SOLR-18188: Misc test fixes (#4496)

Accumulated from several commits on the misc-test-fixes branch.

PrepRecoveryOp: add class-level javadoc to explain its purpose.

ShowFileRequestHandlerTest, TestPrometheusResponseWriter,
TestCborDataFormat: close response streams to fix resource leaks
flagged by the test framework.

TestDistributedTracing: add retry logic around span assertions to
reduce flakiness caused by timing-sensitive telemetry delivery.

SocketProxy: call setSoTimeout(1000) on the server socket so the
accept loop unblocks promptly when close() is called. Without a
timeout the acceptor thread blocks indefinitely in accept() and
leaks, causing test hangs or "thread leaked" warnings.

JettySolrRunner: move proxy.close() to before server.stop() rather
than leaving it in the finally block. If qtp.join() hangs (e.g. stuck
PrepRecoveryOp handlers or H2C session threads) the finally block is
never reached, leaving the SocketProxy acceptor thread leaked. Closing
the proxy first ensures cleanup even when server shutdown hangs.

HttpJettySolrClientCompatibilityTest: switch from @ClassRule to @rule
so the Jetty server lifecycle is per-test as intended.

TestSolrJ: delete this file -- it contains no actual tests.

ClientUtils: add Objects.requireNonNull() guard on serverRootUrl to
surface null earlier with a clear error rather than a cryptic NPE
downstream.

AbstractFullDistribZkTestBase: wrap control-collection creation in
RetryUtil.retryOnException() to tolerate transient ZooKeeper errors
during setup. Also move coreClients.clear(),
solrClientByCollection.clear(), and super.destroyServers() into a
finally block after ExecutorUtil.shutdownAndAwaitTermination() so
teardown always completes even if the executor shutdown throws.

HttpPartitionTest: decrease leaderConflictResolveWait to 10sec so 
stale PrepRecoveryOp handlers time out within the Jetty graceful stop window

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dsmiley

solr/core/src/java/org/apache/solr/handler/admin/PrepRecoveryOp.java

@@ -37,6 +37,13 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+/**
+ * Long-polling request sent by a recovering replica to the shard leader. The leader holds the
+ * request open, waiting until it observes the replica reach the expected state (typically
+ * RECOVERING) in ZooKeeper before responding. This synchronization ensures the leader is ready to
+ * accept updates from the replica before recovery proceeds. The wait is bounded by {@code
+ * leaderConflictResolveWait} (default 180s).
+ */
 class PrepRecoveryOp implements CoreAdminHandler.CoreAdminOp {
   private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
 

solr/core/src/test/org/apache/solr/cloud/HttpPartitionTest.java

@@ -83,6 +83,8 @@ public static void setupSysProps() {
     System.setProperty("solr.httpclient.retries", "0");
     System.setProperty("solr.retries.on.forward", "0");
     System.setProperty("solr.retries.to.followers", "0");
+    // Keep short so stale PrepRecoveryOp handlers time out within the Jetty graceful stop window
+    System.setProperty("leaderConflictResolveWait", "10000");
   }
 
   public HttpPartitionTest() {

solr/core/src/test/org/apache/solr/handler/admin/ShowFileRequestHandlerTest.java

@@ -142,6 +142,7 @@ public void testIllegalContentType() throws SolrServerException, IOException {
         createShowFileRequest(params("file", "managed-schema", "contentType", "not/known"));
     request.setResponseParser(new InputStreamResponseParser("xml"));
     NamedList<Object> response = client.request(request);
+    closeResponseStream(response);
     assertEquals(response.get("responseStatus"), 404);
   }
 
@@ -152,6 +153,7 @@ public void testAbsoluteFilename() throws SolrServerException, IOException {
             params("file", "/etc/passwd", "contentType", "text/plain; charset=utf-8"));
     request.setResponseParser(new InputStreamResponseParser("xml"));
     NamedList<Object> response = client.request(request);
+    closeResponseStream(response);
     assertEquals(response.get("responseStatus"), 404);
   }
 
@@ -162,6 +164,7 @@ public void testEscapeConfDir() throws SolrServerException, IOException {
             params("file", "../../solr.xml", "contentType", "application/xml; charset=utf-8"));
     request.setResponseParser(new InputStreamResponseParser("xml"));
     NamedList<Object> response = client.request(request);
+    closeResponseStream(response);
     assertEquals(response.get("responseStatus"), 400);
   }
 
@@ -176,6 +179,7 @@ public void testPathTraversalFilename() throws SolrServerException, IOException
                 "text/plain; charset=utf-8"));
     request.setResponseParser(new InputStreamResponseParser("xml"));
     NamedList<Object> response = client.request(request);
+    closeResponseStream(response);
     assertEquals(response.get("responseStatus"), 400);
   }
 
@@ -202,4 +206,11 @@ public void testGetSafeContentType() {
     // Non-known content types are rejected with 400 error
     expectThrows(SolrException.class, () -> ShowFileRequestHandler.getSafeContentType("foo/bar"));
   }
+
+  private void closeResponseStream(NamedList<Object> response) throws IOException {
+    InputStream stream = (InputStream) response.get("stream");
+    if (stream != null) {
+      stream.close();
+    }
+  }
 }

solr/core/src/test/org/apache/solr/response/TestPrometheusResponseWriter.java

@@ -193,6 +193,8 @@ public void testUnsupportedMetricsFormat() throws Exception {
 
     try (SolrClient adminClient = getHttpSolrClient(solrTestRule.getBaseUrl())) {
       NamedList<Object> res = adminClient.request(req);
+      InputStream stream = (InputStream) res.get("stream");
+      if (stream != null) stream.close();
       // Unknown wt parameter should return a 400 error
       assertEquals(400, res.get("responseStatus"));
     }

solr/core/src/test/org/apache/solr/search/TestSolrJ.java

@@ -135,8 +135,10 @@ private byte[] runQuery(String testCollection, CloudSolrClient client, String wt
       request.setResponseParser(new InputStreamResponseParser(wt));
     }
     result = client.request(request, testCollection);
-    InputStream inputStream = (InputStream) result.get("stream");
-    byte[] b = inputStream.readAllBytes();
+    byte[] b;
+    try (InputStream inputStream = (InputStream) result.get("stream")) {
+      b = inputStream.readAllBytes();
+    }
     System.out.println(wt + "_time : " + timer.getTime());
     System.out.println(wt + "_size : " + b.length);
     return b;