[EXPORTER] Avoid std::terminate when the OTLP HTTP response body cannot be processed

[YuEfSaEDU]

ResponseHandler::OnResponse is declared noexcept, but copying the response body and parsing it with JsonStringToMessage or ParseFromString can throw; any exception escaping a noexcept function calls std::terminate(), so a single malformed or oversized response from a misbehaving collector or intermediary could take down the exporting process.

This change guards the body copy and both parse branches with try/catch, logs any exception through the internal logger, and reports the export as ExportResult::kFailure. The session-completion logic remains outside the guarded region so the result callback still runs exactly once and no caller is left waiting when an exception is caught, matching the completion contract established in #4298.

Tests added to otlp_http_exporter_custom_client_test cover the JSON and protobuf parse-failure paths against the nosend stub client, asserting a single failure report and that ForceFlush returns without waiting out the deadline.

Fixes #4534

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: YuEfSaEDU / name: Yusuf Efe Saglam (33d59b7)

[mateenali66]

the try needs an #if OPENTELEMETRY_HAVE_EXCEPTIONS guard. bazel.noexcept in ci.yml builds //exporters/otlp:otlp_http_client with -fno-exceptions (only the builders are in NOEXCEPT_EXCLUDES). checked with clang++ -fsyntax-only -fno-exceptions on otlp_http_client.cc: main at e62f627 is clean, 33d59b7 fails at :126 with "cannot use 'try' with exceptions disabled". CI has not run here yet because of the CLA, so it will show up then. otlp_file_client.cc:1454 and periodic_exporting_metric_reader.cc:164 already use that pattern.

separately, both new tests send bodies that make the parser return false (\xff... and {some bad JSON). main already turns those into kFailure at :147 and :153, so neither test reaches the catch. would a stub response whose GetBody() throws work, so the test fails on main?

[codecov]

Codecov Report

❌ Patch coverage is 70.83333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.48%. Comparing base (e62f627) to head (33d59b7).

Files with missing lines	Patch %	Lines
exporters/otlp/src/otlp_http_client.cc	70.84%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4587      +/-   ##
==========================================
- Coverage   86.52%   86.48%   -0.03%     
==========================================
  Files         525      525              
  Lines       20464    20472       +8     
==========================================
  Hits        17704    17704              
- Misses       2760     2768       +8     

Files with missing lines	Coverage Δ
exporters/otlp/src/otlp_http_client.cc	72.73% <70.84%> (-0.75%)	⬇️

... and 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.