fix(backup): detect the engine by its dump tool, not by the image name

36b2336 matched postgres and mariadb against the image's repository path. That name is not a property of the software: a dedicated Postgres inside an app's own stack is tagged <app>-database or postgis/postgis and carries no engine token at all, so it was never recognised, never dumped, and its data directory was copied as files without a single warning - the fallback notice hangs on found_db, which stayed false.

The container is now asked what it can run. pg_dumpall, mariadb-dump and mysqldump are probed by executing them, not by asking a shell for them, because a distroless image has no shell and would deny every tool it ships. The verdict is cached per image ID rather than per container, so replicas of one image cost a single probe.

Because the probe names the tool it found, the dump uses it instead of the hardcoded /usr/bin/mariadb-dump, which makes an image that ships only mysqldump dumpable rather than silently file-copied.

image_name and has_image are gone with their registry-host and tag stripping; the trap they worked around cannot occur when nothing reads the name. get_image_info stays, since the --images-* lists match exact references.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/e2e/test_e2e_engine_detection_by_tool.py

@@ -0,0 +1,177 @@
+"""The engine comes from the tools a container ships, not from its image name.
+
+Two containers in one backup run, each lying in one direction:
+
+* a real Postgres tagged `<prefix>-database`, the way a dedicated database is
+  built inside an app's own stack - no engine token anywhere in the name;
+* an Alpine tagged `postgres:<prefix>`, carrying the token without shipping a
+  single Postgres binary.
+
+Reading the name gets both wrong, and the second one fatally: pg_dump exits 127
+inside Alpine and takes the whole run with it.
+"""
+
+import unittest
+
+from .helpers import (
+    POSTGRES_DATA_DIR,
+    POSTGRES_IMAGE,
+    backup_path,
+    backup_run,
+    cleanup_docker,
+    create_minimal_compose_dir,
+    ensure_empty_dir,
+    latest_version_dir,
+    require_docker,
+    run,
+    unique,
+    wait_for_postgres,
+    write_databases_csv,
+)
+
+IMPOSTOR_BASE_IMAGE = "alpine:3.20"
+MARKER = "engine-detection-by-tool"
+
+
+class TestE2EEngineDetectionByTool(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls) -> None:
+        require_docker()
+        cls.prefix = unique("baudolo-e2e-engine-by-tool")
+        cls.backups_dir = f"/tmp/{cls.prefix}/Backups"
+        ensure_empty_dir(cls.backups_dir)
+        cls.compose_dir = create_minimal_compose_dir(f"/tmp/{cls.prefix}")
+        cls.repo_name = cls.prefix
+
+        cls.engine_image = f"{cls.prefix}-database:17"
+        cls.impostor_image = f"postgres:{cls.prefix}"
+
+        cls.engine_container = f"{cls.prefix}-engine"
+        cls.impostor_container = f"{cls.prefix}-impostor"
+        cls.engine_volume = f"{cls.prefix}-engine-vol"
+        cls.impostor_volume = f"{cls.prefix}-impostor-vol"
+
+        cls.containers = [cls.engine_container, cls.impostor_container]
+        cls.volumes = [cls.engine_volume, cls.impostor_volume]
+
+        run(["docker", "pull", POSTGRES_IMAGE])
+        run(["docker", "pull", IMPOSTOR_BASE_IMAGE])
+        run(["docker", "tag", POSTGRES_IMAGE, cls.engine_image])
+        run(["docker", "tag", IMPOSTOR_BASE_IMAGE, cls.impostor_image])
+        run(["docker", "volume", "create", cls.engine_volume])
+        run(["docker", "volume", "create", cls.impostor_volume])
+
+        run(
+            [
+                "docker",
+                "run",
+                "-d",
+                "--name",
+                cls.engine_container,
+                "-e",
+                "POSTGRES_PASSWORD=pgpw",
+                "-e",
+                "POSTGRES_DB=appdb",
+                "-e",
+                "POSTGRES_USER=postgres",
+                "-v",
+                f"{cls.engine_volume}:{POSTGRES_DATA_DIR}",
+                cls.engine_image,
+            ]
+        )
+        wait_for_postgres(cls.engine_container, user="postgres", timeout_s=90)
+        run(
+            [
+                "docker",
+                "exec",
+                cls.engine_container,
+                "sh",
+                "-lc",
+                (
+                    "psql -U postgres -d appdb -c "
+                    '"CREATE TABLE t (id int primary key, v text); '
+                    "INSERT INTO t VALUES (1,'ok');\""
+                ),
+            ]
+        )
+
+        run(
+            [
+                "docker",
+                "run",
+                "-d",
+                "--name",
+                cls.impostor_container,
+                "-v",
+                f"{cls.impostor_volume}:/data",
+                cls.impostor_image,
+                "sh",
+                "-lc",
+                f"echo '{MARKER}' > /data/marker.txt && sleep 3600",
+            ]
+        )
+
+        cls.databases_csv = f"/tmp/{cls.prefix}/databases.csv"
+        write_databases_csv(
+            cls.databases_csv,
+            [
+                (cls.engine_container, "appdb", "postgres", "pgpw"),
+                (cls.impostor_container, "appdb", "postgres", "pgpw"),
+            ],
+        )
+
+        backup_run(
+            backups_dir=cls.backups_dir,
+            repo_name=cls.repo_name,
+            compose_dir=cls.compose_dir,
+            databases_csv=cls.databases_csv,
+            database_containers=[cls.engine_container, cls.impostor_container],
+            images_no_stop_required=[cls.engine_image, cls.impostor_image],
+            only_sql=True,
+        )
+
+        cls.hash, cls.version = latest_version_dir(cls.backups_dir, cls.repo_name)
+
+    @classmethod
+    def tearDownClass(cls) -> None:
+        cleanup_docker(containers=cls.containers, volumes=cls.volumes)
+        run(["docker", "rmi", cls.engine_image], check=False)
+        run(["docker", "rmi", cls.impostor_image], check=False)
+
+    def _volume_dir(self, volume: str):
+        return backup_path(self.backups_dir, self.repo_name, self.version, volume)
+
+    def test_an_engine_without_an_engine_name_is_still_dumped(self) -> None:
+        dump = self._volume_dir(self.engine_volume) / "sql" / "appdb.backup.sql"
+        self.assertTrue(
+            dump.is_file(),
+            f"a Postgres tagged '{self.engine_image}' produced no dump at {dump}",
+        )
+        self.assertIn("Dumped by pg_dump", dump.read_text(encoding="utf-8"))
+
+    def test_an_engine_name_without_an_engine_is_not_dumped(self) -> None:
+        sql_dir = self._volume_dir(self.impostor_volume) / "sql"
+        dumps = list(sql_dir.glob("*.sql")) if sql_dir.exists() else []
+        self.assertEqual(
+            dumps,
+            [],
+            f"'{self.impostor_image}' ships no Postgres yet was dumped: {dumps}",
+        )
+
+    def test_the_recognised_engine_is_dumped_instead_of_copied(self) -> None:
+        files = self._volume_dir(self.engine_volume) / "files"
+        self.assertFalse(
+            files.exists(),
+            f"--only-sql still copied the engine's files to {files}",
+        )
+
+    def test_the_impostor_falls_through_to_a_file_backup(self) -> None:
+        files = self._volume_dir(self.impostor_volume) / "files"
+        self.assertTrue(files.is_dir(), f"expected a file backup at {files}")
+        self.assertEqual(
+            (files / "marker.txt").read_text(encoding="utf-8").strip(), MARKER
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()