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                     23: .TH CURLOPT_HTTP_VERSION 3 "September 14, 2019" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_HTTP_VERSION \- specify HTTP protocol version to use
                     27: .SH SYNOPSIS
                     28: #include <curl/curl.h>
                     29: 
                     30: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTP_VERSION, long version);
                     31: .SH DESCRIPTION
                     32: Pass \fIversion\fP a long, set to one of the values described below. They ask
                     33: libcurl to use the specific HTTP versions.
                     34: 
                     35: Note that the HTTP version is just a request. libcurl will still prioritize to
                     36: re-use an existing connection so it might then re-use a connection using a
                     37: HTTP version you haven't asked for.
                     38: 
                     39: .IP CURL_HTTP_VERSION_NONE
                     40: We don't care about what version the library uses. libcurl will use whatever
                     41: it thinks fit.
                     42: .IP CURL_HTTP_VERSION_1_0
                     43: Enforce HTTP 1.0 requests.
                     44: .IP CURL_HTTP_VERSION_1_1
                     45: Enforce HTTP 1.1 requests.
                     46: .IP CURL_HTTP_VERSION_2_0
                     47: Attempt HTTP 2 requests. libcurl will fall back to HTTP 1.1 if HTTP 2 can't be
                     48: negotiated with the server. (Added in 7.33.0)
                     49: 
                     50: The alias \fICURL_HTTP_VERSION_2\fP was added in 7.43.0 to better reflect the
                     51: actual protocol name.
                     52: .IP CURL_HTTP_VERSION_2TLS
                     53: Attempt HTTP 2 over TLS (HTTPS) only. libcurl will fall back to HTTP 1.1 if
                     54: HTTP 2 can't be negotiated with the HTTPS server. For clear text HTTP servers,
                     55: libcurl will use 1.1. (Added in 7.47.0)
                     56: .IP CURL_HTTP_VERSION_2_PRIOR_KNOWLEDGE
                     57: Issue non-TLS HTTP requests using HTTP/2 without HTTP/1.1 Upgrade. It requires
                     58: prior knowledge that the server supports HTTP/2 straight away. HTTPS requests
                     59: will still do HTTP/2 the standard way with negotiated protocol version in the
                     60: TLS handshake. (Added in 7.49.0)
                     61: .IP CURL_HTTP_VERSION_3
                     62: (Added in 7.66.0) Setting this value will make libcurl attempt to use HTTP/3
                     63: directly to server given in the URL. Note that this cannot gracefully
                     64: downgrade to earlier HTTP version if the server doesn't support HTTP/3.
                     65: 
                     66: For more reliably upgrading to HTTP/3, set the preferred version to something
                     67: lower and let the server announce its HTTP/3 support via Alt-Svc:. See
                     68: \fICURLOPT_ALTSVC(3)\fP.
                     69: .SH DEFAULT
                     70: Since curl 7.62.0: CURL_HTTP_VERSION_2TLS
                     71: 
                     72: Before that: CURL_HTTP_VERSION_1_1
                     73: .SH PROTOCOLS
                     74: HTTP
                     75: .SH EXAMPLE
                     76: .nf
                     77: CURL *curl = curl_easy_init();
                     78: if(curl) {
                     79:   CURLcode ret;
                     80:   curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
                     81:   curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
                     82:   ret = curl_easy_perform(curl);
                     83:   if(ret == CURLE_HTTP_RETURNED_ERROR) {
                     84:     /* an HTTP response error problem */
                     85:   }
                     86: }
                     87: .fi
                     88: .SH AVAILABILITY
                     89: Along with HTTP
                     90: .SH RETURN VALUE
                     91: Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
                     92: .SH "SEE ALSO"
                     93: .BR CURLOPT_SSLVERSION "(3), " CURLOPT_HTTP200ALIASES "(3), "
                     94: .BR CURLOPT_HTTP09_ALLOWED "(3), " CURLOPT_ALTSVC "(3) "