Pin the HTTP target's unpinned error checks (closes #285)

withRetry's check on a failed result write could be removed with
every test still passing, and so could six other error checks in
target_http.go. Each now has a test that fails without it: the
circuit breaker learning a failed send whose result went unrecorded,
the result write for an invalid config, building the request,
reading the response body, decoding the target config, and decoding
the stored inbound headers.

The two backoff lookups' error checks stay unpinned: without them a
failed lookup leaves a zero time, which gives the same answer, so no
test can tell the difference.

Model: opus-5-5

internal/delivery/engine_integration_test.go

@@ -1425,6 +1425,32 @@ func TestDeliverHTTP_InvalidConfig(t *testing.T) {
 	)
 }
 
+// TestDeliverHTTP_InvalidConfigUnrecordedStaysPending: a delivery is
+// failed for an invalid config only once the reason is recorded.
+// Unrecorded, it stays pending, where the sweep finds it again.
+func TestDeliverHTTP_InvalidConfigUnrecordedStaysPending(t *testing.T) {
+	t.Parallel()
+
+	db := testWebhookDB(t)
+	e := testEngine(t, 1)
+
+	event, del := iSeedEventAndDelivery(
+		t, db, `{"config":"invalid"}`, "",
+	)
+
+	task, d := iHTTPTaskAndDelivery(
+		event, del, "bad-config", `not-json`, 0, 1,
+	)
+
+	require.NoError(t, db.Exec("drop table delivery_results").Error)
+
+	e.ExportDeliverHTTP(context.TODO(), db, d, task)
+
+	iAssertStatus(t, db, del.ID,
+		database.DeliveryStatusPending,
+	)
+}
+
 // --- Notify batching ---
 
 func TestNotify_MultipleTasks(t *testing.T) {

internal/delivery/engine_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"io"
 	"log/slog"
 	"net/http"
 	"net/http/httptest"
@@ -1056,6 +1057,21 @@ func TestParseHTTPConfig_MissingURL(t *testing.T) {
 	)
 }
 
+func TestParseHTTPConfig_Undecodable(t *testing.T) {
+	t.Parallel()
+
+	e := testEngine(t, 1)
+
+	_, err := e.ExportParseHTTPConfig(
+		`{"url":"https://example.com/hook","timeout":"soon"}`,
+	)
+
+	assert.Error(t, err,
+		"config that does not decode should return error, "+
+			"even when the part that did names a URL",
+	)
+}
+
 func TestScheduleRetry_SendsToRetryChannel(
 	t *testing.T,
 ) {
@@ -1241,6 +1257,33 @@ func TestDoHTTPRequest_ForwardsHeaders(t *testing.T) {
 	)
 }
 
+// A response that ends before the length it announced is an error, not
+// a short body.
+func TestDoHTTPRequest_CutShortResponseIsAnError(t *testing.T) {
+	t.Parallel()
+
+	ts := httptest.NewServer(
+		http.HandlerFunc(
+			func(w http.ResponseWriter, _ *http.Request) {
+				w.Header().Set("Content-Length", "100")
+				_, _ = w.Write([]byte("cut short"))
+			},
+		),
+	)
+	defer ts.Close()
+
+	e := testEngine(t, 1)
+
+	_, body, _, err := e.ExportDoHTTPRequest(
+		context.TODO(),
+		&delivery.HTTPTargetConfig{URL: ts.URL},
+		&database.Event{},
+	)
+
+	require.ErrorIs(t, err, io.ErrUnexpectedEOF)
+	assert.Empty(t, body)
+}
+
 // The event's stored inbound headers carry the same Content-Type the
 // receiver saved as the event's ContentType, so a delivery could send
 // it twice. It must go out exactly once, with a Content-Type configured
@@ -1317,6 +1360,34 @@ func TestApplyRequestHeaders_SendsOneContentType(t *testing.T) {
 	}
 }
 
+// Stored inbound headers that do not decode forward nothing, not the
+// part of them that happened to decode.
+func TestApplyRequestHeaders_UndecodableInboundForwardsNothing(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	req, err := http.NewRequestWithContext(
+		context.Background(),
+		http.MethodPost,
+		"https://target.example.com/hook",
+		http.NoBody,
+	)
+	require.NoError(t, err)
+
+	names := delivery.ExportApplyRequestHeaders(
+		req,
+		&database.Event{
+			Headers: `{"X-Custom":["value1"],"X-Broken":"not a list"}`,
+		},
+		&delivery.HTTPTargetConfig{},
+		"webhooker/dev",
+	)
+
+	assert.Empty(t, names)
+	assert.Empty(t, req.Header.Get("X-Custom"))
+}
+
 func TestProcessDelivery_RoutesToCorrectHandler(
 	t *testing.T,
 ) {

internal/delivery/recovery_durability_test.go

@@ -376,3 +376,90 @@ func TestFailedResultWriteLeavesDeliveryRecoverable(
 		database.DeliveryStatusPending,
 	)
 }
+
+// TestFailedResultWriteWithRetriesLeavesDeliveryRecoverable is the same
+// rule for a target with retries: whatever the receiver answered, the
+// delivery stays pending and no retry is scheduled. The circuit breaker
+// still learns the answer, because it describes the target's health,
+// not the database's.
+func TestFailedResultWriteWithRetriesLeavesDeliveryRecoverable(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	tests := []struct {
+		name        string
+		answer      int
+		wantBreaker delivery.CircuitState
+	}{
+		{"send succeeded", http.StatusOK, delivery.CircuitClosed},
+		{"send failed", http.StatusBadGateway, delivery.CircuitOpen},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			s := newISetup(t)
+			targetID := uuid.New().String()
+
+			ts := httptest.NewServer(http.HandlerFunc(
+				func(w http.ResponseWriter, _ *http.Request) {
+					w.WriteHeader(tc.answer)
+				},
+			))
+			defer ts.Close()
+
+			event := iSeedEvent(
+				t, s.WebhookDB, s.WebhookID, `{"unwritable":true}`,
+			)
+
+			d := iSeedDelivery(
+				t, s.WebhookDB, event.ID, targetID,
+				database.DeliveryStatusPending,
+			)
+
+			require.NoError(
+				t,
+				s.WebhookDB.Exec("drop table delivery_results").Error,
+			)
+
+			// A single failure opens this breaker.
+			cb := delivery.NewTestCircuitBreaker(1, time.Minute)
+			s.Engine.ExportSetCircuitBreaker(targetID, cb)
+
+			full := &database.Delivery{
+				EventID:  event.ID,
+				TargetID: targetID,
+				Status:   database.DeliveryStatusPending,
+				Event:    event,
+				Target: database.Target{
+					Name:       "unwritable",
+					Type:       database.TargetTypeHTTP,
+					Config:     iHTTPConfig(ts.URL),
+					MaxRetries: 3,
+				},
+			}
+			full.ID = d.ID
+
+			sched := &recordingScheduler{}
+
+			s.Engine.ExportDeliverHTTPWithScheduler(
+				context.Background(), s.WebhookDB, full,
+				&delivery.Task{
+					DeliveryID: d.ID,
+					TargetID:   targetID,
+					AttemptNum: 1,
+				},
+				sched,
+			)
+
+			iAssertStatus(
+				t, s.WebhookDB, d.ID,
+				database.DeliveryStatusPending,
+			)
+			assert.Empty(t, sched.delays, "no retry may be scheduled")
+			assert.Equal(t, tc.wantBreaker, cb.State())
+		})
+	}
+}

internal/delivery/url_mask_test.go

@@ -179,6 +179,27 @@ func TestDoHTTPRequest_TransportErrorMasksURL(t *testing.T) {
 	)
 }
 
+// TestDoHTTPRequest_UnparsableURLIsMasked is the same for an HTTP
+// target URL that no request can be built from.
+func TestDoHTTPRequest_UnparsableURLIsMasked(t *testing.T) {
+	t.Parallel()
+
+	e := testEngine(t, 1)
+
+	statusCode, _, _, reqErr := e.ExportDoHTTPRequest(
+		context.TODO(),
+		&delivery.HTTPTargetConfig{
+			URL: "https://hooks.example.com" + maskSecretPath + "\n",
+		},
+		&database.Event{},
+	)
+	require.Error(t, reqErr)
+	assert.Zero(t, statusCode)
+
+	assertNoCredential(t, reqErr.Error())
+	assert.Contains(t, reqErr.Error(), "invalid control character")
+}
+
 // TestValidateTargetURL_UnparsableURLIsMasked proves the SSRF
 // validator's error does not carry the submitted URL, which
 // the handler both logs and shows.