[NTG-context] Files on a server

Henri Menke henrimenke at gmail.com
Wed May 16 13:45:08 CEST 2018


On 05/16/2018 11:23 PM, Hans van der Meer wrote:
> I would be satisfied when a returned 404 error code will be handled
> within a reasonable (configurable) time delay. As for redirection, there
> I would not mind if it is not included.
> Restrictions like that are not a problem for me, because this is for
> building a pdf that accesses many internet located files. The check on
> existence is therefore especially meant for spotting missing or misnamed
> files.

You can use libcurl via ffi: https://curl.haxx.se/libcurl/

\startluacode
local ffi = require("ffi")

ffi.cdef[[
typedef struct Curl_easy CURL;
typedef int CURLcode;
typedef int CURLoption;
typedef int CURLINFO;
typedef size_t(*callback)(void *buffer, size_t size, size_t nmemb, void
*userp);

CURLcode curl_global_init(long flags);
CURL *curl_easy_init(void);
CURLcode curl_easy_setopt(CURL *curl, CURLoption option, ...);
CURLcode curl_easy_perform(CURL *curl);
CURLcode curl_easy_getinfo(CURL *curl, CURLINFO info, ...);
void curl_easy_cleanup(CURL *curl);
void curl_global_cleanup(void);
]]

-- magic numbers
local CURL_GLOBAL_DEFAULT = 3
local CURLOPT_URL = 10002
local CURLOPT_NOBODY = 44
local CURLOPT_HEADER = 42
local CURLOPT_WRITEFUNCTION = 20011
local CURLINFO_RESPONSE_CODE = 0x200000 + 2

local lcurl = ffi.load("curl")

local function discard(buffer, size, nmemb, userp)
    return size * nmemb
end

function check_status(url)
    lcurl.curl_global_init(CURL_GLOBAL_DEFAULT)

    local curl = lcurl.curl_easy_init()

    lcurl.curl_easy_setopt(curl, CURLOPT_URL, url)
    lcurl.curl_easy_setopt(curl, CURLOPT_NOBODY, ffi.cast("long",1))
    lcurl.curl_easy_setopt(curl, CURLOPT_HEADER, ffi.cast("long",1))
    lcurl.curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION,
ffi.cast("callback",discard));

    local res = lcurl.curl_easy_perform(curl)
    local c_http_code = ffi.new("long[1]")
    lcurl.curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, c_http_code);

    lcurl.curl_easy_cleanup(curl)
    lcurl.curl_global_cleanup()

    return tonumber(c_http_code[0])
end
\stopluacode

\starttext

\ctxlua{context(check_status("http://example.com/"))}

\ctxlua{context(check_status("https://example.com/"))}

\ctxlua{context(check_status("https://example.com/xyz"))}

\stoptext

> 
> Hans van der Meer
> 
>> On 16 May 2018, at 12:41, Henri Menke <henrimenke at gmail.com
>> <mailto:henrimenke at gmail.com>> wrote:
>>
>> On 05/16/2018 09:31 PM, Hans van der Meer wrote:
>>> I tried to determine the existence of a file on the internet. See the
>>> following macro call:
>>>
>>>         % Test if file exists.
>>>         \edef\theurl{\linkprotocol://\urlbase\xmlatt{#1}{link}\thesuffix}
>>>         \doiffileelse
>>>         {\theurl}
>>>         {\verbose{HVDM-PEV-TEST}{file exists: \theurl}}
>>>         {\verbose{HVDM-PEV-TEST}{file does not exist: \theurl}}
>>>
>>> It seems that \doiffileelse always results in true except for local
>>> files where nonexistence is correctly handled.
>>>
>>> For example the following url definitely does not exist but nevertheless
>>> \doiffileelse reports its existence:
>>> HVDM-PEV-TEST   > file exists:
>>> http://hansvandermeer.myqnapcloud.com/archive/denhaag/hga-dtb-1869-6040.pdf
>>>
>>> Is it possible that the \doiffile macros are extended for files on the
>>> internet or a correponding set \doifurl is developed?
>>
>> I'm not speaking for the devs here, but I don't think that this is going
>> to be included.  It would require that all webpages send proper 404
>> codes and timeout after reasonable delay.  Also how would you handle
>> redirects?  Should the ConTeXt run be stalled because checking for a
>> files existence on the web is caught in a redirect loop?
>>
>>>
>>> Hans van der Meer
>>>
>>>
>>>
>>> ___________________________________________________________________________________
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>>> entry to the Wiki!
>>>
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>>> wiki     : http://contextgarden.net
>>> ___________________________________________________________________________________
>>>
>>
>> ___________________________________________________________________________________
>> If your question is of interest to others as well, please add an entry
>> to the Wiki!
>>
>> maillist : ntg-context at ntg.nl
>> <mailto:ntg-context at ntg.nl> / http://www.ntg.nl/mailman/listinfo/ntg-context
>> webpage  : http://www.pragma-ade.nl
>> <http://www.pragma-ade.nl/> / http://context.aanhet.net
>> <http://context.aanhet.net/>
>> archive  : https://bitbucket.org/phg/context-mirror/commits/
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>> ___________________________________________________________________________________
> 
> 
> 
> ___________________________________________________________________________________
> If your question is of interest to others as well, please add an entry to the Wiki!
> 
> maillist : ntg-context at ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
> webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
> archive  : https://bitbucket.org/phg/context-mirror/commits/
> wiki     : http://contextgarden.net
> ___________________________________________________________________________________
> 



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