Quic v2 support

docs/HTTP3.md

@@ -11,7 +11,7 @@ SPDX-License-Identifier: curl
 [HTTP/3 Explained](https://http3-explained.haxx.se/en/) - the online free
 book describing the protocols involved.
 
-[quicwg.org](https://quicwg.org/) - home of the official protocol drafts
+[quicwg.org](https://quicwg.org/) - home of the official QUIC protocol drafts
 
 ## QUIC libraries
 
@@ -411,6 +411,18 @@ those until one succeeds - just as with all other protocols. If those IP
 addresses contain both IPv6 and IPv4, those attempts happen, delayed, in
 parallel (the actual eyeballing).
 
+## --quic-v2
+
+The `--quic-v2` option instructs curl to attempt to connect to the server using exclusively QUIC version 2.
+QUIC version 2 is identified by the protocol ID `0x6b3343cf`.
+
+If this option is used, curl will only try to establish a QUIC version 2 connection. It will not fall back to other QUIC versions (like v1) or other HTTP versions (like HTTP/2 or HTTP/1.1) if the QUIC v2 connection attempt fails or is not supported by the server. This behavior is similar to `--http3-only` but specifically targets QUIC version 2 for the QUIC layer.
+
+This option requires a QUIC backend library (e.g., ngtcp2, quiche, OpenSSL with QUIC support) that is capable of and configured to use QUIC version 2. If the backend does not support QUIC v2 or cannot be configured for it, using this flag might result in a connection failure or the flag having no specific effect on the QUIC version chosen (depending on the backend).
+
+Example:
+    % curl --quic-v2 https://example.com
+
 ## Known Bugs
 
 Check out the [list of known HTTP3 bugs](https://curl.se/docs/knownbugs.html#HTTP3).

docs/MANUAL.md

@@ -846,6 +846,15 @@ still have `foo.example.com` do it, set `NO_PROXY` to `www.example.com`.
 
 The usage of the `-x`/`--proxy` flag overrides the environment variables.
 
+--quic-v2
+              (HTTP/3) Tells curl to attempt to connect using QUIC version 2 only.
+              This option makes curl try to connect to the target server using the
+              QUIC version 2 protocol (`0x6b3343cf`). If the server does not
+              support QUIC version 2, the connection will fail. This option does
+              not fall back to other QUIC versions or other HTTP versions.
+              This requires a QUIC backend that supports QUIC version 2.
+              (Added in 8.X.Y)
+
 ## Netrc
 
 Unix introduced the `.netrc` concept a long time ago. It is a way for a user

docs/cmdline-opts/quic-v2.md

@@ -0,0 +1,36 @@
+---
+c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
+SPDX-License-Identifier: curl
+Long: quic-v2
+Help: Use QUIC version 2 only for HTTP/3 connections
+Protocols: HTTP
+Category: http important tls
+Added: 8.X.Y
+See-also:
+  - http3
+  - http-version
+---
+# NAME
+
+--quic-v2 - Use QUIC version 2 only for HTTP/3
+
+# SYNOPSIS
+
+`--quic-v2`
+
+# DESCRIPTION
+
+This option tells curl to attempt to connect to the server using exclusively
+QUIC version 2. QUIC version 2 is identified by the protocol ID `0x6b3343cf`.
+
+If this option is used, curl will only try to establish a QUIC version 2
+connection. It will not fall back to other QUIC versions (like v1) or other
+HTTP versions (like HTTP/2 or HTTP/1.1) if the QUIC v2 connection attempt
+fails or is not supported by the server. This behavior is similar to
+`--http3-only` but specifically targets QUIC version 2 for the QUIC layer.
+
+This option requires a QUIC backend library (e.g., ngtcp2, quiche, OpenSSL
+with QUIC support) that is capable of and configured to use QUIC version 2.
+If the backend does not support QUIC v2 or cannot be configured for it, using
+this flag might result in a connection failure or the flag having no specific
+effect on the QUIC version chosen (depending on the backend).

docs/libcurl/curl_easy_setopt.md

@@ -878,6 +878,21 @@ Add transfer mode to URL over proxy. See CURLOPT_PROXY_TRANSFER_MODE(3)
 
 **Deprecated option** Issue an HTTP PUT request. See CURLOPT_PUT(3)
 
+## CURLOPT_QUIC_VERSION
+
+Pass a long specifying the QUIC version to use. Set to `0` (default) to allow
+negotiation by the QUIC library, `1` to request QUIC version 1
+(`0x00000001`), or `2` to request QUIC version 2 (`0x6b3343cf`).
+
+Using `1` or `2` will instruct libcurl to attempt to use that specific QUIC
+version only and not attempt other QUIC versions or fall back to other HTTP
+versions if the specified QUIC version fails.
+
+This option is used by HTTP/3 connections. It requires a QUIC-enabled build of
+libcurl with a backend that supports the specified version. If the selected
+QUIC version is not supported by the backend or the server, the connection
+attempt may fail.
+
 ## CURLOPT_QUICK_EXIT
 
 To be set by toplevel tools like "curl" to skip lengthy cleanups when they are

docs/libcurl/opts/Makefile.inc

@@ -313,6 +313,7 @@ man_MANS =                                      \
   CURLOPT_PROXYUSERNAME.3                       \
   CURLOPT_PROXYUSERPWD.3                        \
   CURLOPT_PUT.3                                 \
+  CURLOPT_QUIC_VERSION.3                        \
   CURLOPT_QUICK_EXIT.3                          \
   CURLOPT_QUOTE.3                               \
   CURLOPT_RANDOM_FILE.3                         \

docs/libcurl/symbols-in-versions

@@ -787,6 +787,8 @@ CURLOPT_PROXYTYPE               7.10
 CURLOPT_PROXYUSERNAME           7.19.1
 CURLOPT_PROXYUSERPWD            7.1
 CURLOPT_PUT                     7.1           7.12.1
+CURLOPT_QUIC_VERSION	8.X.Y
+CURLOPT_QUICK_EXIT              7.87.0
 CURLOPT_QUOTE                   7.1
 CURLOPT_RANDOM_FILE             7.7           7.84.0
 CURLOPT_RANGE                   7.1

include/curl/curl.h

@@ -2249,6 +2249,9 @@ typedef enum {
   /* set TLS supported signature algorithms */
   CURLOPT(CURLOPT_SSL_SIGNATURE_ALGORITHMS, CURLOPTTYPE_STRINGPOINT, 328),
 
+  /* long, for specific QUIC version (0 = default, 1 = v1, 2 = v2) */
+  CURLOPT(CURLOPT_QUIC_VERSION, CURLOPTTYPE_LONG, 329),
+
   CURLOPT_LASTENTRY /* the last unused */
 } CURLoption;