An application and LAN Server use three basic components to interact:

• API call

  Issued by the application, an API call tells LAN Server or LAN Requester which function to invoke.

• Return code

  Issued by LAN Server or LAN Requester, the return code tells the application whether the function was successful or, if not, why it failed.

• Data structures

  When an API call is issued, pertinent data (for example, a user ID or workstation profile) also is passed between the application and LAN Server or LAN Requester. This data is placed in a data structure in local workstation memory, where both LAN Server and your application can read and write to it.

  Depending on the nature of the API, this data can be sent:

  • From the caller to the requester
    
  • From the caller to the server
    
  • From the server to the caller
    
  • From the requester to the caller
  Any call issued to an API must contain pointers to the associated data structure whether the application is sending or requesting data.

  Each type of API has one or more unique data structures associated with it. Typically, the buf, usBuflen, and sLevel parameters (described in Common Parameter Definitions) are used with an API call to specify which data structure to use.