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Commitae65f60

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Provide for forward compatibility with future minor protocol versions.
Previously, any attempt to request a 3.x protocol version other than3.0 would lead to a hard connection failure, which made the minorprotocol version really no different from the major protocol versionand precluded gentle protocol version breaks. Instead, when theclient requests a 3.x protocol version where x is greater than 0, sendthe new NegotiateProtocolVersion message to convey that we supportonly 3.0. This makes it possible to introduce new minor protocolversions without requiring a connection retry when the server isolder.In addition, if the startup packet includes name/value pairs wherethe name starts with "_pq_.", assume that those are protocol options,not GUCs. Include those we don't support (i.e. all of them, atpresent) in the NegotiateProtocolVersion message so that the clientknows they were not understood. This makes it possible for theclient to request previously-unsupported features without bumpingthe protocol version at all; the client can tell from the server'sresponse whether the option was understood.It will take some time before servers that support these newfacilities become common in the wild; to speed things up and makethings easier for a future 3.1 protocol version, back-patch to allsupported releases.Robert Haas and Badrul ChowdhuryDiscussion:http://postgr.es/m/BN6PR21MB0772FFA0CBD298B76017744CD1730@BN6PR21MB0772.namprd21.prod.outlook.comDiscussion:http://postgr.es/m/30788.1498672033@sss.pgh.pa.us
1 parentf3b0897 commitae65f60

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2 files changed

+159
-16
lines changed

2 files changed

+159
-16
lines changed

‎doc/src/sgml/protocol.sgml

Lines changed: 106 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -22,10 +22,18 @@
2222
<productname>PostgreSQL</productname> 7.4 and later. For descriptions
2323
of the earlier protocol versions, see previous releases of the
2424
<productname>PostgreSQL</productname> documentation. A single server
25-
can support multiple protocol versions. The initial
26-
startup-request message tells the server which protocol version the
27-
client is attempting to use, and then the server follows that protocol
28-
if it is able.
25+
can support multiple protocol versions. The initial startup-request
26+
message tells the server which protocol version the client is attempting to
27+
use. If the major version requested by the client is not supported by
28+
the server, the connection will be rejected (for example, this would occur
29+
if the client requested protocol version 4.0, which does not exist as of
30+
this writing). If the minor version requested by the client is not
31+
supported by the server (e.g. the client requests version 3.1, but the
32+
server supports only 3.0), the server may either reject the connection or
33+
may respond with a NegotiateProtocolVersion message containing the highest
34+
minor protocol version which it supports. The client may then choose either
35+
to continue with the connection using the specified protocol version or
36+
to abort the connection.
2937
</para>
3038

3139
<para>
@@ -406,6 +414,21 @@
406414
</listitem>
407415
</varlistentry>
408416

417+
<varlistentry>
418+
<term>NegotiateProtocolVersion</term>
419+
<listitem>
420+
<para>
421+
The server does not support the minor protocol version requested
422+
by the client, but does support an earlier version of the protocol;
423+
this message indicates the highest supported minor version. This
424+
message will also be sent if the client requested unsupported protocol
425+
options (i.e. beginning with <literal>_pq_.</literal>) in the
426+
startup packet. This message will be followed by an ErrorResponse or
427+
a message indicating the success or failure of authentication.
428+
</para>
429+
</listitem>
430+
</varlistentry>
431+
409432
</variablelist>
410433
</para>
411434

@@ -420,8 +443,10 @@
420443
for further messages from the server. In this phase a backend process
421444
is being started, and the frontend is just an interested bystander.
422445
It is still possible for the startup attempt
423-
to fail (ErrorResponse), but in the normal case the backend will send
424-
some ParameterStatus messages, BackendKeyData, and finally ReadyForQuery.
446+
to fail (ErrorResponse) or the server to decline support for the requested
447+
minor protocol version (NegotiateProtocolVersion), but in the normal case
448+
the backend will send some ParameterStatus messages, BackendKeyData, and
449+
finally ReadyForQuery.
425450
</para>
426451

427452
<para>
@@ -4715,6 +4740,74 @@ GSSResponse (F)
47154740
</listitem>
47164741
</varlistentry>
47174742

4743+
<varlistentry>
4744+
<term>
4745+
NegotiateProtocolVersion (B)
4746+
</term>
4747+
<listitem>
4748+
<para>
4749+
4750+
<variablelist>
4751+
<varlistentry>
4752+
<term>
4753+
Byte1('v')
4754+
</term>
4755+
<listitem>
4756+
<para>
4757+
Identifies the message as a protocol version negotiation
4758+
message.
4759+
</para>
4760+
</listitem>
4761+
</varlistentry>
4762+
<varlistentry>
4763+
<term>
4764+
Int32
4765+
</term>
4766+
<listitem>
4767+
<para>
4768+
Length of message contents in bytes, including self.
4769+
</para>
4770+
</listitem>
4771+
</varlistentry>
4772+
<varlistentry>
4773+
<term>
4774+
Int32
4775+
</term>
4776+
<listitem>
4777+
<para>
4778+
Newest minor protocol version supported by the server
4779+
for the major protocol version requested by the client.
4780+
</para>
4781+
</listitem>
4782+
</varlistentry>
4783+
<varlistentry>
4784+
<term>
4785+
Int32
4786+
</term>
4787+
<listitem>
4788+
<para>
4789+
Number of protocol options not recognized by the server.
4790+
</para>
4791+
</listitem>
4792+
</varlistentry>
4793+
</variablelist>
4794+
Then, for protocol option not recognized by the server, there
4795+
is the following:
4796+
<variablelist>
4797+
<varlistentry>
4798+
<term>
4799+
String
4800+
</term>
4801+
<listitem>
4802+
<para>
4803+
The option name.
4804+
</para>
4805+
</listitem>
4806+
</varlistentry>
4807+
</variablelist>
4808+
</para>
4809+
</listitem>
4810+
</varlistentry>
47184811

47194812
<varlistentry>
47204813
<term>
@@ -5670,11 +5763,13 @@ StartupMessage (F)
56705763
</varlistentry>
56715764
</variablelist>
56725765

5673-
In addition to the above, any run-time parameter that can be
5674-
set at backend start time might be listed. Such settings
5675-
will be applied during backend start (after parsing the
5676-
command-line arguments if any). The values will act as
5677-
session defaults.
5766+
In addition to the above, others parameter may be listed.
5767+
Parameter names beginning with <literal>_pq_.</literal> are
5768+
reserved for use as protocol extensions, while others are
5769+
treated as run-time parameters to be set at backend start
5770+
time. Such settings will be applied during backend start
5771+
(after parsing the command-line arguments if any) and will
5772+
act as session defaults.
56785773
</para>
56795774
</listitem>
56805775
</varlistentry>

‎src/backend/postmaster/postmaster.c

Lines changed: 53 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -101,6 +101,7 @@
101101
#include"lib/ilist.h"
102102
#include"libpq/auth.h"
103103
#include"libpq/libpq.h"
104+
#include"libpq/pqformat.h"
104105
#include"libpq/pqsignal.h"
105106
#include"miscadmin.h"
106107
#include"pg_getopt.h"
@@ -412,6 +413,7 @@ static void ExitPostmaster(int status) pg_attribute_noreturn();
412413
staticintServerLoop(void);
413414
staticintBackendStartup(Port*port);
414415
staticintProcessStartupPacket(Port*port,boolSSLdone);
416+
staticvoidSendNegotiateProtocolVersion(List*unrecognized_protocol_options);
415417
staticvoidprocessCancelRequest(Port*port,void*pkt);
416418
staticintinitMasks(fd_set*rmask);
417419
staticvoidreport_fork_failure_to_client(Port*port,interrnum);
@@ -2052,12 +2054,9 @@ ProcessStartupPacket(Port *port, bool SSLdone)
20522054
*/
20532055
FrontendProtocol=proto;
20542056

2055-
/* Check we can handle the protocol the frontend is using. */
2056-
2057+
/* Check that the major protocol version is in range. */
20572058
if (PG_PROTOCOL_MAJOR(proto)<PG_PROTOCOL_MAJOR(PG_PROTOCOL_EARLIEST)||
2058-
PG_PROTOCOL_MAJOR(proto)>PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST)||
2059-
(PG_PROTOCOL_MAJOR(proto)==PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST)&&
2060-
PG_PROTOCOL_MINOR(proto)>PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST)))
2059+
PG_PROTOCOL_MAJOR(proto)>PG_PROTOCOL_MAJOR(PG_PROTOCOL_LATEST))
20612060
ereport(FATAL,
20622061
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
20632062
errmsg("unsupported frontend protocol %u.%u: server supports %u.0 to %u.%u",
@@ -2079,6 +2078,7 @@ ProcessStartupPacket(Port *port, bool SSLdone)
20792078
if (PG_PROTOCOL_MAJOR(proto) >=3)
20802079
{
20812080
int32offset=sizeof(ProtocolVersion);
2081+
List*unrecognized_protocol_options=NIL;
20822082

20832083
/*
20842084
* Scan packet body for name/option pairs. We can assume any string
@@ -2128,6 +2128,16 @@ ProcessStartupPacket(Port *port, bool SSLdone)
21282128
valptr),
21292129
errhint("Valid values are: \"false\", 0, \"true\", 1, \"database\".")));
21302130
}
2131+
elseif (strncmp(nameptr,"_pq_.",5)==0)
2132+
{
2133+
/*
2134+
* Any option beginning with _pq_. is reserved for use as a
2135+
* protocol-level option, but at present no such options are
2136+
* defined.
2137+
*/
2138+
unrecognized_protocol_options=
2139+
lappend(unrecognized_protocol_options,pstrdup(nameptr));
2140+
}
21312141
else
21322142
{
21332143
/* Assume it's a generic GUC option */
@@ -2147,6 +2157,16 @@ ProcessStartupPacket(Port *port, bool SSLdone)
21472157
ereport(FATAL,
21482158
(errcode(ERRCODE_PROTOCOL_VIOLATION),
21492159
errmsg("invalid startup packet layout: expected terminator as last byte")));
2160+
2161+
/*
2162+
* If the client requested a newer protocol version or if the client
2163+
* requested any protocol options we didn't recognize, let them know
2164+
* the newest minor protocol version we do support and the names of any
2165+
* unrecognized options.
2166+
*/
2167+
if (PG_PROTOCOL_MINOR(proto)>PG_PROTOCOL_MINOR(PG_PROTOCOL_LATEST)||
2168+
unrecognized_protocol_options!=NIL)
2169+
SendNegotiateProtocolVersion(unrecognized_protocol_options);
21502170
}
21512171
else
21522172
{
@@ -2260,6 +2280,34 @@ ProcessStartupPacket(Port *port, bool SSLdone)
22602280
returnSTATUS_OK;
22612281
}
22622282

2283+
/*
2284+
* Send a NegotiateProtocolVersion to the client. This lets the client know
2285+
* that they have requested a newer minor protocol version than we are able
2286+
* to speak. We'll speak the highest version we know about; the client can,
2287+
* of course, abandon the connection if that's a problem.
2288+
*
2289+
* We also include in the response a list of protocol options we didn't
2290+
* understand. This allows clients to include optional parameters that might
2291+
* be present either in newer protocol versions or third-party protocol
2292+
* extensions without fear of having to reconnect if those options are not
2293+
* understood, while at the same time making certain that the client is aware
2294+
* of which options were actually accepted.
2295+
*/
2296+
staticvoid
2297+
SendNegotiateProtocolVersion(List*unrecognized_protocol_options)
2298+
{
2299+
StringInfoDatabuf;
2300+
ListCell*lc;
2301+
2302+
pq_beginmessage(&buf,'v');/* NegotiateProtocolVersion */
2303+
pq_sendint32(&buf,PG_PROTOCOL_LATEST);
2304+
pq_sendint32(&buf,list_length(unrecognized_protocol_options));
2305+
foreach(lc,unrecognized_protocol_options)
2306+
pq_sendstring(&buf,lfirst(lc));
2307+
pq_endmessage(&buf);
2308+
2309+
/* no need to flush, some other message will follow */
2310+
}
22632311

22642312
/*
22652313
* The client has sent a cancel request packet, not a normal

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