From bded1e349662eeb634383ad46ec3e1605b317ec7 Mon Sep 17 00:00:00 2001
From: Ilya Etingof <etingof@gmail.com>
Date: Thu, 10 Jan 2019 23:12:06 +0100
Subject: Emit low-level sendmsg/recvmsg debugging

When running in transparent proxy mode, log syscall parameters
to aid troubleshooting
---
 pysnmp/carrier/asyncore/dgram/base.py |  7 +++++++
 pysnmp/carrier/sockmsg.py             | 21 +++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/pysnmp/carrier/asyncore/dgram/base.py b/pysnmp/carrier/asyncore/dgram/base.py
index 274b1eba..4edae19b 100644
--- a/pysnmp/carrier/asyncore/dgram/base.py
+++ b/pysnmp/carrier/asyncore/dgram/base.py
@@ -75,8 +75,10 @@ class DgramSocketTransport(AbstractSocketTransport):
         try:
             if self.socket.family in (socket.AF_INET, socket.AF_INET6):
                 self.socket.setsockopt(socket.SOL_IP, socket.IP_PKTINFO, flag)
+
             if self.socket.family == socket.AF_INET6:
                 self.socket.setsockopt(socket.SOL_IPV6, socket.IPV6_RECVPKTINFO, flag)
+
         except socket.error:
             raise error.CarrierError('setsockopt() for %s failed: %s' % (self.socket.family == socket.AF_INET6 and "IPV6_RECVPKTINFO" or "IP_PKTINFO", sys.exc_info()[1]))
 
@@ -96,8 +98,10 @@ class DgramSocketTransport(AbstractSocketTransport):
                 self.socket.setsockopt(
                     socket.SOL_IPV6, socket.IP_TRANSPARENT, flag
                 )
+
         except socket.error:
             raise error.CarrierError('setsockopt() for IP_TRANSPARENT failed: %s' % sys.exc_info()[1])
+
         except OSError:
             raise error.CarrierError('IP_TRANSPARENT socket option requires superusre previleges')
 
@@ -113,14 +117,17 @@ class DgramSocketTransport(AbstractSocketTransport):
     def normalizeAddress(self, transportAddress):
         if not isinstance(transportAddress, self.addressType):
             transportAddress = self.addressType(transportAddress)
+
         if not transportAddress.getLocalAddress():
             transportAddress.setLocalAddress(self.getLocalAddress())
+
         return transportAddress
 
     def getLocalAddress(self):
         # one evil OS does not seem to support getsockname() for DGRAM sockets
         try:
             return self.socket.getsockname()
+
         except Exception:
             return '0.0.0.0', 0
 
diff --git a/pysnmp/carrier/sockmsg.py b/pysnmp/carrier/sockmsg.py
index 0d79b2c7..0b21233b 100644
--- a/pysnmp/carrier/sockmsg.py
+++ b/pysnmp/carrier/sockmsg.py
@@ -17,6 +17,8 @@
 #
 import sys
 
+from pysnmp import debug
+
 if sys.version_info[:2] < (3, 3):
     # noinspection PyUnusedLocal
     def getRecvFrom(addressType):
@@ -69,38 +71,57 @@ else:
 
 
     def getRecvFrom(addressType):
+
         def recvfrom(s, sz):
             _to = None
+
             data, ancdata, msg_flags, _from = s.recvmsg(sz, socket.CMSG_LEN(sz))
+
             for anc in ancdata:
                 if anc[0] == socket.SOL_IP and anc[1] == socket.IP_PKTINFO:
                     addr = in_pktinfo.from_buffer_copy(anc[2])
                     addr = ipaddress.IPv4Address(memoryview(addr.ipi_addr).tobytes())
                     _to = (str(addr), s.getsockname()[1])
+                    break
+
                 elif anc[0] == socket.SOL_IPV6 and anc[1] == socket.IPV6_PKTINFO:
                     addr = in6_pktinfo.from_buffer_copy(anc[2])
                     addr = ipaddress.ip_address(memoryview(addr.ipi6_addr).tobytes())
                     _to = (str(addr), s.getsockname()[1])
+                    break
+
+            debug.logger & debug.flagIO and debug.logger(
+                'recvfrom: received %d octets from %s to %s; '
+                'iov blob %r' % (len(data), _from, _to, ancdata))
+
             return data, addressType(_from).setLocalAddress(_to)
 
         return recvfrom
 
 
     def getSendTo(addressType):
+
         def sendto(s, _data, _to):
             ancdata = []
             if type(_to) == addressType:
                 addr = ipaddress.ip_address(_to.getLocalAddress()[0])
+
             else:
                 addr = ipaddress.ip_address(s.getsockname()[0])
+
             if type(addr) == ipaddress.IPv4Address:
                 _f = in_pktinfo()
                 _f.ipi_spec_dst = in_addr.from_buffer_copy(addr.packed)
                 ancdata = [(socket.SOL_IP, socket.IP_PKTINFO, memoryview(_f).tobytes())]
+
             elif s.family == socket.AF_INET6 and type(addr) == ipaddress.IPv6Address:
                 _f = in6_pktinfo()
                 _f.ipi6_addr = in6_addr.from_buffer_copy(addr.packed)
                 ancdata = [(socket.SOL_IPV6, socket.IPV6_PKTINFO, memoryview(_f).tobytes())]
+
+            debug.logger & debug.flagIO and debug.logger(
+                'sendto: sending %d octets to %s; iov blob %r' % (len(data), _to, ancdata))
+
             return s.sendmsg([_data], ancdata, 0, _to)
 
         return sendto
-- 
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