Check every statement in the webhook deletion transaction (closes #262)

deleteWebhookResources issued three deletes without checking any of
them. A failing delete sets .Error on the returned session but leaves
the transaction usable, so the handler committed whatever succeeded,
redirected to /sources as though deletion had worked, and then
hard-deleted the per-webhook event database anyway. A webhook could
end up with its entrypoints or targets still in the main database and
its entire event history permanently gone, reported as a success.

The transaction moves into commitWebhookDeletion, which checks each
statement and rolls back on any failure, matching commitWebhook in the
same file. deleteWebhookResources reports the failure with
h.serverError and leaves the event database alone.

The configuration commit deliberately precedes DeleteDB: no
transaction spans SQLite and the filesystem, and a failure after the
commit leaves an unreferenced event database file, which the operator
can remove, rather than destroying history for a webhook that still
exists. That failure is reported with h.serverError too instead of a
success redirect.

internal/handlers/source_delete_test.go

@@ -2,6 +2,7 @@ package handlers_test
 
 import (
 	"context"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -11,6 +12,7 @@ import (
 	"github.com/go-chi/chi"
 	"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/handlers"
@@ -73,6 +75,77 @@ func seedTarget(
 	return tgt
 }
 
+// errInjectedDelete is the failure failDeleteOnTable reports
+// from a delete statement.
+var errInjectedDelete = errors.New("injected delete failure")
+
+// seedEntrypoint inserts an entrypoint for a webhook.
+func seedEntrypoint(
+	t *testing.T,
+	db *database.Database,
+	webhookID string,
+) {
+	t.Helper()
+
+	ep := &database.Entrypoint{
+		WebhookID: webhookID,
+		Path:      "ep-" + webhookID,
+		Active:    true,
+	}
+
+	require.NoError(
+		t,
+		db.DB().Omit(clause.Associations).Create(ep).Error,
+	)
+}
+
+// countRows counts the live (not soft-deleted) rows of a model
+// matching column = value.
+func countRows(
+	t *testing.T,
+	db *database.Database,
+	model any,
+	column, value string,
+) int64 {
+	t.Helper()
+
+	var n int64
+
+	require.NoError(
+		t,
+		db.DB().Model(model).
+			Where(column+" = ?", value).
+			Count(&n).Error,
+	)
+
+	return n
+}
+
+// failDeleteOnTable makes every delete against the named table
+// fail the way a database-level error does: the statement
+// reports an error but leaves the surrounding transaction
+// usable, so a caller that does not check it can go on to
+// commit the statements that did succeed.
+func failDeleteOnTable(
+	t *testing.T,
+	db *database.Database,
+	table string,
+) {
+	t.Helper()
+
+	require.NoError(t, db.DB().Callback().Delete().
+		Before("gorm:delete").
+		Register(
+			"test:fail_delete_"+table,
+			func(tx *gorm.DB) {
+				if tx.Statement.Table == table {
+					_ = tx.AddError(errInjectedDelete)
+				}
+			},
+		),
+	)
+}
+
 // archivePathFor returns the archive database path the
 // delivery engine would use for a webhook: beside the webhook's
 // event database in the data directory.
@@ -209,6 +282,159 @@ func TestHandleSourceDelete_KeepsArchiveFile(t *testing.T) {
 	)
 }
 
+// TestHandleSourceDelete_FailedDeleteKeepsEverything proves
+// that a failing delete statement loses nothing: the
+// configuration is rolled back whole, the event database
+// survives, and the operator is told the deletion failed
+// instead of being redirected as though it worked.
+func TestHandleSourceDelete_FailedDeleteKeepsEverything(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	var (
+		h    *handlers.Handlers
+		sess *session.Session
+		db   *database.Database
+		mgr  *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &mgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	seedEntrypoint(t, db, wh.ID)
+	seedTarget(t, db, wh.ID, database.TargetTypeDatabase)
+
+	require.NoError(t, mgr.CreateDB(wh.ID))
+
+	eventDBPath := mgr.DBPath(wh.ID)
+	require.FileExists(t, eventDBPath)
+
+	// The entrypoint delete runs first and succeeds; the target
+	// delete then fails, which is what the whole transaction has
+	// to be rolled back over.
+	failDeleteOnTable(t, db, "targets")
+
+	cookies := authenticatedCookies(
+		t, sess, deleteTestUserID, deleteTestUsername,
+	)
+
+	req := postRequest(
+		"/source/"+wh.ID+"/delete",
+		cookies,
+		map[string]string{paramSourceID: wh.ID},
+	)
+	w := httptest.NewRecorder()
+
+	h.HandleSourceDelete().ServeHTTP(w, req)
+
+	assert.Equal(
+		t, http.StatusInternalServerError, w.Code,
+		"a failed deletion must be reported, not redirected",
+	)
+	assert.Empty(
+		t, w.Header().Get("Location"),
+		"a failed deletion must not redirect to /sources",
+	)
+
+	assert.Equal(
+		t, int64(1),
+		countRows(t, db, &database.Webhook{}, "id", wh.ID),
+		"the webhook must survive a failed deletion",
+	)
+	assert.Equal(
+		t, int64(1),
+		countRows(
+			t, db, &database.Entrypoint{}, "webhook_id", wh.ID,
+		),
+		"the entrypoint delete must be rolled back",
+	)
+	assert.Equal(
+		t, int64(1),
+		countRows(
+			t, db, &database.Target{}, "webhook_id", wh.ID,
+		),
+		"the target must survive a failed deletion",
+	)
+
+	assert.FileExists(
+		t, eventDBPath,
+		"event history must not be destroyed when the "+
+			"configuration delete did not commit",
+	)
+}
+
+// TestHandleSourceDelete_RemovesConfigAndEventDatabase is the
+// positive control for the rollback above: an ordinary deletion
+// still removes the webhook, its children and its event
+// database.
+func TestHandleSourceDelete_RemovesConfigAndEventDatabase(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	var (
+		h    *handlers.Handlers
+		sess *session.Session
+		db   *database.Database
+		mgr  *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &mgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	seedEntrypoint(t, db, wh.ID)
+	seedTarget(t, db, wh.ID, database.TargetTypeDatabase)
+
+	require.NoError(t, mgr.CreateDB(wh.ID))
+
+	eventDBPath := mgr.DBPath(wh.ID)
+	require.FileExists(t, eventDBPath)
+
+	cookies := authenticatedCookies(
+		t, sess, deleteTestUserID, deleteTestUsername,
+	)
+
+	req := postRequest(
+		"/source/"+wh.ID+"/delete",
+		cookies,
+		map[string]string{paramSourceID: wh.ID},
+	)
+	w := httptest.NewRecorder()
+
+	h.HandleSourceDelete().ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(t, "/sources", w.Header().Get("Location"))
+
+	assert.Equal(
+		t, int64(0),
+		countRows(t, db, &database.Webhook{}, "id", wh.ID),
+	)
+	assert.Equal(
+		t, int64(0),
+		countRows(
+			t, db, &database.Entrypoint{}, "webhook_id", wh.ID,
+		),
+	)
+	assert.Equal(
+		t, int64(0),
+		countRows(
+			t, db, &database.Target{}, "webhook_id", wh.ID,
+		),
+	)
+	assert.NoFileExists(
+		t, eventDBPath,
+		"a successful deletion removes the event database",
+	)
+}
+
 // TestHandleTargetDelete_EvictsWhenLastDatabaseTargetGone
 // proves that removing the last database target releases the
 // archive writer.