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Re: Some help needed to use curl lib to download binary file
From: |
Sébastien Rey-Coyrehourcq |
Subject: |
Re: Some help needed to use curl lib to download binary file |
Date: |
Mon, 01 Aug 2022 09:48:47 +0200 |
User-agent: |
mu4e 1.6.11; emacs 28.1.90 |
Thanks a lot for this very detailled explanation Vivien, that’s help me a lot
to understand what happens here !!
I’m trying to continue my learning of Lisp/Scheme like language, this is a new
fascinating world to explore :)
Best regards,
Vivien Kraus <vivien@planete-kraus.eu> writes:
> Hello,
>
> I see in the paste:
>
>> ;; function taken on
>> <https://gist.github.com/amirouche/138a27bdbef5a672a0135f90ca26ec41>
>> ;; then adapted to use cookie jar
>> (define-public (http-get url cookie-exist)
>> ;; Create a Curl handle
>> (let ((handle (curl-easy-init)))
>> ;; Set the URL from which to get the data
>> (curl-easy-setopt handle ’url url)
>> (if cookie-exist
>> (curl-easy-setopt handle ’cookie “cookie.txt”)
>> (curl-easy-setopt handle ’cookiejar “cookie.txt”))
>>
>> ;; Request that the HTTP headers be included in the response
>> (curl-easy-setopt handle ’header #t)
>> ;; Get the result as a Latin-1 string
>> (let* ((response-string (curl-easy-perform handle))
>> ;; Create a string port from the response
>> (response-port (open-input-string response-string))
>> ;; Have the (web response) module to parse the response
>> (response (read-response response-port))
>> (body (utf8->string (read-response-body response))))
>> (close response-port)
>> ;; Have the (web response) module extract the body from the
>> ;; response
>> (values response body))))
>
> So here the call expects the response to be UTF-8 text. If it is a
> binary file that you are downloading, the function will raise an
> exception. Guile has that python3 feeling where you are supposed to
> know in advance whether what you are using is text or binary, which is
> hurting you here.
>
> However, you can avoid the problem by either having bytevectors
> everywhere, so removing the call to utf8->string and bind the “body”
> variable directly to (read-response-body response), or pretend that you
> know better than guile and pretend that it is latin-1-encoded, so you
> lose no information and guile won’t complain. In that case, load (ice-9
> iconv) and replace (utf8->string …) with (bytevector->string … “ISO-
> 8859-1”).
>
> If you go the first route, you get a bytevector back. If you go the
> second one, you get a string, but you must remember that it contains
> raw bytes and not text (unless the response body was indeed text).
>
> There are some cases when you might want to have such strings-that-
> contain-binary-or-text, such as if you want to use the strings API on
> them and the bytevector API does not provide what you want, or you want
> to interface with NUL-terminated strings. In other cases you might
> prefer bytevectors. Anyway, there is no encoding cost to convert
> between strings-that-contain-binary-or-toxt and bytevectors, it is as
> simple as a copy.
>
>> ;; write content into file
>> (call-with-output-file “download.zip” (lambda (current-output-port)
>> (get-file get-file-link)
>> (put-bytevector (current-
>> output-port) body)))
>
> call-with-output-file calls its function argument with a port. Plus,
> you just ignore the result of get-file, so instead you should do
> something with it.
>
> If you chose to have get-file return a bytevector, you can do:
>
> (call-with-output-file “download.zip”
> (lambda (port)
> (put-bytevector port (get-file get-file-link)))
> #:binary #t)
>
> If get-file returns a string, you can do:
>
> (call-with-output-file “download.zip”
> (lambda (port)
> (put-string port (get-file get-file-link)))
> #:encoding “ISO-8859-1”)
>
> Best regards,
>
> Vivien
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