feat(handlers): add supported platforms tag to handlers

Handler and DirectoryHandler can now indicate the specific platforms
they do support through the SUPPORTED_PLATFORMS field. This field is a
set of Platform objects, an enum with values corresponding to the
currently supported platforms by unblob (Linux, OSX).

With this addition, a handler such as partclone that uses an extractor
that is unavailable on OSX can indicate that it only supports Linux.

When starting, unblob will only load handlers that are supported by the
platform its currently being executed on. This is done by filtering them
in BUILTIN_HANDLERS and BUILTIN_DIR_HANDLERS.

Author: qkaiser

python/unblob/handlers/__init__.py

@@ -52,7 +52,7 @@
 )
 from .filesystem.android import erofs, sparse
 
-BUILTIN_HANDLERS: Handlers = (
+ALL_HANDLERS: Handlers = (
     cramfs.CramFSHandler,
     extfs.EXTHandler,
     fat.FATHandler,
@@ -122,8 +122,14 @@
     erofs.EROFSHandler,
     partclone.PartcloneHandler,
 )
+BUILTIN_HANDLERS: Handlers = tuple(
+    handler for handler in ALL_HANDLERS if handler.is_supported_here()
+)
 
-BUILTIN_DIR_HANDLERS: DirectoryHandlers = (
+ALL_DIR_HANDLERS: DirectoryHandlers = (
     sevenzip.MultiVolumeSevenZipHandler,
     gzip.MultiVolumeGzipHandler,
 )
+BUILTIN_DIR_HANDLERS: DirectoryHandlers = tuple(
+    handler for handler in ALL_DIR_HANDLERS if handler.is_supported_here()
+)

python/unblob/handlers/archive/partclone.py

@@ -5,7 +5,7 @@
 
 from unblob.extractors import Command
 from unblob.file_utils import File, InvalidInputFormat, get_endian
-from unblob.models import Regex, StructHandler, ValidChunk
+from unblob.models import Platform, Regex, StructHandler, ValidChunk
 
 C_DEFINITIONS = r"""
     typedef struct partclone_header{
@@ -51,6 +51,7 @@ class PartcloneHandler(StructHandler):
         "-L",
         "/dev/stdout",
     )
+    SUPPORTED_PLATFORMS = {Platform.LINUX}
 
     def is_valid_header(self, header) -> bool:
         calculated_crc = binascii.crc32(header.dumps()[0:-4])

python/unblob/models.py

@@ -1,8 +1,11 @@
 import abc
+import enum
 import itertools
 import json
+import sys
 from collections.abc import Iterable
 from enum import Enum
+from functools import lru_cache
 from pathlib import Path
 from typing import Generic, Optional, TypeVar, Union
 
@@ -30,6 +33,19 @@
 #
 
 
+class Platform(enum.Enum):
+    LINUX = "linux"
+    MACOS = "darwin"
+
+
+@lru_cache
+def current_platform() -> Platform:
+    try:
+        return Platform(sys.platform)
+    except KeyError:
+        raise ValueError(f"Unsupported platform: {sys.platform}") from None
+
+
 @attrs.define(frozen=True)
 class Task:
     path: Path
@@ -417,13 +433,20 @@ class DirectoryHandler(abc.ABC):
 
     PATTERN: DirectoryPattern
 
+    SUPPORTED_PLATFORMS: set[Platform] = {Platform.LINUX, Platform.MACOS}
+
     @classmethod
     def get_dependencies(cls):
         """Return external command dependencies needed for this handler to work."""
         if cls.EXTRACTOR:
             return cls.EXTRACTOR.get_dependencies()
         return []
 
+    @classmethod
+    def is_supported_here(cls) -> bool:
+        """Check if the current platform is supported by this handler."""
+        return current_platform() in cls.SUPPORTED_PLATFORMS
+
     @abc.abstractmethod
     def calculate_multifile(self, file: Path) -> Optional[MultiFile]:
         """Calculate the MultiFile in a directory, using a file matched by the pattern as a starting point."""
@@ -453,13 +476,20 @@ class Handler(abc.ABC, Generic[TExtractor]):
 
     EXTRACTOR: TExtractor
 
+    SUPPORTED_PLATFORMS: set[Platform] = {Platform.LINUX, Platform.MACOS}
+
     @classmethod
     def get_dependencies(cls):
         """Return external command dependencies needed for this handler to work."""
         if cls.EXTRACTOR is not None:
             return cls.EXTRACTOR.get_dependencies()
         return []
 
+    @classmethod
+    def is_supported_here(cls) -> bool:
+        """Check if the current platform is supported by this handler."""
+        return current_platform() in cls.SUPPORTED_PLATFORMS
+
     @abc.abstractmethod
     def calculate_chunk(self, file: File, start_offset: int) -> Optional[ValidChunk]:
         """Calculate the Chunk offsets from the File and the file type headers."""