fix(docker): migrate retained SearXNG settings

docker-compose.gpu-amd.yml

@@ -129,12 +129,17 @@ services:
           fi
           sed "s|__SEARXNG_SECRET__|$$secret|g" /tmp/searxng-settings.yml.template > /etc/searxng/settings.yml
         fi
+        # Advisory: a settings file the migration cannot parse or rewrite must
+        # not be what stops searxng from booting. It explains itself on stderr
+        # and we carry on, letting searxng report anything genuinely wrong.
+        /usr/local/searxng/.venv/bin/python /tmp/migrate-searxng-settings.py /etc/searxng/settings.yml || true
         exec /usr/local/searxng/entrypoint.sh
     ports:
       - "127.0.0.1:8080:8080"
     volumes:
       - searxng-data:/etc/searxng
       - ./config/searxng/settings.yml:/tmp/searxng-settings.yml.template:ro,z
+      - ./scripts/migrate_searxng_settings.py:/tmp/migrate-searxng-settings.py:ro,z
     environment:
       - SEARXNG_BASE_URL=http://localhost:8080/
       - SEARXNG_SECRET=${SEARXNG_SECRET:-}

docker-compose.gpu-nvidia.yml

@@ -132,12 +132,17 @@ services:
           fi
           sed "s|__SEARXNG_SECRET__|$$secret|g" /tmp/searxng-settings.yml.template > /etc/searxng/settings.yml
         fi
+        # Advisory: a settings file the migration cannot parse or rewrite must
+        # not be what stops searxng from booting. It explains itself on stderr
+        # and we carry on, letting searxng report anything genuinely wrong.
+        /usr/local/searxng/.venv/bin/python /tmp/migrate-searxng-settings.py /etc/searxng/settings.yml || true
         exec /usr/local/searxng/entrypoint.sh
     ports:
       - "127.0.0.1:8080:8080"
     volumes:
       - searxng-data:/etc/searxng
       - ./config/searxng/settings.yml:/tmp/searxng-settings.yml.template:ro,z
+      - ./scripts/migrate_searxng_settings.py:/tmp/migrate-searxng-settings.py:ro,z
     environment:
       - SEARXNG_BASE_URL=http://localhost:8080/
       - SEARXNG_SECRET=${SEARXNG_SECRET:-}

docker-compose.yml

@@ -110,12 +110,17 @@ services:
           fi
           sed "s|__SEARXNG_SECRET__|$$secret|g" /tmp/searxng-settings.yml.template > /etc/searxng/settings.yml
         fi
+        # Advisory: a settings file the migration cannot parse or rewrite must
+        # not be what stops searxng from booting. It explains itself on stderr
+        # and we carry on, letting searxng report anything genuinely wrong.
+        /usr/local/searxng/.venv/bin/python /tmp/migrate-searxng-settings.py /etc/searxng/settings.yml || true
         exec /usr/local/searxng/entrypoint.sh
     ports:
       - "127.0.0.1:8080:8080"
     volumes:
       - searxng-data:/etc/searxng
       - ./config/searxng/settings.yml:/tmp/searxng-settings.yml.template:ro,z
+      - ./scripts/migrate_searxng_settings.py:/tmp/migrate-searxng-settings.py:ro,z
     environment:
       - SEARXNG_BASE_URL=http://localhost:8080/
       - SEARXNG_SECRET=${SEARXNG_SECRET:-}

scripts/migrate_searxng_settings.py

@@ -0,0 +1,166 @@
+#!/usr/bin/env python3
+"""Make retained SearXNG settings inherit defaults without replacing them."""
+
+from __future__ import annotations
+
+import os
+import stat
+import sys
+import tempfile
+from pathlib import Path
+
+import yaml
+from yaml.nodes import MappingNode
+from yaml.tokens import BlockMappingStartToken, FlowMappingStartToken
+
+
+_UTF8_BOM = b"\xef\xbb\xbf"
+
+
+def _parse_root_mapping(text: str) -> tuple[MappingNode | None, dict]:
+    """Parse settings with the same safe YAML semantics SearXNG uses."""
+    try:
+        loaded = yaml.safe_load(text)
+        node = yaml.compose(text, Loader=yaml.SafeLoader)
+    except yaml.YAMLError:
+        raise ValueError("settings file is not valid single-document YAML") from None
+
+    if loaded is None and node is None:
+        return None, {}
+    if not isinstance(loaded, dict) or not isinstance(node, MappingNode):
+        raise ValueError("settings root is not a mapping")
+    return node, loaded
+
+
+def _flow_mapping_start(text: str) -> int:
+    """Return the root flow mapping's opening-brace character offset."""
+    try:
+        for token in yaml.scan(text, Loader=yaml.SafeLoader):
+            if isinstance(token, FlowMappingStartToken):
+                return token.start_mark.index
+    except yaml.YAMLError:
+        pass
+    raise ValueError("flow-style settings mapping has no opening brace")
+
+
+def _newline_for(contents: bytes) -> bytes:
+    first_lf = contents.find(b"\n")
+    if first_lf > 0 and contents[first_lf - 1 : first_lf + 1] == b"\r\n":
+        return b"\r\n"
+    return b"\n"
+
+
+def _block_mapping_position(text: str, root: MappingNode | None) -> tuple[int, int]:
+    """Return a safe character offset and indent for a root block mapping key."""
+    if root is None:
+        return len(text), 0
+
+    try:
+        for token in yaml.scan(text, Loader=yaml.SafeLoader):
+            if not isinstance(token, BlockMappingStartToken):
+                continue
+            line_start = token.start_mark.index - token.start_mark.column
+            if not text[line_start : token.start_mark.index].strip():
+                return line_start, token.start_mark.column
+            return root.end_mark.index, token.start_mark.column
+    except yaml.YAMLError:
+        pass
+    return root.end_mark.index, root.start_mark.column
+
+
+def _add_block_default_inheritance(
+    contents: bytes, text: str, root: MappingNode | None
+) -> bytes:
+    newline = _newline_for(contents)
+    character_offset, indent_width = _block_mapping_position(text, root)
+    bom_length = len(_UTF8_BOM) if contents.startswith(_UTF8_BOM) else 0
+    offset = bom_length + len(text[:character_offset].encode("utf-8"))
+    separator = b""
+    if offset not in (0, bom_length) and not contents[:offset].endswith((b"\n", b"\r")):
+        separator = newline
+    addition = (
+        separator
+        + b" " * indent_width
+        + b"use_default_settings: true"
+        + newline
+    )
+    return contents[:offset] + addition + contents[offset:]
+
+
+def migrate_settings(path: Path) -> bool:
+    """Add the missing inheritance key atomically; return whether the file changed."""
+    source_stat = path.lstat()
+    if not stat.S_ISREG(source_stat.st_mode):
+        raise ValueError(f"settings path is not a regular file: {path}")
+
+    contents = path.read_bytes()
+    if not contents:
+        return False
+
+    text = contents.decode("utf-8-sig")
+    root, loaded = _parse_root_mapping(text)
+    if "use_default_settings" in loaded:
+        return False
+
+    if root is not None and root.flow_style:
+        start = _flow_mapping_start(text)
+        bom_length = len(_UTF8_BOM) if contents.startswith(_UTF8_BOM) else 0
+        offset = bom_length + len(text[: start + 1].encode("utf-8"))
+        separator = b", " if root.value else b""
+        updated = (
+            contents[:offset]
+            + b"use_default_settings: true"
+            + separator
+            + contents[offset:]
+        )
+    else:
+        updated = _add_block_default_inheritance(contents, text, root)
+    fd, temporary_name = tempfile.mkstemp(
+        prefix=f".{path.name}.odysseus-", dir=path.parent
+    )
+    temporary = Path(temporary_name)
+    try:
+        # chmod before chown: the Compose cap set is `cap_drop: ALL` plus
+        # CHOWN/SETGID/SETUID/DAC_OVERRIDE, with no FOWNER. Once the temporary
+        # file belongs to searxng:searxng — which every retained settings file
+        # does, because searxng's entrypoint chowns /etc/searxng — root can no
+        # longer chmod it and the migration dies with EPERM.
+        os.fchmod(fd, stat.S_IMODE(source_stat.st_mode))
+        os.fchown(fd, source_stat.st_uid, source_stat.st_gid)
+        with os.fdopen(fd, "wb") as handle:
+            fd = -1
+            handle.write(updated)
+            handle.flush()
+            os.fsync(handle.fileno())
+        os.replace(temporary, path)
+        directory_fd = os.open(path.parent, os.O_RDONLY | os.O_DIRECTORY)
+        try:
+            os.fsync(directory_fd)
+        finally:
+            os.close(directory_fd)
+    finally:
+        if fd >= 0:
+            os.close(fd)
+        temporary.unlink(missing_ok=True)
+    return True
+
+
+def main(argv: list[str]) -> int:
+    if len(argv) > 2:
+        print(f"usage: {Path(argv[0]).name} [settings.yml]", file=sys.stderr)
+        return 2
+
+    path = Path(argv[1]) if len(argv) == 2 else Path("/etc/searxng/settings.yml")
+    try:
+        changed = migrate_settings(path)
+    except (OSError, UnicodeError, ValueError) as exc:
+        print(f"SearXNG settings migration failed: {exc}", file=sys.stderr)
+        return 1
+
+    if changed:
+        print("Added use_default_settings inheritance to retained SearXNG settings")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main(sys.argv))