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                     23: .TH CURLMOPT_PUSHFUNCTION 3 "March 23, 2020" "libcurl 7.70.0" "curl_multi_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLMOPT_PUSHFUNCTION \- callback that approves or denies server pushes
                     27: .SH SYNOPSIS
                     28: .nf
                     29: #include <curl/curl.h>
                     30: 
                     31: char *curl_pushheader_bynum(struct curl_pushheaders *h, size_t num);
                     32: char *curl_pushheader_byname(struct curl_pushheaders *h, const char *name);
                     33: 
                     34: int curl_push_callback(CURL *parent,
                     35:                        CURL *easy,
                     36:                        size_t num_headers,
                     37:                        struct curl_pushheaders *headers,
                     38:                        void *userp);
                     39: 
                     40: CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_PUSHFUNCTION,
                     41:                             curl_push_callback func);
                     42: .fi
                     43: .SH DESCRIPTION
                     44: This callback gets called when a new HTTP/2 stream is being pushed by the
                     45: server (using the PUSH_PROMISE frame). If no push callback is set, all offered
                     46: pushes will be denied automatically.
                     47: .SH CALLBACK DESCRIPTION
                     48: The callback gets its arguments like this:
                     49: 
                     50: \fIparent\fP is the handle of the stream on which this push arrives. The new
                     51: handle has been duphandle()d from the parent, meaning that it has gotten all
                     52: its options inherited. It is then up to the application to alter any options
                     53: if desired.
                     54: 
                     55: \fIeasy\fP is a newly created handle that represents this upcoming transfer.
                     56: 
                     57: \fInum_headers\fP is the number of name+value pairs that was received and can
                     58: be accessed
                     59: 
                     60: \fIheaders\fP is a handle used to access push headers using the accessor
                     61: functions described below. This only accesses and provides the PUSH_PROMISE
                     62: headers, the normal response headers will be provided in the header callback
                     63: as usual.
                     64: 
                     65: \fIuserp\fP is the pointer set with \fICURLMOPT_PUSHDATA(3)\fP
                     66: 
                     67: If the callback returns CURL_PUSH_OK, the 'easy' handle will be added to the
                     68: multi handle, the callback must not do that by itself.
                     69: 
                     70: The callback can access PUSH_PROMISE headers with two accessor
                     71: functions. These functions can only be used from within this callback and they
                     72: can only access the PUSH_PROMISE headers. The normal response headers will be
                     73: passed to the header callback for pushed streams just as for normal streams.
                     74: .IP curl_pushheader_bynum
                     75: Returns the header at index 'num' (or NULL). The returned pointer points to a
                     76: "name:value" string that will be freed when this callback returns.
                     77: .IP curl_pushheader_byname
                     78: Returns the value for the given header name (or NULL). This is a shortcut so
                     79: that the application doesn't have to loop through all headers to find the one
                     80: it is interested in. The data pointed will be freed when this callback
                     81: returns. If more than one header field use the same name, this returns only
                     82: the first one.
                     83: .SH CALLBACK RETURN VALUE
                     84: .IP "CURL_PUSH_OK (0)"
                     85: The application has accepted the stream and it can now start receiving data,
                     86: the ownership of the CURL handle has been taken over by the application.
                     87: .IP "CURL_PUSH_DENY (1)"
                     88: The callback denies the stream and no data for this will reach the
                     89: application, the easy handle will be destroyed by libcurl.
                     90: .IP *
                     91: All other return codes are reserved for future use.
                     92: .SH DEFAULT
                     93: NULL, no callback
                     94: .SH PROTOCOLS
                     95: HTTP(S) (HTTP/2 only)
                     96: .SH EXAMPLE
                     97: .nf
                     98: /* only allow pushes for file names starting with "push-" */
                     99: int push_callback(CURL *parent,
                    100:                   CURL *easy,
                    101:                   size_t num_headers,
                    102:                   struct curl_pushheaders *headers,
                    103:                   void *userp)
                    104: {
                    105:   char *headp;
                    106:   int *transfers = (int *)userp;
                    107:   FILE *out;
                    108:   headp = curl_pushheader_byname(headers, ":path");
                    109:   if(headp && !strncmp(headp, "/push-", 6)) {
                    110:     fprintf(stderr, "The PATH is %s\\n", headp);
                    111: 
                    112:     /* save the push here */
                    113:     out = fopen("pushed-stream", "wb");
                    114: 
                    115:     /* write to this file */
                    116:     curl_easy_setopt(easy, CURLOPT_WRITEDATA, out);
                    117: 
                    118:     (*transfers)++; /* one more */
                    119: 
                    120:     return CURL_PUSH_OK;
                    121:   }
                    122:   return CURL_PUSH_DENY;
                    123: }
                    124: 
                    125: curl_multi_setopt(multi, CURLMOPT_PUSHFUNCTION, push_callback);
                    126: curl_multi_setopt(multi, CURLMOPT_PUSHDATA, &counter);
                    127: .fi
                    128: .SH AVAILABILITY
                    129: Added in 7.44.0
                    130: .SH RETURN VALUE
                    131: Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.
                    132: .SH "SEE ALSO"
                    133: .BR CURLMOPT_PUSHDATA "(3), " CURLMOPT_PIPELINING "(3), " CURLOPT_PIPEWAIT "(3), "
                    134: .BR RFC 7540