HttpSM - make sure we have a valid buffer to write on. (#13039)

Add a check to make sure we have a valid buffer for tunnel producer to
write on.

Co-authored-by: Damian Meden <dmeden@apache.org>

Author: bneradt

proxy/http/HttpSM.cc

@@ -2972,7 +2972,6 @@ HttpSM::tunnel_handler_100_continue(int event, void *data)
     //  does not free the memory from the header
     t_state.hdr_info.client_response.destroy();
     tunnel.deallocate_buffers();
-    this->postbuf_clear();
     tunnel.reset();
 
     if (server_entry->eos) {
@@ -6103,8 +6102,8 @@ HttpSM::do_setup_post_tunnel(HttpVC_t to_vc_type)
   // YTS Team, yamsat Plugin
   // if redirect_in_process and redirection is enabled add static producer
 
-  if (is_using_post_buffer ||
-      (t_state.redirect_info.redirect_in_process && enable_redirection && this->_postbuf.postdata_copy_buffer_start != nullptr)) {
+  if ((is_using_post_buffer && this->_postbuf.is_valid()) || // Make sure  we have a valid buffer in case is buffering.
+      (t_state.redirect_info.redirect_in_process && enable_redirection && this->_postbuf.is_valid())) {
     post_redirect = true;
     // copy the post data into a new producer buffer for static producer
     MIOBuffer *postdata_producer_buffer      = new_empty_MIOBuffer(t_state.http_config_param->max_payload_iobuf_index);

tests/gold_tests/post/simple-post-valid-buffer-check.test.py

@@ -0,0 +1,59 @@
+'''
+'''
+#  Licensed to the Apache Software Foundation (ASF) under one
+#  or more contributor license agreements.  See the NOTICE file
+#  distributed with this work for additional information
+#  regarding copyright ownership.  The ASF licenses this file
+#  to you under the Apache License, Version 2.0 (the
+#  "License"); you may not use this file except in compliance
+#  with the License.  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+Test.Summary = '''
+Make sure we have a valid buffer to write on. This used to make ats crash.
+'''
+Test.ContinueOnFail = True
+
+# Use microserver instead of httpbin
+server = Test.MakeOriginServer("server")
+
+# Add a simple response for POST
+request_header = {"headers": "POST /post HTTP/1.1\r\nHost: *\r\n\r\n", "timestamp": "1469733493.993", "body": ""}
+response_header = {
+    "headers": "HTTP/1.1 200 OK\r\nConnection: close\r\nContent-Length: 2\r\n\r\n",
+    "timestamp": "1469733493.993",
+    "body": "OK"
+}
+server.addResponse("sessionfile.log", request_header, response_header)
+
+ts = Test.MakeATSProcess("ts")
+
+ts.Disk.remap_config.AddLine('map / http://127.0.0.1:{0}'.format(server.Variables.Port))
+
+ts.Disk.records_config.update(
+    {
+        'proxy.config.diags.debug.enabled': 1,
+        'proxy.config.diags.debug.tags': 'http',
+        'proxy.config.http.request_buffer_enabled': 1,
+        'proxy.config.http.number_of_redirections': 1,
+    })
+
+test_run = Test.AddTestRun("post buffer test")
+test_run.Processes.Default.StartBefore(server)
+test_run.Processes.Default.StartBefore(ts)
+test_run.Processes.Default.Command = f'curl -v -H "Expect: 100-continue" -d "abc" http://127.0.0.1:{ts.Variables.port}/post'
+test_run.Processes.Default.ReturnCode = 0
+test_run.StillRunningAfter = server
+test_run.StillRunningAfter = ts  # TS should not crash
+
+# Verify request with Expect header was processed
+ts.Disk.traffic_out.Content += Testers.ContainsExpression("100-continue", "Has Expect header")
+# Verify ATS handled the POST request (no crash)
+ts.Disk.traffic_out.Content += Testers.ContainsExpression("client post", "POST tunnel started")