url: connection reuse on h3 connections

- When searching for existing connections, interpret the
  default CURL_HTTP_VERSION_2TLS as "anything goes". This
  will allow us to reuse HTTP/3 connections better
- add 'http/1.1' as allowed protocol identifier in Alt-Svc
  files
- add test_02_0[345] for testing protocol selection on
  provided alt-svc files

Fixes #14890
Reported-by: MacKenzie
Closes #14966

lib/altsvc.c

@@ -64,6 +64,8 @@ static enum alpnid alpn2alpnid(char *name)
     return ALPN_h2;
   if(strcasecompare(name, H3VERSION))
     return ALPN_h3;
+  if(strcasecompare(name, "http/1.1"))
+    return ALPN_h1;
   return ALPN_none; /* unknown, probably rubbish input */
 }
 

lib/url.c

@@ -1031,13 +1031,25 @@ static bool url_match_conn(struct connectdata *conn, void *userdata)
     return FALSE;
 
   /* If looking for HTTP and the HTTP version we want is less
-   * than the HTTP version of conn, continue looking */
+   * than the HTTP version of conn, continue looking.
+   * CURL_HTTP_VERSION_2TLS is default which indicates no preference,
+   * so we take any existing connection. */
   if((needle->handler->protocol & PROTO_FAMILY_HTTP) &&
-     (((conn->httpversion >= 20) &&
+     (data->state.httpwant != CURL_HTTP_VERSION_2TLS)) {
-       (data->state.httpwant < CURL_HTTP_VERSION_2_0))
+    if((conn->httpversion >= 20) &&
-      || ((conn->httpversion >= 30) &&
+       (data->state.httpwant < CURL_HTTP_VERSION_2_0)) {
-          (data->state.httpwant < CURL_HTTP_VERSION_3))))
+      DEBUGF(infof(data, "nor reusing conn #%" CURL_FORMAT_CURL_OFF_T
-    return FALSE;
+             " with httpversion=%d, we want a version less than h2",
+             conn->connection_id, conn->httpversion));
+    }
+    if((conn->httpversion >= 30) &&
+       (data->state.httpwant < CURL_HTTP_VERSION_3)) {
+      DEBUGF(infof(data, "nor reusing conn #%" CURL_FORMAT_CURL_OFF_T
+             " with httpversion=%d, we want a version less than h3",
+             conn->connection_id, conn->httpversion));
+      return FALSE;
+    }
+  }
 #ifdef USE_SSH
   else if(get_protocol_family(needle->handler) & PROTO_FAMILY_SSH) {
     if(!ssh_config_matches(needle, conn))
@@ -3016,7 +3028,7 @@ static CURLcode parse_connect_to_slist(struct Curl_easy *data,
        )) {
     /* no connect_to match, try alt-svc! */
     enum alpnid srcalpnid;
-    bool hit;
+    bool hit = FALSE;
     struct altsvc *as;
     const int allowed_versions = ( ALPN_h1
 #ifdef USE_HTTP2
@@ -3026,24 +3038,27 @@ static CURLcode parse_connect_to_slist(struct Curl_easy *data,
                                    | ALPN_h3
 #endif
       ) & data->asi->flags;
+    static int alpn_ids[] = {
+#ifdef USE_HTTP3
+      ALPN_h3,
+#endif
+#ifdef USE_HTTP2
+      ALPN_h2,
+#endif
+      ALPN_h1,
+    };
+    size_t i;
 
     host = conn->host.rawalloc;
-#ifdef USE_HTTP2
+    DEBUGF(infof(data, "check Alt-Svc for host %s", host));
-    /* with h2 support, check that first */
+    for(i = 0; !hit && (i < ARRAYSIZE(alpn_ids)); ++i) {
-    srcalpnid = ALPN_h2;
+      srcalpnid = alpn_ids[i];
-    hit = Curl_altsvc_lookup(data->asi,
-                             srcalpnid, host, conn->remote_port, /* from */
-                             &as /* to */,
-                             allowed_versions);
-    if(!hit)
-#endif
-    {
-      srcalpnid = ALPN_h1;
       hit = Curl_altsvc_lookup(data->asi,
                                srcalpnid, host, conn->remote_port, /* from */
                                &as /* to */,
                                allowed_versions);
     }
+
     if(hit) {
       char *hostd = strdup((char *)as->dst.host);
       if(!hostd)

tests/http/test_12_reuse.py

@@ -28,6 +28,7 @@ import difflib
 import filecmp
 import logging
 import os
+from datetime import datetime, timedelta
 import pytest
 
 from testenv import Env, CurlClient
@@ -78,3 +79,72 @@ class TestReuse:
         r.check_response(count=count, http_status=200)
         # Connections time out on server before we send another request,
         assert r.total_connects == count
+
+    @pytest.mark.skipif(condition=not Env.have_h3(), reason="h3 not supported")
+    def test_12_03_alt_svc_h2h3(self, env: Env, httpd, nghttpx):
+        httpd.clear_extra_configs()
+        httpd.reload()
+        count = 2
+        # write a alt-svc file the advises h3 instead of h2
+        asfile = os.path.join(env.gen_dir, 'alt-svc-12_03.txt')
+        ts = datetime.now() + timedelta(hours=24)
+        expires = f'{ts.year:04}{ts.month:02}{ts.day:02} {ts.hour:02}:{ts.minute:02}:{ts.second:02}'
+        with open(asfile, 'w') as fd:
+            fd.write(f'h2 {env.domain1} {env.https_port} h3 {env.domain1} {env.https_port} "{expires}" 0 0')
+        log.info(f'altscv: {open(asfile).readlines()}')
+        curl = CurlClient(env=env)
+        urln = f'https://{env.authority_for(env.domain1, "h2")}/data.json?[0-{count-1}]'
+        r = curl.http_download(urls=[urln], with_stats=True, extra_args=[
+            '--alt-svc', f'{asfile}',
+        ])
+        r.check_response(count=count, http_status=200)
+        # We expect the connection to be reused
+        assert r.total_connects == 1
+        for s in r.stats:
+            assert s['http_version'] == '3', f'{s}'
+
+    def test_12_04_alt_svc_h3h2(self, env: Env, httpd, nghttpx):
+        httpd.clear_extra_configs()
+        httpd.reload()
+        count = 2
+        # write a alt-svc file the advises h2 instead of h3
+        asfile = os.path.join(env.gen_dir, 'alt-svc-12_04.txt')
+        ts = datetime.now() + timedelta(hours=24)
+        expires = f'{ts.year:04}{ts.month:02}{ts.day:02} {ts.hour:02}:{ts.minute:02}:{ts.second:02}'
+        with open(asfile, 'w') as fd:
+            fd.write(f'h3 {env.domain1} {env.https_port} h2 {env.domain1} {env.https_port} "{expires}" 0 0')
+        log.info(f'altscv: {open(asfile).readlines()}')
+        curl = CurlClient(env=env)
+        urln = f'https://{env.authority_for(env.domain1, "h2")}/data.json?[0-{count-1}]'
+        r = curl.http_download(urls=[urln], with_stats=True, extra_args=[
+            '--alt-svc', f'{asfile}',
+        ])
+        r.check_response(count=count, http_status=200)
+        # We expect the connection to be reused
+        assert r.total_connects == 1
+        for s in r.stats:
+            assert s['http_version'] == '2', f'{s}'
+
+    def test_12_05_alt_svc_h3h1(self, env: Env, httpd, nghttpx):
+        httpd.clear_extra_configs()
+        httpd.reload()
+        count = 2
+        # write a alt-svc file the advises h1 instead of h3
+        asfile = os.path.join(env.gen_dir, 'alt-svc-12_05.txt')
+        ts = datetime.now() + timedelta(hours=24)
+        expires = f'{ts.year:04}{ts.month:02}{ts.day:02} {ts.hour:02}:{ts.minute:02}:{ts.second:02}'
+        with open(asfile, 'w') as fd:
+            fd.write(f'h3 {env.domain1} {env.https_port} http/1.1 {env.domain1} {env.https_port} "{expires}" 0 0')
+        log.info(f'altscv: {open(asfile).readlines()}')
+        curl = CurlClient(env=env)
+        urln = f'https://{env.authority_for(env.domain1, "h2")}/data.json?[0-{count-1}]'
+        r = curl.http_download(urls=[urln], with_stats=True, extra_args=[
+            '--alt-svc', f'{asfile}',
+        ])
+        r.check_response(count=count, http_status=200)
+        # We expect the connection to be reused
+        assert r.total_connects == 1
+        # When using http/1.1 from alt-svc, we ALPN-negotiate 'h2,http/1.1' anyway
+        # which means our server gives us h2
+        for s in r.stats:
+            assert s['http_version'] == '2', f'{s}'