[racket] Issue reading bytes from TCP port

Have you tried closing the ports? -- Matthias



On Sep 3, 2014, at 6:01 PM, Gilbert Martinez wrote:

> I'm having issues reading the response from a TCP server.  Specifically, any attempt to read the input port does not terminate.  I've used port->bytes, read-byte, and read-line. In all cases the effect is the same.
> 
> I thought that if there were no bytes available on an input port that the read attempt would just return <eof>.  Is this some kind of exclusivity issue?  Can I not read from the port until the connection with the server is closed or something?
> 
> My traffic monitor shows that the server is receiving the request and responding (here is the exchange):
> 
> Time	Src. & Dst.	Type	Function Code	Data
> 908.875   	10.10.10.10:49967<-	TCP Req.	0x04	[0x000 - 0x027]     00 01 00 00 00 06 0B 04    00 3B 00 03
> 908.905	10.10.10.10:49967->	TCP Resp.	0x04	[0x000 - 0x027]     00 01 00 00 00 09 0B 04    06 00 00 00 00 00 00
> 
> Here is the code I am using to query:
> 
> #lang racket
> 
> 
> (define (hex-bytes->bytes hex-bytes-list)
>   (define (hex-byte->dec-byte hex-byte)
>     (string->number (string-append "#x" ((if (symbol? hex-byte)
>                                              symbol->string
>                                              number->string)
>                                          hex-byte))))
>   (apply bytes (for/list ((hex-byte (in-list hex-bytes-list)))
>                  (hex-byte->dec-byte hex-byte))))
> 
> (define-values (c-in c-out) (tcp-connect "10.10.10.11" 502))
> 
> (write-bytes (hex-bytes->bytes '(00 01 00 00 00 06 0B 04 00 3B 00 03)) c-out)
> (flush-output c-out)
> 
> 
> I run the code above and execute the following in the interactions pane:
> 
> Welcome to DrRacket, version 6.1.0.5--2014-08-25(32ae3f8/a) [3m].
> Language: racket [custom].
> 12
> >(for ((byte (in-bytes (port->bytes c-in))))
>   (printf "~x " byte))
> 
> 
> The entry above above hangs on port->bytes.
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