Example patch for handling only known protocols

UserAgent.diff

diff --git a/lib/Mojo/UserAgent.pm b/lib/Mojo/UserAgent.pm
index ebe9537..25f2160 100644
--- a/lib/Mojo/UserAgent.pm
+++ b/lib/Mojo/UserAgent.pm
@@ -84,18 +84,19 @@ sub _connect {
   if (my $local = $self->local_address) { $options{local_address} = $local }
   $options{handle} = $handle if $handle;
 
-  # SOCKS
-  if ($proto eq 'socks') {
+  if ($proto eq 'socks') {       # SOCKS
     @options{qw(socks_address socks_port)} = @options{qw(address port)};
     ($proto, @options{qw(address port)}) = $t->endpoint($tx);
     my $userinfo = $tx->req->via_proxy(0)->proxy->userinfo;
     @options{qw(socks_user socks_pass)} = split ':', $userinfo if $userinfo;
+  } elsif ($proto eq 'https') {  # TLS
+    $options{tls} = 1;
+    map { $options{"tls_$_"} = $self->$_ } qw(ca cert key);
+  } elsif ($proto ne 'http') {   # invalid unless HTTP
+    $self->_error(undef, 'Invalid protocol');
+    return undef;
   }
 
-  # TLS
-  map { $options{"tls_$_"} = $self->$_ } qw(ca cert key)
-    if ($options{tls} = $proto eq 'https');
-
   weaken $self;
   my $id;
   return $id = $loop->client(