Bug#40264: Aborted cached query causes query to hang indefinitely on next cache hit

The problem is that the query cache was storing partial results
if the statement failed when sending the results to the client.
This could cause clients to hang when trying to read the results
from the cache as they would, for example, wait indefinitely for
a eof packet that wasn't saved.

The solution is to always discard the caching of a query that
failed to send its results to the associated client.

mysql-test/r/query_cache_notembedded.result

@@ -345,3 +345,19 @@ id
 drop table t1;
 drop function f1;
 set GLOBAL query_cache_size=0;
+DROP TABLE IF EXISTS t1;
+FLUSH STATUS;
+SET GLOBAL query_cache_size=1048576;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3),(4),(5);
+SHOW STATUS LIKE 'Qcache_queries_in_cache';
+Variable_name	Value
+Qcache_queries_in_cache	0
+LOCK TABLES t1 WRITE;
+SELECT * FROM t1;
+UNLOCK TABLES;
+SHOW STATUS LIKE 'Qcache_queries_in_cache';
+Variable_name	Value
+Qcache_queries_in_cache	0
+DROP TABLE t1;
+SET GLOBAL query_cache_size= default;

mysql-test/t/query_cache_notembedded.test

@@ -222,3 +222,34 @@ disconnect con2;
 connection default;
 
 set GLOBAL query_cache_size=0;
+
+#
+# Bug#40264: Aborted cached query causes query to hang indefinitely on next cache hit
+#
+
+--disable_warnings
+DROP TABLE IF EXISTS t1;
+--enable_warnings
+
+FLUSH STATUS;
+SET GLOBAL query_cache_size=1048576;
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3),(4),(5);
+SHOW STATUS LIKE 'Qcache_queries_in_cache';
+LOCK TABLES t1 WRITE;
+connect(con1,localhost,root,,);
+--send SELECT * FROM t1
+connection default;
+let $show_type= open tables where `table`='t1' and in_use=2;
+let $show_pattern= '%t1%2%';
+--source include/wait_show_pattern.inc
+dirty_close con1;
+UNLOCK TABLES;
+let $show_type= open tables where `table`='t1' and in_use=0;
+let $show_pattern= '%t1%0%';
+--source include/wait_show_pattern.inc
+SHOW STATUS LIKE 'Qcache_queries_in_cache';
+DROP TABLE t1;
+SET GLOBAL query_cache_size= default;
+
+# End of 5.0 tests

sql/sql_cache.cc

@@ -710,7 +710,12 @@ void query_cache_end_of_result(THD *thd)
   if (thd->net.query_cache_query == 0)
     DBUG_VOID_RETURN;
 
-  if (thd->killed)
+  /*
+    Check if the NET layer raised a unreported error -- my_error() and
+    as a consequence query_cache_abort() haven't been called. Abort the
+    cached result as it might be only partially complete.
+  */
+  if (thd->killed || thd->net.report_error)
   {
     query_cache_abort(&thd->net);
     DBUG_VOID_RETURN;