unpacker: add broadcom SAO image support

fact_extractor/plugins/unpacking/broadcom/code/broadcom-sao.py

@@ -0,0 +1,47 @@
+'''
+This plugin unpacks Broadcom SAO images.
+'''
+
+import os
+from pathlib import Path
+from common_helper_files import write_binary_to_file
+
+NAME = "Broadcom SAO"
+MIME_PATTERNS = ['firmware/broadcom-sao']
+VERSION = '0.1'
+
+def unpack_function(file_path, tmp_dir):
+    '''
+    file_path specifies the input file.
+    tmp_dir must be used to store the extracted files.
+    Optional: Return a dict with meta information
+    '''
+
+    FILE_SIZE = os.stat(file_path).st_size
+
+    try:
+        with open(file_path, 'rb') as f:
+            while (f.tell() < FILE_SIZE):
+                f.read(8) # skip 8 bytes to part name offset
+                name = f.read(4).decode('utf-8')
+                f.read(4) # skip 4 more bytes to size offset
+                size = int.from_bytes(f.read(4), 'big')
+                f.read(44) # skip rest of header
+                data = f.read(size)
+                outfile = Path(tmp_dir) / name
+                write_binary_to_file(data, outfile)
+
+    except IOError as io_error:
+        return {'output': 'failed to read file: {}'.format(str(io_error))}
+
+    except struct.error as struct_error:
+        return {'output': 'failed to recognized firmware container: {}'.format(str(struct_error))}
+
+    return {
+            'output': 'successfully unpacked Broadcom SAO image'
+    }
+
+# ----> Do not edit below this line <----
+def setup(unpack_tool):
+    for item in MIME_PATTERNS:
+        unpack_tool.register_plugin(item, (unpack_function, NAME, VERSION))