mpm: Fix ECHO command

The echo server was using the wrong socket options, allowing responses
to be fragmented. Since we use the echo server for MTU discovery, that
would have beaten the purpose.

Also includes minor formatting fixes.

1 files changed, 16 insertions, 8 deletions

diff --git a/mpm/python/usrp_mpm/discovery.py b/mpm/python/usrp_mpm/discovery.py
index 9860958c9..7a133af15 100644
--- a/mpm/python/usrp_mpm/discovery.py
+++ b/mpm/python/usrp_mpm/discovery.py
@@ -18,6 +18,12 @@ from usrp_mpm.mpmlog import get_main_logger
 RESPONSE_PREAMBLE = "USRP-MPM"
 RESPONSE_SEP = ";"
 RESPONSE_CLAIMED_KEY = "claimed"
+# "Max MTU" is not a redundant name. We don't know the total path MTU, but we
+# can say for sure that it won't exceed a certain value, and that's the max MTU
+MAX_MTU = 8000
+# For setsockopt
+IP_MTU_DISCOVER = 10
+IP_PMTUDISC_DO = 2
 
 def spawn_discovery_process(device_info, shared_state, discovery_addr):
     """
@@ -57,15 +63,16 @@ def _discovery_process(device_info, state, discovery_addr):
     # working yet
     sock.bind((("0.0.0.0", MPM_DISCOVERY_PORT)))
     send_sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    send_sock.setsockopt(socket.IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DO)
 
     # TODO yeah I know that's not how you do this
-    discovery_addr_prefix  = discovery_addr.replace('.255', '')
+    discovery_addr_prefix = discovery_addr.replace('.255', '')
     if discovery_addr == '0.0.0.0':
         discovery_addr_prefix = ''
 
     try:
         while True:
-            data, sender = sock.recvfrom(8000)
+            data, sender = sock.recvfrom(MAX_MTU)
             log.info("Got poked by: %s", sender[0])
             # TODO this is still part of the awful subnet identification
             if not sender[0].startswith(discovery_addr_prefix):
@@ -77,14 +84,15 @@ def _discovery_process(device_info, state, discovery_addr):
                 log.info(send_data)
                 send_sock.sendto(send_data, sender)
             elif data.strip(b"\0").startswith(b"MPM-ECHO"):
-                log.info("Received echo request from {sender}".format(
-                    sender=sender[0])
-                )
+                log.info("Received echo request from {sender}"
+                         .format(sender=sender[0]))
                 send_data = data
-                send_sock.sendto(send_data, sender)
+                try:
+                    send_sock.sendto(send_data, sender)
+                except OSError as ex:
+                    log.debug("ECHO send error: %s", str(ex))
     except Exception as err:
-        log.error("Error: %s", err)
-        log.error("Error type: %s", type(err))
+        log.error("Unexpected error: `%s' Type: `%s'", str(err), type(err))
         sock.close()
         send_sock.close()
         exit(1)