fix(cli): add ability to extend default skip magic rather than overwrite it.

unblob has a decent default skip magic list that gets overwritten if a
user provides its own, which means unblob users need to redefine all of
unblob's default skip magic through the CLI whenever they provide their
own.

Changed the logic so that user provided skip magic values are simply
appended to unblob's default list unless the user explicitly provides the
"--clear-skip-magics" flag.

Co-authored-by: Krisztián Fekete <1246751+e3krisztian@users.noreply.github.com>

Author: qkaiser

tests/test_cli.py

@@ -1,5 +1,5 @@
 from pathlib import Path
-from typing import List, Optional, Type
+from typing import Iterable, List, Optional, Type
 from unittest import mock
 
 import pytest
@@ -10,7 +10,12 @@
 from unblob.extractors.command import MultiFileCommand
 from unblob.handlers import BUILTIN_HANDLERS
 from unblob.models import DirectoryHandler, Glob, Handler, HexString, MultiFile
-from unblob.processing import DEFAULT_DEPTH, DEFAULT_PROCESS_NUM, ExtractionConfig
+from unblob.processing import (
+    DEFAULT_DEPTH,
+    DEFAULT_PROCESS_NUM,
+    DEFAULT_SKIP_MAGIC,
+    ExtractionConfig,
+)
 from unblob.ui import (
     NullProgressReporter,
     ProgressReporter,
@@ -367,3 +372,51 @@ def test_skip_extraction(
     assert (
         process_file_mock.call_args.args[0].skip_extraction == skip_extraction
     ), fail_message
+
+
+@pytest.mark.parametrize(
+    "args, skip_magic, fail_message",
+    [
+        ([], DEFAULT_SKIP_MAGIC, "Should have kept default skip magics"),
+        (
+            ["--skip-magic", "SUPERMAGIC"],
+            (*DEFAULT_SKIP_MAGIC, "SUPERMAGIC"),
+            "Should have kept default skip magics",
+        ),
+        (["--clear-skip-magics"], [], "Should have cleared default skip magics"),
+        (
+            ["--clear-skip-magics", "--skip-magic", "SUPERMAGIC"],
+            ["SUPERMAGIC"],
+            "Should have cleared default skip magics",
+        ),
+        (
+            ["--clear-skip-magics", "--skip-magic", DEFAULT_SKIP_MAGIC[1]],
+            [DEFAULT_SKIP_MAGIC[1]],
+            "Should allow user specified and remove the rest",
+        ),
+    ],
+)
+def test_clear_skip_magics(
+    args: List[str], skip_magic: Iterable[str], fail_message: str, tmp_path: Path
+):
+    runner = CliRunner()
+    in_path = (
+        Path(__file__).parent
+        / "integration"
+        / "archive"
+        / "zip"
+        / "regular"
+        / "__input__"
+        / "apple.zip"
+    )
+    params = [*args, "--extract-dir", str(tmp_path), str(in_path)]
+
+    process_file_mock = mock.MagicMock()
+    with mock.patch.object(unblob.cli, "process_file", process_file_mock):
+        result = runner.invoke(unblob.cli.cli, params)
+
+    assert result.exit_code == 0
+    process_file_mock.assert_called_once()
+    assert sorted(process_file_mock.call_args.args[0].skip_magic) == sorted(
+        skip_magic
+    ), fail_message

unblob/cli.py

@@ -168,9 +168,11 @@ def __init__(
     "--skip-magic",
     "skip_magic",
     type=click.STRING,
-    default=DEFAULT_SKIP_MAGIC,
-    help="Skip processing files with given magic prefix",
-    show_default=True,
+    help=f"""Skip processing files with given magic prefix.
+        The provided values are appended to unblob's own skip magic list unless
+        --clear-skip-magic is provided.
+        [default: {', '.join(DEFAULT_SKIP_MAGIC)}]
+    """,
     multiple=True,
 )
 @click.option(
@@ -182,6 +184,14 @@ def __init__(
     show_default=True,
     multiple=True,
 )
+@click.option(
+    "--clear-skip-magics",
+    "clear_skip_magics",
+    is_flag=True,
+    show_default=True,
+    default=False,
+    help="Clear unblob's own skip magic list.",
+)
 @click.option(
     "-p",
     "--process-num",
@@ -246,6 +256,7 @@ def cli(
     entropy_depth: int,
     skip_magic: Iterable[str],
     skip_extension: Iterable[str],
+    clear_skip_magics: bool,  # noqa: FBT001
     skip_extraction: bool,  # noqa: FBT001
     keep_extracted_chunks: bool,  # noqa: FBT001
     handlers: Handlers,
@@ -263,6 +274,9 @@ def cli(
     extra_dir_handlers = plugin_manager.load_dir_handlers_from_plugins()
     dir_handlers += tuple(extra_dir_handlers)
 
+    extra_magics_to_skip = () if clear_skip_magics else DEFAULT_SKIP_MAGIC
+    skip_magic = tuple(sorted(set(skip_magic).union(extra_magics_to_skip)))
+
     config = ExtractionConfig(
         extract_root=extract_root,
         force_extract=force,

unblob/processing.py

@@ -52,31 +52,31 @@
 DEFAULT_PROCESS_NUM = multiprocessing.cpu_count()
 DEFAULT_SKIP_MAGIC = (
     "BFLT",
-    "JPEG",
+    "Composite Document File V2 Document",
+    "Erlang BEAM file",
     "GIF",
-    "PNG",
-    "SQLite",
-    "compiled Java class",
-    "TrueType Font data",
-    "PDF document",
-    "magic binary file",
-    "MS Windows icon resource",
-    "Web Open Font Format",
     "GNU message catalog",
-    "Xilinx BIT data",
+    "HP Printer Job Language",
+    "Intel serial flash for PCH ROM",
+    "JPEG",
+    "MPEG",
+    "MS Windows icon resource",
+    "Macromedia Flash data",
     "Microsoft Excel",
-    "Microsoft Word",
-    "Microsoft PowerPoint",
     "Microsoft OOXML",
+    "Microsoft PowerPoint",
+    "Microsoft Word",
     "OpenDocument",
-    "Macromedia Flash data",
-    "MPEG",
-    "HP Printer Job Language",
-    "Erlang BEAM file",
-    "python",  # (e.g. python 2.7 byte-compiled)
-    "Composite Document File V2 Document",
+    "PDF document",
+    "PNG",
+    "SQLite",
+    "TrueType Font data",
+    "Web Open Font Format",
     "Windows Embedded CE binary image",
-    "Intel serial flash for PCH ROM",
+    "Xilinx BIT data",
+    "compiled Java class",
+    "magic binary file",
+    "python",  #   # (e.g. python 2.7 byte-compiled)
 )
 DEFAULT_SKIP_EXTENSION = (".rlib",)