get_nbd_info: use hostname if cert parsing fails

If the x509 library raises an exception when trying to parse a host's
certificate and read a subject out of it, log the error and fall back
to using Host.hostname.

Signed-off-by: Thomas Sanders <[email protected]>

Author: thomassa

ocaml/xapi/xapi_vdi.ml

@@ -1072,12 +1072,16 @@ let _get_nbd_info ~__context ~self ~get_server_certificate =
     if ips = [] then [] else
     let cert = get_server_certificate ~host in
     let port = 10809L in
-    let subject = match Certificates.hostnames_of_pem_cert cert with
+    let subject = try match Certificates.hostnames_of_pem_cert cert with
       | [] -> (
           error "Found no subject DNS names in this hosts's certificate. Returning empty string as subject.";
           ""
         )
       | name :: _ -> name
+    with e -> (
+      error "get_nbd_info: failed to read subject from TLS certificate! Falling back to Host.hostname. Exn was %s" (ExnHelper.string_of_exn e);
+      Db.Host.get_hostname ~__context ~self:host
+    )
     in
     let template = API.{
       vdi_nbd_server_info_exportname = exportname;