DoH with HTTPS, fix response handling

[icing]

Fix handling of DoH response that only asks for HTTPS records.

Add test 2117 for checking that a HTTPS-RR resolve is processed, even though the actual answer is invalid.

[Copilot]

Pull request overview

Fixes DoH resolution handling when the query set includes HTTPS records (including the HTTPS-only case), and adds coverage for processing an HTTPS-RR resolve even when the actual answer is invalid. The PR also refactors tracing by introducing a dedicated DoH trace feature and updating related trace output and documentation.

Changes:

• Add test 2117 to validate HTTPS-RR processing behavior with DoH under ECH/HTTPSRR-enabled configurations.
• Adjust DoH result handling and tracing to better support non-address queries and HTTPS-RR decode flow.
• Introduce a new Curl_trc_feat_doh trace feature and document curl_global_trace’s doh option.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/data/test2117	Adds a new DoH + HTTPS-RR focused regression test (with ECH) validating processing of HTTPS RR resolves.
tests/data/Makefile.am	Registers the new test2117 in the test suite list.
lib/httpsrr.c	Updates HTTPS RR trace message prefixes/wording.
lib/doh.c	Refines DoH probe/consume logic for HTTPS-RR cases and adjusts verbosity/tracing behavior.
lib/curl_trc.h	Declares the new DoH trace feature (guarded by !CURL_DISABLE_DOH).
lib/curl_trc.c	Defines/registers the new DoH trace feature in the trace feature table.
docs/libcurl/curl_global_trace.md	Documents doh tracing, but currently ends up with duplicate/conflicting doh sections.

Comments suppressed due to low confidence (2)

lib/doh.c:371

• The DoH probe's CURLOPT_VERBOSE is now only enabled when Curl_trc_feat_doh is verbose. Because curl_global_trace("doh") is currently aliased to dns in Curl_trc_opt(), this condition will remain false in practice and the probe handle loses verbose output compared to dns tracing. Consider accepting either doh or dns verbosity here (or fix the option parsing).

  if(data->set.err && data->set.err != stderr)
    ERROR_CHECK_SETOPT(CURLOPT_STDERR, data->set.err);
  if(Curl_trc_ft_is_verbose(data, &Curl_trc_feat_doh))
    ERROR_CHECK_SETOPT(CURLOPT_VERBOSE, 1L);

lib/doh.c:1255

• doh_show() output is now gated solely on Curl_trc_feat_doh. Given curl_global_trace("doh") is currently parsed as an alias for dns, this prevents the detailed DoH response dump from showing up under DNS tracing. Either make doh independently enableable, or also respect dns verbosity for this debug output.

        if(Curl_trc_ft_is_verbose(data, &Curl_trc_feat_doh)) {
          CURL_TRC_DNS(data, "hostname: %s", dohp->host);
          doh_show(data, &de);

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