unpacker: add broadcom SAO image support

fact_extractor/plugins/unpacking/broadcom/code/broadcom_sao.py

@@ -0,0 +1,45 @@
+"""
+This plugin unpacks Broadcom SAO images.
+"""
+
+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 = Path(file_path)
+    file_size = file.stat().st_size
+
+    try:
+        with file.open('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 OSError as io_error:
+        return {'output': f'failed to read file: {io_error!s}'}
+
+    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))

fact_extractor/plugins/unpacking/broadcom/test/test_plugin_broadcom_sao.py

@@ -0,0 +1,23 @@
+from pathlib import Path
+
+from test.unit.unpacker.test_unpacker import TestUnpackerBase
+
+TEST_DATA_DIR = Path(__file__).parent / 'data'
+
+EXPECTED_FILE_COUNT = 4
+
+
+class TestBroadcomSAOUnpacker(TestUnpackerBase):
+    def test_unpacker_selection_generic(self):
+        self.check_unpacker_selection('firmware/broadcom-sao', 'Broadcom SAO')
+
+    def test_extraction(self):
+        test_file_path = Path(TEST_DATA_DIR) / 'broadcom-sao.bin'
+        extracted_files, meta_data = self.unpacker.extract_files_from_file(str(test_file_path), self.tmp_dir.name)
+
+        assert meta_data['plugin_used'] == 'Broadcom SAO', 'wrong plugin applied'
+
+        assert len(extracted_files) == EXPECTED_FILE_COUNT, 'not all files extracted'
+        assert all(
+            Path(element).name in ['META', 'DTBB', 'KRNL', 'RTFS'] for element in extracted_files
+        ), 'not all files extracted'