Add: Server-side TLS handshake milestones and timing fixes

[bryancall]

Description

Add TS_MILESTONE_SERVER_TLS_HANDSHAKE_START and TS_MILESTONE_SERVER_TLS_HANDSHAKE_END milestones to capture origin-side TLS handshake timing. Previously, only client-side TLS timing was available via TS_MILESTONE_TLS_HANDSHAKE_START/END, making it impossible to measure origin TLS handshake overhead in the slow log or via the milestone API.

Changes

New server-side TLS milestones (commit 1)

• Add TS_MILESTONE_SERVER_TLS_HANDSHAKE_START/END enum values in apidefs.h.in (ABI compatible — appended before TS_MILESTONE_LAST_ENTRY)
• Capture server TLS timing in HttpSM::state_http_server_open() for both the direct (VC_EVENT_WRITE_COMPLETE) and multiplexed (CONNECT_EVENT_TXN) connection paths
• Fix: SSLNetVConnection::sslClientHandShakeEvent() was recording TLS handshake start time for outbound connections but never calling _record_tls_handshake_end_time() — outbound TLS end time was always 0
• Rename slow log field tls_handshake → ua_tls_handshake for clarity, add new server_tls_handshake field in logical position after server_connect_end
• Update LogField.cc milestone-to-string mappings for custom log fields
• Add Lua plugin milestone constants (TS_LUA_MILESTONE_SERVER_TLS_HANDSHAKE_START/END)
• Update TSHttpTxnMilestoneGet API documentation
• Update slow_log_report.pl to parse new field names

Fix difference_msec() milestone check (commit 2)

• difference_msec() only checked if ms_end == 0 (unset) before returning the missing sentinel. If ms_start was unset but ms_end was set, the subtraction would produce a garbage value. Now checks both ms_start and ms_end for 0.

Use SM_START as base for server_tls_handshake (commit 3)

• Change server_tls_handshake from a duration to an offset from SM_START, consistent with all other server-side fields in the slow log timeline.

Add comments explaining connection paths (commit 4)

• Clarify that CONNECT_EVENT_TXN is the multiplexed path (HTTP/2) and VC_EVENT_WRITE_COMPLETE is the direct path (HTTP/1).

Make slow_log_report.pl backward compatible (commit 5)

• The tls_handshake → ua_tls_handshake rename broke parsing of old-format logs. The report script now accepts both field names.

Use pre-remap URL in slow log (commit 6)

• The slow log was printing the post-remap (origin-facing) URL. Changed to use t_state.unmapped_url (the pre-remap URL) so the log shows the URL the client actually requested.

Behavior Notes

• When no server TLS handshake occurs (non-TLS origin, connection reuse), the milestones remain 0 and the slow log reports -0.001 (the "missing" sentinel), consistent with other unset milestones.
• The tls_handshake → ua_tls_handshake rename is a slow log text change only — it does not affect ABI.
• Existing TS_MILESTONE_TLS_HANDSHAKE_START/END enum values and behavior are unchanged.

Testing

• Build passes (including ASAN build)
• Manual testing with client-side and server-side TLS verified both milestone pairs populate correctly
• slow_log_report.pl correctly parses and reports both ua_tls_handshake and server_tls_handshake
• Verified milestones remain 0 for non-TLS and connection-reuse scenarios

[Copilot]

Pull request overview

This pull request adds server-side TLS handshake milestones to Apache Traffic Server, enabling measurement of origin TLS handshake overhead. The PR addresses two main issues: (1) missing visibility into server-side TLS handshake timing, and (2) bugs in milestone timing capture and calculation.

Changes:

• Adds TS_MILESTONE_SERVER_TLS_HANDSHAKE_START/END enum values and captures server TLS timing in both direct and multiplexed connection paths
• Fixes missing TLS handshake end time recording for outbound connections in SSLNetVConnection::sslClientHandShakeEvent()
• Fixes difference_msec() to check both start and end milestones for 0 before computing difference
• Renames slow log field tls_handshake to ua_tls_handshake for clarity and adds server_tls_handshake field

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
include/ts/apidefs.h.in	Adds TS_MILESTONE_SERVER_TLS_HANDSHAKE_START/END enum values before TS_MILESTONE_LAST_ENTRY (ABI-compatible)
include/proxy/Milestones.h	Fixes difference_msec() to check both start and end for zero before subtraction
src/iocore/net/SSLNetVConnection.cc	Adds missing _record_tls_handshake_end_time() call for outbound TLS connections
src/proxy/http/HttpSM.cc	Captures server TLS milestones in both connection paths (direct and multiplexed); renames slow log field to ua_tls_handshake and adds server_tls_handshake
src/proxy/logging/LogField.cc	Adds milestone string mappings for new server TLS milestones with TODO comments for ATS 11 rename
plugins/lua/ts_lua_http_milestone.cc	Adds Lua plugin constants for server TLS handshake milestones
doc/developer-guide/api/functions/TSHttpTxnMilestoneGet.en.rst	Updates API documentation to clarify client vs. server TLS handshake milestones
doc/admin-guide/plugins/lua.en.rst	Documents new Lua milestone constants
tools/slow_log_report.pl	Updates regex to parse renamed ua_tls_handshake field and new server_tls_handshake field

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