Don't set custom push/pull functions unconditionally

We set custom push/pull functions for GnuTLS so that it works under
socket-wrapper.

However, this has downsides:
- There is a slight performance impact
- We have also observed issues with nonblocking IO causing floods of
  EAGAIN errors in the test suite.

This is fine for a test environment, but not when running for real.

To avoid issues when the code is actually being used, only set the
custom push/pull functions when SOCKET_WRAPPER_DIR environment variable
is set, indicating that we're running under socket-wrapper.

Signed-Off-By: Wouter Verhelst <w@uter.be>

Author: yoe

crypto-gnutls.c

@@ -386,8 +386,12 @@ tlssession_mainloop (int cryptfd, int plainfd, tlssession_t * s)
   /* set it up to work with our FD using custom push/pull functions */
   gnutls_transport_set_ptr (s->session,
 			    (gnutls_transport_ptr_t) (intptr_t) cryptfd);
-  gnutls_transport_set_push_function (s->session, custom_gnutls_push);
-  gnutls_transport_set_pull_function (s->session, custom_gnutls_pull);
+  /* Only use custom push/pull functions when running under cwrap */
+  char *socket_wrapper_dir = getenv("SOCKET_WRAPPER_DIR");
+  if (socket_wrapper_dir && socket_wrapper_dir[0] != '\0') {
+    gnutls_transport_set_push_function (s->session, custom_gnutls_push);
+    gnutls_transport_set_pull_function (s->session, custom_gnutls_pull);
+  }
 
 
   /* Now do the handshake */