easy: reset errorbuf on eyeballing success

Any failf() that fill the errorbuf need to be forgotten once happy
eyeballing finds a succssful winner. Because the errorbuf, once set, is
not overwritten with future error information.

Adds test_05_05 to verify.

Reported-by: Tim Friedrich Brüggemann
Fixes #20608

Closes #20613

docs/libcurl/libcurl-env-dbg.md

@@ -58,6 +58,10 @@ only send 800.
 The percentage of send() calls that should be answered with EAGAIN at random.
 QUIC only.
 
+## `CURL_DBG_SOCK_FAIL_IPV6`
+
+Fail opening of sockets for the IPv6 address family.
+
 ## `CURL_DEBUG`
 
 Trace logging behavior as an alternative to calling curl_global_trace(3).

lib/cf-https-connect.c

@@ -222,6 +222,8 @@ static CURLcode baller_connected(struct Curl_cfilter *cf,
   /* install the winning filter below this one. */
   cf->next = winner->cf;
   winner->cf = NULL;
+  /* whatever errors where reported by ballers, clear our errorbuf */
+  Curl_reset_fail(data);
 
 #ifdef USE_NGHTTP2
   {

lib/cf-ip-happy.c

@@ -427,6 +427,10 @@ evaluate:
       addr = cf_ai_iter_next(&bs->addr_iter);
       ai_family = bs->addr_iter.ai_family;
     }
+    /* We are (re-)starting attempts. We are not interested in
+     * keeping old failure information. The new attempt will either
+     * succeed or persist new failure. */
+    Curl_reset_fail(data);
 
     if(addr) {  /* try another address */
       result = cf_ip_attempt_new(&a, cf, data, addr, ai_family,
@@ -793,6 +797,8 @@ static CURLcode cf_ip_happy_connect(struct Curl_cfilter *cf,
       ctx->ballers.winner->cf = NULL;
       cf_ip_happy_ctx_clear(cf, data);
       Curl_expire_done(data, EXPIRE_HAPPY_EYEBALLS);
+      /* whatever errors where reported by ballers, clear our errorbuf */
+      Curl_reset_fail(data);
 
       if(cf->conn->scheme->protocol & PROTO_FAMILY_SSH)
         Curl_pgrsTime(data, TIMER_APPCONNECT); /* we are connected already */

lib/cf-socket.c

@@ -332,6 +332,12 @@ static CURLcode socket_open(struct Curl_easy *data,
   }
   else {
     /* opensocket callback not set, so simply create the socket now */
+#ifdef DEBUGBUILD
+    if((addr->family == AF_INET6) && getenv("CURL_DBG_SOCK_FAIL_IPV6")) {
+      failf(data, "CURL_DBG_SOCK_FAIL_IPV6: failed to open socket");
+      return CURLE_COULDNT_CONNECT;
+    }
+#endif
     *sockfd = CURL_SOCKET(addr->family, addr->socktype, addr->protocol);
     if((*sockfd == CURL_SOCKET_BAD) && (SOCKERRNO == SOCKENOMEM))
       return CURLE_OUT_OF_MEMORY;

lib/curl_trc.c

@@ -194,6 +194,13 @@ void Curl_failf(struct Curl_easy *data, const char *fmt, ...)
   }
 }
 
+void Curl_reset_fail(struct Curl_easy *data)
+{
+  if(data->set.errorbuffer)
+    data->set.errorbuffer[0] = 0;
+  data->state.errorbuf = FALSE;
+}
+
 #ifdef CURLVERBOSE
 struct curl_trc_feat Curl_trc_feat_multi = {
   "MULTI",

lib/curl_trc.h

@@ -61,6 +61,11 @@ void Curl_failf(struct Curl_easy *data,
 
 #define failf Curl_failf
 
+/* In case failf() reported into the errorbuf, clear it again.
+ * This is used to clear information from happy eyeballing attempts
+ * when ultimately a successful attempt was made. */
+void Curl_reset_fail(struct Curl_easy *data);
+
 #define CURL_LOG_LVL_NONE  0
 #define CURL_LOG_LVL_INFO  1
 

tests/http/test_05_errors.py

@@ -25,6 +25,7 @@
 ###########################################################################
 #
 import logging
+import os
 import pytest
 
 from testenv import Env, CurlClient
@@ -123,3 +124,19 @@ class TestErrors:
         else:
             r.check_exit_code(0)
             r.check_response(http_status=200, count=count)
+
+    # Make a connect with a fail for '::1' and wrong certificate for '127.0.0.1'
+    # The error message reported needs to be from the certificate.
+    # verifies issue #20608
+    @pytest.mark.parametrize("proto", Env.http_h1_h2_protos())
+    def test_05_05_failed_peer(self, env: Env, proto, httpd, nghttpx):
+        domain = f'invalid.{env.tld}'
+        url = f'https://{domain}:{env.port_for(proto)}/'
+        run_env = os.environ.copy()
+        run_env['CURL_DBG_SOCK_FAIL_IPV6'] = '1'
+        curl = CurlClient(env=env, run_env=run_env)
+        r = curl.http_download(urls=[url], alpn_proto=proto, extra_args=[
+            '--resolve', f'{domain}:{env.port_for(proto)}:::1,127.0.0.1',
+        ])
+        assert r.exit_code == 60, f'{r}'
+        assert r.stats[0]['errormsg'] != 'CURL_DBG_SOCK_FAIL_IPV6: failed to open socket'