CURLOPT\_CHUNK\_DATA(3) Library Functions Manual CURLOPT\_CHUNK\_DATA(3)

# [NAME](#NAME)

CURLOPT\_CHUNK\_DATA - pointer passed to the FTP chunk callbacks

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CHUNK_DATA, void *pointer);
```

# [DESCRIPTION](#DESCRIPTION)

Pass a *pointer* that is untouched by libcurl and passed as the ptr argument to the [*CURLOPT\_CHUNK\_BGN\_FUNCTION(3)*](/man/os/curl/CURLOPT_CHUNK_BGN_FUNCTION.3) and [*CURLOPT\_CHUNK\_END\_FUNCTION(3)*](/man/os/curl/CURLOPT_CHUNK_END_FUNCTION.3).

# [DEFAULT](#DEFAULT)

NULL

# [PROTOCOLS](#PROTOCOLS)

This functionality affects ftp only

# [EXAMPLE](#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(void)
{


  /* 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](#AVAILABILITY)

Added in curl 7.21.0

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_easy\_setopt(3)*](/man/os/curl/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)*](/man/os/curl/libcurl-errors.3).

# [SEE ALSO](#SEE_ALSO)

[**CURLOPT\_CHUNK\_BGN\_FUNCTION**(3)](/man/os/curl/CURLOPT_CHUNK_BGN_FUNCTION.3), [**CURLOPT\_WILDCARDMATCH**(3)](/man/os/curl/CURLOPT_WILDCARDMATCH.3)

2026-10-31 libcurl

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Document: CURLOPT_CHUNK_DATA(3) from curl 8.23.0-r3 (Chainguard OS)
Source: https://github.com/curl/curl.git