Make the payload encoder's -key argument usable

app/utility/payload_encoder.py

@@ -10,7 +10,7 @@
 Additionally, payload_encoder.py can be used from the command-line to add a new encoded payload.
 
 ```
-python /path/to/payload_encoder.py input_file output_file
+python /path/to/payload_encoder.py [-key KEY] input_file output_file
 ```
 
 NOTE: In order for the server to detect the availability of an encoded payload, the payload file's
@@ -44,7 +44,9 @@ def xor_file(input_file, output_file=None, key=None):
 
 if __name__ == '__main__':
     parser = argparse.ArgumentParser()
-    parser.add_argument('-key', default=DEFAULT_KEY)
+    # A str indexes to str, which cannot be XOR'ed with an int. The server path in
+    # file_svc encodes its key the same way before calling xor_bytes.
+    parser.add_argument('-key', default=DEFAULT_KEY, type=lambda key: key.encode())
     parser.add_argument('input')
     parser.add_argument('output')
 

tests/utility/test_payload_encoder.py

@@ -0,0 +1,39 @@
+import subprocess
+import sys
+
+from pathlib import Path
+
+from app.utility.payload_encoder import DEFAULT_KEY, xor_bytes
+
+
+ENCODER = Path(__file__).parents[2] / 'app' / 'utility' / 'payload_encoder.py'
+
+
+def _run_encoder(args):
+    return subprocess.run([sys.executable, str(ENCODER)] + args, capture_output=True, text=True)
+
+
+def test_xor_bytes_accepts_a_byte_string_key():
+    assert xor_bytes(b'\x00\x01', key=b'\x0f\x0f') == b'\x0f\x0e'
+
+
+def test_command_line_uses_the_default_key(tmp_path):
+    payload = tmp_path / 'payload'
+    payload.write_bytes(b'hello payload')
+    encoded = tmp_path / 'payload.xored'
+
+    result = _run_encoder([str(payload), str(encoded)])
+
+    assert result.returncode == 0, result.stderr
+    assert encoded.read_bytes() == xor_bytes(b'hello payload', key=DEFAULT_KEY)
+
+
+def test_command_line_key_argument_is_usable(tmp_path):
+    payload = tmp_path / 'payload'
+    payload.write_bytes(b'hello payload')
+    encoded = tmp_path / 'payload.xored'
+
+    result = _run_encoder(['-key', 'somekey', str(payload), str(encoded)])
+
+    assert result.returncode == 0, result.stderr
+    assert encoded.read_bytes() == xor_bytes(b'hello payload', key=b'somekey')