A tool to extract statistics from apache-like http logs. It is not a library, but it's structured in a way that should be easy for you to adapt for your own needs.

Practically me, or anyone else who, due to an organisational accident, cannot have their logs in a proper service like Kinbana or Azure Application Insights, and has to parse them with in-house tools.

The ConsoleLogAnalyser project is just a very simple exe to test and run the tool.
All the logic is in the LogAnalyser project, which is a .NET Standard library, so it could be used in most OSes and many flavours of .NET (in our case, it's designed to be called by a legacy WinForms application which presents the different search options and results).
The project uses preview features of C#8 (strict nulls and range operators). You can already use them now.

The Parser is navigating the structure of your logs. You might need to adapt apacheLogRegex, as most probably in your logs the fields might be in a different order or with a different separator (you can find apache log http logs regexes on the internet).
You will most probably need to define new implementations of ISearchStrategy, to suit your needs. The included ones can be used as examples:

• SimpleSearch is searching for strings in the url, and/or a specific parameter (in our case the id of the person). It has no real state and will give the same results regarding of the parsing order.
• SuccessAnalysis is used for A/B testing in our case. It finds the start of a task, and searches for the end of that task until a timeout has passed. It can track multiple attempts to a task in parallel, but it needs to read each node sequentially (if you don't use sticky sessions, you will need to algorithm which defines when the attempt to perform a task has failed).

If you find it useful, I'd love to know it! I am sure in your context you will have more interesting search patterns.