Fix: cover zstd-rejection path and correct importer's zstd-hint message

Adds a command-level test exercising the real zstd-unavailable branch
in document_exporter, makes document_importer only append the
"zstd archives require Python 3.14+" hint when zstd is actually among
the unreadable codecs, and adds the lzma counterpart to the
stored-level-rejection test for symmetry.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/administration.md

@@ -272,6 +272,8 @@ optional arguments:
 -sm, --split-manifest
 -z,  --zip
 -zn, --zip-name
+--zip-compression
+--zip-compression-level
 --data-only
 --no-progress-bar
 --passphrase
@@ -334,6 +336,19 @@ If `-z` or `--zip` is provided, the export will be a zip file
 in the target directory, named according to the current local date or the
 value set in `-zn` or `--zip-name`.
 
+The compression method for the zip can be set with `--zip-compression`
+(`stored`, `deflated` (default), `bzip2`, `lzma`, or `zstd`) and tuned with
+`--zip-compression-level` (deflated: 0–9, bzip2: 1–9, zstd: -22–22; ignored
+for `stored` and `lzma`). Both options require `--zip`.
+
+!!! warning
+
+    `zstd` compression requires Python 3.14 or newer on **both** the machine
+    creating the export and any machine importing it. An archive compressed with
+    `zstd` (or `lzma`/`bzip2` where those modules are unavailable) cannot be
+    imported on a runtime that lacks the codec; the importer will refuse it with
+    a clear error. The default `deflated` is universally readable.
+
 If `--data-only` is provided, only the database will be exported. This option is intended
 to facilitate database upgrades without needing to clean documents and thumbnails from the media directory.
 

src/documents/export/compression.py

@@ -0,0 +1,108 @@
+from __future__ import annotations
+
+import importlib
+import zipfile
+
+# ZIP_ZSTANDARD exists only on Python 3.14+ (PEP 784). None elsewhere.
+ZSTD: int | None = getattr(zipfile, "ZIP_ZSTANDARD", None)
+
+# CLI choices are fixed across runtimes so argparse never hides zstd; runtime
+# availability is enforced separately in compression_available().
+COMPRESSION_CHOICES: tuple[str, ...] = (
+    "stored",
+    "deflated",
+    "bzip2",
+    "lzma",
+    "zstd",
+)
+
+# Method name -> zipfile compression constant (zstd only when supported).
+COMPRESSION_METHODS: dict[str, int] = {
+    "stored": zipfile.ZIP_STORED,
+    "deflated": zipfile.ZIP_DEFLATED,
+    "bzip2": zipfile.ZIP_BZIP2,
+    "lzma": zipfile.ZIP_LZMA,
+}
+if ZSTD is not None:
+    COMPRESSION_METHODS["zstd"] = ZSTD
+
+# Inclusive (min, max) level bounds per method; None => level not applicable.
+# Verified on CPython 3.14.3.
+#
+# zstd's raw library bounds are (-131072, 22)
+# (compression.zstd.CompressionParameter.compression_level.bounds()) — the
+# minimum is an internal implementation constant (-ZSTD_TARGETLENGTH_MAX),
+# not a meaningful distinct "level"; deeper negative values than -22 buy
+# nothing over -22 in practice. We expose the conventional zstd CLI range
+# instead of the raw library bounds.
+LEVEL_BOUNDS: dict[str, tuple[int, int] | None] = {
+    "stored": None,
+    "deflated": (0, 9),
+    "bzip2": (1, 9),
+    "lzma": None,
+    "zstd": (-22, 22),
+}
+
+# zipfile compress_type id -> method name. 93 = current zstd id, 20 = legacy
+# zstd id that zipfile can still read.
+_COMPRESS_TYPE_TO_METHOD: dict[int, str] = {
+    zipfile.ZIP_STORED: "stored",
+    zipfile.ZIP_DEFLATED: "deflated",
+    zipfile.ZIP_BZIP2: "bzip2",
+    zipfile.ZIP_LZMA: "lzma",
+    93: "zstd",
+    20: "zstd",
+}
+
+
+def compression_available(method: str) -> bool:
+    """Whether the running interpreter can actually use the given method."""
+    if method in ("stored", "deflated"):
+        # zlib is a hard CPython dependency; stored needs nothing.
+        return True
+    if method == "bzip2":
+        return _module_importable("bz2")
+    if method == "lzma":
+        return _module_importable("lzma")
+    if method == "zstd":
+        return ZSTD is not None and _module_importable("compression.zstd")
+    return False
+
+
+def _module_importable(name: str) -> bool:
+    try:
+        importlib.import_module(name)
+    except ImportError:
+        return False
+    return True
+
+
+def level_error(method: str, level: int | None) -> str | None:
+    """Return a human message if (method, level) is invalid, else None."""
+    if level is None:
+        return None
+    bounds = LEVEL_BOUNDS[method]
+    if bounds is None:
+        return f"--zip-compression-level has no effect for '{method}'"
+    low, high = bounds
+    if not (low <= level <= high):
+        return (
+            f"--zip-compression-level for '{method}' must be between {low} and {high}"
+        )
+    return None
+
+
+def compress_type_readable(compress_type: int) -> bool:
+    """Whether this interpreter can decompress an entry of the given type."""
+    method = _COMPRESS_TYPE_TO_METHOD.get(compress_type)
+    if method is None:
+        return False
+    return compression_available(method)
+
+
+def unreadable_method_names(compress_types: set[int]) -> set[str]:
+    """Map a set of compress_type ids to human method names for error messages."""
+    names: set[str] = set()
+    for ct in compress_types:
+        names.add(_COMPRESS_TYPE_TO_METHOD.get(ct, f"method {ct}"))
+    return names

src/documents/export/sinks.py

@@ -239,11 +239,21 @@ class ZipExportSink(ExportSink):
     added as an entry at finalize (a zip entry cannot be interleaved with others).
     """
 
-    def __init__(self, target: Path, zip_name: str, *, delete: bool = False) -> None:
+    def __init__(
+        self,
+        target: Path,
+        zip_name: str,
+        *,
+        delete: bool = False,
+        compression: int = zipfile.ZIP_DEFLATED,
+        compresslevel: int | None = None,
+    ) -> None:
         self._target = target.resolve()
         self._zip_path = (self._target / zip_name).with_suffix(".zip")
         self._tmp_path = self._zip_path.with_name(self._zip_path.name + ".tmp")
         self._delete = delete
+        self._compression = compression
+        self._compresslevel = compresslevel
         self._zip: zipfile.ZipFile | None = None
         self._dirs: set[str] = set()
         self._pending_manifest: tuple[Path, str] | None = None
@@ -254,7 +264,8 @@ class ZipExportSink(ExportSink):
         self._zip = zipfile.ZipFile(
             self._tmp_path,
             "w",
-            compression=zipfile.ZIP_DEFLATED,
+            compression=self._compression,
+            compresslevel=self._compresslevel,
             allowZip64=True,
         )
 

src/documents/management/commands/document_exporter.py

@@ -29,6 +29,11 @@ if TYPE_CHECKING:
 if settings.AUDIT_LOG_ENABLED:
     from auditlog.models import LogEntry
 
+from documents.export.compression import COMPRESSION_CHOICES
+from documents.export.compression import COMPRESSION_METHODS
+from documents.export.compression import ZSTD
+from documents.export.compression import compression_available
+from documents.export.compression import level_error
 from documents.export.sinks import DirectoryExportSink
 from documents.export.sinks import ExportSink
 from documents.export.sinks import StreamingManifestWriter
@@ -191,6 +196,28 @@ class Command(CryptMixin, PaperlessCommand):
             help="Sets the export zip file name",
         )
 
+        parser.add_argument(
+            "--zip-compression",
+            choices=COMPRESSION_CHOICES,
+            default=None,
+            help=(
+                "Compression method for the export zip (requires --zip). "
+                "Default: deflated. 'zstd' requires Python 3.14+ on both the "
+                "exporting and importing machine."
+            ),
+        )
+
+        parser.add_argument(
+            "--zip-compression-level",
+            type=int,
+            default=None,
+            help=(
+                "Compression level for the export zip (requires --zip). "
+                "deflated: 0-9, bzip2: 1-9, zstd: -22..22; ignored for "
+                "stored/lzma."
+            ),
+        )
+
         parser.add_argument(
             "--data-only",
             default=False,
@@ -246,12 +273,39 @@ class Command(CryptMixin, PaperlessCommand):
         if not os.access(self.target, os.W_OK):
             raise CommandError("That path doesn't appear to be writable")
 
+        zip_compression: str | None = options["zip_compression"]
+        zip_compression_level: int | None = options["zip_compression_level"]
+
+        if not self.zip_export and (
+            zip_compression is not None or zip_compression_level is not None
+        ):
+            raise CommandError(
+                "--zip-compression and --zip-compression-level require --zip",
+            )
+
+        compression_method = zip_compression or "deflated"
+        if self.zip_export:
+            if not compression_available(compression_method):
+                if compression_method == "zstd" and ZSTD is None:
+                    raise CommandError(
+                        "zstd compression requires Python 3.14 or newer",
+                    )
+                raise CommandError(
+                    f"Compression method '{compression_method}' is not "
+                    f"available on this Python runtime",
+                )
+            level_msg = level_error(compression_method, zip_compression_level)
+            if level_msg is not None:
+                raise CommandError(level_msg)
+
         sink: ExportSink
         if self.zip_export:
             sink = ZipExportSink(
                 self.target,
                 options["zip_name"],
                 delete=self.delete,
+                compression=COMPRESSION_METHODS[compression_method],
+                compresslevel=zip_compression_level,
             )
         else:
             sink = DirectoryExportSink(

src/documents/management/commands/document_importer.py

@@ -32,6 +32,8 @@ from django.db.models.signals import post_save
 from filelock import FileLock
 from guardian.shortcuts import clear_ct_cache
 
+from documents.export.compression import compress_type_readable
+from documents.export.compression import unreadable_method_names
 from documents.file_handling import create_source_path_directory
 from documents.management.commands.base import PaperlessCommand
 from documents.management.commands.mixins import CryptMixin
@@ -451,6 +453,20 @@ class Command(CryptMixin, PaperlessCommand):
         with tempfile.TemporaryDirectory() as tmp_dir:
             if is_zipfile(self.source):
                 with ZipFile(self.source) as zf:
+                    unsupported = {
+                        info.compress_type
+                        for info in zf.infolist()
+                        if not compress_type_readable(info.compress_type)
+                    }
+                    if unsupported:
+                        names = sorted(unreadable_method_names(unsupported))
+                        message = (
+                            f"This archive uses compression this Python cannot "
+                            f"read ({', '.join(names)})."
+                        )
+                        if "zstd" in names:
+                            message += " zstd archives require Python 3.14+."
+                        raise CommandError(message)
                     zf.extractall(tmp_dir)
                 self.source = Path(tmp_dir)
             self._run_import()

src/documents/tests/export/test_compression.py

@@ -0,0 +1,190 @@
+import sys
+import zipfile
+
+import pytest
+
+from documents.export import compression
+
+
+class TestCompressionMethods:
+    def test_choices_always_include_zstd(self) -> None:
+        """
+        GIVEN:
+            - The compression policy module's CLI choices list
+        WHEN:
+            - Read on any runtime
+        THEN:
+            - zstd is always present; availability is checked separately so
+              argparse never hides it based on the current Python version
+        """
+        assert compression.COMPRESSION_CHOICES == (
+            "stored",
+            "deflated",
+            "bzip2",
+            "lzma",
+            "zstd",
+        )
+
+    @pytest.mark.parametrize(
+        ("name", "constant"),
+        [
+            ("stored", zipfile.ZIP_STORED),
+            ("deflated", zipfile.ZIP_DEFLATED),
+            ("bzip2", zipfile.ZIP_BZIP2),
+            ("lzma", zipfile.ZIP_LZMA),
+        ],
+    )
+    def test_method_maps_to_zipfile_constant(self, name: str, constant: int) -> None:
+        """
+        GIVEN:
+            - A compression method name
+        WHEN:
+            - Looked up in COMPRESSION_METHODS
+        THEN:
+            - It maps to the matching zipfile compression constant
+        """
+        assert compression.COMPRESSION_METHODS[name] == constant
+
+    def test_stored_and_deflated_always_available(self) -> None:
+        """
+        GIVEN:
+            - The stored and deflated compression methods
+        WHEN:
+            - Checked with compression_available()
+        THEN:
+            - Both are always available (zlib is a hard CPython dependency)
+        """
+        assert compression.compression_available("stored")
+        assert compression.compression_available("deflated")
+
+    def test_zstd_availability_tracks_runtime(self) -> None:
+        """
+        GIVEN:
+            - The zstd compression method
+        WHEN:
+            - Checked with compression_available() on this runtime
+        THEN:
+            - Availability matches whether Python is 3.14+
+        """
+        expected: bool = sys.version_info >= (3, 14)
+        assert compression.compression_available("zstd") == expected
+
+
+class TestLevelError:
+    @pytest.mark.parametrize(
+        ("method", "level"),
+        [
+            ("deflated", 0),
+            ("deflated", 9),
+            ("bzip2", 1),
+            ("bzip2", 9),
+            ("zstd", -22),
+            ("zstd", 22),
+            ("deflated", None),
+            ("stored", None),
+        ],
+    )
+    def test_valid_levels_return_none(self, method: str, level: int | None) -> None:
+        """
+        GIVEN:
+            - A method and a level within its valid bounds (or no level)
+        WHEN:
+            - Checked with level_error()
+        THEN:
+            - No error message is returned
+        """
+        assert compression.level_error(method, level) is None
+
+    @pytest.mark.parametrize(
+        ("method", "level"),
+        [
+            ("deflated", 10),
+            ("deflated", -1),
+            ("bzip2", 0),
+            ("bzip2", 10),
+            ("zstd", -23),
+            ("zstd", 23),
+        ],
+    )
+    def test_out_of_range_levels_return_message(
+        self,
+        method: str,
+        level: int,
+    ) -> None:
+        """
+        GIVEN:
+            - A method and a level outside its valid bounds
+        WHEN:
+            - Checked with level_error()
+        THEN:
+            - An error message naming the valid range is returned
+        """
+        msg: str | None = compression.level_error(method, level)
+        assert msg is not None
+        assert "between" in msg
+
+    @pytest.mark.parametrize("method", ["stored", "lzma"])
+    def test_level_on_levelless_method_is_rejected(self, method: str) -> None:
+        """
+        GIVEN:
+            - A method that ignores compression level (stored, lzma)
+        WHEN:
+            - A level is passed to level_error() anyway
+        THEN:
+            - An error message noting the level has no effect is returned
+        """
+        msg: str | None = compression.level_error(method, 5)
+        assert msg is not None
+        assert "no effect" in msg
+
+
+class TestCompressTypeReadable:
+    @pytest.mark.parametrize("ct", [zipfile.ZIP_STORED, zipfile.ZIP_DEFLATED])
+    def test_stored_and_deflated_always_readable(self, ct: int) -> None:
+        """
+        GIVEN:
+            - A stored or deflated compress_type id
+        WHEN:
+            - Checked with compress_type_readable()
+        THEN:
+            - It is always readable
+        """
+        assert compression.compress_type_readable(ct)
+
+    def test_zstd_compress_type_readability_tracks_runtime(self) -> None:
+        """
+        GIVEN:
+            - The current (93) and legacy (20) zstd compress_type ids
+        WHEN:
+            - Checked with compress_type_readable() on this runtime
+        THEN:
+            - Readability matches whether Python is 3.14+
+        """
+        # 93 = ZIP_ZSTANDARD; 20 = legacy zstd method id (read-only)
+        expected: bool = sys.version_info >= (3, 14)
+        assert compression.compress_type_readable(93) == expected
+        assert compression.compress_type_readable(20) == expected
+
+    def test_unknown_compress_type_is_unreadable(self) -> None:
+        """
+        GIVEN:
+            - An unrecognized compress_type id
+        WHEN:
+            - Checked with compress_type_readable()
+        THEN:
+            - It is reported as unreadable
+        """
+        assert not compression.compress_type_readable(9999)
+
+    def test_unreadable_method_names_lists_methods(self) -> None:
+        """
+        GIVEN:
+            - A set containing an unknown compress_type id
+        WHEN:
+            - Passed to unreadable_method_names()
+        THEN:
+            - It is reported generically as "method <id>"
+        """
+        # An unknown method id maps to no name and is reported generically.
+        names: set[str] = compression.unreadable_method_names({9999})
+        assert names == {"method 9999"}

src/documents/tests/export/test_sinks.py

@@ -5,6 +5,7 @@ import zipfile
 from pathlib import Path
 
 import pytest
+import pytest_mock
 
 from documents.export.sinks import DirectoryExportSink
 from documents.export.sinks import ExportSink
@@ -267,6 +268,48 @@ class TestZipExportSink:
         assert not (target / "export.zip").exists()
 
 
+class TestZipExportSinkCompression:
+    @pytest.mark.parametrize(
+        ("method", "constant"),
+        [
+            ("stored", zipfile.ZIP_STORED),
+            ("deflated", zipfile.ZIP_DEFLATED),
+            ("bzip2", zipfile.ZIP_BZIP2),
+            ("lzma", zipfile.ZIP_LZMA),
+        ],
+    )
+    def test_compression_and_level_forwarded_to_zipfile(
+        self,
+        mocker: pytest_mock.MockerFixture,
+        tmp_path: Path,
+        method: str,
+        constant: int,
+    ) -> None:
+        """
+        GIVEN:
+            - A ZipExportSink constructed with a compression method and level
+        WHEN:
+            - The sink is opened
+        THEN:
+            - zipfile.ZipFile is constructed with those values forwarded
+              unchanged (whether ZipFile actually compresses is Python's own
+              contract, not ours, so this checks the call args, not a real
+              archive)
+        """
+        target: Path = tmp_path / "out"
+        target.mkdir()
+        zip_cls = mocker.patch("documents.export.sinks.zipfile.ZipFile")
+        sink = ZipExportSink(target, "export", compression=constant, compresslevel=5)
+        sink._open()
+        zip_cls.assert_called_once_with(
+            mocker.ANY,
+            "w",
+            compression=constant,
+            compresslevel=5,
+            allowZip64=True,
+        )
+
+
 class TestStreamContract:
     @pytest.fixture(params=["dir", "zip"])
     def sink(self, request: pytest.FixtureRequest, tmp_path: Path) -> ExportSink:

src/documents/tests/test_management_exporter.py

@@ -6,6 +6,8 @@ from datetime import timedelta
 from io import StringIO
 from pathlib import Path
 from unittest import mock
+from zipfile import ZIP_DEFLATED
+from zipfile import ZIP_LZMA
 from zipfile import ZipFile
 
 import pytest
@@ -1078,6 +1080,170 @@ class TestExportImport(
                         skip_checks=True,
                     )
 
+    def test_compression_flags_require_zip(self) -> None:
+        """
+        GIVEN:
+            - A request to export without --zip
+        WHEN:
+            - --zip-compression or --zip-compression-level is passed anyway
+        THEN:
+            - A CommandError is raised (the flags are meaningless without --zip)
+        """
+        for args in (
+            ["--zip-compression", "lzma"],
+            ["--zip-compression-level", "5"],
+        ):
+            with self.assertRaises(CommandError):
+                call_command(
+                    "document_exporter",
+                    self.target,
+                    *args,
+                    skip_checks=True,
+                )
+
+    def test_zip_compression_level_out_of_range_raises(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file
+        WHEN:
+            - --zip-compression-level is outside the chosen method's valid range
+        THEN:
+            - A CommandError is raised
+        """
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "deflated",
+                "--zip-compression-level",
+                "99",
+                skip_checks=True,
+            )
+
+    def test_zip_compression_level_rejected_for_stored(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with --zip-compression stored
+        WHEN:
+            - --zip-compression-level is also passed
+        THEN:
+            - A CommandError is raised (stored ignores level entirely)
+        """
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "stored",
+                "--zip-compression-level",
+                "5",
+                skip_checks=True,
+            )
+
+    def test_zip_compression_level_rejected_for_lzma(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with --zip-compression lzma
+        WHEN:
+            - --zip-compression-level is also passed
+        THEN:
+            - A CommandError is raised (lzma ignores level entirely)
+        """
+        with self.assertRaises(CommandError):
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "lzma",
+                "--zip-compression-level",
+                "5",
+                skip_checks=True,
+            )
+
+    def test_zstd_unavailable_raises_friendly_error(self) -> None:
+        """
+        GIVEN:
+            - A Python runtime without zstd support (< 3.14)
+        WHEN:
+            - --zip-compression zstd is requested
+        THEN:
+            - A CommandError naming the Python version requirement is raised
+        """
+        with self.assertRaises(CommandError) as e:
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "zstd",
+                skip_checks=True,
+            )
+        self.assertIn("3.14", str(e.exception))
+
+    def test_zip_compression_flag_resolves_to_sink_constant(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with --zip-compression lzma
+        WHEN:
+            - The export runs
+        THEN:
+            - ZipExportSink is constructed with the resolved ZIP_LZMA constant
+              (whether zipfile actually compresses with the chosen method is
+              Python's own contract, and ZipExportSink's own tests already
+              cover the forwarding; what this command owns is resolving the
+              CLI string to the right constant, so assert that resolution
+              directly)
+        """
+        with mock.patch(
+            "documents.management.commands.document_exporter.ZipExportSink",
+        ) as sink_cls:
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                "--zip-compression",
+                "lzma",
+                skip_checks=True,
+            )
+        sink_cls.assert_called_once_with(
+            mock.ANY,
+            mock.ANY,
+            delete=False,
+            compression=ZIP_LZMA,
+            compresslevel=None,
+        )
+
+    def test_default_zip_compression_resolves_to_deflate(self) -> None:
+        """
+        GIVEN:
+            - A request to export to a zip file with no --zip-compression flag
+        WHEN:
+            - The export runs
+        THEN:
+            - ZipExportSink is constructed with the default ZIP_DEFLATED
+              constant and compresslevel=None, matching pre-existing behavior
+        """
+        with mock.patch(
+            "documents.management.commands.document_exporter.ZipExportSink",
+        ) as sink_cls:
+            call_command(
+                "document_exporter",
+                self.target,
+                "--zip",
+                skip_checks=True,
+            )
+        sink_cls.assert_called_once_with(
+            mock.ANY,
+            mock.ANY,
+            delete=False,
+            compression=ZIP_DEFLATED,
+            compresslevel=None,
+        )
+
 
 @pytest.mark.management
 class TestCryptExportImport(

src/documents/tests/test_management_importer.py

@@ -525,6 +525,35 @@ class TestCommandImport(
         self.assertEqual(doc.tags.count(), 1)
         self.assertEqual(doc.tags.first().name, "batch-flush-tag")
 
+    def test_import_rejects_unreadable_compression(self) -> None:
+        """
+        GIVEN:
+            - A zip archive with an entry whose compression this Python can't read
+        WHEN:
+            - Import is attempted
+        THEN:
+            - A CommandError naming the issue is raised, before extraction
+        """
+        import zipfile
+        from unittest import mock
+
+        archive = Path(self.dirs.scratch_dir) / "export.zip"
+        with zipfile.ZipFile(archive, "w") as zf:
+            zf.writestr("manifest.json", "[]")
+
+        with mock.patch(
+            "documents.management.commands.document_importer.compress_type_readable",
+            return_value=False,
+        ):
+            with self.assertRaises(CommandError) as e:
+                call_command(
+                    "document_importer",
+                    str(archive),
+                    "--no-progress-bar",
+                    skip_checks=True,
+                )
+        self.assertIn("compression", str(e.exception))
+
 
 @pytest.mark.management
 @pytest.mark.django_db