[plt-scheme] Re: gzipped file + pipe hangs at the end

Okay -

I found out the issue and solution - the output-port has to be explicitly
closed in order for the pipe to know there are no more data coming through.
I guess I misconstrue the meaning of "The ports do not need to be explicitly
closed" in
http://docs.plt-scheme.org/reference/pipeports.html#(def._((quote._~23~25kernel)._make-pipe)).

Problem solved - thanks.
yc

On Thu, Sep 3, 2009 at 8:47 PM, YC <yinso.chen at gmail.com> wrote:

> Update -
>
> I was able to isolate the problem to just the pipe.
>
> (define-values (in out)
>   (make-pipe #f))
> (write-bytes #"this is a test" out)
> (read-bytes 14 in) ;; reads out #"this is a test"
> (read-bytes 1 in) ;; hangs.
>
> It seems that unlike regular input-port, pipe does not produce #<eof> in
> this situation.  How can I make the pipe generate #<eof>?
>
> Thanks,
> yc
>
>
> On Thu, Sep 3, 2009 at 7:37 PM, YC <yinso.chen at gmail.com> wrote:
>
>> Hi -
>>
>> I am trying to pipe a gzipped file and it seems to hang at the end when I
>> am trying to read the data.  It's unclear to me why it hangs at the end (I
>> observed this by seeing it hangs immediately with small files, read quite a
>> bit of data with medium files, and read lots of data with large files before
>> it hangs), and hopefully others can see what I am missing here.
>>
>> Thanks,
>> yc
>>
>> ;; gzip.ss
>> #lang scheme/base
>> (require file/gunzip file/gzip mzlib/trace scheme/port)
>>
>> (define (open-gzip-file path)
>>   (let-values (((in out)
>>                 (make-pipe-with-specials #f path)))
>>     (thread (lambda ()
>>               (call-with-input-file path
>>                 (lambda (in)
>>                   (gunzip-through-ports in out)))))
>>     in))
>>
>> (define (read-bytes* num in)
>>     (read-bytes num in))
>>
>> (trace read-bytes*)
>>
>> (define (reader in)
>>   (let loop ((b (read-bytes* 4096 in)))
>>     (if (eof-object? b)
>>         ;; (reverse acc)
>>         (void)
>>         (loop (read-bytes* 4096 in)))))
>>
>> (provide reader open-gzip-file)
>>
>> ;; test ;; uncomment and run the two lines below in REPL
>> ;; (require "gzip.ss")
>> ;; (reader (open-gzip-file path-to-gzipped-file))
>> ;; observe the it eventually hangs on calling read-bytes*.
>>
>>
>
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