Most of the traffic between computers on a network is the in the form of a
client machine communicating with a server machine. The client machine is
the computer at which a person logs on and the server machine is a machine
such as a File Server or Printer Server. However other types of servers can
be added to a network.

The difficulty is for a client machine to determine which computer on the
network is the server, and what network port to use. For a File Server and
a Printer Server this is not a problem as the NFS and NetPrint systems have
built-in defaults.

With other types of servers clients should use the FindServer protocol to
locate a particular type of server and the [[Econet ports|port]] numbers
further communication should use.

==Find Server Protocol==
===Client to server===
  port             &B0
  control byte     &80
  Data             name of server in capitals padded with spaces to a length
                   of eight characters as ASCII data.

===Server to client===
  port             &B1
  control byte     &80
  Data             0 or error number
  Data+1           base port for further exchanges
  Data+2           binary version number of server software, eg &12 for 1.20
  Data+3           server type (8 characters, format as for Client to server)
  Data+11          length of server name (0 if not present)
  Data+12          server name (optional)
  Data+12+NameLen  server dependant information or 0-terminated error string
                   if ?Data<>0

All servers should respond to the wildcard name of eight spaces. This makes
it possible to interrogate your network to find all the servers available.
The server will respond with a maximum of 32 bytes to a FindServer request.

==Coding==
===Client Program===

  REM > FindServer
  REM Use FindServer protocol to find a server
  :
  DIM ctrl% 31:X%=ctrl%:Y%=X%DIV256
  DIM rxBuf% 31,txBuf% 15:rx%=0:tx%=0
  :
  ON ERROR REPORT:PROCNet_RxKill(tx%):PRINT:END
  :
  rx%=FNNet_RxOpen(0,&B1,rxBuf%,&20)
  $txBuf%="DESPOOL "              :REM Look for a DESPOOL server
  $txBuf%="MUGINS  "              :REM Look for a MUGINS server
  $txBuf%="RISCOS  "              :REM Look for a RISCOS server
  $txBuf%="TELETEXT"              :REM Look for a TELETEXT server
  $txBuf%="UNIX    "              :REM Look for a UNIX server
  $txBuf%="        "              :REM Look for all server types
  try%=10
  REPEAT
    tx%=FNNet_TxCount(&FFFF,&80,&B0,txBuf%,8,0,0,0)
    IF tx% THEN PRINT FNNet_Err(tx%):END
    rxok%=FNNet_Rx(rx%)
    IF NOT rxok%:A%=TIME+50:REPEATUNTILTIME>A%:try%=try%-1
  UNTIL rxok% OR try%<1
  IF NOT rxok% THEN PROCNet_RxKill(rx%):PRINT "No server found":END
  rxnum%=FNNet_RxRead(rx%):stn%=X%!3
  PRINT "Server found on station ";FNNet_Stn(stn%)
  IF ?rxBuf% THEN PRINT "Server error: ";$(rxBuf%+1):END
  rxBuf%?(12+rxBuf%?11)=13:name$=$(rxBuf%+12)
  rxBuf%?11=13:server$=$(rxBuf%+3)
  vers%=rxBuf%?2
  portBase%=rxBuf%?1
  PRINT "Type: ";server$;"   Name: ";name$
  PRINT "Base port: &";FNh0(portBase%,2);"   Version: ";vers%DIV16;".";(vers%AND15)*10
  END

This code uses the [http://mdfs.net/blib Net] library.

===Server Program===

  REM > ServReply
  REM Sample to to respond to FindServer requests
  :
  DIM ctrl% 15,txBuf% 255,rxBuf% 127,svBuf% 15:X%=ctrl%:Y%=X%DIV256
  MyName$="MUGINS  "              :REM My server type
  MyPort%=ASC"M"                  :REM Port for clients to use to talk to me
  ver$="1.00"                     :REM My version number
  svNum%=0:rxNum%=0
  PROCopenServ:PROCopenAction     :REM Listen to server port and command port
  REPEAT
    IFFNNet_Rx(svNum%):PROCserver:PROCopenServ   :REM FindServer request
    IFFNNet_Rx(rxNum%):PROCaction:PROCopenAction :REM Action request
  UNTIL FALSE
  :
  DEFPROCopenServ:svNum%=FNNet_RxOpen(0,&B0,svBuf%,12):ENDPROC
  DEFPROCopenAction:rxNum%=FNNet_RxOpen(0,MyPort%,rxBuf%,256):ENDPROC
  :
  DEFPROCserver:rx%=FNNet_RxRead(svNum%):stn%=X%!3:svBuf%?8=13
  IF$svBuf%<>MyName$ AND $svBuf%<>"        ":ENDPROC
  ?txBuf%=0:txBuf%?1=MyPort%:txBuf%?2=EVAL("&"+STR$(10*VALver$))
  $(txBuf%+3)=MyName$:txBuf%?11=0
  REM Additional data can be returned, txBuf%?11=length, txBuf%+12=data
  tx%=FNNet_Tx(stn%,&80,&B1,txBuf%,12+txBuf%?11,0)
  ENDPROC
  :
  DEFPROCaction
  rx%=FNNet_RxRead(rxNum%)
  :
  REM Do something with contents of received data
  :
  ENDPROC

This code uses the [http://mdfs.net/blib Net] library.

==References==
* SJ MDFS Manual, Chapter 10
* RISC OS PRM

[[User:Jgharston|Jgharston]] 23:29, 15 May 2009 (UTC)
[[Title:FindServer]]
[[Category:Networking]]