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106 lines
2.7 KiB
Markdown
106 lines
2.7 KiB
Markdown
---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_ALTSVC_CTRL
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_ALTSVC (3)
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- CURLOPT_CONNECT_TO (3)
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- CURLOPT_RESOLVE (3)
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Protocol:
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- HTTP
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Added-in: 7.64.1
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---
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# NAME
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CURLOPT_ALTSVC_CTRL - control alt-svc behavior
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# SYNOPSIS
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~~~c
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#include <curl/curl.h>
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#define CURLALTSVC_READONLYFILE (1L << 2)
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#define CURLALTSVC_H1 (1L << 3)
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#define CURLALTSVC_H2 (1L << 4)
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#define CURLALTSVC_H3 (1L << 5)
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC_CTRL, long bitmask);
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~~~
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# DESCRIPTION
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Populate the long *bitmask* with the correct set of features to instruct
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libcurl how to handle Alt-Svc for the transfers using this handle.
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libcurl only accepts Alt-Svc headers over HTTPS. It also only completes a
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request to an alternative origin if that origin is properly hosted over HTTPS.
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These requirements are there to make sure both the source and the destination
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are legitimate.
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Alternative services are only used when setting up new connections. If there
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exists an existing connection to the host in the connection pool, then that is
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preferred.
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If CURLOPT_ALTSVC(3) is set, CURLOPT_ALTSVC_CTRL(3) gets a default value
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corresponding to CURLALTSVC_H1 | CURLALTSVC_H2 | CURLALTSVC_H3 - the HTTP/2
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and HTTP/3 bits are only set if libcurl was built with support for those
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versions.
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Setting any bit enables the alt-svc engine.
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## CURLALTSVC_READONLYFILE
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Do not write the alt-svc cache back to the file specified with
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CURLOPT_ALTSVC(3) even if it gets updated. By default a file specified
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with that option is read and written to as deemed necessary.
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## CURLALTSVC_H1
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Accept alternative services offered over HTTP/1.1.
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## CURLALTSVC_H2
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Accept alternative services offered over HTTP/2. This is only used if libcurl
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was also built to actually support HTTP/2, otherwise this bit is ignored.
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## CURLALTSVC_H3
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Accept alternative services offered over HTTP/3. This is only used if libcurl
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was also built to actually support HTTP/3, otherwise this bit is ignored.
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# DEFAULT
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0 - Alt-Svc handling is disabled
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# %PROTOCOLS%
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# EXAMPLE
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~~~c
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int main(void)
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{
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CURL *curl = curl_easy_init();
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if(curl) {
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curl_easy_setopt(curl, CURLOPT_ALTSVC_CTRL, CURLALTSVC_H1);
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curl_easy_setopt(curl, CURLOPT_ALTSVC, "altsvc-cache.txt");
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curl_easy_perform(curl);
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}
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}
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~~~
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# HISTORY
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**CURLALTSVC_*** macros became `long` types in 8.16.0, prior to this version
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a `long` cast was necessary when passed to curl_easy_setopt(3).
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# %AVAILABILITY%
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# RETURN VALUE
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curl_easy_setopt(3) returns a CURLcode indicating success or error.
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CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
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libcurl-errors(3).
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