lua-nginx-module build failure due to request time tracking changes (commit 3329aa9)

[u5surf]

Summary

The lua-nginx-module fails to build with FreeNginx due to breaking changes in request time tracking introduced in commit 3329aa9d66a78d147a3a5186004f5122bfa9277a.

Root Cause Analysis

Specific Commit: 3329aa9

This commit introduced significant changes to time tracking in FreeNginx:

Key Changes:

1. Removed fields from ngx_http_request_t:

   • start_sec (time_t)
   • start_msec (ngx_msec_t)

2. Added new field:

   • start_time (ngx_msec_t) - using monotonic time via ngx_current_msec

3. Changed time calculation logic:

   • Old method: (tp->sec - r->start_sec) * 1000 + (tp->msec - r->start_msec)
   • New method: ngx_current_msec - r->start_time

Impact on lua-nginx-module:

The lua-nginx-module likely contains code that directly accesses r->start_sec and r->start_msec fields, which no longer exist in FreeNginx. This causes compilation failures when building the module against FreeNginx.

Environment

• FreeNginx version: Post-commit 3329aa9 (latest)
• lua-nginx-module version: Latest from OpenResty
• Related failure: https://github.com/vozlt/nginx-module-vts/actions/runs/16381462851/job/46293696855?pr=326

Problem Description

When attempting to build lua-nginx-module with FreeNginx, the build fails because:

1. The module tries to access r->start_sec and r->start_msec
2. These fields were removed in the monotonic time tracking changes
3. No compatibility layer exists for modules using the old time tracking API

Expected vs Actual Behavior

• Expected: lua-nginx-module builds successfully with FreeNginx (as FreeNginx aims to be drop-in compatible)
• Actual: Build fails due to missing struct members

Suggested Solutions

Option 1: Compatibility Layer (Recommended)

Add compatibility macros or inline functions to maintain API compatibility:

#ifdef FREENGINX_VERSION
#define ngx_http_request_start_sec(r)  ((r)->start_time / 1000)
#define ngx_http_request_start_msec(r) ((r)->start_time % 1000)
/* Or provide actual fields for backward compatibility */
#endif

Option 2: Document Breaking Changes

• Clearly document this as a breaking change in FreeNginx release notes
• Provide migration guide for module developers
• List affected popular modules (lua-nginx-module, nginx-module-vts, etc.)

Option 3: Conditional Compilation Support

Ensure modules can detect FreeNginx version and adapt accordingly:

#ifdef FREENGINX_VERSION
    // Use new start_time field
    ms = ngx_current_msec - r->start_time;
#else
    // Use legacy start_sec/start_msec
    ms = (tp->sec - r->start_sec) * 1000 + (tp->msec - r->start_msec);
#endif

Impact Assessment

This change affects any nginx module that:

• Accesses r->start_sec or r->start_msec directly
• Performs custom request timing calculations
• Relies on the traditional nginx time tracking API

Known affected modules:

• lua-nginx-module (OpenResty)
• nginx-module-vts (and likely many others)

Request

Given that FreeNginx aims to be a drop-in replacement for nginx, could the maintainers consider:

1. Adding a compatibility layer to maintain API compatibility for existing modules
2. Providing clear migration documentation for module developers
3. Testing against popular modules like lua-nginx-module in CI
4. Coordinating with module maintainers on the transition

The goal would be to maintain FreeNginx's drop-in compatibility promise while improving the time tracking implementation.

Additional Context

• Commit purpose: "Ensures that $request_time is not affected by system time changes on platforms with monotonic time available"
• This is a valuable improvement but breaks existing module ecosystem
• Balance needed between technical improvements and ecosystem compatibility

Thank you for the excellent work on FreeNginx and for considering module compatibility!

[mdounin]

Duplicate of #12. As suggested in #12 (comment), affected modules needs to be updated with something like:

#if (defined freenginx && nginx_version >= 1029000)
... use r->start_time
#else
... use r->start_sec
#endif