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CURLOPT_CH...N_FUNCTION(3)  Library Functions Manual  CURLOPT_CH...N_FUNCTION(3)

NAME
     CURLOPT_CHUNK_BGN_FUNCTION  -  callback before a transfer with FTP wildcard
     match

SYNOPSIS
     #include <curl/curl.h>

     struct curl_fileinfo {
       char *filename;
       curlfiletype filetype;
       time_t time;   /* always zero */
       unsigned int perm;
       int uid;
       int gid;
       curl_off_t size;
       long int hardlinks;

       struct {
	 /* If some of these fields is not NULL, it is a pointer to b_data. */
	 char *time;
	 char *perm;
	 char *user;
	 char *group;
	 char *target; /* pointer to the target filename of a symlink */
       } strings;

       unsigned int flags;

       /* used internally */
       char *b_data;
       size_t b_size;
       size_t b_used;
     };

     long chunk_bgn_callback(const void *transfer_info, void *ptr,
			     int remains);

     CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CHUNK_BGN_FUNCTION,
			       chunk_bgn_callback);

DESCRIPTION
     Pass a pointer to your callback function, which should match the  prototype
     shown above.

     This  callback  function gets called by libcurl before a part of the stream
     is going to be transferred (if the transfer supports chunks).

     The transfer_info pointer points to a  curl_fileinfo  struct  with  details
     about the file that is about to get transferred.

     This  callback makes sense only when using the CURLOPT_WILDCARDMATCH(3) op-
     tion for now.

     The target of transfer_info parameter is a  "feature  depended"  structure.
     For  the  FTP wildcard download, the target is curl_fileinfo structure (see
     curl/curl.h).  The   parameter   ptr   is	 a   pointer   given   by   CUR-
     LOPT_CHUNK_DATA(3). The parameter remains contains number of chunks remain-
     ing  per  the  transfer. If the feature is not available, the parameter has
     zero value.

     Return	CURL_CHUNK_BGN_FUNC_OK	   if	   everything	   is	   fine,
     CURL_CHUNK_BGN_FUNC_SKIP  if  you	want  to  skip	the  concrete  chunk  or
     CURL_CHUNK_BGN_FUNC_FAIL to tell libcurl to stop if some error occurred.

DEFAULT
     NULL

PROTOCOLS
     This functionality affects ftp only

EXAMPLE
     #include <stdio.h>

     struct callback_data {
       FILE *output;
     };

     static long file_is_coming(struct curl_fileinfo *finfo,
				void *ptr,
				int remains)
     {
       struct callback_data *data = ptr;
       printf("%3d %40s %10luB ", remains, finfo->filename,
	      (unsigned long)finfo->size);

       switch(finfo->filetype) {
       case CURLFILETYPE_DIRECTORY:
	 printf(" DIR\n");
	 break;
       case CURLFILETYPE_FILE:
	 printf("FILE ");
	 break;
       default:
	 printf("OTHER\n");
	 break;
       }

       if(finfo->filetype == CURLFILETYPE_FILE) {
	 /* do not transfer files >= 50B */
	 if(finfo->size > 50) {
	   printf("SKIPPED\n");
	   return CURL_CHUNK_BGN_FUNC_SKIP;
	 }

	 data->output = fopen(finfo->filename, "wb");
	 if(!data->output) {
	   return CURL_CHUNK_BGN_FUNC_FAIL;
	 }
       }

       return CURL_CHUNK_BGN_FUNC_OK;
     }

     int main()
     {
       /* data for callback */
       struct callback_data callback_info;

       CURL *curl = curl_easy_init();

       /* callback is called before download of concrete file started */
       curl_easy_setopt(curl, CURLOPT_CHUNK_BGN_FUNCTION, file_is_coming);
       curl_easy_setopt(curl, CURLOPT_CHUNK_DATA, &callback_info);
     }

AVAILABILITY
     Added in curl 7.21.0

RETURN VALUE
     curl_easy_setopt(3) returns a CURLcode indicating success or error.

     CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
     libcurl-errors(3).

SEE ALSO
     CURLOPT_CHUNK_END_FUNCTION(3), CURLOPT_WILDCARDMATCH(3)

libcurl 			   2026-06-11	      CURLOPT_CH...N_FUNCTION(3)

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