Connecting to a Remote Database

This example shows one method of connecting to a remote database, as used by the gateway sample application. Since the connection is to a SQL Server database, DB-Library structures and function calls are used to establish the connection and to communicate with the remote database.

Declare a structure to hold connection information for accessing a remote database. This structure is passed to Open Data Services event handlers in the SRV_PROC structure:
```
{
    LOGINREC * login     // Pointer to a LOGINREC structure   
    DBPROCESS * dbproc;  // Pointer to a DBPROCESS structure  
} REMOTE_DBMS
```
where

login

Is a pointer to a LOGINREC structure. This structure is defined by the client and contains login and connection information to connect a client to a server.

dbproc

Is a pointer to a DBPROCESS structure. This structure is defined by Open Data Services and contains information to manage communications between the client and the server.
Add the init_remote function to the gateway callback program, GATECBS.C:
```
int init_remote (srvproc)
SRV_PROC * srvproc;
```

Allocate a REMOTE_DBMS information structure, which holds the private data space associated with a remote database connection:

// Private data area to keep track of remote database connection. 

REMOTE_DBMS * remote;
remote = (REMOTE_DBMS *) srv_alloc ((DBINT)sizeof(*remote));

Use the DB-Library call dblogin to allocate and return a pointer to a LOGINREC structure, which is used to make the connection to the remote server. Put the pointer to LOGINREC in remote->login:

// Now we'll allocate our LOGINREC structure that     
// we'll use to make connections to the               
// remote server. We'll actually open the connection  
// in the SRV_CONNECT handler.                        

remote->login = dblogin();

Use the ODS Library srv_pfield function to copy the user name, password, application name, and language defined in the client's SRV_PROC structure to remote->login:

// Set the user name, password, application name for the   
// remote database.                                        

DBSETLUSER (remote->login, srv_pfield(srvproc, SRV_USER, (int *)
NULL));

DBSETLPWD (remote->login, srv_pfield(srvproc, SRV_PWD, (int *)
NULL));

DBSETLAPP (remote->login, srv_pfield(srvproc, SRV_APPLNAME, (int *)
NULL));

DBSETLNATLANG(remote->login, srv_pfield(srvproc, SRV_NATLANG, 
    (int *) NULL));

Use the DB-Library dbopen function with the parameters in remote->login and the server name to connect to the host:

// Try to open a connection to the remote database.         

if ((remote->dbproc = dbopen(remote->login, remote_server))
== (DBPROCESS *) NULL)
{

//  Send a message to the Open Data Services client if the remote 
//  connection cannot be made.                                    

srv_sendmsg    (srvproc,
               SRV_MSG_ERROR,
               (DBINT)REMOTE_FAIL,
               (DBTINYINT)0,
               (DBTINYINT)0,
               NULL,
               0,
               0,
               "Login to remote DBMS failed.",
               SRV_NULLTERM);

//  Deallocate remote structure and set the user data pointer in  
//  the SRV_PROC connection structure to NULL so that the         
//  disconnect handler won't try to disconnect from the remote    
//  database.                                                     
srv_free (remote);
srv_setuserdata (srvproc, (BYTE *) NULL);

After the connection is made, save the remote data structure in the SRV_PROC connection structure so that it will be available to the other handlers using srv_setuserdata and dbsetuserdata, and return the SRV_CONTINUE constant:

// Connection to the remote database is successful. Save remote    
// data structure in the SRV_PROC connection structure so that it  
// will be available to the other handlers. Map the remote         
// database connection to the SRV_PROC connection structure.       

srv_setuserdata(srvproc, (VOID *)remote);
dbsetuserdata(remote->dbproc, (VOID *)srvproc);