Consolidated RegEx to parse syslog data - regex

Question

Goal
I am trying to craft a RegEx that will parse out specific data from various syslog entries that contain subtle differences in logged content. While I am able to accomplish my goal using multiple RegEx statements, if possible, I would like to combine these statements into a single consolidated RegEx.
Log entries
The main issue I'm having is that some log entries have a URL that needs to be parsed to a named group and other log entries do not have any URL. Examples of these two different log entries are provided below.
Entry with URL
Nov 3 11:33:04 host1 postfix/smtpd[12812]: NOQUEUE: reject: RCPT from 178.red-83-59-180.dynamicip.rima-tde.net[83.59.180.178]: 554 5.7.1 Service unavailable; Client host [83.59.180.178] blocked using b.barracudacentral.org; http://www.barracudanetworks.com/reputation/?pr=1&ip=83.59.180.178; from=<lmclapp68#newmail.spamcop.net> to=<user1#example.com> proto=ESMTP helo=<178.red-83-59-180.dynamicip.rima-tde.net>
Entry without URL
Nov 2 16:01:25 host1 postfix/smtpd[31667]: NOQUEUE: reject_warning: RCPT from mail1.sendersrv.com[185.3.229.125]: 554 5.7.1 Service unavailable; Client host [185.3.229.125] blocked using bl.spamcop.net; from=<bounces+rL59wUXq98_inBrG#sendersrv.com> to=<user1#example.com> proto=ESMTP helo=<mail1.sendersrv.com>
RegEx statements
In the RegEx statements that follow, the first two are what I currently use for each of the previous log messages. The third RegEx is my attempt at consolidating these both into a single RegEx that will parse data from either log message. My attempt was to use a conditional statement that would basically check for the existence of http(s) and if found, then to parse the URL to a named group. If http(s) was not found, then it would parse out everything until the next RegEx token.
The issue is that when I test the RegEx against a log entry that has a URL, the RegEx does not seem to find http(s) despite this token being set as optional (i.e. using the ? quantifier). However, if I remove the ? quantifier, it does find http(s) and then parses the URL as desired. However, without the quantifier, the RegEx does not work with log entries that do not have a URL.
Parse entries with URL
^(?P<datetime>.+) host1 postfix.+RCPT from (?P<srcDns>.+)\[(?P<srcIp>[0-9\.]+)\]:.+blocked using (?P<blkList>.+);.+https?:\/{2}(?P<entryUrl>.+);\s.+\sto=\<(?P<destEm>.+)>.+$
Parse entries without URL
^(?P<datetime>.+) host1 postfix.+RCPT from (?P<srcDns>.+)\[(?P<srcIp>[0-9\.]+)\]:.+blocked using (?P<blkList>.+);\s.+\sto=\<(?P<destEm>.+)>.+$
Attempt at consolidating RegEx
^(?P<datetime>.+) host1 postfix.+RCPT from (?P<srcDns>.+)\[(?P<srcIp>[0-9\.]+)\]:.+blocked using (?P<blkList>.+)(?<=[a-z]);.+(https?:\/{2})?(?(5)(?P<entryUrl>.+)|.+)to=\<(?P<destEm>.+)>.+$
I'm sure the issue is my misunderstanding as to how the conditional statements and the ? quantifier works.

Answer 1

Looking at your patterns, the email address for to: is between tags < and > but due to the formatting in the question they are not shown.
The parts in your pattern like .+ first match until the end of the string, and will then backtrack and try to match the rest of the pattern.
You can make the pattern a bit more performant making the parts that you want and know more specific.
For the datetime, you can make the pattern match the specified format instead of .+ using ^(?P<datetime>[A-Z][a-z]{2}\s+\d{1,2}\s* \d{1,2}:\d{1,2}:\d{1,2})
For (?P<blkList>[^;]+) and (?P<entryUrl>[^;]+) you can use a negated character class matching any char except ;
For group (?P<destEm>[^<>\s]+) you can exclude matching tags.
To make match the url, instead of using a condition you can make the group optional using ?
For example
^(?P<datetime>[A-Z][a-z]{2}\s+\d{1,2}\s* \d{1,2}:\d{1,2}:\d{1,2}) host1 postfix\b.*? RCPT from (?P<srcDns>.*?)\[(?P<srcIp>[0-9\.]+)\]:.*? blocked using (?P<blkList>[^;]+);(?:.+?https?:\/\/(?P<entryUrl>[^;]+);)?\s.*? to=[^<]*<(?P<destEm>[^<>\s]+)>
See a regex demo.

Answer 2

Have you tried to test your regex on page like regex101?
to=\<(?P<destEm>.+)> doesn't seem to match your examples. You should either remove <> or replace to with helo. Be careful to make your quantifier lazy after blkList otherwise you might catch too much text.
You can then make your url optional with ? and it should work in both cases:
^(?P<datetime>.+) host1 postfix.+RCPT from (?P<srcDns>.+)\[(?P<srcIp>[0-9\.]+)\]:.+blocked using (?P<blkList>.+?);(.+https?:\/{2}(?P<entryUrl>.+);\s)?.+\sto=(?P<destEm>.+?)\s.*$

Answer 3

One approach would be to replace in the first regex .+https?:\/{2}(?P<entryUrl>.+); with (?:.+https?:\/{2}(?P<entryUrl>.+);)? where ?: indicates that it is a non-capturing group and the ? at the end means that it is optional.
However, it still does not work because .+ is greedy, so use lazy .+? instead.
Final regex:
^(?P<datetime>.+?) host1 postfix.+?RCPT from (?P<srcDns>.+?)\[(?P<srcIp>[0-9\.]+)\]:.+?blocked using (?P<blkList>.+?);(?:.+?https?:\/{2}(?P<entryUrl>.+?);)?\s.+?\sto=\<(?P<destEm>.+?)>.+?$
https://regex101.com/r/QkmXWz (to see it in action)