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Updated: Thursday, June 13, 2019
 
 

curl_mime_data_cb (3)

Name

curl_mime_data_cb - based data source for a mime part's body

Synopsis

#include <curl/curl.h>

size_t readfunc(char *buffer, size_t size, size_t nitems, void *arg);
int seekfunc(void *arg, curl_off_t offset, int origin);
void freefunc(void *arg);

CURLcode curl_mime_data_cb(curl_mimepart * part, curl_off_t datasize,
curl_read_callback readfunc, curl_seek_callback seekfunc,
curl_free_callback freefunc, void * arg);

Description

curl_mime_data_cb(3)            libcurl Manual            curl_mime_data_cb(3)



NAME
       curl_mime_data_cb  - set a callback-based data source for a mime part's
       body

SYNOPSIS
       #include <curl/curl.h>

       size_t readfunc(char *buffer, size_t size, size_t nitems, void *arg);
       int seekfunc(void *arg, curl_off_t offset, int origin);
       void freefunc(void *arg);

       CURLcode curl_mime_data_cb(curl_mimepart * part, curl_off_t datasize,
               curl_read_callback readfunc, curl_seek_callback seekfunc,
               curl_free_callback freefunc, void * arg);

DESCRIPTION
       curl_mime_data_cb(3) sets the data source of a mime part's body content
       from a data read callback function.

       part is the part's to assign contents to.

       readfunc  is  a pointer to a data read callback function, with a signa-
       ture as shown by the above prototype. It may not be set to NULL.

       seekfunc is a pointer to a seek callback function, with a signature  as
       shown by the above prototype. This function will be used upon resending
       data (i.e.: after a redirect); this pointer may  be  set  to  NULL,  in
       which case a resend is not possible.

       freefunc  is  a  pointer  to a user resource freeing callback function,
       with a signature as shown by the above prototype. If no resource is  to
       be  freed,  it  may safely be set to NULL. This function will be called
       upon mime structure freeing.

       arg is a user defined argument to callback functions.

       The read callback function gets called by libcurl as soon as  it  needs
       to  read  data  in order to send it to the peer - like if you ask it to
       upload or post data to the server. The data  area  pointed  at  by  the
       pointer  buffer  should  be filled up with at most size multiplied with
       nmemb number of bytes by your function.

       Your read function must then return the actual number of bytes that  it
       stored  in that memory area. Returning 0 will signal end-of-file to the
       library and cause it to stop the current transfer.

       If you stop the current transfer by returning  0  "pre-maturely"  (i.e.
       before  the server expected it, like when you've said you will upload N
       bytes and you upload less than N bytes), you may  experience  that  the
       server "hangs" waiting for the rest of the data that won't come.

       The  read  callback  may return CURL_READFUNC_ABORT to stop the current
       operation immediately, resulting in a  CURLE_ABORTED_BY_CALLBACK  error
       code from the transfer.

       The  callback can return CURL_READFUNC_PAUSE to cause reading from this
       connection to pause. See curl_easy_pause(3) for further details.

       The seek function gets called by libcurl to rewind input stream data or
       to seek to a certain position. The function shall work like fseek(3) or
       lseek(3) and it gets SEEK_SET, SEEK_CUR or  SEEK_END  as  argument  for
       origin, although libcurl currently only passes SEEK_SET.

       The   callback   function  must  return  CURL_SEEKFUNC_OK  on  success,
       CURL_SEEKFUNC_FAIL to cause the upload operation to fail or  CURL_SEEK-
       FUNC_CANTSEEK  to  indicate that while the seek failed, libcurl is free
       to work around the problem if possible. The  latter  can  sometimes  be
       done by instead reading from the input or similar.

       Care  must  be taken if the part is bound to a curl easy handle that is
       later duplicated: the arg pointer argument is also duplicated,  result-
       ing  in  the  pointed  item  to  be shared between the original and the
       copied handle.  In particular, special attention should be given to the
       freefunc  procedure  code  since  it will be called twice with the same
       argument.


AVAILABILITY
       As long as at least one of HTTP, SMTP or  IMAP  is  enabled.  Added  in
       7.56.0.

RETURN VALUE
       CURLE_OK or a CURL error code upon failure.

EXAMPLE
       Sending  a  huge data string will cause the same amount of memory to be
       allocated: to avoid overhead resources consumption, one might  want  to
       use a callback source to avoid data duplication. In this case, original
       data must be retained until after the transfer terminates.

       char hugedata[512000];

       struct ctl {
         char *buffer;
         curl_off_t size;
         curl_off_t position;
       };

       size_t read_callback(char *buffer, size_t size, size_t nitems, void *arg)
       {
         struct ctl *p = (struct ctl *) arg;
         curl_off_t sz = p->size - p->position;

         nitems *= size;
         if(sz > nitems)
           sz = nitems;
         if(sz)
           memcpy(buffer, p->buffer + p->position, sz);
         p->position += sz;
         return sz;
       }

       int seek_callback(void *arg, curl_off_t offset, int origin)
       {
         struct ctl *p = (struct ctl *) arg;

         switch(origin) {
         case SEEK_END:
           offset += p->size;
           break;
         case SEEK_CUR:
           offset += p->position;
           break;
         }

         if(offset < 0)
           return CURL_SEEKFUNC_FAIL;
         p->position = offset;
         return CURL_SEEKFUNC_OK;
       }

        CURL *easy = curl_easy_init();
        curl_mime *mime = curl_mime_init(easy);
        curl_mimepart *part = curl_mime_addpart(mime);
        struct ctl hugectl;

        hugectl.buffer = hugedata;
        hugectl.size = sizeof hugedata;
        hugectl.position = 0;
        curl_mime_data_cb(part, hugectl.size, read_callback, seek_callback, NULL,
                          &hugectl);



ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:


       +---------------+------------------+
       |ATTRIBUTE TYPE | ATTRIBUTE VALUE  |
       +---------------+------------------+
       |Availability   | web/curl         |
       +---------------+------------------+
       |Stability      | Uncommitted      |
       +---------------+------------------+
SEE ALSO
       curl_mime_addpart(3),       curl_mime_data(3),       curl_mime_name(3),
       curl_easy_duphandle(3)



NOTES
       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source    was    downloaded    from    https://github.com/curl/curl/ar-
       chive/curl-7_64_0.zip

       Further information about this software can be found on the open source
       community website at http://curl.haxx.se/.



libcurl 7.56.0                  22 August 2017            curl_mime_data_cb(3)