v4-0005-Bump-protocol-version-to-3.2.patch

From fd49b5ec9bad0e50ebea84b48a6d7eadacabe450 Mon Sep 17 00:00:00 2001
From: Jelte Fennema-Nio <postgres@jeltef.nl>
Date: Wed, 14 Aug 2024 18:25:16 +0200
Subject: [PATCH v4 5/7] Bump protocol version to 3.2

In preparation of new additions to the protocol in a follow up commit
this bumps the minor protocol version number. Instead of bumping the
version number to 3.1, which would be the next minor version, we skip
that one and bump straight to 3.2. The reason for this is that many
PgBouncer releases have, due to an off-by-one bug, reported 3.1 as
supported[1]. These versions would interpret 3.1 as equivalent to 3.0. So
if we would now add extra messages to the 3.1 protocol, clients would
succeed to connect to PgBouncer, but would then cause connection
failures when sending such new messages.

So instead of bumping to 3.1, we bump the protocol version to 3.2, for
which these buggy PgBouncer releases will correctly close the connection
at the startup packet. It's a bit strange to skip a version number due
to a bug in a third-party application, but PgBouncer is used widely
enough that it seems worth it to not cause user confusion when
connecting to recent versions of it. Especially since skipping a single
minor version number in the protocol versioning doesn't really cost us
anything. So, while this is not the most theoretically sound decission,
it is the most pragmatic one.

[1]: https://github.com/pgbouncer/pgbouncer/pull/1007
---
 doc/src/sgml/libpq.sgml                       |   8 +-
 doc/src/sgml/protocol.sgml                    |  31 ++++-
 src/include/libpq/pqcomm.h                    |   3 +-
 src/interfaces/libpq/fe-connect.c             |   9 ++
 src/interfaces/libpq/fe-protocol3.c           |   8 +-
 .../modules/libpq_pipeline/libpq_pipeline.c   | 110 +++++++++++++++---
 6 files changed, 142 insertions(+), 27 deletions(-)

diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index f249bbd9263..ed099598c38 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -2158,7 +2158,8 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         The current supported values are
-        <literal>3.0</literal>
+        <literal>3.0</literal>,
+        <literal>3.2</literal>,
         and <literal>latest</literal>. The <literal>latest</literal> value is
         equivalent to the latest protocol version that is supported by the used
         libpq version, which currently is <literal>3.2</literal>, but this will
@@ -2185,10 +2186,11 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
 
        <para>
         The current supported values are
-        <literal>3.0</literal>
+        <literal>3.0</literal>,
+        <literal>3.2</literal>,
         and <literal>latest</literal>. The <literal>latest</literal> value is
         equivalent to the latest protocol version that is supported by the used
-        libpq version, which currently is <literal>3.0</literal>, but this will
+        libpq version, which currently is <literal>3.2</literal>, but this will
         change in future libpq releases.
        </para>
       </listitem>
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 3bd9e68e6ce..6bb97dbba55 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -18,17 +18,23 @@
  </para>
 
  <para>
-  This document describes version 3.0 of the protocol, implemented in
+  This document describes version 3.2 of the protocol, introduced in
+  <productname>PostgreSQL</productname> version 17. The server is compatible with
+  protocol version 3.0, implemented in
   <productname>PostgreSQL</productname> 7.4 and later.  For descriptions
-  of the earlier protocol versions, see previous releases of the
-  <productname>PostgreSQL</productname> documentation.  A single server
+  of earlier protocol versions, see previous releases of the
+  <productname>PostgreSQL</productname> documentation.
+ </para>
+
+ <para>
+  A single server
   can support multiple protocol versions.  The initial startup-request
   message tells the server which protocol version the client is attempting to
   use.  If the major version requested by the client is not supported by
   the server, the connection will be rejected (for example, this would occur
   if the client requested protocol version 4.0, which does not exist as of
   this writing).  If the minor version requested by the client is not
-  supported by the server (e.g., the client requests version 3.1, but the
+  supported by the server (e.g., the client requests version 3.2, but the
   server supports only 3.0), the server may either reject the connection or
   may respond with a NegotiateProtocolVersion message containing the highest
   minor protocol version which it supports.  The client may then choose either
@@ -36,6 +42,13 @@
   to abort the connection.
  </para>
 
+ <para>
+  The protocol negotiation was introduced in
+  <productname>PostgreSQL</productname> version 9.3.21. Earlier versions would
+  reject the connection if the client requested a minor version that was not
+  supported by the server.
+ </para>
+
   <para>
    In order to serve multiple clients efficiently, the server launches
    a new <quote>backend</quote> process for each client.
@@ -413,8 +426,14 @@
         this message indicates the highest supported minor version.  This
         message will also be sent if the client requested unsupported protocol
         options (i.e., beginning with <literal>_pq_.</literal>) in the
-        startup packet.  This message will be followed by an ErrorResponse or
-        a message indicating the success or failure of authentication.
+        startup packet.
+       </para>
+       <para>
+        After this message, the authentication will continue using the version
+        indicated by the server.  If the client does not support the older
+        version, it should immediately close the connection.  If the server
+        does not send this message, it supports the client's requested
+        protocol version and all the protocol options.
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/include/libpq/pqcomm.h b/src/include/libpq/pqcomm.h
index 46b37e0e4eb..0aceb7147c7 100644
--- a/src/include/libpq/pqcomm.h
+++ b/src/include/libpq/pqcomm.h
@@ -91,11 +91,10 @@ is_unixsock_path(const char *path)
 
 /*
  * The earliest and latest frontend/backend protocol version supported.
- * (Only protocol version 3 is currently supported)
  */
 
 #define PG_PROTOCOL_EARLIEST	PG_PROTOCOL(3,0)
-#define PG_PROTOCOL_LATEST		PG_PROTOCOL(3,0)
+#define PG_PROTOCOL_LATEST		PG_PROTOCOL(3,2)
 
 typedef uint32 ProtocolVersion; /* FE/BE protocol version number */
 
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7f08b143fa7..559964a6a25 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -8216,6 +8216,15 @@ pqParseProtocolVersion(const char *value, ProtocolVersion *result, PGconn *conn,
 		return true;
 	}
 
+	if (strcmp(value, "3.1") == 0)
+	{
+		conn->status = CONNECTION_BAD;
+		libpq_append_conn_error(conn, "invalid %s value: \"%s\"",
+								context,
+								value);
+		return false;
+	}
+
 	major = strtol(value, &end, 10);
 	if (*end != '.')
 	{
diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 221627bdea6..f33766c7df4 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -1428,7 +1428,13 @@ pqGetNegotiateProtocolVersion3(PGconn *conn)
 		libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requests downgrade to pre-3.0 protocol version");
 		goto failure;
 	}
-	
+
+	if (their_version == PG_PROTOCOL(3, 1))
+	{
+		libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requests downgrade to 3.1 protocol version");
+		goto failure;
+	}
+
 	if (num < 0)
 	{
 		libpq_append_conn_error(conn, "received invalid protocol negotiation message: server reported negative number of unsupported parameters");
diff --git a/src/test/modules/libpq_pipeline/libpq_pipeline.c b/src/test/modules/libpq_pipeline/libpq_pipeline.c
index 7ff18e91e66..656f437826e 100644
--- a/src/test/modules/libpq_pipeline/libpq_pipeline.c
+++ b/src/test/modules/libpq_pipeline/libpq_pipeline.c
@@ -198,24 +198,15 @@ send_cancellable_query_impl(int line, PGconn *conn, PGconn *monitorConn)
 }
 
 /*
- * Create a new connection with the same conninfo as the given one.
+ * Fills keywords and vals, with the same options as the ones in the opts
+ * linked-list. Returns the length of the filled in list.
  */
-static PGconn *
-copy_connection(PGconn *conn)
+static
+int
+copy_connection_options(PQconninfoOption *opts, const char **keywords, const char **vals)
 {
-	PGconn	   *copyConn;
-	PQconninfoOption *opts = PQconninfo(conn);
-	const char **keywords;
-	const char **vals;
-	int			nopts = 1;
 	int			i = 0;
 
-	for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
-		nopts++;
-
-	keywords = pg_malloc(sizeof(char *) * nopts);
-	vals = pg_malloc(sizeof(char *) * nopts);
-
 	for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
 	{
 		if (opt->val)
@@ -225,8 +216,28 @@ copy_connection(PGconn *conn)
 			i++;
 		}
 	}
-	keywords[i] = vals[i] = NULL;
+	return i;
+}
+
+/*
+ * Create a new connection with the same conninfo as the given one.
+ */
+static PGconn *
+copy_connection(PGconn *conn)
+{
+	const char **keywords;
+	const char **vals;
+	PGconn	   *copyConn;
+	PQconninfoOption *opts = PQconninfo(conn);
+	int			nopts = 1;		/* 1 for the NULL terminator */
 
+	for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
+		nopts++;
+
+	keywords = pg_malloc0(sizeof(char *) * nopts);
+	vals = pg_malloc0(sizeof(char *) * nopts);
+
+	copy_connection_options(opts, keywords, vals);
 	copyConn = PQconnectdbParams(keywords, vals, false);
 
 	if (PQstatus(copyConn) != CONNECTION_OK)
@@ -1406,6 +1417,72 @@ test_prepared(PGconn *conn)
 	fprintf(stderr, "ok\n");
 }
 
+static void
+test_protocol_version(PGconn *conn)
+{
+	const char **keywords;
+	const char **vals;
+	int			nopts = 2;		/* NULL terminator + max_protocol_version */
+	PQconninfoOption *opts = PQconninfo(conn);
+	int			protocol_version;
+	int			max_protocol_version_index;
+
+	for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
+		nopts++;
+
+	keywords = pg_malloc0(sizeof(char *) * nopts);
+	vals = pg_malloc0(sizeof(char *) * nopts);
+
+	max_protocol_version_index = copy_connection_options(opts, keywords, vals);
+
+	keywords[max_protocol_version_index] = "max_protocol_version";
+	vals[max_protocol_version_index] = "3.0";
+
+	conn = PQconnectdbParams(keywords, vals, false);
+
+	if (PQstatus(conn) != CONNECTION_OK)
+		pg_fatal("Connection to database failed: %s",
+				 PQerrorMessage(conn));
+
+	protocol_version = PQfullProtocolVersion(conn);
+	if (protocol_version != 30000)
+		pg_fatal("expected 30000, got %d", protocol_version);
+
+	PQfinish(conn);
+
+	vals[max_protocol_version_index] = "3.1";
+	conn = PQconnectdbParams(keywords, vals, false);
+
+	if (PQstatus(conn) != CONNECTION_BAD)
+		pg_fatal("Connecting with max_protocol_version 3.1 should have failed.");
+
+	PQfinish(conn);
+
+	vals[max_protocol_version_index] = "3.2";
+	conn = PQconnectdbParams(keywords, vals, false);
+
+	if (PQstatus(conn) != CONNECTION_OK)
+		pg_fatal("Connection to database failed: %s",
+				 PQerrorMessage(conn));
+
+	protocol_version = PQfullProtocolVersion(conn);
+	if (protocol_version != 30002)
+		pg_fatal("expected 30002, got %d", protocol_version);
+	PQfinish(conn);
+
+	vals[max_protocol_version_index] = "latest";
+	conn = PQconnectdbParams(keywords, vals, false);
+
+	if (PQstatus(conn) != CONNECTION_OK)
+		pg_fatal("Connection to database failed: %s",
+				 PQerrorMessage(conn));
+
+	protocol_version = PQfullProtocolVersion(conn);
+	if (protocol_version != 30002)
+		pg_fatal("expected 30002, got %d", protocol_version);
+	PQfinish(conn);
+}
+
 /* Notice processor: print notices, and count how many we got */
 static void
 notice_processor(void *arg, const char *message)
@@ -2154,6 +2231,7 @@ print_test_list(void)
 	printf("pipeline_idle\n");
 	printf("pipelined_insert\n");
 	printf("prepared\n");
+	printf("protocol_version\n");
 	printf("simple_pipeline\n");
 	printf("singlerow\n");
 	printf("transaction\n");
@@ -2264,6 +2342,8 @@ main(int argc, char **argv)
 		test_pipelined_insert(conn, numrows);
 	else if (strcmp(testname, "prepared") == 0)
 		test_prepared(conn);
+	else if (strcmp(testname, "protocol_version") == 0)
+		test_protocol_version(conn);
 	else if (strcmp(testname, "simple_pipeline") == 0)
 		test_simple_pipeline(conn);
 	else if (strcmp(testname, "singlerow") == 0)
-- 
2.43.0