util: add docstrings

trezor_agent/tests/test_utils.py

@@ -38,7 +38,7 @@ class FakeSocket(object):
 def test_send_recv():
     s = FakeSocket()
     util.send(s, b'123')
-    util.send(s, data=[42], fmt='B')
+    util.send(s, b'*')
     assert s.buf.getvalue() == b'123*'
 
     s.buf.seek(0)

trezor_agent/util.py

@@ -1,14 +1,20 @@
+"""Various I/O and serialization utilities."""
 import io
 import struct
 
 
-def send(conn, data, fmt=None):
+def send(conn, data):
-    if fmt:
+    """Send data blob to connection socket."""
-        data = struct.pack(fmt, *data)
     conn.sendall(data)
 
 
 def recv(conn, size):
+    """
+    Receive bytes from connection socket or stream.
+
+    If size is struct.calcsize()-compatible format, use it to unpack the data.
+    Otherwise, return the plain blob as bytes.
+    """
     try:
         fmt = size
         size = struct.calcsize(fmt)
@@ -34,11 +40,13 @@ def recv(conn, size):
 
 
 def read_frame(conn):
+    """Read size-prefixed frame from connection."""
     size, = recv(conn, '>L')
     return recv(conn, size)
 
 
 def bytes2num(s):
+    """Convert MSB-first bytes to an unsigned integer."""
     res = 0
     for i, c in enumerate(reversed(bytearray(s))):
         res += c << (i * 8)
@@ -46,6 +54,7 @@ def bytes2num(s):
 
 
 def num2bytes(value, size):
+    """Convert an unsigned integer to MSB-first bytes with specified size."""
     res = []
     for _ in range(size):
         res.append(value & 0xFF)
@@ -55,10 +64,12 @@ def num2bytes(value, size):
 
 
 def pack(fmt, *args):
+    """Serialize MSB-first message."""
     return struct.pack('>' + fmt, *args)
 
 
 def frame(*msgs):
+    """Serialize MSB-first length-prefixed frame."""
     res = io.BytesIO()
     for msg in msgs:
         res.write(msg)