[BUG] End the Elasticsearch exporter's wait on a read or write error

ResponseHandler::OnEvent records a completion for each session state that
ends the session, but ReadError and WriteError only log. A client that
reports either of them as its last event leaves the synchronous Export()
blocked on its condition variable with nothing left to wake it.

The bundled curl client dispatches neither state, so this does not change
behaviour for callers who use it. It matters for the HttpClient that the
exporter's constructor accepts.

The cases live in the existing synchronous fixture, which skips when the
exporter is built for async export, and a CTest timeout bounds them because
a regression here stalls the job rather than failing an assertion.

Signed-off-by: thc1006 <84045975+thc1006@users.noreply.github.com>

Author: thc1006

CHANGELOG.md

@@ -79,6 +79,8 @@ Increment the:
   Note that `AsyncMetricStorage`'s constructor now takes the view's
   `AttributesProcessor`, matching `SyncMetricStorage`.
   [#1724](https://github.com/open-telemetry/opentelemetry-cpp/issues/1724)
+* [BUG] End the Elasticsearch exporter's wait on a read or write error
+  [#4331](https://github.com/open-telemetry/opentelemetry-cpp/pull/4331)
 
 * [BUG] Keep the curl retry deadline stable within each attempt
   [#4452](https://github.com/open-telemetry/opentelemetry-cpp/pull/4452)

exporters/elasticsearch/CMakeLists.txt

@@ -55,4 +55,8 @@ if(OTELCPP_BUILD_TESTING)
     TARGET es_log_record_exporter_test
     TEST_PREFIX exporter.
     TEST_LIST es_log_record_exporter_test)
+
+  # These cases exist to catch a wait that never returns. Without a per test
+  # bound a regression stalls the job instead of failing it.
+  set_tests_properties(${es_log_record_exporter_test} PROPERTIES TIMEOUT 30)
 endif() # OTELCPP_BUILD_TESTING

exporters/elasticsearch/src/es_log_record_exporter.cc

@@ -110,8 +110,8 @@ class ResponseHandler : public http_client::EventHandler
 
   /**
    * A method the user calls to block their thread until the request has either produced a
-   * response or failed. The longest duration is the timeout of the request, set by
-   * SetTimeoutMs(), which arrives here as a TimedOut session event.
+   * response or failed. It has no deadline of its own and relies on the HTTP client
+   * reporting one of the terminal session states.
    */
   bool waitForResponse()
   {
@@ -183,11 +183,15 @@ class ResponseHandler : public http_client::EventHandler
         OTEL_INTERNAL_LOG_ERROR("[ES Log Exporter] Network error");
         recordCompletion(CompletionState::Failure);
         break;
+      // Both of these end the session, so each has to release the waiter. Without that a
+      // synchronous export whose transfer fails this way blocks until the process ends.
       case http_client::SessionState::ReadError:
         OTEL_INTERNAL_LOG_DEBUG("[ES Log Exporter] Read error");
+        recordCompletion(CompletionState::Failure);
         break;
       case http_client::SessionState::WriteError:
         OTEL_INTERNAL_LOG_DEBUG("[ES Log Exporter] Write error");
+        recordCompletion(CompletionState::Failure);
         break;
       case http_client::SessionState::Cancelled:
         OTEL_INTERNAL_LOG_ERROR("[ES Log Exporter] (manually) cancelled");