return "Replay queued: a new delivery was created against " +
+			"the target's current configuration.", true
+	case replayTargetDeleted:
+		return "Not replayed: the target this delivery was for has " +
+			"been deleted. Recreate the target, then replay.", false
+	case replayTargetMissing:
+		return "Not replayed: the target this delivery was for no " +
+			"longer exists.", false
+	case replayTargetInactive:
+		return "Not replayed: the target this delivery was for is " +
+			"deactivated. Activate it, then replay.", false
+	case replayNotTerminal:
+		return "Not replayed: this delivery has not finished yet.",
+			false
+	case replayInFlight:
+		return "Not replayed: a delivery of this event to this " +
+			"target is already in flight.", false
+	default:
+		return "", false
+	}
+}
+
+// HandleDeliveryReplay re-sends a finished delivery's event to its
+// target.
+//
+// A replay never touches the delivery it repeats. It creates a NEW
+// pending delivery row for the same event and target and hands it to
+// the delivery engine through the same Notifier the receiver uses, so
+// the original's status, attempts and timestamps stand as the record
+// of what actually happened, and the replay is retried, SSRF-guarded
+// and circuit-broken exactly as a first attempt is.
+//
+// What is re-sent is the stored EVENT body, never the response the
+// original delivery received.
+//
+// The target's configuration is read now rather than as it stood when
+// the original ran: a replay exists to deliver where the operator
+// currently wants the event to go. That is also why a deleted target
+// is refused rather than delivered to from stale configuration.
+func (h *Handlers) HandleDeliveryReplay() http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		webhook, ok := h.ownedWebhook(w, r)
+		if !ok {
+			return
+		}
+
+		// The body size cap is enforced by the MaxBodySize
+		// middleware, which runs before CSRF parses the form.
+		err := r.ParseForm()
+		if err != nil {
+			http.Error(
+				w, "Bad request", http.StatusBadRequest,
+			)
+
+			return
+		}
+
+		h.replayDelivery(w, r, webhook)
+	}
+}
+
+// replayDelivery performs the replay for a webhook the caller has
+// already established the session's user owns.
+func (h *Handlers) replayDelivery(
+	w http.ResponseWriter,
+	r *http.Request,
+	webhook database.Webhook,
+) {
+	if !h.dbMgr.DBExists(webhook.ID) {
+		http.NotFound(w, r)
+
+		return
+	}
+
+	webhookDB, err := h.dbMgr.GetDB(webhook.ID)
+	if err != nil {
+		h.serverError(w, "failed to get webhook database", err)
+
+		return
+	}
+
+	original, ok := h.loadReplaySource(w, r, webhookDB)
+	if !ok {
+		return
+	}
+
+	if !original.Status.Terminal() {
+		h.finishReplay(w, r, webhook, replayNotTerminal)
+
+		return
+	}
+
+	target, code := h.replayTarget(webhook.ID, original.TargetID)
+	if target == nil {
+		h.finishReplay(w, r, webhook, code)
+
+		return
+	}
+
+	h.queueReplay(w, r, webhookDB, webhook, original, target)
+}
+
+// loadReplaySource loads the delivery to be replayed, selecting only
+// the columns the replay needs so no association is populated. A
+// delivery id that names no row in this webhook's database is a 404.
+func (h *Handlers) loadReplaySource(
+	w http.ResponseWriter,
+	r *http.Request,
+	webhookDB *gorm.DB,
+) (*database.Delivery, bool) {
+	var original database.Delivery
+
+	err := webhookDB.
+		Select("id", "event_id", "target_id", "status").
+		First(
+			&original, "id = ?", chi.URLParam(r, "deliveryID"),
+		).Error
+	if err != nil {
+		http.NotFound(w, r)
+
+		return nil, false
+	}
+
+	return &original, true
+}
+
+// queueReplay writes the new delivery and hands it to the engine.
+func (h *Handlers) queueReplay(
+	w http.ResponseWriter,
+	r *http.Request,
+	webhookDB *gorm.DB,
+	webhook database.Webhook,
+	original *database.Delivery,
+	target *database.Target,
+) {
+	inFlight, err := countInFlightDeliveries(
+		webhookDB, original.EventID, target.ID,
+	)
+	if err != nil {
+		h.serverError(
+			w, "failed to count in-flight deliveries", err,
+		)
+
+		return
+	}
+
+	if inFlight > 0 {
+		h.finishReplay(w, r, webhook, replayInFlight)
+
+		return
+	}
+
+	var event database.Event
+
+	err = webhookDB.
+		First(&event, "id = ?", original.EventID).Error
+	if err != nil {
+		h.serverError(w, "failed to load event for replay", err)
+
+		return
+	}
+
+	task, err := createReplayDelivery(
+		webhookDB, webhook.ID, &event, target,
+	)
+	if err != nil {
+		h.serverError(
+			w, "failed to create replay delivery", err,
+		)
+
+		return
+	}
+
+	h.mtr.DeliveryReplayed(target.Type)
+	h.notifier.Notify([]delivery.Task{task})
+
+	h.log.Info(
+		"delivery replay queued",
+		"webhook_id", webhook.ID,
+		"event_id", event.ID,
+		"target_id", target.ID,
+		"replayed_delivery_id", original.ID,
+		"delivery_id", task.DeliveryID,
+	)
+
+	h.finishReplay(w, r, webhook, replayQueued)
+}
+
+// replayTarget loads the delivery's target as it stands now.
+//
+// The load is Unscoped so that a soft-deleted row is still found:
+// deletes are soft and a delivery carries no foreign key to its
+// target, so a target's history outlives it, and without the deleted
+// row there is no way to tell "you deleted this target" from "this id
+// never named anything". A nil target means the replay is refused,
+// with the returned code saying why.
+func (h *Handlers) replayTarget(
+	webhookID, targetID string,
+) (*database.Target, replayOutcomeCode) {
+	var target database.Target
+
+	err := h.db.DB().Unscoped().Where(
+		"id = ? AND webhook_id = ?", targetID, webhookID,
+	).First(&target).Error
+	if err != nil {
+		return nil, replayTargetMissing
+	}
+
+	if target.DeletedAt.Valid {
+		return nil, replayTargetDeleted
+	}
+
+	if !target.Active {
+		return nil, replayTargetInactive
+	}
+
+	return &target, replayQueued
+}
+
+// countInFlightDeliveries reports how many deliveries of this event to
+// this target the engine has not finished.
+//
+// It is the replay-storm guard: a replay is refused while an earlier
+// one is still pending or retrying, so a held-down button or a scripted
+// loop cannot stack copies of work already queued. It is a check and
+// not a lock, so two simultaneous POSTs can still both pass it; the
+// per-client rate limit on the route is what bounds that.
+func countInFlightDeliveries(
+	webhookDB *gorm.DB, eventID, targetID string,
+) (int64, error) {
+	var count int64
+
+	err := webhookDB.Model(&database.Delivery{}).Where(
+		"event_id = ? AND target_id = ? AND status IN ?",
+		eventID, targetID,
+		[]database.DeliveryStatus{
+			database.DeliveryStatusPending,
+			database.DeliveryStatusRetrying,
+		},
+	).Count(&count).Error
+
+	return count, err
+}
+
+// createReplayDelivery writes the new pending delivery row and returns
+// the task that carries it to the delivery engine.
+//
+// The row is written with associations omitted, and neither Event nor
+// Target is populated on it: GORM's SaveBeforeAssociations would
+// otherwise upsert the whole target row — plaintext config, which for a
+// Slack target is the credential — into the per-webhook event database.
+// See https://git.eeqj.de/sneak/webhooker/issues/206.
+func createReplayDelivery(
+	webhookDB *gorm.DB,
+	webhookID string,
+	event *database.Event,
+	target *database.Target,
+) (delivery.Task, error) {
+	dlv := &database.Delivery{
+		EventID:  event.ID,
+		TargetID: target.ID,
+		Status:   database.DeliveryStatusPending,
+	}
+
+	err := webhookDB.Omit(clause.Associations).Create(dlv).Error
+	if err != nil {
+		return delivery.Task{}, err
+	}
+
+	return delivery.Task{
+		DeliveryID:   dlv.ID,
+		EventID:      event.ID,
+		WebhookID:    webhookID,
+		EntrypointID: event.EntrypointID,
+		TargetID:     target.ID,
+		TargetName:   target.Name,
+		TargetType:   target.Type,
+		TargetConfig: target.Config,
+		MaxRetries:   target.MaxRetries,
+		Method:       event.Method,
+		Headers:      event.Headers,
+		ContentType:  event.ContentType,
+		Body:         replayBody(event.Body),
+		AttemptNum:   1,
+	}, nil
+}
+
+// replayBody returns the stored event body for a replay task to carry
+// inline, or nil when it is large enough that the engine should fetch
+// it from the per-webhook database instead.
+func replayBody(body string) *string {
+	if len(body) >= delivery.MaxInlineBodySize {
+		return nil
+	}
+
+	return &body
+}
+
+// finishReplay redirects back to the event log the replay was
+// triggered from, carrying the outcome code the page turns into a
+// banner and the page number the form submitted.
+func (h *Handlers) finishReplay(
+	w http.ResponseWriter,
+	r *http.Request,
+	webhook database.Webhook,
+	code replayOutcomeCode,
+) {
+	dest := "/source/" + webhook.ID + "/logs?" +
+		replayOutcomeParam + "=" + string(code)
+
+	// The page is read from the form rather than the query string:
+	// this is a POST, and its query string is what logs and Referer
+	// headers record.
+	if page := parseNonNegativeInt(
+		r.PostFormValue("page"),
+	); page > 1 {
+		dest += "&page=" + strconv.Itoa(page)
+	}
+
+	http.Redirect(w, r, dest, http.StatusSeeOther)
+}

internal/handlers/delivery_replay_test.go

@@ -0,0 +1,526 @@
+package handlers_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
+	"sneak.berlin/go/webhooker/internal/database"
+	"sneak.berlin/go/webhooker/internal/delivery"
+	"sneak.berlin/go/webhooker/internal/handlers"
+	"sneak.berlin/go/webhooker/internal/session"
+)
+
+// paramDeliveryID is the chi URL parameter name the replay handler
+// reads.
+const paramDeliveryID = "deliveryID"
+
+// replayTargetURL is a public destination, so a target configured with
+// it is one the SSRF guard would accept. Nothing in these tests
+// dispatches to it: the notifier is recorded, not run.
+const replayTargetURL = "http://93.184.216.34/hook"
+
+// seedFailedDelivery records an event, a terminally failed delivery of
+// it to the given target, and the attempt that failed.
+func seedFailedDelivery(
+	t *testing.T,
+	dbMgr *database.WebhookDBManager,
+	webhookID, targetID string,
+) (*database.Event, *database.Delivery) {
+	t.Helper()
+
+	webhookDB, err := dbMgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	event := &database.Event{
+		WebhookID:    webhookID,
+		EntrypointID: "entrypoint-" + webhookID,
+		Method:       http.MethodPost,
+		Headers:      `{"X-Test":["yes"]}`,
+		Body:         `{"replay":"me"}`,
+		ContentType:  "application/json",
+	}
+
+	require.NoError(t, webhookDB.Omit(
+		clause.Associations,
+	).Create(event).Error)
+
+	dlv := &database.Delivery{
+		EventID:  event.ID,
+		TargetID: targetID,
+		Status:   database.DeliveryStatusFailed,
+	}
+
+	require.NoError(t, webhookDB.Omit(
+		clause.Associations,
+	).Create(dlv).Error)
+
+	result := &database.DeliveryResult{
+		DeliveryID: dlv.ID,
+		AttemptNum: 1,
+		Success:    false,
+		StatusCode: http.StatusBadGateway,
+		Error:      "connection refused",
+	}
+
+	require.NoError(t, webhookDB.Omit(
+		clause.Associations,
+	).Create(result).Error)
+
+	return event, dlv
+}
+
+// loadDelivery reads a delivery back out of a webhook's database.
+func loadDelivery(
+	t *testing.T, webhookDB *gorm.DB, deliveryID string,
+) database.Delivery {
+	t.Helper()
+
+	var dlv database.Delivery
+
+	require.NoError(
+		t,
+		webhookDB.First(&dlv, "id = ?", deliveryID).Error,
+	)
+
+	return dlv
+}
+
+// listDeliveries reads every delivery of an event.
+func listDeliveries(
+	t *testing.T, webhookDB *gorm.DB, eventID string,
+) []database.Delivery {
+	t.Helper()
+
+	var deliveries []database.Delivery
+
+	require.NoError(t, webhookDB.Where(
+		"event_id = ?", eventID,
+	).Find(&deliveries).Error)
+
+	return deliveries
+}
+
+// theOtherDelivery returns the one delivery in the slice that is not
+// excludeID. Identity is used rather than an ordering because the rows
+// are minted milliseconds apart and their ids are random.
+func theOtherDelivery(
+	t *testing.T,
+	deliveries []database.Delivery,
+	excludeID string,
+) database.Delivery {
+	t.Helper()
+
+	var found []database.Delivery
+
+	for _, d := range deliveries {
+		if d.ID != excludeID {
+			found = append(found, d)
+		}
+	}
+
+	require.Len(t, found, 1)
+
+	return found[0]
+}
+
+// postReplay runs the real replay handler for one delivery.
+func postReplay(
+	t *testing.T,
+	h *handlers.Handlers,
+	sess *session.Session,
+	webhookID, deliveryID string,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	req := postRequest(
+		"/source/"+webhookID+"/deliveries/"+
+			deliveryID+"/replay",
+		authenticatedCookies(
+			t, sess, deleteTestUserID, deleteTestUsername,
+		),
+		map[string]string{
+			paramSourceID:   webhookID,
+			paramDeliveryID: deliveryID,
+		},
+	)
+
+	w := httptest.NewRecorder()
+	h.HandleDeliveryReplay().ServeHTTP(w, req)
+
+	return w
+}
+
+// TestHandleDeliveryReplay_AppendsDeliveryAndLeavesOriginal is the
+// core requirement: replaying a failed delivery succeeds, appends a
+// new delivery, and leaves the original row and its recorded attempt
+// exactly as they were.
+//
+// It also pins the two things a replay would be wrong to get from the
+// original: the task carries the target's CURRENT configuration, which
+// this test changes between the failure and the replay, and it carries
+// the stored EVENT body rather than anything the failed attempt
+// received back.
+func TestHandleDeliveryReplay_AppendsDeliveryAndLeavesOriginal(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		notif *recordingNotifier
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &notif)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	tgt := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+
+	event, original := seedFailedDelivery(
+		t, dbMgr, wh.ID, tgt.ID,
+	)
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	before := loadDelivery(t, webhookDB, original.ID)
+
+	// The operator fixes the destination, which is the whole reason
+	// to replay. The replay must use this, not the config the
+	// original delivery ran against.
+	const fixedConfig = `{"url":"http://93.184.216.34/fixed"}`
+
+	require.NoError(t, db.DB().Model(&database.Target{}).
+		Where("id = ?", tgt.ID).
+		Update("config", fixedConfig).Error)
+
+	w := postReplay(t, h, sess, wh.ID, original.ID)
+
+	require.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(
+		t,
+		"/source/"+wh.ID+"/logs?replay=queued",
+		w.Header().Get("Location"),
+	)
+
+	deliveries := listDeliveries(t, webhookDB, event.ID)
+	require.Len(
+		t, deliveries, 2,
+		"replay must append a delivery, not reuse one",
+	)
+
+	replayed := theOtherDelivery(t, deliveries, original.ID)
+	assert.Equal(t, tgt.ID, replayed.TargetID)
+	assert.Equal(t, event.ID, replayed.EventID)
+	assert.Equal(
+		t, database.DeliveryStatusPending, replayed.Status,
+	)
+
+	assertDeliveryUntouched(t, webhookDB, before)
+
+	tasks := notif.Tasks()
+	require.Len(t, tasks, 1)
+	assertReplayTask(
+		t, tasks[0], wh.ID, event, tgt, replayed.ID, fixedConfig,
+	)
+	assertNoLeakedTarget(t, webhookDB)
+}
+
+// assertDeliveryUntouched proves a delivery row is exactly as it was
+// read before: same terminal status, same timestamps, and the same
+// recorded attempts.
+func assertDeliveryUntouched(
+	t *testing.T,
+	webhookDB *gorm.DB,
+	before database.Delivery,
+) {
+	t.Helper()
+
+	after := loadDelivery(t, webhookDB, before.ID)
+	assert.Equal(
+		t, before.Status, after.Status,
+		"replay must not resurrect the original delivery",
+	)
+	assert.Equal(t, before.UpdatedAt, after.UpdatedAt)
+	assert.Equal(t, before.CreatedAt, after.CreatedAt)
+
+	var attempts int64
+
+	require.NoError(t, webhookDB.
+		Model(&database.DeliveryResult{}).
+		Where("delivery_id = ?", before.ID).
+		Count(&attempts).Error)
+	assert.Equal(
+		t, int64(1), attempts,
+		"the original delivery's attempt history must stand",
+	)
+}
+
+// assertReplayTask proves the task handed to the delivery engine is
+// the one the receiver would build for this event and this target, and
+// that it carries wantConfig — the target's configuration as it stands
+// now rather than as the original delivery ran against it.
+func assertReplayTask(
+	t *testing.T,
+	task delivery.Task,
+	webhookID string,
+	event *database.Event,
+	target *database.Target,
+	wantDeliveryID, wantConfig string,
+) {
+	t.Helper()
+
+	assert.Equal(t, wantDeliveryID, task.DeliveryID)
+	assert.Equal(t, event.ID, task.EventID)
+	assert.Equal(t, webhookID, task.WebhookID)
+	assert.Equal(t, event.EntrypointID, task.EntrypointID)
+	assert.Equal(t, target.ID, task.TargetID)
+	assert.Equal(t, target.Type, task.TargetType)
+	assert.JSONEq(
+		t, wantConfig, task.TargetConfig,
+		"replay must use the target's current configuration",
+	)
+	assert.Equal(t, event.Method, task.Method)
+	assert.Equal(t, event.Headers, task.Headers)
+	assert.Equal(t, event.ContentType, task.ContentType)
+	assert.Equal(t, 1, task.AttemptNum)
+	require.NotNil(t, task.Body)
+	assert.Equal(
+		t, event.Body, *task.Body,
+		"replay re-sends the stored event body",
+	)
+}
+
+// assertNoLeakedTarget proves the per-webhook database holds no target
+// rows. AutoMigrate creates the table there because Delivery declares
+// the relation, so it is a ROW that signals a leak: an association
+// write would have upserted the whole target, plaintext config and
+// all, into the event database. See
+// https://git.eeqj.de/sneak/webhooker/issues/206.
+func assertNoLeakedTarget(t *testing.T, webhookDB *gorm.DB) {
+	t.Helper()
+
+	var leaked int64
+
+	require.NoError(t, webhookDB.Unscoped().
+		Model(&database.Target{}).Count(&leaked).Error)
+	assert.Zero(
+		t, leaked,
+		"replay must not write the target into the event database",
+	)
+}
+
+// TestHandleDeliveryReplay_RefusesDeletedTarget proves the required
+// refusal: a target deleted since the delivery ran is reported as
+// deleted rather than erroring, and nothing is created or queued.
+func TestHandleDeliveryReplay_RefusesDeletedTarget(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		notif *recordingNotifier
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &notif)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	tgt := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+
+	event, original := seedFailedDelivery(
+		t, dbMgr, wh.ID, tgt.ID,
+	)
+
+	// Deletes are soft, so the delivery history outlives the target.
+	require.NoError(t, db.DB().Where(
+		"id = ?", tgt.ID,
+	).Delete(&database.Target{}).Error)
+
+	w := postReplay(t, h, sess, wh.ID, original.ID)
+
+	require.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(
+		t,
+		"/source/"+wh.ID+"/logs?replay=target-deleted",
+		w.Header().Get("Location"),
+	)
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	assert.Len(
+		t, listDeliveries(t, webhookDB, event.ID), 1,
+		"a refused replay must create no delivery",
+	)
+	assert.Empty(
+		t, notif.Tasks(),
+		"a refused replay must queue nothing",
+	)
+
+	// The refusal is specific, which is why the target is looked up
+	// including soft-deleted rows: an id that never named a target
+	// is a different outcome, and a different message, from one the
+	// operator deleted.
+	_, orphan := seedFailedDelivery(
+		t, dbMgr, wh.ID, "target-that-never-existed",
+	)
+
+	missing := postReplay(t, h, sess, wh.ID, orphan.ID)
+	require.Equal(t, http.StatusSeeOther, missing.Code)
+	assert.Equal(
+		t,
+		"/source/"+wh.ID+"/logs?replay=target-missing",
+		missing.Header().Get("Location"),
+	)
+}
+
+// TestHandleDeliveryReplay_RefusesWhileEarlierReplayInFlight proves
+// the replay-storm guard: a second replay of the same event to the
+// same target is refused while the first is still queued, so repeated
+// submissions cannot stack copies of work the engine has not done.
+func TestHandleDeliveryReplay_RefusesWhileEarlierReplayInFlight(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+		notif *recordingNotifier
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr, &notif)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	tgt := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+
+	event, original := seedFailedDelivery(
+		t, dbMgr, wh.ID, tgt.ID,
+	)
+
+	first := postReplay(t, h, sess, wh.ID, original.ID)
+	require.Equal(t, http.StatusSeeOther, first.Code)
+	require.Equal(
+		t,
+		"/source/"+wh.ID+"/logs?replay=queued",
+		first.Header().Get("Location"),
+	)
+
+	second := postReplay(t, h, sess, wh.ID, original.ID)
+	require.Equal(t, http.StatusSeeOther, second.Code)
+	assert.Equal(
+		t,
+		"/source/"+wh.ID+"/logs?replay=in-flight",
+		second.Header().Get("Location"),
+	)
+
+	webhookDB, err := dbMgr.GetDB(wh.ID)
+	require.NoError(t, err)
+
+	assert.Len(
+		t, listDeliveries(t, webhookDB, event.ID), 2,
+		"the refused second replay must add nothing",
+	)
+	assert.Len(
+		t, notif.Tasks(), 1,
+		"only the first replay reaches the delivery engine",
+	)
+
+	// A delivery the engine has not finished is not replayable
+	// either, which is the same rule seen from the other side.
+	queued := theOtherDelivery(
+		t, listDeliveries(t, webhookDB, event.ID), original.ID,
+	)
+
+	pending := postReplay(t, h, sess, wh.ID, queued.ID)
+	require.Equal(t, http.StatusSeeOther, pending.Code)
+	assert.Equal(
+		t,
+		"/source/"+wh.ID+"/logs?replay=not-terminal",
+		pending.Header().Get("Location"),
+	)
+}
+
+// TestHandleSourceLogs_RendersReplayControlAndBanner proves the action
+// reaches the page it belongs on: a finished delivery renders a POST
+// form carrying a CSRF token, and the outcome code a refusal redirects
+// with becomes a readable message.
+func TestHandleSourceLogs_RendersReplayControlAndBanner(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	tgt := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+
+	_, original := seedFailedDelivery(t, dbMgr, wh.ID, tgt.ID)
+
+	body := renderSourceLogsPage(t, h, sess, wh.ID)
+
+	assert.Contains(
+		t, body,
+		`action="/source/`+wh.ID+`/deliveries/`+
+			original.ID+`/replay"`,
+	)
+	assert.Contains(t, body, `method="POST"`)
+	assert.Contains(t, body, `name="csrf_token"`)
+	assert.Contains(t, body, ">Replay<")
+
+	refused := renderSourceLogsPageWithQuery(
+		t, h, sess, wh.ID, "?replay=target-deleted",
+	)
+
+	assert.Contains(t, refused, "alert-error")
+	assert.Contains(t, refused, "has been deleted")
+
+	// An outcome code nobody issued renders no banner at all.
+	unknown := renderSourceLogsPageWithQuery(
+		t, h, sess, wh.ID, "?replay=made-up",
+	)
+
+	assert.NotContains(t, unknown, "alert-error")
+	assert.NotContains(t, unknown, "alert-success")
+	assert.NotContains(t, unknown, "made-up")
+}

internal/handlers/handlers_test.go

@@ -24,9 +24,32 @@ import (
 	"sneak.berlin/go/webhooker/internal/session"
 )
 
-type noopNotifier struct{}
+// recordingNotifier is a delivery.Notifier that records the tasks it
+// was handed, so a test can prove a handler queued the delivery it
+// claims to have queued — and, on the refusal paths, that it queued
+// nothing.
+type recordingNotifier struct {
+	mu    sync.Mutex
+	tasks []delivery.Task
+}
 
-func (n *noopNotifier) Notify([]delivery.Task) {}
+func (n *recordingNotifier) Notify(tasks []delivery.Task) {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+
+	n.tasks = append(n.tasks, tasks...)
+}
+
+// Tasks returns a copy of the recorded tasks.
+func (n *recordingNotifier) Tasks() []delivery.Task {
+	n.mu.Lock()
+	defer n.mu.Unlock()
+
+	out := make([]delivery.Task, len(n.tasks))
+	copy(out, n.tasks)
+
+	return out
+}
 
 // recordingEvictor is a delivery.WebhookEvictor that records
 // the webhook ids it was asked to evict, so a test can prove
@@ -74,8 +97,11 @@ func newTestApp(
 			database.NewWebhookDBManager,
 			healthcheck.New,
 			session.New,
-			func() delivery.Notifier {
-				return &noopNotifier{}
+			func() *recordingNotifier {
+				return &recordingNotifier{}
+			},
+			func(n *recordingNotifier) delivery.Notifier {
+				return n
 			},
 			func() *recordingEvictor {
 				return &recordingEvictor{}

internal/handlers/source_logs_test.go

@@ -60,10 +60,26 @@ func renderSourceLogsPage(
 ) string {
 	t.Helper()
 
+	return renderSourceLogsPageWithQuery(
+		t, h, sess, webhookID, "",
+	)
+}
+
+// renderSourceLogsPageWithQuery is renderSourceLogsPage over a
+// caller-supplied query string, for the page state a redirect back to
+// the log carries in one.
+func renderSourceLogsPageWithQuery(
+	t *testing.T,
+	h *handlers.Handlers,
+	sess *session.Session,
+	webhookID, query string,
+) string {
+	t.Helper()
+
 	req := httptest.NewRequestWithContext(
 		context.Background(),
 		http.MethodGet,
-		"/source/"+webhookID+"/logs",
+		"/source/"+webhookID+"/logs"+query,
 		nil,
 	)
 

internal/handlers/source_management.go

@@ -777,9 +777,18 @@ func (h *Handlers) HandleSourceLogs() http.HandlerFunc {
 			totalPages++
 		}
 
+		// The banner a replay POST redirected back with. The
+		// message comes from a fixed set keyed by the outcome
+		// code, never from the query string itself.
+		replayMsg, replayOK := replayOutcome(
+			r.URL.Query().Get(replayOutcomeParam),
+		)
+
 		data := map[string]any{
 			tmplKeyWebhook:  &webhook,
 			"Events":        evts,
+			"ReplayMessage": replayMsg,
+			"ReplayQueued":  replayOK,
 			"Page":          page,
 			"TotalPages":    totalPages,
 			"TotalEvents":   total,

internal/metrics/metrics.go

@@ -82,6 +82,7 @@ type Set struct {
 	deliveriesSucceeded *prometheus.CounterVec
 	deliveriesFailed    *prometheus.CounterVec
 	deliveryRetries     *prometheus.CounterVec
+	deliveryReplays     *prometheus.CounterVec
 	deliveryDuration    *prometheus.HistogramVec
 	deliveriesPending   *prometheus.GaugeVec
 	deliveriesRetrying  *prometheus.GaugeVec
@@ -149,6 +150,22 @@ func (s *Set) ObserveDeliveryDuration(
 		Observe(d.Seconds())
 }
 
+// DeliveryReplayed counts one delivery an operator replayed from the
+// event log.
+//
+// A replay runs the ordinary engine path, so it already moves the
+// attempt, outcome and duration series exactly as a first delivery
+// does — deliberately, since a replay is a real delivery and hiding it
+// from those would misreport the pipeline. This counter is the one
+// place the two are distinguishable, and it carries the existing
+// target-type label rather than adding a replay dimension to every
+// other series.
+func (s *Set) DeliveryReplayed(t database.TargetType) {
+	s.deliveryReplays.
+		WithLabelValues(normalizeTargetType(t)).
+		Inc()
+}
+
 // DeliveryStatusChanged counts a delivery's transition into a new
 // status. The mapping from status to counter lives here, next to the
 // collectors, so the engine has a single call for every transition it
@@ -271,6 +288,16 @@ func (s *Set) registerCounters(factory promauto.Factory) {
 		},
 		[]string{targetTypeLabel},
 	)
+
+	s.deliveryReplays = factory.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: namespace,
+			Name:      "delivery_replays_total",
+			Help: "Deliveries an operator replayed from the " +
+				"event log, by target type.",
+		},
+		[]string{targetTypeLabel},
+	)
 }
 
 func (s *Set) registerGauges(factory promauto.Factory) {
@@ -322,6 +349,7 @@ func (s *Set) initSeries() {
 		s.deliveriesSucceeded.WithLabelValues(label)
 		s.deliveriesFailed.WithLabelValues(label)
 		s.deliveryRetries.WithLabelValues(label)
+		s.deliveryReplays.WithLabelValues(label)
 		s.deliveriesPending.WithLabelValues(label)
 		s.deliveriesRetrying.WithLabelValues(label)
 		s.circuitBreakersOpen.WithLabelValues(label)

internal/middleware/ratelimit.go

@@ -34,6 +34,16 @@ const (
 	// password change rate limit.
 	passwordChangeRateInterval = 1 * time.Minute
 
+	// replayRateLimit is the maximum number of delivery replays one
+	// client may queue per interval. Each replay puts a delivery on
+	// the engine's queue, so without a ceiling one operator holding
+	// the button down — or scripting it — queues unbounded outbound
+	// work. It sits far above any rate a person clicks at.
+	replayRateLimit = 30
+
+	// replayRateInterval is the time window for the replay limit.
+	replayRateInterval = 1 * time.Minute
+
 	// receiverRateInterval is the time window for the webhook
 	// receiver rate limit. The configured limit is expressed in
 	// requests per minute.
@@ -290,6 +300,21 @@ func (m *Middleware) PasswordChangeRateLimit() func(http.Handler) http.Handler {
 	)
 }
 
+// ReplayRateLimit returns middleware that enforces per-IP rate
+// limiting on delivery replays.
+//
+// Like the password-change limit it is spent on arrival, which is safe
+// for the same reason: RequireAuth runs ahead of it, so only a request
+// already carrying a valid session can reach the bucket.
+func (m *Middleware) ReplayRateLimit() func(http.Handler) http.Handler {
+	return m.postRateLimit(
+		replayRateLimit,
+		replayRateInterval,
+		"delivery replay rate limit exceeded",
+		"Too many replays. Please try again later.",
+	)
+}
+
 // postRateLimit builds middleware that enforces a per-IP rate
 // limit on POST requests only; all other methods pass through
 // unaffected. Requests over the limit receive a 429 with the

internal/server/routes.go

@@ -201,6 +201,18 @@ func (s *Server) setupSourceRoutes() {
 			"/logs/{eventID}/body",
 			s.h.HandleEventBodyDownload(),
 		)
+		// Replay is the one page action that queues outbound work:
+		// it creates a delivery from a stored event and hands it to
+		// the delivery engine. The rate limit is what bounds a
+		// held-down button or a scripted loop; the handler
+		// separately refuses a replay while an earlier one for the
+		// same event and target is still in flight. POST only, so
+		// the action cannot be taken by a link, a prefetch or an
+		// image tag.
+		r.With(s.mw.ReplayRateLimit()).Post(
+			"/deliveries/{deliveryID}/replay",
+			s.h.HandleDeliveryReplay(),
+		)
 		r.Post(
 			"/entrypoints",
 			s.h.HandleEntrypointCreate(),

internal/server/routes_test.go

@@ -310,6 +310,75 @@ func (e *testEnv) seedEvent(
 	return event
 }
 
+// seedTarget creates an active HTTP target for a webhook.
+func (e *testEnv) seedTarget(
+	t *testing.T,
+	webhookID string,
+) *database.Target {
+	t.Helper()
+
+	tgt := &database.Target{
+		WebhookID: webhookID,
+		Name:      "routed-target",
+		Type:      database.TargetTypeHTTP,
+		Active:    true,
+		Config:    `{"url":"http://93.184.216.34/hook"}`,
+	}
+
+	require.NoError(
+		t,
+		e.db.DB().Omit(clause.Associations).Create(tgt).Error,
+	)
+
+	return tgt
+}
+
+// seedFailedDelivery records a terminally failed delivery of an event
+// to a target in the webhook's own database.
+func (e *testEnv) seedFailedDelivery(
+	t *testing.T,
+	webhookID, eventID, targetID string,
+) *database.Delivery {
+	t.Helper()
+
+	webhookDB, err := e.dbMgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	dlv := &database.Delivery{
+		EventID:  eventID,
+		TargetID: targetID,
+		Status:   database.DeliveryStatusFailed,
+	}
+
+	require.NoError(
+		t,
+		webhookDB.Omit(clause.Associations).Create(dlv).Error,
+	)
+
+	return dlv
+}
+
+// countDeliveries reports how many deliveries a webhook's database
+// holds.
+func (e *testEnv) countDeliveries(
+	t *testing.T, webhookID string,
+) int64 {
+	t.Helper()
+
+	webhookDB, err := e.dbMgr.GetDB(webhookID)
+	require.NoError(t, err)
+
+	var count int64
+
+	require.NoError(
+		t,
+		webhookDB.Model(&database.Delivery{}).
+			Count(&count).Error,
+	)
+
+	return count
+}
+
 // storedHash reads the current password hash for a username.
 func (e *testEnv) storedHash(t *testing.T, username string) string {
 	t.Helper()
@@ -674,6 +743,85 @@ func TestSourceLogsBody_OtherUser404s(t *testing.T) {
 	assert.Equal(t, "/pages/login", anon.Header().Get("Location"))
 }
 
+// TestDeliveryReplay_PostOnlyAndCSRFProtected walks the replay action
+// through the production router rather than a forged route context,
+// which is the only way to prove what the route group actually gives
+// it: a GET cannot trigger a replay, an unauthenticated request never
+// reaches the handler, a POST without the token is refused by CSRF,
+// and the form the template emits — token and action URL both — works
+// as rendered.
+func TestDeliveryReplay_PostOnlyAndCSRFProtected(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	userID, _ := env.seedUser(t, "replayer", "somepassword")
+	cookies := env.authCookies(t, userID, "replayer")
+
+	wh := env.seedWebhook(t, userID)
+	tgt := env.seedTarget(t, wh.ID)
+	evt := env.seedEvent(t, wh.ID, `{"replay":"me"}`)
+	dlv := env.seedFailedDelivery(t, wh.ID, evt.ID, tgt.ID)
+
+	path := "/source/" + wh.ID + "/deliveries/" + dlv.ID +
+		"/replay"
+
+	assert.Equal(
+		t, http.StatusMethodNotAllowed,
+		env.get(path, cookies).Code,
+		"a replay must not be reachable by GET",
+	)
+
+	assert.Equal(
+		t, http.StatusForbidden,
+		env.post(path, url.Values{}, cookies).Code,
+		"a replay POST without a CSRF token must be refused",
+	)
+
+	anon := env.post(path, url.Values{}, nil)
+	assert.Equal(t, http.StatusForbidden, anon.Code)
+
+	require.Equal(
+		t, int64(1), env.countDeliveries(t, wh.ID),
+		"no refused request may have created a delivery",
+	)
+
+	// The token and the action URL both come out of the rendered
+	// page, so a typo in either the route pattern or the template
+	// fails here.
+	logsPath := "/source/" + wh.ID + "/logs"
+
+	token, cookies := env.csrfFrom(t, logsPath, cookies)
+
+	page := env.get(logsPath, cookies)
+	require.Equal(t, http.StatusOK, page.Code)
+
+	action := regexp.MustCompile(
+		`action="(/source/[^"]+/replay)"`,
+	).FindStringSubmatch(page.Body.String())
+	require.Len(
+		t, action, 2,
+		"a finished delivery should render a replay form",
+	)
+
+	form := url.Values{}
+	form.Set("csrf_token", token)
+
+	w := env.post(
+		html.UnescapeString(action[1]), form, cookies,
+	)
+
+	require.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(
+		t, logsPath+"?replay=queued",
+		w.Header().Get("Location"),
+	)
+	assert.Equal(
+		t, int64(2), env.countDeliveries(t, wh.ID),
+		"the replay appends a delivery",
+	)
+}
+
 // metricsConfig is a Config differing from the routing default only
 // in the two /metrics credentials.
 func metricsConfig(

templates/source_logs.html

@@ -12,6 +12,10 @@
         </div>
     </div>
 
+    {{if .ReplayMessage}}
+    <div class="{{if .ReplayQueued}}alert-success{{else}}alert-error{{end}}">{{.ReplayMessage}}</div>
+    {{end}}
+
     <div class="card">
         <div class="divide-y divide-gray-100">
             {{range .Events}}
@@ -40,6 +44,23 @@
                     {{if .BodyTruncated}}
                     <p class="mt-2 text-xs text-gray-500">Body truncated for display: showing {{.BodyShownBytes}} of {{.BodyBytes}} bytes. The stored body is unchanged &mdash; <a href="/source/{{$.Webhook.ID}}/logs/{{.ID}}/body" class="text-primary-600 hover:text-primary-700 underline">download the full body</a>.</p>
                     {{end}}
+
+                    {{if .Deliveries}}
+                    <div class="mt-3 pt-4 border-t border-gray-200">
+                        {{range .Deliveries}}
+                        <div class="flex items-center justify-between py-2 text-xs text-gray-700">
+                            <span><span class="font-medium">{{.Target.Name}}</span>: {{.Status}}</span>
+                            {{if .Status.Terminal}}
+                            <form method="POST" action="/source/{{$.Webhook.ID}}/deliveries/{{.ID}}/replay" class="inline">
+                                <input type="hidden" name="csrf_token" value="{{$.CSRFToken}}">
+                                <input type="hidden" name="page" value="{{$.Page}}">
+                                <button type="submit" class="text-xs text-primary-600 hover:text-primary-700" title="Send this event to the target again">Replay</button>
+                            </form>
+                            {{end}}
+                        </div>
+                        {{end}}
+                    </div>
+                    {{end}}
                 </div>
             </div>
             {{else}}