CURLOPT_IPRESOLVE: preventing wrong IP version from being used

In some situations, it was possible that a transfer was setup to
use an specific IP version, but due do DNS caching or connection
reuse, it ended up using a different IP version from requested.

This commit changes the effect of CURLOPT_IPRESOLVE from simply
restricting address resolution to preventing the wrong connection
type being used, when choosing a connection from the pool, and
to restricting what addresses could be used when establishing
a new connection.

It is important that all addresses versions are resolved, even if
not used in that transfer in particular, because the result is
cached, and could be useful for a different transfer with a
different CURLOPT_IPRESOLVE setting.

Closes #6853

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/url.c b/lib/url.c
index 5f6462617..1ee38af0d 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -1172,6 +1172,12 @@ ConnectionExists(struct Curl_easy *data,
         continue;
       }
 
+      if(data->set.ipver != CURL_IPRESOLVE_WHATEVER
+          && data->set.ipver != check->ip_version) {
+        /* skip because the connection is not via the requested IP version */
+        continue;
+      }
+
       if(bundle->multiuse == BUNDLE_MULTIPLEX)
         multiplexed = CONN_INUSE(check);