Use PyCapsule name to check capsule pointer types

[sloretz]

Feature request

Feature description

Currently rclpy creates PyCapsule with NULL names. This means if a function is given a PyCapsule containing rcl_client_t * but it expects rcl_node_t * the C code will still attempt to use it as such. If the capsules were given a name at creation then the methods could use the name as a type check when getting the pointer.

Implementation considerations

https://docs.python.org/3/c-api/capsule.html
PyCapsule_New accepts a const char *name argument. It could be given a string like "rcl_node_t *".

// rcl_node_t * node;
PyObject * pynode = PyCapsule_New(node, "rcl_node_t *");

PyCapsule_GetPointer accepts a const char *name argument, and it sets a python exception and returns NULL if the name does not match (it uses strcmp() ).

rcl_node_t * node = (rcl_node_t *)PyCapsule_GetPointer(pynode, "rcl_node_t *");
if (!node)
{
  // GetPointer already set an exception
  return NULL;
}

If the default exception isn't appropriate, PyCapsule_GetPointer is guaranteed to succeed if PyCapsule_IsValid returns true. This can be checked first with custom handling code to run if it returns False.

// PyObject * pynode;
if (!PyCapsule_IsValid(pynode, "rcl_node_t *"))
{
  // Do something about it
}

[mikaelarguedas]

👍 we discussed it but never got around renaming all the capsules

[mikaelarguedas]

that's totally done and working now