psql: Forbid use of COPY and \copy while in a pipeline

michaelpq · michaelpq · commit 6e951f279bea · 2025-06-13T10:15:17.000+09:00
Running COPY within a pipeline can break protocol synchronization in multiple ways. psql is limited in terms of result processing if mixing COPY commands with normal queries while controlling a pipeline with the new meta-commands, as an effect of the following reasons: - In COPY mode, the backend ignores additional Sync messages and will not send a matching ReadyForQuery expected by the frontend. Doing a \syncpipeline just after COPY will leave the frontend waiting for a ReadyForQuery message that won't be sent, leaving psql out-of-sync. - libpq automatically sends a Sync with the Copy message which is not tracked in the command queue, creating an unexpected synchronisation point that psql cannot really know about. While it is possible to track such activity for a \copy, this cannot really be done sanely with plain COPY queries. Backend failures during a COPY would leave the pipeline in an aborted state while the backend would be in a clean state, ready to process commands. At the end, fixing those issues would require modifications in how libpq handles pipeline and COPY. So, rather than implementing workarounds in psql to shortcut the libpq internals (with command queue handling for one), and because meta-commands for pipelines in psql are a new feature with COPY in a pipeline having a limited impact compared to other queries, this commit forbids the use of COPY within a pipeline to avoid possible break of protocol synchronisation within psql. If there is a use-case for COPY support within pipelines in libpq, this could always be added in the future, if necessary. Most of the changes of this commit impacts the tests for psql pipelines, removing the tests related to COPY. Some TAP tests still exist for COPY TO/FROM and \copy to/from, to check that that connections are aborted when this operation is attempted. Reported-by: Nikita Kalinin <n.kalinin@postgrespro.ru> Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com> Discussion: https://postgr.es/m/AC468509-06E8-4E2A-A4B1-63046A4AC6AB@postgrespro.ru
diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
@@ -3733,6 +3733,10 @@ testdb=&gt; <userinput>\setenv LESS -imx4F</userinput>
         See <xref linkend="app-psql-prompting-p-uc"/> for more details
        </para>
 
+       <para>
+        <command>COPY</command> is not supported while in pipeline mode.
+       </para>
+
        <para>
         Example:
 <programlisting>
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
@@ -1867,18 +1867,30 @@ ExecQueryAndProcessResults(const char *query,
 		{
 			FILE	   *copy_stream = NULL;
 
-			if (pset.piped_syncs > 1)
+			if (PQpipelineStatus(pset.db) != PQ_PIPELINE_OFF)
 			{
 				/*
-				 * When reading COPY data, the backend ignores sync messages
-				 * and will not send a matching ReadyForQuery response.  Even
-				 * if we adjust piped_syncs and requested_results, it is not
-				 * possible to salvage this as the sync message would still be
-				 * in libpq's command queue and we would be stuck in a busy
-				 * pipeline state.  Thus, we abort the connection to avoid
-				 * this state.
+				 * Running COPY within a pipeline can break the protocol
+				 * synchronisation in multiple ways, and psql shows its limits
+				 * when it comes to tracking this information.
+				 *
+				 * While in COPY mode, the backend process ignores additional
+				 * Sync messages and will not send the matching ReadyForQuery
+				 * expected by the frontend.
+				 *
+				 * Additionally, libpq automatically sends a Sync with the
+				 * Copy message, creating an unexpected synchronisation point.
+				 * A failure during COPY would leave the pipeline in an
+				 * aborted state while the backend would be in a clean state,
+				 * ready to process commands.
+				 *
+				 * Improving those issues would require modifications in how
+				 * libpq handles pipelines and COPY.  Hence, for the time
+				 * being, we forbid the use of COPY within a pipeline,
+				 * aborting the connection to avoid an inconsistent state on
+				 * psql side if trying to use a COPY command.
 				 */
-				pg_log_info("\\syncpipeline after COPY is not supported, aborting connection");
+				pg_log_info("COPY in a pipeline is not supported, aborting connection");
 				exit(EXIT_BADCONN);
 			}
 
diff --git a/src/bin/psql/t/001_basic.pl b/src/bin/psql/t/001_basic.pl
@@ -483,8 +483,8 @@ sub psql_fails_like
 my $c4 = slurp_file($g_file);
 like($c4, qr/foo.*bar/s);
 
-# Tests with pipelines.  These trigger FATAL failures in the backend,
-# so they cannot be tested via SQL.
+# Test COPY within pipelines.  These abort the connection from
+# the frontend so they cannot be tested via SQL.
 $node->safe_psql('postgres', 'CREATE TABLE psql_pipeline()');
 my $log_location = -s $node->logfile;
 psql_fails_like(
@@ -493,53 +493,41 @@ sub psql_fails_like
 COPY psql_pipeline FROM STDIN;
 SELECT 'val1';
 \\syncpipeline
-\\getresults
 \\endpipeline},
-	qr/server closed the connection unexpectedly/,
-	'protocol sync loss in pipeline: direct COPY, SELECT, sync and getresult'
-);
+	qr/COPY in a pipeline is not supported, aborting connection/,
+	'COPY FROM in pipeline: fails');
 $node->wait_for_log(
 	qr/FATAL: .*terminating connection because protocol synchronization was lost/,
 	$log_location);
 
+# Remove \syncpipeline here.
 psql_fails_like(
 	$node,
 	qq{\\startpipeline
-COPY psql_pipeline FROM STDIN \\bind \\sendpipeline
-SELECT 'val1' \\bind \\sendpipeline
-\\syncpipeline
-\\getresults
-\\endpipeline},
-	qr/server closed the connection unexpectedly/,
-	'protocol sync loss in pipeline: bind COPY, SELECT, sync and getresult');
-
-# This time, test without the \getresults and \syncpipeline.
-psql_fails_like(
-	$node,
-	qq{\\startpipeline
-COPY psql_pipeline FROM STDIN;
+COPY psql_pipeline TO STDOUT;
 SELECT 'val1';
 \\endpipeline},
-	qr/server closed the connection unexpectedly/,
-	'protocol sync loss in pipeline: COPY, SELECT and sync');
+	qr/COPY in a pipeline is not supported, aborting connection/,
+	'COPY TO in pipeline: fails');
 
-# Tests sending a sync after a COPY TO/FROM.  These abort the connection
-# from the frontend.
 psql_fails_like(
 	$node,
 	qq{\\startpipeline
-COPY psql_pipeline FROM STDIN;
+\\copy psql_pipeline from stdin;
+SELECT 'val1';
 \\syncpipeline
 \\endpipeline},
-	qr/\\syncpipeline after COPY is not supported, aborting connection/,
-	'sending sync after COPY FROM');
+	qr/COPY in a pipeline is not supported, aborting connection/,
+	'\copy from in pipeline: fails');
+
+# Sync attempt after a COPY TO/FROM.
 psql_fails_like(
 	$node,
 	qq{\\startpipeline
-COPY psql_pipeline TO STDOUT;
+\\copy psql_pipeline to stdout;
 \\syncpipeline
 \\endpipeline},
-	qr/\\syncpipeline after COPY is not supported, aborting connection/,
-	'sending sync after COPY TO');
+	qr/COPY in a pipeline is not supported, aborting connection/,
+	'\copy to in pipeline: fails');
 
 done_testing();
diff --git a/src/test/regress/expected/psql_pipeline.out b/src/test/regress/expected/psql_pipeline.out
@@ -228,192 +228,6 @@ BEGIN \bind \sendpipeline
 INSERT INTO psql_pipeline VALUES ($1) \bind 1 \sendpipeline
 COMMIT \bind \sendpipeline
 \endpipeline
--- COPY FROM STDIN
--- with \sendpipeline and \bind
-\startpipeline
-SELECT $1 \bind 'val1' \sendpipeline
-COPY psql_pipeline FROM STDIN \bind \sendpipeline
-\endpipeline
- ?column? 
-----------
- val1
-(1 row)
-
--- with semicolon
-\startpipeline
-SELECT 'val1';
-COPY psql_pipeline FROM STDIN;
-\endpipeline
- ?column? 
-----------
- val1
-(1 row)
-
--- COPY FROM STDIN with \flushrequest + \getresults
--- with \sendpipeline and \bind
-\startpipeline
-SELECT $1 \bind 'val1' \sendpipeline
-COPY psql_pipeline FROM STDIN \bind \sendpipeline
-\flushrequest
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-message type 0x5a arrived from server while idle
-\endpipeline
--- with semicolon
-\startpipeline
-SELECT 'val1';
-COPY psql_pipeline FROM STDIN;
-\flushrequest
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-message type 0x5a arrived from server while idle
-\endpipeline
--- COPY FROM STDIN with \syncpipeline + \getresults
--- with \bind and \sendpipeline
-\startpipeline
-SELECT $1 \bind 'val1' \sendpipeline
-COPY psql_pipeline FROM STDIN \bind \sendpipeline
-\syncpipeline
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-\endpipeline
--- with semicolon
-\startpipeline
-SELECT 'val1';
-COPY psql_pipeline FROM STDIN;
-\syncpipeline
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-\endpipeline
--- COPY TO STDOUT
--- with \bind and \sendpipeline
-\startpipeline
-SELECT $1 \bind 'val1' \sendpipeline
-copy psql_pipeline TO STDOUT \bind \sendpipeline
-\endpipeline
- ?column? 
-----------
- val1
-(1 row)
-
-1	\N
-2	test2
-20	test2
-3	test3
-30	test3
-4	test4
-40	test4
--- with semicolon
-\startpipeline
-SELECT 'val1';
-copy psql_pipeline TO STDOUT;
-\endpipeline
- ?column? 
-----------
- val1
-(1 row)
-
-1	\N
-2	test2
-20	test2
-3	test3
-30	test3
-4	test4
-40	test4
--- COPY TO STDOUT with \flushrequest + \getresults
--- with \bind and \sendpipeline
-\startpipeline
-SELECT $1 \bind 'val1' \sendpipeline
-copy psql_pipeline TO STDOUT \bind \sendpipeline
-\flushrequest
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-1	\N
-2	test2
-20	test2
-3	test3
-30	test3
-4	test4
-40	test4
-\endpipeline
--- with semicolon
-\startpipeline
-SELECT 'val1';
-copy psql_pipeline TO STDOUT;
-\flushrequest
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-1	\N
-2	test2
-20	test2
-3	test3
-30	test3
-4	test4
-40	test4
-\endpipeline
--- COPY TO STDOUT with \syncpipeline + \getresults
--- with \bind and \sendpipeline
-\startpipeline
-SELECT $1 \bind 'val1' \sendpipeline
-copy psql_pipeline TO STDOUT \bind \sendpipeline
-\syncpipeline
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-1	\N
-2	test2
-20	test2
-3	test3
-30	test3
-4	test4
-40	test4
-\endpipeline
--- with semicolon
-\startpipeline
-SELECT 'val1';
-copy psql_pipeline TO STDOUT;
-\syncpipeline
-\getresults
- ?column? 
-----------
- val1
-(1 row)
-
-1	\N
-2	test2
-20	test2
-3	test3
-30	test3
-4	test4
-40	test4
-\endpipeline
 -- Use \parse and \bind_named
 \startpipeline
 SELECT $1 \parse ''
@@ -740,7 +554,7 @@ SELECT COUNT(*) FROM psql_pipeline \bind \sendpipeline
 
  count 
 -------
-     7
+     1
 (1 row)
 
 -- After an error, pipeline is aborted and requires \syncpipeline to be
diff --git a/src/test/regress/sql/psql_pipeline.sql b/src/test/regress/sql/psql_pipeline.sql
