python - psycopg2.OperationalError: FATAL: unsupported frontend protocol 1234.5679: server supports 2.0 to 3.0

Question

I'm using Macbook

Psycopg2 works well when connecting the localhost db (PostgreSQL on Mac). The error was raised when I tried to connect PostgreSQL db on a Windows10.

the following code is what I have for connection, the host is just the IP of the windows10

db= psycopg2.connect(database='dbname',user='username',password="secret",host="192.168.3.9",port="5432")

Errors:

  File "path/to/psycopg2/__init__.py", line 126, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
psycopg2.OperationalError: FATAL:  unsupported frontend protocol 1234.5679: server supports 2.0 to 3.0

Is this because of system compatibility or something else? I've tried other Windows machine and I got no luck to make it work. However, I was able to connect PostgreSQL on windows while I using Node.JS module pg

Answer 1

1234.5679 is the special code sent by the client to request SSL-encrypted database connections, and support for that has been in PostgreSQL since commit e0e7daef6da in 1999. But your PostgreSQL cannot be that old, because support for protocol version 3.0 was not added before 2003.

Actually, from studying src/backend/postmaster/postmaster.c and reading the mailing list, this is a bug on the PostgreSQL server:

The client must be configured to try GSS authentication, and when the server rejects, it wants to negotiate an SSL connections, but the server doesn't expect that at this point; hence the error.

See the discussion here. The bug has been fixed with release 12.3.

As a workaround, disable either GSS authentication or SSL negotiation on the client.

In psycopg2, disabling SSL is done by using sslmode="disable" in the connection string, and disabling GSS is done with gssencmode="disable". See the documentation for details.