Compare thin pointers to find the connection

Connection is a trait, so "*const Connection" is a fat pointer (128
bits, 64 bits pointing to the instance, 64 bits pointing to the vtable).

For some reason (a bug?), in Router::remove(), the connection passed as
argument has a vtable different from the (same) connection stored in the
"connections" field.

This has the unexpected consequence that for some x and y:

    println!("{:p} == {:p} ? {}", x, y, ptr::eq(x, y));

prints:

    0x7f87a8c3a618 == 0x7f87a8c3a618 ? false

Thus, the connection to remove was not found, leading to the panic
"Removing an unknown connection".

Instead, compare only the data part, by casting the fat pointers to thin
pointers.

See <#61 (comment)>

Thanks to mbrubeck on IRC freenode/##rust, who helped a lot to
understand the issue.

Author: rom1v

relay-rust/src/relay/binary.rs

@@ -35,3 +35,12 @@ pub fn to_string(data: &[u8]) -> String {
     }
     s
 }
+
+// only compare the data part for fat pointers (ignore the vtable part)
+// for some (buggy) reason, the vtable part may be different even if the data reference the same
+// object
+// See <https://github.com/Genymobile/gnirehtet/issues/61#issuecomment-370933770>
+pub fn ptr_data_eq<T: ?Sized>(lhs: *const T, rhs: *const T) -> bool {
+    // cast to thin pointers to ignore the vtable part
+    lhs as *const () == rhs as *const ()
+}

relay-rust/src/relay/router.rs

@@ -150,8 +150,8 @@ impl Router {
         let index = self.connections
             .iter()
             .position(|item| {
-                // compare pointers to find the connection to remove
-                ptr::eq(connection, item.as_ptr())
+                // compare (thin) pointers to find the connection to remove
+                binary::ptr_data_eq(connection, item.as_ptr())
             })
             .expect("Removing an unknown connection");
         debug!(