Re: Extensibility of the PostgreSQL wire protocol

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От Jan Wieck
Тема Re: Extensibility of the PostgreSQL wire protocol
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Msg-id CAGBW59empGcTqdf38DCmLxSB5vfSD6vbLxNGTfVeHGeCZyJfXQ@mail.gmail.com
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Ответ на Re: Extensibility of the PostgreSQL wire protocol  (Kuntal Ghosh <kuntalghosh.2007@gmail.com>)
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Thank you Kuntal,

On Fri, Feb 19, 2021 at 4:36 AM Kuntal Ghosh <kuntalghosh.2007@gmail.com> wrote:
On Thu, Feb 18, 2021 at 9:32 PM Jan Wieck <jan@wi3ck.info> wrote:


Few comments in the extension code (although experimental):

1. In telnet_srv.c,
+ static int        pe_port;
..
+       DefineCustomIntVariable("telnet_srv.port",
+                                                       "Telnet server port.",
+                                                       NULL,
+                                                       &pe_port,
+                                                       pe_port,
+                                                       1024,
+                                                       65536,
+                                                       PGC_POSTMASTER,
+                                                       0,
+                                                       NULL,
+                                                       NULL,
+                                                       NULL);

The variable pe_port should be initialized to a value which is > 1024
and < 65536. Otherwise, the following assert will fail,
TRAP: FailedAssertion("newval >= conf->min", File: "guc.c", Line:
5541, PID: 12100)


Right, forgot to turn on Asserts.
 
2. The function pq_putbytes shouldn't be used by anyone other than
old-style COPY out.
+       pq_putbytes(msg, strlen(msg));
Otherwise, the following assert will fail in the same function:
    /* Should only be called by old-style COPY OUT */
    Assert(DoingCopyOut);

I would argue that the Assert needs to be changed. It is obvious that the Assert in place is meant to guard against direct usage of pg_putbytes() in an attempt to force all code to use pq_putmessage() instead. This is good when speaking libpq wire protocol since all messages there are prefixed with a one byte message type. It does not apply to other protocols.

I propose to create another global boolean IsNonLibpqFrontend which the protocol extension will set to true when accepting the connection and the above then will change to

    Assert(DoingCopyOut || IsNonLibpqFrontend);


Regards, Jan

 

--
Thanks & Regards,
Kuntal Ghosh
Amazon Web Services


--
Jan Wieck

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