RE: [HACKERS] LIBPQ for WIN32 - Mailing list pgsql-hackers

> > Hi All.
> > I tested libpq for win32 coming with 6.4-BETA and have a
> > question about
> > LIBPQ.
> >
> > I used LIBPQ from a C program,but coundn't connect PostgreSQL DB.
> >
> > Calling pg_connect() without WSAStartup() failed because of
> > gethostbyname()
> > error in LIBPQ.
> > so I modified DllMain in LIBPQ as follows.
> >
> > BOOL WINAPI DllMain( HINSTANCE hinstDLL,   DWORD fdwReason,
> >                      LPVOID lpReserved ){
> >
> >     WSADATA wsaData;
> >     switch (fdwReason)
> >            {
> >      case DLL_PROCESS_ATTACH:
> >           WSAStartup( WSAStartup(MAKEWORD(1, 1), &wsaData);
> >           break;
> >      case DLL_PROCESS_DETACH:
> >           WSACleanup();
> >           break;
> >            }
> >
> >     return (TRUE);
> > }
> >
> > and the connection to DB was OK.
> >
> > Why WSAStartup() is  not called in LIBPQ?
>
> This is probably a good thing to do :-)
> When I wrote the code, I thought that I was only allowed to
> a) Call WSAStartup() once or
> b) All calls to WSAStartup() had to have the same version number
> But after reading the specs a little more careful, I see that this is not
> the case.
>
> The specs say:
> An application or DLL can call WSAStartup more than once if it needs to
> obtain the WSAData structure information more than once. On each such call
> the application can specify any version number supported by the DLL.
>
> The question is - what will happen when you call it with different
versions.
> Say the application asks for Winsock 2.0, and then the Libpq library goes
in
> and asks for Winsock 1.1. Will the application still have access to
Winsock
> 2.0 functions?

I think that current DLL supports version 1.0,1.1,2.0,2.1 and 2.2 and we can
specify any version from 1.0 to 2.2 .
For example,if we call WSAStartup(MAKEWORD(1.0),&wsaData) from libpq
and call WSAStartup(MAKEWORD(2,2),&wsaData) from psql,both return OK
and wsaData.wVersion is 1.0 for libpq and 2.2 for psql.

> With the current implementation, I don't beleive it will make a
difference -
> I don't think that any part of the Winsock system is actually hidden if
you
> ask for a lower version. But it is _permitted_ by the specification that
the
> DLL can hide parts that belong to a higher version than the one requested.
>
> So I'm not 100% sure... Does anybody have access to a Winsock　that
actually
> hides some details when you ask for the wrong version?
>

By the specs there may be the DLL that doesn't support lower versions.
In that case my code doesn't work well.
But we can delay to call WSAStartup() after the first socket call in LIBPQ.
My example code in fe-connect.c is such as follows.

    hp = gethostbyname(conn->pghost);
#ifdef    WIN32
    if ((hp == NULL) && (GetLastError() == WSANOTINITIALISED))
    {
        WSADATA    wsaData;
        if (WSAStartup(MAKEWORD(1,1),&wsaData))
        {
            fprintf(stderr, "Failed to start winsock: %i\n", WSAGetLastError());
            exit(1);
        }
        ....
        ???? for WSACleanup() ????
        ....
        hp = gethostbyname(conn->host);
    }
#endif
    if ((hp == NULL) || (hp->h_addrtype != AF_INET))
    {
        (void) sprintf(conn->errorMessage,
                       "connectDB() --  unknown hostname: %s\n",
                       conn->pghost);
        goto connect_errReturn;
    }

Hiroshi Inoue
inoue@tpf.co.jp