From b4af80fdecfe5f3249bd4680d1ddbc4fb23aa5ad Mon Sep 17 00:00:00 2001
From: Ian Barwick <ian@2ndquadrant.com>
Date: Fri, 14 Feb 2020 10:39:28 +0900
Subject: [PATCH] Add optional check for unsupported future PostgreSQL releases

This is for backbranches to prevent them running against newer
PostgreSQL versions with which they are not compatible, for example
4.4.x with PostgreSQL 12 and later.
---
 repmgr-action-standby.c |  3 +++
 repmgr-client.c         | 44 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/repmgr-action-standby.c b/repmgr-action-standby.c
index 8cd7c84b..f2da7c5f 100644
--- a/repmgr-action-standby.c
+++ b/repmgr-action-standby.c
@@ -1081,6 +1081,9 @@ _do_create_replication_conf(void)
 	/* check connection */
 	source_conn = establish_db_connection_by_params(&source_conninfo, true);
 
+	/* Verify that source is a supported server version */
+	(void) check_server_version(source_conn, "source node", true, NULL);
+
 	/* determine node for primary_conninfo */
 
 	if (runtime_options.upstream_node_id != UNKNOWN_NODE_ID)
diff --git a/repmgr-client.c b/repmgr-client.c
index e3e93066..ab1bae85 100644
--- a/repmgr-client.c
+++ b/repmgr-client.c
@@ -2814,15 +2814,25 @@ create_repmgr_extension(PGconn *conn)
 int
 check_server_version(PGconn *conn, char *server_type, bool exit_on_error, char *server_version_string)
 {
-	int			conn_server_version_num = get_server_version(conn, server_version_string);
+	char		version_string[MAXVERSIONSTR] = "";
+	int			conn_server_version_num = get_server_version(conn, version_string);
+
+	/* Copy the version string, if the caller wants it */
+	if (server_version_string != NULL)
+		strncpy(server_version_string, version_string, MAXVERSIONSTR);
 
 	if (conn_server_version_num < MIN_SUPPORTED_VERSION_NUM)
 	{
 		if (conn_server_version_num > 0)
+		{
 			log_error(_("%s requires %s to be PostgreSQL %s or later"),
 					  progname(),
 					  server_type,
 					  MIN_SUPPORTED_VERSION);
+			log_detail(_("%s server version is %s"),
+					   server_type,
+					   version_string);
+		}
 
 		if (exit_on_error == true)
 		{
@@ -2833,6 +2843,38 @@ check_server_version(PGconn *conn, char *server_type, bool exit_on_error, char *
 		return UNKNOWN_SERVER_VERSION_NUM;
 	}
 
+	/*
+	 * If it's clear a particular repmgr feature branch won't be able to support
+	 * PostgreSQL from a particular PostgreSQL release onwards (e.g. 4.4 with PostgreSQL
+	 * 12 and later due to recovery.conf removal), set MAX_UNSUPPORTED_VERSION and
+	 * MAX_UNSUPPORTED_VERSION_NUM in "repmgr.h" to define the first PostgreSQL
+	 * version which can't be suppored.
+	 */
+#ifdef MAX_UNSUPPORTED_VERSION_NUM
+	if (conn_server_version_num >= MAX_UNSUPPORTED_VERSION_NUM)
+	{
+		if (conn_server_version_num > 0)
+		{
+			log_error(_("%s %s does not support PostgreSQL %s or later"),
+					  progname(),
+					  REPMGR_VERSION,
+					  MAX_UNSUPPORTED_VERSION);
+			log_detail(_("%s server version is %s"),
+					   server_type,
+					   version_string);
+			log_hint(_("For details of supported versions see: https://repmgr.org/docs/current/install-requirements.html#INSTALL-COMPATIBILITY-MATRIX"));
+		}
+
+		if (exit_on_error == true)
+		{
+			PQfinish(conn);
+			exit(ERR_BAD_CONFIG);
+		}
+
+		return UNKNOWN_SERVER_VERSION_NUM;
+	}
+#endif
+
 	return conn_server_version_num;
 }