I'm trying to need to access/parse all outgoing connections on a particular port number on a Linux machine using a Python script. The simplest implementation seems to be to open a subprocess for netstat and parse its stdout.
I imagine someone somewhere has had this problem before, and am surprised not to find any netstat parsers online. Is this just not big enough of a problem for people to feel the need to share?
If you want to control the connection opened by a certain process you can use psutil:
>>> p = psutil.Process(1694)
>>> p.name()
'firefox'
>>> p.connections()
[connection(fd=115, family=2, type=1, local_address=('10.0.0.1', 48776), remote_address=('93.186.135.91', 80), status='ESTABLISHED'),
connection(fd=117, family=2, type=1, local_address=('10.0.0.1', 43761), remote_address=('72.14.234.100', 80), status='CLOSING'),
connection(fd=119, family=2, type=1, local_address=('10.0.0.1', 60759), remote_address=('72.14.234.104', 80), status='ESTABLISHED'),
connection(fd=123, family=2, type=1, local_address=('10.0.0.1', 51314), remote_address=('72.14.234.83', 443), status='SYN_SENT')]
Internally psutil uses /proc. If you're interested in connections to/from a particular port number at system level you might take a look at how psutil implements it.
Edit: starting from psutil 2.1.0 you can also gather system-wide connections using net_connections():
>>> import psutil
>>> psutil.net_connections()
[pconn(fd=115, family=2, type=1, laddr=('10.0.0.1', 48776), raddr=('93.186.135.91', 80), status='ESTABLISHED', pid=1254),
pconn(fd=117, family=2, type=1, laddr=('10.0.0.1', 43761), raddr=('72.14.234.100', 80), status='CLOSING', pid=2987),
pconn(fd=-1, family=2, type=1, laddr=('10.0.0.1', 60759), raddr=('72.14.234.104', 80), status='ESTABLISHED', pid=None),
pconn(fd=-1, family=2, type=1, laddr=('10.0.0.1', 51314), raddr=('72.14.234.83', 443), status='SYN_SENT', pid=None)
...]
psutil.net_connections() on FreeBSD. I will report this case if my next debugs confirm that. python Python 3.8.12 (default, Nov 5 2021, 16:04:17) [Clang 10.0.1 ([email protected]:llvm/llvm-project.git llvmorg-10.0.1-0-gef32c611a on freebsd12 >>> import psutil >>> len([ (sconn.laddr, sconn.raddr) for sconn in psutil.net_connections(kind="tcp4") if sconn.status == "ESTABLISHED" and sconn.laddr.port == 2049]) 0