CURLOPT_ALTSVC_CTRL - control alt-svc behavior
#define CURLALTSVC_READONLYFILE (1<<2)
#define CURLALTSVC_H1 (1<<3)
#define CURLALTSVC_H2 (1<<4)
#define CURLALTSVC_H3 (1<<5)
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ALTSVC_CTRL, long bitmask);
Populate the long bitmask with the correct set of features to instruct
libcurl how to handle Alt-Svc for the transfers using this handle.
libcurl only accepts Alt-Svc headers over a secure transport,
meaning HTTPS. It will also only complete a request to an alternative origin
if that origin is properly hosted over HTTPS. These requirements are there
to make sure both the source and the destination are legitimate.
Alternative services are only used when setting up new
connections. If there exists an existing connection to the host in the
connection pool, then that will be preferred.
Setting any bit will enable the alt-svc engine.
Alt-Svc handling is disabled by default. If CURLOPT_ALTSVC(3) is set,
CURLOPT_ALTSVC_CTRL(3) has a default value corresponding to
CURLALTSVC_H1 | CURLALTSVC_H2 | CURLALTSVC_H3 - the HTTP/2 and HTTP/3 bits are
only set if libcurl was built with support for those versions.
- Do not write the alt-svc cache back to the file specified with
CURLOPT_ALTSVC(3) even if it gets updated. By default a file
specified with that option will be read and written to as deemed
- Accept alternative services offered over HTTP/1.1.
- Accept alternative services offered over HTTP/2. This will only be used if
libcurl was also built to actually support HTTP/2, otherwise this bit will
- Accept alternative services offered over HTTP/3. This will only be used if
libcurl was also built to actually support HTTP/3, otherwise this bit will
CURL *curl = curl_easy_init();
curl_easy_setopt(curl, CURLOPT_ALTSVC_CTRL, CURLALTSVC_H1);
curl_easy_setopt(curl, CURLOPT_ALTSVC, "altsvc-cache.txt");
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.