capnp_cookbook_1/src/main.rs
2018-01-16 19:32:49 -05:00

58 lines
2.2 KiB
Rust

// Note that we use `capnp` here, NOT `capnpc`
extern crate capnp;
// We create a module here to define how we are to access the code
// being included.
pub mod point_capnp {
// The environment variable OUT_DIR is set by Cargo, and
// is the location of all the code that was built as part
// of the codegen step.
// point_capnp.rs is the actual file to include
include!(concat!(env!("OUT_DIR"), "/point_capnp.rs"));
}
fn main() {
// The process of building a Cap'N Proto message is a bit tedious.
// We start by creating a generic Builder; it acts as the message
// container that we'll later be filling with content of our `Point`
let mut builder = capnp::message::Builder::new_default();
// Because we need a mutable reference to the `builder` later,
// we fence off this part of the code to allow sequential mutable
// borrows. As I understand it, non-lexical lifetimes:
// https://github.com/rust-lang/rust-roadmap/issues/16
// will make this no longer necessary
{
// And now we can set up the actual message we're trying to create
let mut point_msg = builder.init_root::<point_capnp::point::Builder>();
// Stuff our message with some content
point_msg.set_x(12);
point_msg.set_y(14);
}
// It's now time to serialize our message to binary. Let's set up a buffer for that:
let mut buffer = Vec::new();
// And actually fill that buffer with our data
capnp::serialize::write_message(&mut buffer, &builder).unwrap();
// Finally, let's deserialize the data
let deserialized = capnp::serialize::read_message(
&mut buffer.as_slice(),
capnp::message::ReaderOptions::new()
).unwrap();
// `deserialized` is currently a generic reader; it understands
// the content of the message we gave it (i.e. that there are two
// int32 values) but doesn't really know what they represent (the Point).
// This is where we map the generic data back into our schema.
let point_reader = deserialized.get_root::<point_capnp::point::Reader>().unwrap();
// We can now get our x and y values back, and make sure they match
assert_eq!(point_reader.get_x(), 12);
assert_eq!(point_reader.get_y(), 14);
}