Module capnp::message

Untyped root container for a Cap'n Proto value.

Notes about type specialization

This module provides [TypedReader] and [TypedBuilder] structs which are strongly-typed variants of [Reader] and [Builder].

Code autogenerated by capnpc will have an individual module for each of structures and each of modules will have Owned struct which implements [Owned] trait.

Example from a real auto-generated file:

pub mod simple_struct {
    #[derive(Copy, Clone)]
    pub struct Owned(());
    impl <'a> ::capnp::traits::Owned<'a> for Owned { type Reader = Reader<'a>; type Builder = Builder<'a>; }
    ....
}

[TypedReader] and [TypedBuilder] accept generic type parameter T. This parameter must be a corresponding Owned type which was auto-generated inside the corresponding module.

For example, for auto-generated module crate::test_data::simple_struct you'd supply crate::test_data::simple_struct::Owned type into [TypedReader]/[TypedBuilder]

include!(concat!(env!("OUT_DIR"), "/simple_struct_capnp.rs"));

use capnp::message::{self, TypedBuilder, TypedReader};
 
fn main() {
    let mut builder = TypedBuilder::<simple_struct::Owned>::new_default();
    let mut builder_root = builder.init_root();
    builder_root.set_x(10);
    builder_root.set_y(20);
 
    let mut buffer = vec![];
    capnp::serialize_packed::write_message(&mut buffer, builder.borrow_inner()).unwrap();
 
    let reader = capnp::serialize_packed::read_message(buffer.as_slice(), ReaderOptions::new()).unwrap();
    let typed_reader = TypedReader::<_, simple_struct::Owned>::new(reader);
 
    let reader_root = typed_reader.get().unwrap();
    assert_eq!(reader_root.get_x(), 10);
    assert_eq!(reader_root.get_x(), 20);
}

Structs

Builder	A container used to build a message.
HeapAllocator	Standard segment allocator. Allocates each segment via alloc::alloc::alloc_zeroed().
Reader	A container used to read a message.
ReaderOptions	Options controlling how data is read.
ScratchSpaceHeapAllocator	An Allocator whose first segment is a backed by a user-provided buffer.
SegmentArray	An array of segments.
TypedBuilder	Stongly typed variant of the [Builder]
TypedReader	A message reader whose value is known to be of type T. Please see module documentation for more info about reader type specialization.

Enums

AllocationStrategy

Constants

DEFAULT_READER_OPTIONS
SUGGESTED_ALLOCATION_STRATEGY
SUGGESTED_FIRST_SEGMENT_WORDS

Traits

Allocator	An object that allocates memory for a Cap'n Proto message as it is being built.
ReaderSegments	An object that manages the buffers underlying a Cap'n Proto message reader.