core: Add filtering capability to log outputs (fixes #83)

Ayush Surirequested to merge
mastersolutions136/ns-3-dev:feature/issue-83-log-filtering into master

Resolves

Fixes #83

Description

This MR introduces string-based filtering for NS_LOG components. Users can now append a filter_<string> keyword to their environment variable configurations to selectively print logs that contain specific text (e.g., isolating logs by Node ID, time markers, or specific variable states).

Example Usage: NS_LOG="UdpEchoClientApplication=level_all|filter_sent" ./ns3 run first

Architecture & Performance

To ensure this feature introduces zero performance overhead when filtering is inactive, a fast-path/slow-path architecture was implemented inside log-macros-enabled.h:

  • Fast Path: If HasFilter() is false, the macro executes the original, unbuffered std::clog stream injection.
  • Slow Path: If a filter is active, the macro evaluates the log expression into a std::ostringstream, checks the resulting string against the filter, and flushes to std::clog upon a match.

Testing

  • Tested against standard examples (e.g., first.cc) to verify both unfiltered and filtered outputs function as expected.
  • Verified compilation under debug profile with NS3_ASSERT enabled.

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