Apple AppleShare 3.0 File Server Controls - Manual (Page 4)

The File Sharing Extension contains no user interface of its own. The user
interface is provided by the Network Extension, which allows users to start
and to control the File Sharing Extension. The File Sharing Extension
communicates with the Network Extension primarily by means of server control
calls. The File Sharing Extension communicates with the Finder by means of
PPC events, and with a remote AppleShare client through AFP sessions. The
File Sharing Extension also communicates with local volumes and files by
means of Macintosh File Manager routines, and with server additions by means
of server control calls.
When the File Sharing Extension is launched, it checks its environment, the
Users & Groups Data File, and the desktop databases and AppleShare PDS files
of appropriate volumes. (The File Sharing Extension does not attempt to share
remote volumes, or volumes such as floppy disks or volumes that are ejected
and off line during startup.) If an important required condition is not
satisfied, the offending volume will not be prepared for use with the file
server or file sharing will not be enabled.
Once started, the File Sharing Extension takes over the dispatching of all
file system calls -- both local calls and remote requests. Essentially, the
File Sharing Extension acts as a mediator between the network and your local
HFS volumes. The File Sharing Extension imposes access privilege constraints
on AFP requests and implements some calls that are not implemented in HFS --
such as those that govern byte-range locking, access privileges, and extended
file access permissions.
Network Extension The Network Extension provides the user interface for
Macintosh File Sharing. It is an extension of the Finder and resides in the
Extensions folder. The Network Extension is dynamically linked with the
Finder code at startup time and uses the Finder's code to control its user
interface. The user interface includes what appears to users to be the
Sharing Setup, Users & Groups, and File Sharing Monitor control panels. When
a user opens any one of these control panels, the Network Extension code
intercepts the launch command, opens the appropriate window, and controls the
interaction with the user.
Based on user interactions, the Network Extension communicates with the
server primarily by means of server control calls. The File Server Extension
communicates with users through the Network Extension by sending high-level
Apple events to display dialog boxes. The Network Extension relies on the
AppleShare PDS file and the Users & Groups Data File for information about
server volumes and the users and groups defined for the server, respectively.
Finder The Finder provides part of the Macintosh File Sharing services. The
Sharing menu item in the Finder's File menu lets users view and set the
access privileges for disks and folders. In addition, through its extension
mechanism, the Finder provides an environment for running the Network
Extension code. The Finder communicates with the file server by using
augmented Macintosh File Manager routines.
File Sharing Monitor, Sharing Setup, and Users & Groups These control panel
files trigger execution of the appropriate Network Extension code. The
control panel files themselves contain no executable code.
Network AppleShare clients Network workstations with AppleShare client
software installed can connect to the File Sharing Extension. AppleShare
clients communicate with the server by means of AFP packets.