I am trying to help a U2 VAR migrate their custom-developed socket interface
that uses the GCI to a pure BASIC solution using the U2 socket functions.
They realize that by doing this their customers will need to license
additional U2 seats, but they hate the UV GCI support issue on UNIX as UV
must be re-linked. Unfortunately, the initServerSocket() function has a few
flaws that stopped this project.
1) The initServerSocket() function precludes using the standard socket
behavior of letting the socket sub-system assign any available port number
when the port number 0 is specified. The initServerSocket() function
translates all port numbers less than 1 to port 40001. This behavior of
forcing port 40001 breaks an important standard feature often used when a
server process is spawned to provide a cooperative service for another
process. As long as the two cooperative processes can agree and communicate
the randomly assigned port number, there is no reason to hard-code the port
for either process. In fact, when it is possible to have an indeterminate
number of these cooperative processes, trying to assign and track which
ports are available, raises to the application level something that is
otherwise handled at the kernel layer. That is never a good thing. I can not
imagine why U2 restricts a valuable server socket feature. This reminds me
of a documentation error that made it into code.
2) The other issue with the initServerSocket() is that it does not recognize
when another process already has a given port open for listening. The
example program below demonstrates this issue. This flaw prevents the
application level from randomly assigning the port number and knowing that
the port is actually available. Of course, this would not have been an issue
if number 1 above let the socket kernel assign random port numbers. This is
an ugly flaw as a program could wait forever for a port, never knowing that
another process already has the port in use.
I am using UV 10.1.11 PE on Windows. I am hoping someone has developed a
work-around (other than GCI) or knows when the fix is scheduled.
Best regards,
Gyle
Program SERVER.SOCKET
Print "Select a port number that is already in use on the system to test
for contention : "
Input listenPort
If listenPort = "" Then
Stop
End
result = initServerSocket( "", listenPort, 1, listenerSocket )
If result Then
function = "initServerSocket()"
Gosub DisplaySocketError:
Stop
End Else
Print "initServerSocket(): listening on port " : listenPort
End
result = getSocketInformation( listenerSocket, -1, socketInformation )
If result Then
function = "getSocketInformation()"
Gosub DisplaySocketError:
Stop
End
Print "Server socket information"
Print "-----------"
Print "Status : " : socketInformation<1,1>
Print "Host : " : socketInformation<1,2>
Print "Port : " : socketInformation<1,3>
Print "Secure : " : socketInformation<1,4>
Print "Mode : " : socketInformation<1,5>
Print "SERVER.SOCKET ready."
Gosub CloseListenSocket:
Stop
CloseListenSocket:
* Close the listen socket
result = closeSocket( listenerSocket )
If result Then
function = "closeSocket()"
Gosub DisplaySocketError:
Stop
End
Return
DisplaySocketError:
internalResult = getSocketErrorMessage( result, errorMessage )
Print function : " returned: " : result
Print errorMessage
Return
End
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