fix: release the streaming connection and survive a concurrent commit

Two findings from the CodeRabbit review:

- When a streaming body threw, the explicit connection.close() inside session.doWork
  was skipped. session.close() still ran, but the explicit close exists precisely
  because Spring does not reliably release it, so the failure path could hold
  database capacity. It is now in a finally, with assertions on both the completing
  and the throwing path.
- dropStagedStreamingHeaders checked isCommitted and then iterated the headers
  before calling reset(). On the timeout path a stream that started just as the
  timeout fired can commit inside that window, and reset() would throw
  IllegalStateException out of the @ExceptionHandler — replacing the intended 503
  with a container 500 page. It now falls back to leaving the response alone.

Author: JanCizmar

backend/app/src/main/kotlin/io/tolgee/ExceptionHandlers.kt

@@ -318,7 +318,14 @@ class ExceptionHandlers(
       response.headerNames
         .filterNot { STAGED_STREAMING_HEADERS.contains(it) }
         .associateWith { response.getHeaders(it).toList() }
-    response.reset()
+    try {
+      response.reset()
+    } catch (e: IllegalStateException) {
+      // A stream that started just as the timeout fired can commit between the check above and
+      // here. Throwing out of an @ExceptionHandler would replace the 503 with a container 500 page.
+      logger.debug("Response committed while answering a streaming timeout", e)
+      return
+    }
     preserved.forEach { (name, values) -> values.forEach { response.addHeader(name, it) } }
   }
 

backend/app/src/test/kotlin/io/tolgee/util/StreamingResponseBodyProviderMetricsTest.kt

@@ -48,6 +48,7 @@ class StreamingResponseBodyProviderMetricsTest {
 
     timerCount(StreamType.IMPORT_APPLY).assert.isEqualTo(1L)
     Mockito.verify(session).close()
+    Mockito.verify(connection).close()
   }
 
   @Test
@@ -57,6 +58,7 @@ class StreamingResponseBodyProviderMetricsTest {
       .writeTo(ByteArrayOutputStream())
 
     Mockito.verify(session).close()
+    Mockito.verify(connection).close()
   }
 
   @Test

backend/data/src/main/kotlin/io/tolgee/util/StreamingResponseBodyProvider.kt

@@ -51,9 +51,12 @@ class StreamingResponseBodyProvider(
       val session = entityManager.unwrap(Session::class.java)
       try {
         session.doWork { connection ->
-          fn(it)
-          // Manually dispose the connection because spring has a hard time doing so by itself
-          connection.close()
+          try {
+            fn(it)
+          } finally {
+            // Manually dispose the connection because spring has a hard time doing so by itself
+            connection.close()
+          }
         }
       } finally {
         session.close()