On Thu, 10 Apr 2025 at 12:17, Fujii Masao <masao.fu...@oss.nttdata.com> wrote:
> > > On 2025/04/11 0:49, Dave Cramer wrote: > > > > > > On Thu, 10 Apr 2025 at 11:17, Fujii Masao <masao.fu...@oss.nttdata.com > <mailto:masao.fu...@oss.nttdata.com>> wrote: > > > > > > > > On 2025/04/10 23:40, Dave Cramer wrote: > > > > > > On Thu, 10 Apr 2025 at 09:54, Fujii Masao < > masao.fu...@oss.nttdata.com <mailto:masao.fu...@oss.nttdata.com> <mailto: > masao.fu...@oss.nttdata.com <mailto:masao.fu...@oss.nttdata.com>>> wrote: > > > > > > > > > > > > On 2025/04/10 18:52, Dave Cramer wrote: > > > > Greetings, > > > > > > > > The current docs say that if a client asks for a protocol > that the backend doesn't support, it will return the newest minor version. > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION > < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION> > < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION > < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION>> > < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION > < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION> > < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS- > > NEGOTIATEPROTOCOLVERSION < > https://www.postgresql.org/docs/current/protocol-message-formats.html#PROTOCOL-MESSAGE-FORMATS-NEGOTIATEPROTOCOLVERSION > >>> > > > > > > > > However that isn't what it returns. It actually returns > the entire newest protocol that it supports. Attached is a patch to fix the > docs. > > > > > > As far as I read the code, the server returns the protocol > version requested by > > > the client if it's less than or equal to the latest version > the server supports. > > > Otherwise, it returns the latest supported version. So the > proposed description > > > doesn't seem accurate either, does it? > > > > > > I've added a note as to when this is sent. AFAICT through testing > and the fact that the pgjdbc driver has never handled this message > > > I'm pretty sure it only sends this message if the requested > protocol is not equal to the protocol the server supports. > > > > No, the message is also sent when the client requests protocol > options that > > the server doesn't recognize. In that case, if the client requests > an older > > protocol version along with unknown options, the server responds with > > the requested protocol version, not the latest one. > > > > > > OK, I hadn't contemplated the unrecognized options. However AFAICT the > documentation in the code state > > > > /* > > * 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. > > */ > > > > and the code agrees that we send the latest protocol version that we > support, not the requested one. > > SendNegotiateProtocolVersion() sends the NegotiateProtocolVersion message > and > returns the protocol version stored in the FrontendProtocol variable: > > static void > SendNegotiateProtocolVersion(List *unrecognized_protocol_options) > { > StringInfoData buf; > ListCell *lc; > > pq_beginmessage(&buf, PqMsg_NegotiateProtocolVersion); > pq_sendint32(&buf, FrontendProtocol); > > FrontendProtocol is set by ProcessStartupPacket() as Min(proto, > PG_PROTOCOL_LATEST), > where proto is the protocol version requested by the client. So, if the > client > requests an older version, i.e., proto is smaller than PG_PROTOCOL_LATEST, > the server may respond with that requested version: > > /* > * Set FrontendProtocol now so that ereport() knows what format to > send if > * we fail during startup. We use the protocol version requested > by the > * client unless it's higher than the latest version we support. > It's > * possible that error message fields might look different in newer > * protocol versions, but that's something those new clients > should be > * able to deal with. > */ > FrontendProtocol = Min(proto, PG_PROTOCOL_LATEST); > > Am I missing something? > No, you are correct. See new patch Dave
protocol-3.patch
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