Add support for alternative container types for a file, allowing for runtime...

Add support for alternative container types for a file, allowing for runtime (vs import time) control of fallbacks such as adding comments. (Re: #86)

diffoscope/comparators/android.py

@@ -81,7 +81,7 @@ class AndroidBootImgContainer(Archive):
 class AndroidBootImgFile(File):
     DESCRIPTION = "Android boot images"
     FILE_TYPE_RE = re.compile(r'^Android bootimg\b')
-    CONTAINER_CLASS = AndroidBootImgContainer
+    CONTAINER_CLASSES = [AndroidBootImgContainer]
 
     def compare_details(self, other, source=None):
         return [Difference.from_command(AbootimgInfo, self.path, other.path)]

diffoscope/comparators/apk.py

@@ -172,9 +172,9 @@ class ApkFile(File):
     FILE_TYPE_HEADER_PREFIX = b"PK\x03\x04"
     FILE_TYPE_RE = re.compile(r'^(Java|Zip) archive data.*\b')
     FILE_EXTENSION_SUFFIX = '.apk'
-    CONTAINER_CLASS = (
+    CONTAINER_CLASSES = [
         ApkContainer if find_executable('apktool') else ZipContainer
-    )
+    ]
 
     def compare_details(self, other, source=None):
         return zipinfo_differences(self, other)

diffoscope/comparators/ar.py

@@ -60,7 +60,7 @@ class ArSymbolTableDumper(Command):
 
 class ArFile(File):
     DESCRIPTION = "ar(1) archives"
-    CONTAINER_CLASS = ArContainer
+    CONTAINER_CLASSES = [ArContainer]
     FILE_TYPE_RE = re.compile(r'\bar archive\b')
 
     def compare_details(self, other, source=None):

diffoscope/comparators/binwalk.py

@@ -67,7 +67,7 @@ class BinwalkFileContainer(Archive):
 
 class BinwalkFile(File):
     FILE_TYPE_RE = re.compile(r'\bcpio archive\b')
-    CONTAINER_CLASS = BinwalkFileContainer
+    CONTAINER_CLASSES = [BinwalkFileContainer]
 
     @classmethod
     def recognizes(cls, file):

diffoscope/comparators/bzip2.py

@@ -55,5 +55,5 @@ class Bzip2Container(Archive):
 
 class Bzip2File(File):
     DESCRIPTION = "bzip2 archives"
-    CONTAINER_CLASS = Bzip2Container
+    CONTAINER_CLASSES = [Bzip2Container]
     FILE_TYPE_RE = re.compile(r'^bzip2 compressed data\b')

diffoscope/comparators/cbfs.py

@@ -125,7 +125,7 @@ def is_header_valid(buf, size, offset=0):
 
 class CbfsFile(File):
     DESCRIPTION = "Coreboot CBFS filesystem images"
-    CONTAINER_CLASS = CbfsContainer
+    CONTAINER_CLASSES = [CbfsContainer]
 
     @classmethod
     def recognizes(cls, file):

diffoscope/comparators/cpio.py

@@ -28,7 +28,7 @@ from .utils.libarchive import LibarchiveContainer, list_libarchive
 
 class CpioFile(File):
     DESCRIPTION = "cpio archives"
-    CONTAINER_CLASS = LibarchiveContainer
+    CONTAINER_CLASSES = [LibarchiveContainer]
     FILE_TYPE_RE = re.compile(r'\bcpio archive\b')
 
     def compare_details(self, other, source=None):

diffoscope/comparators/deb.py

@@ -111,7 +111,7 @@ class DebContainer(LibarchiveContainer):
 
 
 class DebFile(File):
-    CONTAINER_CLASS = DebContainer
+    CONTAINER_CLASSES = [DebContainer]
     FILE_TYPE_RE = re.compile(r'^Debian binary package')
 
     @property
@@ -233,7 +233,7 @@ class DebTarContainer(TarContainer):
 
 
 class DebDataTarFile(File):
-    CONTAINER_CLASS = DebTarContainer
+    CONTAINER_CLASSES = [DebTarContainer]
 
     @classmethod
     def recognizes(cls, file):

diffoscope/comparators/debian.py

@@ -109,7 +109,7 @@ class DebControlContainer(Container):
 
 
 class DebControlFile(File):
-    CONTAINER_CLASS = DebControlContainer
+    CONTAINER_CLASSES = [DebControlContainer]
 
     @property
     def deb822(self):
@@ -261,7 +261,7 @@ class DotBuildinfoContainer(DebControlContainer):
 
 class DotBuildinfoFile(DebControlFile):
     DESCRIPTION = "Debian .buildinfo files"
-    CONTAINER_CLASS = DotBuildinfoContainer
+    CONTAINER_CLASSES = [DotBuildinfoContainer]
     FILE_EXTENSION_SUFFIX = '.buildinfo'
     FILE_TYPE_RE = re.compile(r'^(ASCII text|UTF-8 Unicode text)')
 

diffoscope/comparators/dex.py

@@ -60,4 +60,4 @@ class DexContainer(Archive):
 class DexFile(File):
     DESCRIPTION = "Dalvik .dex files"
     FILE_TYPE_RE = re.compile(r'^Dalvik dex file .*\b')
-    CONTAINER_CLASS = DexContainer
+    CONTAINER_CLASSES = [DexContainer]

diffoscope/comparators/elf.py

@@ -621,7 +621,7 @@ class ElfContainer(Container):
 
 class ElfFile(File):
     DESCRIPTION = "ELF binaries"
-    CONTAINER_CLASS = ElfContainer
+    CONTAINER_CLASSES = [ElfContainer]
     FILE_TYPE_RE = re.compile(r'^ELF ')
 
     def compare_details(self, other, source=None):

diffoscope/comparators/fsimage.py

@@ -88,7 +88,7 @@ class FsImageContainer(Archive):
 
 class FsImageFile(File):
     DESCRIPTION = "ext2/ext3/ext4/btrfs/fat filesystems"
-    CONTAINER_CLASS = FsImageContainer
+    CONTAINER_CLASSES = [FsImageContainer]
     FILE_TYPE_RE = re.compile(r'^(Linux.*filesystem data|BTRFS Filesystem).*')
 
     @classmethod

diffoscope/comparators/gzip.py

@@ -56,7 +56,7 @@ class GzipContainer(Archive):
 
 class GzipFile(File):
     DESCRIPTION = "Gzipped files"
-    CONTAINER_CLASS = GzipContainer
+    CONTAINER_CLASSES = [GzipContainer]
     FILE_TYPE_RE = re.compile(r'^gzip compressed data\b')
 
     # Work around file(1) Debian bug #876316

diffoscope/comparators/iso9660.py

@@ -76,7 +76,7 @@ class ISO9660Listing(Command):
 
 class Iso9660File(File):
     DESCRIPTION = "ISO 9660 CD images"
-    CONTAINER_CLASS = LibarchiveContainerWithFilelist
+    CONTAINER_CLASSES = [LibarchiveContainerWithFilelist]
     FILE_TYPE_RE = re.compile(r'\bISO 9660\b')
 
     @classmethod

diffoscope/comparators/lz4.py

@@ -56,7 +56,7 @@ class Lz4Container(Archive):
 
 class Lz4File(File):
     DESCRIPTION = "LZ4 compressed files"
-    CONTAINER_CLASS = Lz4Container
+    CONTAINER_CLASSES = [Lz4Container]
     FILE_TYPE_RE = re.compile(r'^LZ4 compressed data \([^\)]+\)$')
 
     # Work around file(1) Debian bug #876316

diffoscope/comparators/rpm.py

@@ -109,7 +109,7 @@ class RpmContainer(Archive):
 
 class RpmFile(AbstractRpmFile):
     DESCRIPTION = "RPM archives"
-    CONTAINER_CLASS = RpmContainer
+    CONTAINER_CLASSES = [RpmContainer]
 
     def compare_details(self, other, source=None):
         return [compare_rpm_headers(self.path, other.path)]

diffoscope/comparators/rust.py

@@ -60,7 +60,7 @@ class RustObjectContainer(Archive):
 
 class RustObjectFile(File):
     DESCRIPTION = "Rust object files (.deflate)"
-    CONTAINER_CLASS = RustObjectContainer
+    CONTAINER_CLASSES = [RustObjectContainer]
     FILE_TYPE_HEADER_PREFIX = b'RUST_OBJECT\x01\x00\x00\x00'
     FILE_EXTENSION_SUFFIX = '.deflate'
 

diffoscope/comparators/squashfs.py

@@ -310,7 +310,7 @@ class SquashfsContainer(Archive):
 
 class SquashfsFile(File):
     DESCRIPTION = "SquashFS filesystems"
-    CONTAINER_CLASS = SquashfsContainer
+    CONTAINER_CLASSES = [SquashfsContainer]
     FILE_TYPE_RE = re.compile(r'^Squashfs filesystem\b')
 
     def compare_details(self, other, source=None):

diffoscope/comparators/tar.py

@@ -31,7 +31,7 @@ class TarContainer(LibarchiveContainer):
 
 class TarFile(File):
     DESCRIPTION = "tape archives (.tar)"
-    CONTAINER_CLASS = TarContainer
+    CONTAINER_CLASSES = [TarContainer]
     FILE_TYPE_RE = re.compile(r'\btar archive\b')
 
     def compare_details(self, other, source=None):

diffoscope/comparators/utils/file.py

@@ -225,37 +225,43 @@ class File(metaclass=abc.ABCMeta):
     def container(self):
         return self._container
 
+    CONTAINER_CLASSES = []
+
     @property
     def as_container(self):
-        if not hasattr(self.__class__, 'CONTAINER_CLASS'):
+        klasses = self.__class__.CONTAINER_CLASSES
+
+        if not klasses:
             if hasattr(self, '_other_file'):
-                return self._other_file.__class__.CONTAINER_CLASS(self)
+                return self._other_file.__class__.CONTAINER_CLASSES[0](self)
             return None
 
         def type_name(klass):
             return "{}.{}".format(klass.__module__, klass.__name__)
 
-        if not hasattr(self, '_as_container'):
+        if hasattr(self, '_as_container'):
+            return self._as_container
+
+        self._as_container = None
+
+        # Try each container class in turn, returning the first one that
+        # instantiates without error.
+        for klass in klasses:
             logger.debug(
-                'Instantiating a %s for %s',
-                type_name(self.__class__.CONTAINER_CLASS),
-                self.name,
+                'Instantiating a %s for %s', type_name(klass), self.name,
             )
             try:
-                self._as_container = self.__class__.CONTAINER_CLASS(self)
+                self._as_container = klass(self)
+                logger.debug(
+                    "Returning a %s for %s", type_name(klass), self.name,
+                )
+                return self._as_container
             except RequiredToolNotFound as exc:
                 logger.debug(
                     "Cannot instantiate a %s; missing tool %s",
-                    type_name(self.__class__.CONTAINER_CLASS),
+                    type_name(klass),
                     exc.command,
                 )
-                return None
-        logger.debug(
-            "Returning a %s for %s",
-            type_name(self._as_container.__class__),
-            self.name,
-        )
-        return self._as_container
 
     @property
     def progress_name(self):