Updated signature module to not load if lzma is not available

src/binwalk/modules/__init__.py

@@ -10,7 +10,12 @@ try:
 except ImportError:
     pass
 
-from binwalk.modules.signature import Signature
+# Don't load the signature module if the lzma module can't be found
+try:
+    from binwalk.modules.signature import Signature
+except ImportError:
+    pass
+
 from binwalk.modules.hexdiff import HexDiff
 from binwalk.modules.general import General
 from binwalk.modules.extractor import Extractor

src/binwalk/modules/signature.py

 # Basic signature scan module. This is the default (and primary) feature of binwalk.
 
+# This module does not directly use the lzma module, but some plugins for this module do.
+# If the lzma import fails, this module won't be loaded at all.
+import lzma
 import binwalk.core.magic
 import binwalk.core.smart
 import binwalk.core.parser

src/binwalk/plugins/lzmavalid.py

-import lzma
 import binwalk.core.plugin
 import binwalk.core.compat
 from binwalk.core.common import BlockFile
@@ -16,12 +15,16 @@ class LZMAPlugin(binwalk.core.plugin.Plugin):
     # Check up to the first 64KB
     MAX_DATA_SIZE = 64 * 1024
 
+    def init(self):
+        import lzma
+        self.decompressor = lzma.decompress
+
     def is_valid_lzma(self, data):
         valid = True
 
         # The only acceptable exceptions are those indicating that the input data was truncated.
         try:
-            lzma.decompress(binwalk.core.compat.str2bytes(data))
+            self.decompressor(binwalk.core.compat.str2bytes(data))
         except IOError as e:
             # The Python2 module gives this error on truncated input data.
             if str(e) != "unknown BUF error":