hostip: show the list of IPs when resolving is done

Getting 'curl.se' today then gets this verbose output which might help
debugging connectivity related matters.

* Host curl.se:80 was resolved.
* IPv6: 2a04:4e42::347, 2a04:4e42:200::347, 2a04:4e42:400::347,
  2a04:4e42:600::347, 2a04:4e42:800::347, 2a04:4e42:a00::347,
  2a04:4e42:c00::347, 2a04:4e42:e00::347
* IPv4: 151.101.193.91, 151.101.1.91, 151.101.65.91, 151.101.129.91

Co-authored-by: Jay Satiro
Closes #12145

lib/hostip.c

@@ -117,6 +117,13 @@
 
 static void freednsentry(void *freethis);
 
+#ifndef CURL_DISABLE_VERBOSE_STRINGS
+static void show_resolve_info(struct Curl_easy *data,
+                              struct Curl_dns_entry *dns);
+#else
+#define show_resolve_info(x,y) Curl_nop_stmt
+#endif
+
 /*
  * Curl_printable_address() stores a printable version of the 1st address
  * given in the 'ai' argument. The result will be stored in the buf that is
@@ -481,9 +488,11 @@ Curl_cache_addr(struct Curl_easy *data,
       return NULL;
   }
 #endif
+  if(!hostlen)
+    hostlen = strlen(hostname);
 
   /* Create a new cache entry */
-  dns = calloc(1, sizeof(struct Curl_dns_entry));
+  dns = calloc(1, sizeof(struct Curl_dns_entry) + hostlen);
   if(!dns) {
     return NULL;
   }
@@ -497,6 +506,9 @@ Curl_cache_addr(struct Curl_easy *data,
   time(&dns->timestamp);
   if(dns->timestamp == 0)
     dns->timestamp = 1;   /* zero indicates permanent CURLOPT_RESOLVE entry */
+  dns->hostport = port;
+  if(hostlen)
+    memcpy(dns->hostname, hostname, hostlen);
 
   /* Store the resolved data in our DNS cache. */
   dns2 = Curl_hash_add(data->dns.hostcache, entry_id, entry_len + 1,
@@ -823,8 +835,10 @@ enum resolve_t Curl_resolv(struct Curl_easy *data,
       if(!dns)
         /* returned failure, bail out nicely */
         Curl_freeaddrinfo(addr);
-      else
+      else {
         rc = CURLRESOLV_RESOLVED;
+        show_resolve_info(data, dns);
+      }
     }
   }
 
@@ -1285,18 +1299,89 @@ err:
   return CURLE_OK;
 }
 
+#ifndef CURL_DISABLE_VERBOSE_STRINGS
+static void show_resolve_info(struct Curl_easy *data,
+                              struct Curl_dns_entry *dns)
+{
+  struct Curl_addrinfo *a;
+  CURLcode result = CURLE_OK;
+#ifdef CURLRES_IPV6
+  struct dynbuf out[2];
+#else
+  struct dynbuf out[1];
+#endif
+  DEBUGASSERT(data);
+  DEBUGASSERT(dns);
+
+  if(!data->set.verbose ||
+     /* ignore no name or numerical IP addresses */
+     !dns->hostname[0] || Curl_host_is_ipnum(dns->hostname))
+    return;
+
+  a = dns->addr;
+
+  infof(data, "Host %s:%d was resolved.",
+        (dns->hostname[0] ? dns->hostname : "(none)"), dns->hostport);
+
+  Curl_dyn_init(&out[0], 1024);
+#ifdef CURLRES_IPV6
+  Curl_dyn_init(&out[1], 1024);
+#endif
+
+  while(a) {
+    if(
+#ifdef CURLRES_IPV6
+       (a->ai_family == PF_INET6) ||
+#endif
+       (a->ai_family == PF_INET)) {
+      char buf[MAX_IPADR_LEN];
+      struct dynbuf *d = &out[(a->ai_family != PF_INET)];
+      Curl_printable_address(a, buf, sizeof(buf));
+      if(Curl_dyn_len(d))
+        result = Curl_dyn_addn(d, ", ", 2);
+      if(!result)
+        result = Curl_dyn_add(d, buf);
+      if(result) {
+        infof(data, "too many IP, can't show");
+        goto fail;
+      }
+    }
+    a = a->ai_next;
+  }
+
+#ifdef CURLRES_IPV6
+  infof(data, "IPv6: %s",
+        (Curl_dyn_len(&out[1]) ? Curl_dyn_ptr(&out[1]) : "(none)"));
+#endif
+  infof(data, "IPv4: %s",
+        (Curl_dyn_len(&out[0]) ? Curl_dyn_ptr(&out[0]) : "(none)"));
+
+fail:
+  Curl_dyn_free(&out[0]);
+#ifdef CURLRES_IPV6
+  Curl_dyn_free(&out[1]);
+#endif
+}
+#endif
+
 CURLcode Curl_resolv_check(struct Curl_easy *data,
                            struct Curl_dns_entry **dns)
 {
+  CURLcode result;
 #if defined(CURL_DISABLE_DOH) && !defined(CURLRES_ASYNCH)
   (void)data;
   (void)dns;
 #endif
 #ifndef CURL_DISABLE_DOH
-  if(data->conn->bits.doh)
-    return Curl_doh_is_resolved(data, dns);
+  if(data->conn->bits.doh) {
+    result = Curl_doh_is_resolved(data, dns);
+  }
+  else
 #endif
-  return Curl_resolver_is_resolved(data, dns);
+  result = Curl_resolver_is_resolved(data, dns);
+  if(*dns)
+    show_resolve_info(data, *dns);
+  return result;
 }
 
 int Curl_resolv_getsock(struct Curl_easy *data,

lib/hostip.h

@@ -64,6 +64,10 @@ struct Curl_dns_entry {
   time_t timestamp;
   /* use-counter, use Curl_resolv_unlock to release reference */
   long inuse;
+  /* hostname port number that resolved to addr. */
+  int hostport;
+  /* hostname that resolved to addr. may be NULL (unix domain sockets). */
+  char hostname[1];
 };
 
 bool Curl_host_is_ipnum(const char *hostname);