---
name: "CURLMOPT_PUSHFUNCTION"
section: "3"
platform: "macos"
package: "curl"
version: "166.0.0.0.1"
release: "macOS 26.5"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/CURLMOPT_PUSHFUNCTION"
---

# CURLMOPT\_PUSHFUNCTION(3)

callback that approves or denies server pushes

## NAME

CURLMOPT\_PUSHFUNCTION - callback that approves or denies server pushes

## 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

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

The callback gets its arguments like this:

*parent* is the handle of the stream on which this push arrives. The new handle has been duplicated from the parent, meaning that it has gotten all its options inherited. It is then up to the application to alter 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)](/CURLMOPT_PUSHDATA/3.md)*

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)](/curl_pushheader_byname/3.md)* and *[curl\_pushheader\_bynum(3)](/curl_pushheader_bynum/3.md)*. The normal response headers are passed to the header callback for pushed streams just as for normal streams.

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

## CALLBACK RETURN VALUE

- CURL\_PUSH\_OK (0)

  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)

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

- CURL\_PUSH\_ERROROUT (2)

  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

NULL, no callback

## PROTOCOLS

HTTP(S) (HTTP/2 only)

## EXAMPLE

```
#include <string.h>
/* only allow pushes for file names starting with "push-" */
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

Added in 7.44.0

## RETURN VALUE

Returns CURLM\_OK if the option is supported, and CURLM\_UNKNOWN\_OPTION if not.

## SEE ALSO

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