implement send_trap()

[atodorov-storpool]

Hello,

I choose your library to implement snmp agent for our company project. It is working fine but there was need to implement functionality to send traps. I am beginner Python developer and it took some time to figure out your code flow and how to add sending trap functionality how to glue python ctypes to libnetsnmp. I do not use your code for defining ASN types because I found net-snmp function that is used in sendtrap tool for creating the needed varbind list for send_trap(). You can find some example scripts for using it. The traps that are received by snmptrapd ara passed to simple shell handler for logging to syslog - I do not found a way to log on console because the handler is started by snmptrapd.

I see in your TODO list that such functionality is planned and I hope the code will help to faster extend your library.

Best Regards,
Anton Todorov

ps. Please bump the pip package - I can confirm the recent commit in master about the string handling are working but pip is not updated.

[pief]

Looks very interesting, I'll have to take a closer look this weekend :)

Once I close #20, I'll prepare a new 0.5.1 stable release.

[atodorov-storpool]

I just spot small bug in the init of snmp_pdu class:

def __init__(self, pduType = SNMP_MSG_TRAP2):
"""create PDU object """
self.pdu = libnsX.snmp_pdu_create(SNMP_MSG_TRAP2)

I am not passing pduType variable to snmp_pdu_create() function usiing hardcoded value instead. It is not important because I use the PDU structure as temporary container where snmp_add_var() function is doing its magic to pdu.variables. Everything other is not used at all so it does not matter actually.

[wreszelewski]

Are there any issues blocking this pull request from being merged?

[pief]

Please note that this PR is still on my to-do list.

[sewashinobi]

@atodorov-storpool Can you please merge master in your branch?

are your commits stable.. can I use it?

[atodorov-storpool]

@sewashinobi merged.

They are working for me, sure you can try using them :)

[pief]

@sewashinobi Does it work for you too, then?

[sewashinobi]

@pief @atodorov-storpool

Sorry for delayed response
yes it works, but I see following warning when Counter64 is used in traps

Warning : send_trap: failed to convert v2->v1 template PDU

Although there is some discussion about it in netsnmp mailing list,
https://sourceforge.net/p/net-snmp/mailman/message/27295298/

FYI.. I have configured snmpd for only v2c, and there is only one trap and that is configured as follows.. not sure then why this warning is coming..

trap2sink xxx.xxx.xxx.xxx <community>

Netsnmp Version ( Ubuntu)

snmpd --version

NET-SNMP version:  5.7.2
Web:               http://www.net-snmp.org/
Email:             [email protected]

[sewashinobi]

@atodorov-storpool I have trap running in production and looks good, but sometime there is race condition and same trap is getting send twice.. from the log I am sure that my agentx is calling it only once..

in my implementation, the trap function is running in separate thread and in the main thread I have called the check_and_process.. Once I bombard approx 20 traps then few traps are coming twice.. I looked in your code but couldn't find the issue.. Appreciate if you can spot something

[sewashinobi]

@atodorov-storpool digged a little more for duplicate trap issue, it is happening when the data update and trap both happen same time ( In production it is very much possible that get request and trap both happen at same time, correct me if this shouldn't be the case )

[sewashinobi]

@atodorov-storpool any suggestion, I tried to debug in your implementation but no luck. This happens when the data update and traps are happening in parallel.

[sewashinobi]

@atodorov-storpool you code doesn't work with Python 3, this part has problem. The c_char expects bytes, I tried to encode but then trap has corrupted data.

				ret = libnsX.snmp_add_var(
						self.pdu,
						ctypes.cast(ctypes.byref(varOid), c_oid_p),
						varOidLen.value,
						ctypes.c_char(varType),
						ctypes.c_char_p('{0}'.format(varData))
				)

I fixed following as has_key is not supported

			for entry in traps:
				if 'oid' in entry:
					varOid = entry['oid']
					if 'val' in entry:
						varData = entry['val']
						varType = None
						if 'type' in entry:
							varType = entry['type']
						pdu.add(varOid, varData, varType)
					else:
						msg = "missing 'val' key in trap list!"
						raise netsnmpAgentException(msg)

While not able to figure out the c_char solution, Will you be able to help?

[sewashinobi]

I was able to fix it with encode, earlier I was trying the ctypes.c_wchar, ctypes.c_wchar_p which was giving unexpected results.

ret = libnsX.snmp_add_var(
self.pdu,
ctypes.cast(ctypes.byref(varOid), c_oid_p),
varOidLen.value,
ctypes.c_char(varType.encode()),
ctypes.c_char_p('{0}'.format(varData).encode())
)

[j123b567]

This no longer works, because in Net-SNMP v 5.8 and up, there is additional field msgMaxSize in the netsnmp_pdu data type which breaks binary compatibility.