libpq: Handle NegotiateProtocolVersion message

Before, receiving a NegotiateProtocolVersion message would result in a
confusing error message like

    expected authentication request from server, but received v

This adds proper handling of this protocol message and produces an
on-topic error message from it.

Reviewed-by: Jacob Champion <jchampion@timescale.com>
Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/f9c7862f-b864-8ef7-a861-c4638c83e209%40enterprisedb.com

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 7d54aa35899c0d0baa51163dcbd41ef32f3a693a..f88d672c6c8a3c97d5f7b04d619880c48b20e08b 100644 (file)
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3194,10 +3194,11 @@ keep_going:                     /* We will come back to here until there is
 
                /*
                 * Validate message type: we expect only an authentication
-                * request or an error here.  Anything else probably means
-                * it's not Postgres on the other end at all.
+                * request, NegotiateProtocolVersion, or an error here.
+                * Anything else probably means it's not Postgres on the other
+                * end at all.
                 */
-               if (!(beresp == 'R' || beresp == 'E'))
+               if (!(beresp == 'R' || beresp == 'v' || beresp == 'E'))
                {
                    libpq_append_conn_error(conn, "expected authentication request from server, but received %c",
                                       beresp);
@@ -3214,14 +3215,15 @@ keep_going:                     /* We will come back to here until there is
                /*
                 * Try to validate message length before using it.
                 * Authentication requests can't be very large, although GSS
-                * auth requests may not be that small.  Errors can be a
+                * auth requests may not be that small.  Same for
+                * NegotiateProtocolVersion.  Errors can be a
                 * little larger, but not huge.  If we see a large apparent
                 * length in an error, it means we're really talking to a
                 * pre-3.0-protocol server; cope.  (Before version 14, the
                 * server also used the old protocol for errors that happened
                 * before processing the startup packet.)
                 */
-               if (beresp == 'R' && (msgLength < 8 || msgLength > 2000))
+               if ((beresp == 'R' || beresp == 'v') && (msgLength < 8 || msgLength > 2000))
                {
                    libpq_append_conn_error(conn, "expected authentication request from server, but received %c",
                                       beresp);
@@ -3351,6 +3353,16 @@ keep_going:                      /* We will come back to here until there is
 
                    goto error_return;
                }
+               else if (beresp == 'v')
+               {
+                   if (pqGetNegotiateProtocolVersion3(conn))
+                   {
+                       goto error_return;
+                   }
+                   /* OK, we read the message; mark data consumed */
+                   conn->inStart = conn->inCursor;
+                   goto error_return;
+               }
 
                /* It is an authentication request. */
                conn->auth_req_received = true;

diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 88dd360c905fce76e2db86e4a452a2dd87381384..364bad2b882c839f62fa02d59b20fb8ee6d99a27 100644 (file)
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -1385,6 +1385,61 @@ reportErrorPosition(PQExpBuffer msg, const char *query, int loc, int encoding)
 }
 
 
+/*
+ * Attempt to read a NegotiateProtocolVersion message.
+ * Entry: 'v' message type and length have already been consumed.
+ * Exit: returns 0 if successfully consumed message.
+ *      returns EOF if not enough data.
+ */
+int
+pqGetNegotiateProtocolVersion3(PGconn *conn)
+{
+   int         tmp;
+   ProtocolVersion their_version;
+   int         num;
+   PQExpBufferData buf;
+
+   if (pqGetInt(&tmp, 4, conn) != 0)
+       return EOF;
+   their_version = tmp;
+
+   if (pqGetInt(&num, 4, conn) != 0)
+       return EOF;
+
+   initPQExpBuffer(&buf);
+   for (int i = 0; i < num; i++)
+   {
+       if (pqGets(&conn->workBuffer, conn))
+       {
+           termPQExpBuffer(&buf);
+           return EOF;
+       }
+       if (buf.len > 0)
+           appendPQExpBufferChar(&buf, ' ');
+       appendPQExpBufferStr(&buf, conn->workBuffer.data);
+   }
+
+   if (their_version < conn->pversion)
+       appendPQExpBuffer(&conn->errorMessage,
+                         libpq_gettext("protocol version not supported by server: client uses %u.%u, server supports up to %u.%u\n"),
+                         PG_PROTOCOL_MAJOR(conn->pversion), PG_PROTOCOL_MINOR(conn->pversion),
+                         PG_PROTOCOL_MAJOR(their_version), PG_PROTOCOL_MINOR(their_version));
+   if (num > 0)
+       appendPQExpBuffer(&conn->errorMessage,
+                         libpq_ngettext("protocol extension not supported by server: %s\n",
+                                        "protocol extensions not supported by server: %s\n", num),
+                         buf.data);
+
+   /* neither -- server shouldn't have sent it */
+   if (!(their_version < conn->pversion) && !(num > 0))
+       appendPQExpBuffer(&conn->errorMessage,
+                         libpq_gettext("invalid %s message"), "NegotiateProtocolVersion");
+
+   termPQExpBuffer(&buf);
+   return 0;
+}
+
+
 /*
  * Attempt to read a ParameterStatus message.
  * This is possible in several places, so we break it out as a subroutine.

diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index c24645b469652089731e059a16a796cb20549033..512762f99917c49369c18ff9e5439ee50a040c92 100644 (file)
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -685,6 +685,7 @@ extern void pqParseInput3(PGconn *conn);
 extern int pqGetErrorNotice3(PGconn *conn, bool isError);
 extern void pqBuildErrorMessage3(PQExpBuffer msg, const PGresult *res,
                                 PGVerbosity verbosity, PGContextVisibility show_context);
+extern int pqGetNegotiateProtocolVersion3(PGconn *conn);
 extern int pqGetCopyData3(PGconn *conn, char **buffer, int async);
 extern int pqGetline3(PGconn *conn, char *s, int maxlen);
 extern int pqGetlineAsync3(PGconn *conn, char *buffer, int bufsize);