CURLMOPT\_PUSHFUNCTION(3) Library Functions Manual CURLMOPT\_PUSHFUNCTION(3)

# [NAME](#NAME)

CURLMOPT\_PUSHFUNCTION - callback that approves or denies server pushes

# [SYNOPSIS](#SYNOPSIS)

```
#include <curl/curl.h>
int curl_push_callback(CURL *parent,


                       CURL *easy,


                       size_t num_headers,


                       struct curl_pushheaders *headers,


                       void *clientp);
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_PUSHFUNCTION,


                            curl_push_callback func);
```

# [DESCRIPTION](#DESCRIPTION)

This callback gets called when a new HTTP/2 stream is being pushed by the server (using the PUSH\_PROMISE frame). If no push callback is set, all offered pushes are denied automatically.

# [CALLBACK DESCRIPTION](#CALLBACK_DESCRIPTION)

The callback gets its arguments like this:

*parent* is the handle of the stream on which this push arrives. The new handle has the following options duplicated from the parent: [*CURLOPT\_WRITEFUNCTION(3)*](/man/os/curl/CURLOPT_WRITEFUNCTION.3), [*CURLOPT\_WRITEDATA(3)*](/man/os/curl/CURLOPT_WRITEDATA.3), [*CURLOPT\_HEADERFUNCTION(3)*](/man/os/curl/CURLOPT_HEADERFUNCTION.3), [*CURLOPT\_HEADERDATA(3)*](/man/os/curl/CURLOPT_HEADERDATA.3), [*CURLOPT\_DEBUGFUNCTION(3)*](/man/os/curl/CURLOPT_DEBUGFUNCTION.3), [*CURLOPT\_DEBUGDATA(3)*](/man/os/curl/CURLOPT_DEBUGDATA.3), [*CURLOPT\_PROGRESSFUNCTION(3)*](/man/os/curl/CURLOPT_PROGRESSFUNCTION.3), [*CURLOPT\_XFERINFOFUNCTION(3)*](/man/os/curl/CURLOPT_XFERINFOFUNCTION.3), [*CURLOPT\_PROGRESSDATA(3)*](/man/os/curl/CURLOPT_PROGRESSDATA.3) and [*CURLOPT\_XFERINFODATA(3)*](/man/os/curl/CURLOPT_XFERINFODATA.3).

It is then up to the application to alter/set any options if desired.

*easy* is a newly created handle that represents this upcoming transfer.

*num\_headers* is the number of name+value pairs that was received and can be accessed

*headers* is a handle used to access push headers using the accessor functions described below. This only accesses and provides the PUSH\_PROMISE headers, the normal response headers are provided in the header callback as usual.

*clientp* is the pointer set with [*CURLMOPT\_PUSHDATA(3)*](/man/os/curl/CURLMOPT_PUSHDATA.3)

If the callback returns CURL\_PUSH\_OK, the new easy handle is added to the multi handle, the callback must not do that by itself.

The callback can access PUSH\_PROMISE headers with two accessor functions. These functions can only be used from within this callback and they can only access the PUSH\_PROMISE headers: [*curl\_pushheader\_byname(3)*](/man/os/curl/curl_pushheader_byname.3) and [*curl\_pushheader\_bynum(3)*](/man/os/curl/curl_pushheader_bynum.3). The normal response headers are passed to the header callback for pushed streams like for normal streams.

The header fields can also be accessed with [*curl\_easy\_header(3)*](/man/os/curl/curl_easy_header.3), introduced in later libcurl versions.

# [CALLBACK RETURN VALUE](#CALLBACK_RETURN_VALUE)

[CURL\_PUSH\_OK (0)](#CURL_PUSH_OK)

The application has accepted the stream and it can now start receiving data, the ownership of the curl handle has been taken over by the application.

[CURL\_PUSH\_DENY (1)](#CURL_PUSH_DENY)

The callback denies the stream and no data reaches the application, the easy handle is destroyed by libcurl.

[CURL\_PUSH\_ERROROUT (2)](#CURL_PUSH_ERROROUT)

Returning this code rejects the pushed stream and returns an error back on the parent stream making it get closed with an error. (Added in 7.72.0)

\*

All other return codes are reserved for future use.

# [DEFAULT](#DEFAULT)

NULL, no callback

# [PROTOCOLS](#PROTOCOLS)

This functionality affects http only

# [EXAMPLE](#EXAMPLE)

```
#include <string.h>
/* only allow pushes for filenames starting with "push-" */
static int push_callback(CURL *parent,


                         CURL *easy,


                         size_t num_headers,


                         struct curl_pushheaders *headers,


                         void *clientp)
{


  char *headp;


  int *transfers = (int *)clientp;


  FILE *out;


  headp = curl_pushheader_byname(headers, ":path");


  if(headp && !strncmp(headp, "/push-", 6)) {


    fprintf(stderr, "The PATH is %s\n", headp);


    /* save the push here */


    out = fopen("pushed-stream", "wb");


    /* write to this file */


    curl_easy_setopt(easy, CURLOPT_WRITEDATA, out);


    (*transfers)++; /* one more */


    return CURL_PUSH_OK;


  }


  return CURL_PUSH_DENY;
}
int main(void)
{


  int counter;


  CURLM *multi = curl_multi_init();


  curl_multi_setopt(multi, CURLMOPT_PUSHFUNCTION, push_callback);


  curl_multi_setopt(multi, CURLMOPT_PUSHDATA, &counter);
}
```

# [AVAILABILITY](#AVAILABILITY)

Added in curl 7.44.0

# [RETURN VALUE](#RETURN_VALUE)

[*curl\_multi\_setopt(3)*](/man/os/curl/curl_multi_setopt.3) returns a CURLMcode indicating success or error.

CURLM\_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)

[**CURLMOPT\_PIPELINING**(3)](/man/os/curl/CURLMOPT_PIPELINING.3), [**CURLMOPT\_PUSHDATA**(3)](/man/os/curl/CURLMOPT_PUSHDATA.3), [**CURLOPT\_PIPEWAIT**(3)](/man/os/curl/CURLOPT_PIPEWAIT.3), **RFC**7540

2026-10-31 libcurl

---

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