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117 lines
3.8 KiB
Groff
117 lines
3.8 KiB
Groff
.\" generated by cd2nroff 0.1 from CURLMOPT_PUSHFUNCTION.md
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.TH CURLMOPT_PUSHFUNCTION 3 "2024-06-01" libcurl
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.SH NAME
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CURLMOPT_PUSHFUNCTION \- callback that approves or denies server pushes
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.SH SYNOPSIS
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.nf
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#include <curl/curl.h>
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int curl_push_callback(CURL *parent,
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CURL *easy,
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size_t num_headers,
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struct curl_pushheaders *headers,
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void *clientp);
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CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_PUSHFUNCTION,
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curl_push_callback func);
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.fi
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.SH DESCRIPTION
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This callback gets called when a new HTTP/2 stream is being pushed by the
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server (using the PUSH_PROMISE frame). If no push callback is set, all offered
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pushes are denied automatically.
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.SH CALLBACK DESCRIPTION
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The callback gets its arguments like this:
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\fIparent\fP is the handle of the stream on which this push arrives. The new
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handle has been duplicated from the parent, meaning that it has gotten all its
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options inherited. It is then up to the application to alter any options if
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desired.
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\fIeasy\fP is a newly created handle that represents this upcoming transfer.
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\fInum_headers\fP is the number of name+value pairs that was received and can
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be accessed
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\fIheaders\fP is a handle used to access push headers using the accessor
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functions described below. This only accesses and provides the PUSH_PROMISE
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headers, the normal response headers are provided in the header callback as
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usual.
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\fIclientp\fP is the pointer set with \fICURLMOPT_PUSHDATA(3)\fP
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If the callback returns CURL_PUSH_OK, the new easy handle is added to the
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multi handle, the callback must not do that by itself.
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The callback can access PUSH_PROMISE headers with two accessor
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functions. These functions can only be used from within this callback and they
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can only access the PUSH_PROMISE headers: \fIcurl_pushheader_byname(3)\fP and
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\fIcurl_pushheader_bynum(3)\fP. The normal response headers are passed to the
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header callback for pushed streams just as for normal streams.
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The header fields can also be accessed with \fIcurl_easy_header(3)\fP,
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introduced in later libcurl versions.
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.SH CALLBACK RETURN VALUE
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.IP "CURL_PUSH_OK (0)"
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The application has accepted the stream and it can now start receiving data,
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the ownership of the CURL handle has been taken over by the application.
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.IP "CURL_PUSH_DENY (1)"
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The callback denies the stream and no data reaches the application, the easy
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handle is destroyed by libcurl.
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.IP "CURL_PUSH_ERROROUT (2)"
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Returning this code rejects the pushed stream and returns an error back on the
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parent stream making it get closed with an error. (Added in 7.72.0)
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.IP *
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All other return codes are reserved for future use.
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.SH DEFAULT
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NULL, no callback
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.SH PROTOCOLS
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HTTP
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.SH EXAMPLE
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.nf
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#include <string.h>
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/* only allow pushes for filenames starting with "push-" */
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int push_callback(CURL *parent,
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CURL *easy,
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size_t num_headers,
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struct curl_pushheaders *headers,
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void *clientp)
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{
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char *headp;
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int *transfers = (int *)clientp;
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FILE *out;
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headp = curl_pushheader_byname(headers, ":path");
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if(headp && !strncmp(headp, "/push-", 6)) {
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fprintf(stderr, "The PATH is %s\\n", headp);
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/* save the push here */
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out = fopen("pushed-stream", "wb");
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/* write to this file */
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curl_easy_setopt(easy, CURLOPT_WRITEDATA, out);
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(*transfers)++; /* one more */
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return CURL_PUSH_OK;
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}
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return CURL_PUSH_DENY;
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}
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int main(void)
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{
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int counter;
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CURLM *multi = curl_multi_init();
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curl_multi_setopt(multi, CURLMOPT_PUSHFUNCTION, push_callback);
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curl_multi_setopt(multi, CURLMOPT_PUSHDATA, &counter);
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}
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.fi
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.SH AVAILABILITY
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Added in 7.44.0
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.SH RETURN VALUE
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Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.
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.SH SEE ALSO
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.BR CURLMOPT_PIPELINING (3),
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.BR CURLMOPT_PUSHDATA (3),
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.BR CURLOPT_PIPEWAIT (3),
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.BR RFC 7540
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