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Re: Streaming responses with Guile's web modules
From: |
Roel Janssen |
Subject: |
Re: Streaming responses with Guile's web modules |
Date: |
Wed, 19 Sep 2018 17:50:20 +0200 |
User-agent: |
mu4e 1.0; emacs 26.1 |
Roel Janssen <address@hidden> writes:
> Amirouche Boubekki <address@hidden> writes:
>
>> On 2018-09-18 21:42, Roel Janssen wrote:
>>> Dear Guilers,
>>>
>>> I'd like to implement a web server using the (web server) module, but
>>> allow for “streaming” results. The way I imagine this would look like,
>>> is something like this:
>>>
>>> (define (request-handler request body)
>>> (values '((content-type . (text/plain)))
>>> ;; This function can build its response by writing to
>>> ;; ‘port’, rather than to return the whole body as a
>>> ;; string.
>>> (lambda (port)
>>> (format port "Hello world!"))))
>>>
>>> (run-server request-handler)
>>>
>>> Is this possible with the (web server) module? If so, how?
>>
>> What you describe is exactly how it works. The second value can
>> be a bytevector, #f or a procedure that takes a port as argument.
>>
>> Here is an example use [0] and here is the code [1]
>>
>> [0]
>> https://framagit.org/a-guile-mind/culturia.next/blob/master/culturia/web/helpers.scm#L34
>> [1]
>> https://git.savannah.gnu.org/cgit/guile.git/tree/module/web/server.scm#n198
>>
>> Regards
>
> Thanks for your quick and elaborate reply! I didn't realize that in
> writing the example I had written a working example.
>
> Looking at memory usage, it looks as if it puts all bytes produced by
> that function into memory at once before sending the HTTP response over
> the network. Is that observation correct? If so, can it be avoided?
As an addition to the above, here's an example implementation:
(use-modules (web server)
(web request)
(web response)
(web http)
(ice-9 receive)
(ice-9 rdelim))
(define (process-input input-port output-port)
(unless (or (port-closed? input-port)
(port-closed? output-port))
(let ((line (read-line input-port)))
(if (eof-object? line)
(begin
(close-port input-port)
#t)
(begin
(format output-port "~a~%" line)
(process-input input-port output-port))))))
(define (request-handler request body)
(values '((content-type . (text/plain))
(transfer-encoding . ((chunked))))
(lambda (port)
(call-with-input-file "large-file.txt"
(lambda (input-port) (process-input input-port port))))))
(run-server request-handler)
In the example, “large-file.txt” is a file of a few gigabytes, and the
Guile process grows to a few gigabytes as well.
Kind regards,
Roel Janssen