Fix incorrect error message for IDENTIFY_SYSTEM

Commit 5a991ef8692e accidentally reversed the order of the tuples
and fields parameters, making the error message incorrectly refer
to 3 tuples with 1 field when IDENTIFY_SYSTEM returns 1 tuple and
3 or 4 fields. Fix by changing the order of the parameters.  This
also adds a comment describing why we check for < 3 when postgres
since 9.4 has been sending 4 fields.

Backpatch all the way since the bug is almost a decade old.

Author: Tomonari Katsumata <t.katsumata1122@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Bug: #18224
Backpatch-through: v12

diff --git a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
index 78a714fe1b3c22829ab36220a08df18e24c4b713..778f4be47b1b0c0ebc94a36244b2204d17da5e0d 100644 (file)
--- a/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
+++ b/src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
@@ -360,6 +360,10 @@ libpqrcv_identify_system(WalReceiverConn *conn, TimeLineID *primary_tli)
                        "the primary server: %s",
                        pchomp(PQerrorMessage(conn->streamConn)))));
    }
+   /*
+    * IDENTIFY_SERVER returns 3 columns in 9.3 and earlier, and 4 columns in
+    * 9.4 and onwards.
+    */
    if (PQnfields(res) < 3 || PQntuples(res) != 1)
    {
        int         ntuples = PQntuples(res);
@@ -370,7 +374,7 @@ libpqrcv_identify_system(WalReceiverConn *conn, TimeLineID *primary_tli)
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("invalid response from primary server"),
                 errdetail("Could not identify system: got %d rows and %d fields, expected %d rows and %d or more fields.",
-                          ntuples, nfields, 3, 1)));
+                          ntuples, nfields, 1, 3)));
    }
    primary_sysid = pstrdup(PQgetvalue(res, 0, 0));
    *primary_tli = pg_strtoint32(PQgetvalue(res, 0, 1));