koderP
diff --git a/‎doc/src/sgml/protocol.sgml
Lines changed: 105 additions & 11 deletions b/‎doc/src/sgml/protocol.sgml
Lines changed: 105 additions & 11 deletions
diff --git a/‎src/backend/postmaster/postmaster.c
Lines changed: 53 additions & 5 deletions b/‎src/backend/postmaster/postmaster.c
Lines changed: 53 additions & 5 deletions
@@ -22,10 +22,18 @@
   <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
-  can support multiple protocol versions.  The initial
-  startup-request message tells the server which protocol version the
-  client is attempting to use, and then the server follows that protocol
-  if it is able.
+  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
+  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
+  to continue with the connection using the specified protocol version or
+  to abort the connection.
  </para>
 
   <para>
@@ -366,6 +374,20 @@
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term>NegotiateProtocolVersion</term>
+      <listitem>
+       <para>
+        The server does not support the minor protocol version requested
+        by the client, but does support an earlier version of the protocol;
+        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
8000
 or failure of authentication.
+       </para>
+      </listitem>
+     </varlistentry>
     </variablelist>
    </para>
 
@@ -380,8 +402,10 @@
     for further messages from the server.  In this phase a backend process
     is being started, and the frontend is just an interested bystander.
     It is still possible for the startup attempt
-    to fail (ErrorResponse), but in the normal case the backend will send
-    some ParameterStatus messages, BackendKeyData, and finally ReadyForQuery.
+    to fail (ErrorResponse) or the server to decline support for the requested
+    minor protocol version (NegotiateProtocolVersion), but in the normal case
+    the backend will send some ParameterStatus messages, BackendKeyData, and
+    finally ReadyForQuery.
    </para>
 
    <para>
@@ -3921,6 +3945,74 @@ FunctionCallResponse (B)
 </listitem>
 </varlistentry>
 
+<varlistentry>
+<term>
+NegotiateProtocolVersion (B)
+</term>
+<listitem>
+<para>
+
+<variablelist>
+<varlistentry>
+<term>
+        Byte1('v')
+</term>
+<listitem>
+<para>
+                Identifies the message as a protocol version negotiation
+                message.
+</para>
+</listitem>
+</varlistentry>
+<varlistentry>
+<term>
+        Int32
+</term>
+<listitem>
+<para>
+                Length of message contents in bytes, including self.
+</para>
+</listitem>
+</varlistentry>
+<varlistentry>
+<term>
+        Int32
+</term>
+<listitem>
+<para>
+                Newest minor protocol version supported by the server
+                for the major protocol version requested by the client.
+</para>
+</listitem>
+</varlistentry>
+<varlistentry>
+<term>
+        Int32
+</term>
+<listitem>
+<para>
+                Number of protocol options not recognized by the server.
+</para>
+</listitem>
+</varlistentry>
+</variablelist>
+        Then, for protocol option not recognized by the server, there
+        is the following:
+<variablelist>
+<varlistentry>
+<term>
+        String
+</term>
+<listitem>
+<para>
+                The option name.
+</para>
+</listitem>
+</varlistentry>
+</variablelist>
+</para>
+</listitem>
+</varlistentry>
 
 <varlistentry>
 <term>
@@ -4748,11 +4840,13 @@ StartupMessage (F)
 </varlistentry>
 </variablelist>
 
-                In addition to the above, any run-time parameter that can be
-                set at backend start time might be listed.  Such settings
-                will be applied during backend start (after parsing the
-                command-line arguments if any).  The values will act as
-                session defaults.
+                In addition to the above, others parameter may be listed.
+                Parameter names beginning with <literal>_pq_.</literal> are
+                reserved for use as protocol extensions, while others are
+                treated as run-time parameters to be set at backend start
+                time.  Such settings will be applied during backend start
+                (after parsing the command-line arguments if any) and will
+                act as session defaults.
 </para>
 </listitem>
 </varlistentry>
 
@@ -99,6 +99,7 @@
 #include "libpq/auth.h"
 #include "libpq/ip.h"
 #include "libpq/libpq.h"
+#include "libpq/pqformat.h"
 #include "libpq/pqsignal.h"
 #include "miscadmin.h"
 #include "pg_getopt.h"
@@ -398,6 +399,7 @@ static void ExitPostmaster(int status) pg_attribute_noreturn();
 static int	ServerLoop(void);
 static int	BackendStartup(Port *port);
 static int	ProcessStartupPacket(Port *port, bool SSLdone);
+static void SendNegotiateProtocolVersion(List *unrecognized_protocol_options);
 static void processCancelRequest(Port *port, void *pkt);
 static int	initMasks(fd_set *rmask);
 static void report_fork_failure_to_client(Port *port, int errnum);
@@ -2000,12 +2002,9 @@ ProcessStartupPacket(Port *port, bool SSLdone)
 	 */
 	FrontendProtocol = proto;
 
-	/* Check we can handle the protocol the frontend is using. */
-
+	/* Check that the major protocol version is in range. */
 	if (PG_PROTOCOL_MAJOR(proto) < PG_PROTOCOL_MAJOR(PG_PROTOCOL_EARLIEST) ||
-		PG_PROTOCOL_MAJOR(proto) > PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST) ||
-		(PG_PROTOCOL_MAJOR(proto) == PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST) &&
-		 PG_PROTOCOL_MINOR(proto) > PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST)))
+		PG_PROTOCOL_MAJOR(proto) > PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST))
 		ereport(FATAL,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("unsupported frontend protocol %u.%u: server supports %u.0 to %u.%u",
@@ -2027,6 +2026,7 @@ ProcessStartupPacket(Port *port, bool SSLdone)
 	if (PG_PROTOCOL_MAJOR(proto) >= 3)
 	{
 		int32		offset = sizeof(ProtocolVersion);
+		List	   *unrecognized_protocol_options = NIL;
 
 		/*
 		 * Scan packet body for name/option pairs.  We can assume any string
@@ -2076,6 +2076,16 @@ ProcessStartupPacket(Port *port, bool SSLdone)
 									valptr),
 							 errhint("Valid values are: \"false\", 0, \"true\", 1, \"database\".")));
 			}
+			else if (strncmp(nameptr, "_pq_.", 5) == 0)
+			{
+				/*
+				 * Any option beginning with _pq_. is reserved for use as a
+				 * protocol-level option, but at present no such options are
+				 * defined.
+				 */
+				unrecognized_protocol_options =
+					lappend(unrecognized_protocol_options, pstrdup(nameptr));
+			}
 			else
 			{
 				/* Assume it's a generic GUC option */
@@ -2095,6 +2105,16 @@ ProcessStartupPacket(Port *port, bool SSLdone)
 			ereport(FATAL,
 					(errcode(ERRCODE_PROTOCOL_VIOLATION),
 					 errmsg("invalid startup packet layout: expected terminator as last byte")));
+
+		/*
+		 * If the client requested a newer protocol version or if the client
+		 * requested any protocol options we didn't recognize, let them know
+		 * the newest minor protocol version we do support and the names of any
+		 * unrecognized options.
+		 */
+		if (PG_PROTOCOL_MINOR(proto) > PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST) ||
+			unrecognized_protocol_options != NIL)
+			SendNegotiateProtocolVersion(unrecognized_protocol_options);
 	}
 	else
 	{
@@ -2208,6 +2228,34 @@ ProcessStartupPacket(Port *port, bool SSLdone)
 	return STATUS_OK;
 }
 
+/*
+ * Send a NegotiateProtocolVersion to the client.  This lets the client know
+ * that they have requested a newer minor protocol version than we are able
+ * to speak.  We'll speak the highest version we know about; the client can,
+ * of course, abandon the connection if that's a problem.
+ *
+ * We also include in the response a list of protocol options we didn't
+ * understand.  This allows clients to include optional parameters that might
+ * be present either in newer protocol versions or third-party protocol
+ * extensions without fear of having to reconnect if those options are not
+ * understood, while at the same time making certain that the client is aware
+ * of which options were actually accepted.
+ */
+static void
+SendNegotiateProtocolVersion(List *unrecognized_protocol_options)
+{
+	StringInfoData buf;
+	ListCell   *lc;
+
+	pq_beginmessage(&buf, 'v'); /* NegotiateProtocolVersion */
+	pq_sendint(&buf, PG_PROTOCOL_LATEST, 4);
+	pq_sendint(&buf, list_length(unrecognized_protocol_options), 4);
+	foreach(lc, unrecognized_protocol_options)
+		pq_sendstring(&buf, lfirst(lc));
+	pq_endmessage(&buf);
+
+	/* no need to flush, some other message will follow */
+}
 
 /*
  * The client has sent a cancel request packet, not a normal