Gate W3C trace support to request phases with ngx.var access

[mtrop-godaddy]

The http library reads ngx.var.http_traceparent in send_request to propagate W3C trace context. ngx.var is only readable in request-bearing phases, so this crashes code running in init/init_worker.

Gate the read on ngx.get_phase() being in a request-bearing phase via a whitelist, so request-less phases (init, init_worker, timer, etc.) are excluded by default. Behavior is unchanged for real requests.

[sriemer]

Looks very good. Thank you very much! 😃
Just the phases should be revisited. TIA

[sriemer]

Reviewed documentation and code:

• https://openresty-reference.readthedocs.io/en/latest/Lua_Nginx_API/#ngxvarvariable
• https://openresty-reference.readthedocs.io/en/latest/Lua_Nginx_API/#ngxget_phase
• grep -R "NGX_HTTP_[A-Z_]\+PHASE" on latest NGINX source
• find . \( -name "*.lua" -o -name "*.t" -o -name "*.c" -o -name "*.h" \) -exec grep --color -RHi "phase" {} \; on latest lua-nginx-module source
• checked https://github.com/openresty/lua-nginx-module#directives for "*by_lua*"

[sriemer]

Phases not listed as supported in https://openresty-reference.readthedocs.io/en/latest/Lua_Nginx_API/#ngxvarvariable:

• server_rewrite
• preread
• balancer
• precontent

Accessible via *by_lua*: server_rewrite, precontent, balancer

[sriemer]

server_rewrite and precontent may do full API calls in a sandbox. balancer has a limited subset. But preread is unlikely to be triggered.
So I would like to go for dropping balancer and preread.
I would like to add precontent as well.
@mtrop-godaddy Is this plan fine for you? TIA

[mtrop-godaddy]

Thanks for taking a look. That works for me - I updated the allow list. I also had to make some changes to the test workflow because of the Node.js 20 deprecation and an ancient OpenResty image (or more accurately it's Alpine base) which doesn't support Node.js 24.

[sriemer]

LGTM. Thanks. 😃

[sriemer]

This PR fixes PR #340 which added the ngx.var.http_traceparent handling.