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.\" generated by cd2nroff 0.1 from CURLOPT_CHUNK_BGN_FUNCTION.md
.TH CURLOPT_CHUNK_BGN_FUNCTION 3 "2025-06-27" libcurl
.SH NAME
CURLOPT_CHUNK_BGN_FUNCTION \- callback before a transfer with FTP wildcard match
.SH SYNOPSIS
.nf
#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);
.fi
.SH 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 \fItransfer_info\fP pointer points to a \fBcurl_fileinfo\fP struct with
details about the file that is about to get transferred.
This callback makes sense only when using the \fICURLOPT_WILDCARDMATCH(3)\fP
option for now.
The target of transfer_info parameter is a "feature depended" structure. For
the FTP wildcard download, the target is \fBcurl_fileinfo\fP structure (see
\fIcurl/curl.h\fP). The parameter \fIptr\fP is a pointer given by
\fICURLOPT_CHUNK_DATA(3)\fP. The parameter remains contains number of chunks
remaining per the transfer. If the feature is not available, the parameter has
zero value.
Return \fICURL_CHUNK_BGN_FUNC_OK\fP if everything is fine,
\fICURL_CHUNK_BGN_FUNC_SKIP\fP if you want to skip the concrete chunk or
\fICURL_CHUNK_BGN_FUNC_FAIL\fP to tell libcurl to stop if some error occurred.
.SH DEFAULT
NULL
.SH PROTOCOLS
This functionality affects ftp only
.SH EXAMPLE
.nf
#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);
}
.fi
.SH AVAILABILITY
Added in curl 7.21.0
.SH RETURN VALUE
\fIcurl_easy_setopt(3)\fP returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non\-zero means an error occurred, see
\fIlibcurl\-errors(3)\fP.
.SH SEE ALSO
.BR CURLOPT_CHUNK_END_FUNCTION (3),
.BR CURLOPT_WILDCARDMATCH (3)