[plt-scheme] Reading on TCP ports and #<eof>

From: Matthew Flatt (mflatt at cs.utah.edu)
Date: Thu Jul 19 06:25:09 EDT 2007

At Thu, 19 Jul 2007 11:31:30 +0200, Erich Rast wrote:
> When (connection-in-port connection) yields a port obtained from a  
> make-pipe, this works well. However, when the port is a TCP-port, it  
> seems that the call to read doesn't block, but instead returns #<eof>  
> each time it is called. The loop becomes rather busy and my info  
> procedure continuously outputs "illegal reply: #<eof" when the server  
> the client has connected to doesn't send anything.
> How do I block the thread until some value different from #<eof> is  
> read? Why is a tcp port behaving differently from one produced by  
> make-pipe?

A TCP connection should indeed behave like a pipe. As long as the other
end hasn't closed the connection, then reading from the port should block:

 > (define l (tcp-listen 6007 5 #t))
 > (define-values (r1 w1) (tcp-connect "localhost" 6007))
 > (define-values (r2 w2) (tcp-accept l))
 > (read r1)
 ^Cuser break
 > (thread (lambda () (sleep 5) (display "x " w2) (flush-output w2)))
 > (read r1)
 x ; after 5 seconds

Can you say more about the way that TCP connections are created in your


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