Don't stop reading from socket after 4096 bytes

Closes #45

puresnmp/transport.py

@@ -22,6 +22,34 @@
 RETRIES = 3
 
 
+def recv_all(sock):
+    '''
+    Read data from socket using ``sock.recv`` until no bytes are left to read.
+
+    Unfortunately, decoding the byte-length is non-trivial according to the
+    X690 standard (see :py:func:`puresnmp.x690.types.pop_tlv` and
+    :py:func:`puresnmp.x690.util.decode_length` for more details.
+
+    This means a simple call to ``recv`` does not have length-information and
+    detecting the end of the stream is more error-prone.
+
+    This could be refactored in the future to meld the x690 and "transport"
+    layers together.
+
+    See https://stackoverflow.com/a/17697651/160665
+    '''
+    buffer_size = 4096 # 4 KiB
+    chunks = []
+    while True:
+        chunk = sock.recv(buffer_size)
+        chunks.append(chunk)
+        if len(chunk) < buffer_size:
+            # either 0 or end of data
+            break
+    data = b''.join(chunks)
+    return data
+
+
 def send(ip, port, packet, timeout=2):  # pragma: no cover
     # type: ( str, int, bytes, int ) -> bytes
     """
@@ -47,7 +75,7 @@ def send(ip, port, packet, timeout=2):  # pragma: no cover
                 LOG.debug('Sending packet to %s:%s (attempt %d/%d)\n%s',
                           ip, port, (num_retry+1), RETRIES, hexdump)
             sock.sendto(packet, (ip, port))
-            response = sock.recv(8192)
+            response = recv_all(sock)
             break
         except socket.timeout:
             LOG.debug('Timeout during attempt #%d',