windowed_infinity/lib.rs
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#![cfg_attr(not(feature = "std"), no_std)]
//! This crate provides the [WindowedInfinity] struct and implementations of various traits to
//! write to it.
//!
//! Its primary purpose is to wrap a small buffer such that writes to it advance a cursor over a larger
//! imaginary buffer, only persisting writes to the small buffer. After the buffer has been
//! processed, a new WindowedInfinity can be set up and the writing process repeated. This is
//! wasteful when the writes are computationally expensive, but convenient when operations only
//! rarely exceed the buffer.
//!
//! A typical practical example of a WindowedInfinity application is the implementation of CoAP
//! block-wise transfer according to [RFC7959](https://tools.ietf.org/html/rfc7959); a simpler
//! example is available in the `demo.rs` example.
//!
//! Features
//! --------
//!
//! The set of traits implemented by [WindowedInfinity] depends on the configured cargo features:
//!
//! * With the `std` feature, it implements [`std::io::Write`]
//! * With the `with_serde_cbor` feature, it uses [`serde_cbor`]'s trait unsealing feature to
//! implement its [`Write`][serde_cbor::ser::Write] trait.
//! * Likewise, there are features for ciborium and minicbor. The minicbor version is a bit special
//! in that there is both a `with_minicbor` / `with_minicbor_0_19` feature.
//! * Starting at `with_minicbor_0_19`, features carry a version. This allows users of different
//! minicbor versions to coexist in the same crate, and moreover ensures that the dependencies
//! expressed in the Cargo.toml files to describe the requirements precisely.
//! * With the `with_embedded_io_0_4`, `_0_6` and `_async_0_6` features, the Write trait of
//! `embedded-io` / `-async` is implemented.
//!
//! Crate size
//! ----------
//!
//! Compared to the original plan of "doing one thing, and doing that right", this crate has grown
//! a bit, in that it contains trait implementations for several serializers, and extra mechanism
//! for combining the own writer with others (from cryptographic digests or CRCs). Both these are
//! temporary -- once there is a 1.0 version of embedded-io, the Tee will be split out into a
//! dedicated crate (with only compatibility re-exports and constructors / destructors remaining),
//! and once serializers start using the stable embedded-io, no more writer implementations will
//! need to be added.
mod tee;
mod wrappers;
/// Return type for [`WindowedInfinity::tee_digest()`]
///
/// This implements all the same writers as [`WindowedInfinity`], and can be destructured
/// `.into_windowed_and_digest(self) -> (WindowedInfinity, D)`.
pub type TeeForDigest<'a, D> = tee::Tee<WindowedInfinity<'a>, wrappers::WritableDigest<D>>;
/// Return type for [`WindowedInfinity::tee_crc32()`] and 64
///
/// This implements all the same writers as [`WindowedInfinity`], and can be destructured
/// `.into_windowed_and_crc(self) -> (WindowedInfinity, crc::Digest<'c, W>)`.
pub type TeeForCrc<'a, 'c, W> = tee::Tee<WindowedInfinity<'a>, wrappers::WritableCrc<'c, W>>;
/// A local trait standing in for embedded_io::blocking::Write while we don't have a stable version
/// to depend on and re-export publicly
///
/// The semantics of write are those of the write_all of embedded_io; the error would be in a
/// separate trait there.
trait MyWrite {
type Error;
fn write(&mut self, buf: &[u8]) -> Result<(), Self::Error>;
fn flush(&mut self) -> Result<(), Self::Error>;
}
/// A WindowedInfinity represents an infinite writable space. A small section of it is mapped to a
/// &mut [u8] to which writes are forwarded; writes to the area outside only advance a cursor.
pub struct WindowedInfinity<'a> {
view: &'a mut [u8],
cursor: isize,
}
impl<'a> WindowedInfinity<'a> {
/// Create a new infinity with the window passed as view. The cursor parameter indicates where
/// (in the index space of the view) the infinity's write operations should start, and is
/// typically either 0 or negative.
pub fn new(view: &'a mut [u8], cursor: isize) -> Self {
WindowedInfinity { view, cursor }
}
/// Report the current write cursor position in the index space of the view.
///
/// This typically used at the end of an infinity's life time to see whether the view needs to
/// be truncated before further processing, and whether there was any data discarded after the
/// view.
pub fn cursor(&self) -> isize {
self.cursor
}
#[deprecated(note = "Renamed to .cursor()")]
pub fn get_cursor(&self) -> isize {
self.cursor()
}
/// At the current cursor position, insert the given data.
///
/// The operation is always successful, and at least changes the write cursor.
pub fn write(&mut self, data: &[u8]) {
let start = self.cursor;
// FIXME determine overflowing and wrapping behavior
self.cursor += data.len() as isize;
let end = self.cursor;
if end <= 0 {
// Not in view yet
return;
}
if start >= self.view.len() as isize {
// Already out of view
return;
}
#[rustfmt::skip]
let (fronttrim, start) = if start < 0 {
(-start, 0)
} else {
(0, start)
};
let data = &data[fronttrim as usize..];
let overshoot = start + data.len() as isize - self.view.len() as isize;
let (tailtrim, end) = if overshoot > 0 {
(overshoot, end - overshoot)
} else {
(0, end)
};
let data = &data[..data.len() - tailtrim as usize];
self.view[start as usize..end as usize].copy_from_slice(data);
}
/// Obtain the written content inside the window, if any.
///
/// The slices could be made to have a longer lifetime if there is demand for that by using the
/// `sealingslice` crate.
pub fn written(&self) -> &[u8] {
if self.cursor > 0 {
// The unwrap_or case is only triggered in the pathological zero-length-view case.
self.view.chunks(self.cursor as usize).next().unwrap_or(&[])
} else {
&[]
}
}
#[deprecated(note = "Renamed to .written()")]
pub fn get_written(&self) -> &[u8] {
self.written()
}
/// Create a Tee (a T-shaped writer) that writes both to this WindowedInfinity and some
/// [digest::Digest].
///
/// The resulting type implements all the same writers as the WindowedInfinity, and offers an
/// `into_windowed_and_digest(self) -> (WindowedInfinity, Digest)` to get both back after
/// writing as completed.
pub fn tee_digest<D: digest::Digest>(self) -> TeeForDigest<'a, D> {
tee::Tee {
w1: self,
w2: wrappers::WritableDigest(D::new()),
}
}
/// Create a Tee (a T-shaped writer) that writes both to this WindowedInfinity and some
/// [crc::Digest].
///
/// This is limited to u64 CRCs due to <https://github.com/mrhooray/crc-rs/issues/79>, and
/// indirectly the availability of const traits.
pub fn tee_crc64<'c>(self, crc: &'c crc::Crc<u64>) -> TeeForCrc<'a, 'c, u64> {
tee::Tee {
w1: self,
w2: wrappers::WritableCrc(crc.digest()),
}
}
/// Create a Tee (a T-shaped writer) that writes both to this WindowedInfinity and some
/// [crc::Digest].
///
/// This is limited to u32 CRCs due to <https://github.com/mrhooray/crc-rs/issues/79>, and
/// indirectly the availability of const traits.
pub fn tee_crc32<'c>(self, crc: &'c crc::Crc<u32>) -> TeeForCrc<'a, 'c, u32> {
tee::Tee {
w1: self,
w2: wrappers::WritableCrc(crc.digest()),
}
}
}
impl MyWrite for WindowedInfinity<'_> {
type Error = core::convert::Infallible;
fn write(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
self.write(buf);
Ok(())
}
fn flush(&mut self) -> Result<(), Self::Error> {
Ok(())
}
}
#[cfg(feature = "std")]
impl std::io::Write for WindowedInfinity<'_> {
fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
self.write(buf);
// As far as success is concerned, everything was written; that not all of it (or none of
// it) may have made its way to memory is immaterial.
Ok(buf.len())
}
fn flush(&mut self) -> std::io::Result<()> {
Ok(())
}
}
impl<'a> core::fmt::Write for WindowedInfinity<'a> {
fn write_str(&mut self, s: &str) -> core::fmt::Result {
self.write(s.as_bytes());
Ok(())
}
}
#[cfg(feature = "serde_cbor")]
impl<'a> serde_cbor::ser::Write for WindowedInfinity<'a> {
// To be changed to ! once that's stable and implements Into-all
type Error = serde_cbor::error::Error;
fn write_all(&mut self, buf: &[u8]) -> Result<(), serde_cbor::error::Error> {
self.write(buf);
Ok(())
}
}
#[cfg(feature = "with_minicbor")]
impl<'a> minicbor::encode::Write for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
self.write(buf);
Ok(())
}
}
#[cfg(feature = "with_minicbor_0_19")]
impl<'a> minicbor_0_19::encode::Write for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
self.write(buf);
Ok(())
}
}
#[cfg(feature = "with_minicbor_0_24")]
impl<'a> minicbor_0_24::encode::Write for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
self.write(buf);
Ok(())
}
}
#[cfg(feature = "with_minicbor_0_25")]
impl<'a> minicbor_0_25::encode::Write for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
self.write(buf);
Ok(())
}
}
#[cfg(feature = "with_ciborium")]
impl<'a> ciborium_io::Write for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
fn write_all(&mut self, buf: &[u8]) -> Result<(), Self::Error> {
self.write(buf);
Ok(())
}
fn flush(&mut self) -> Result<(), Self::Error> {
Ok(())
}
}
#[cfg(feature = "with_embedded_io_0_4")]
impl<'a> embedded_io::Io for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
}
#[cfg(feature = "with_embedded_io_0_4")]
impl<'a> embedded_io::blocking::Write for WindowedInfinity<'a> {
fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
self.write(buf);
Ok(buf.len())
}
fn flush(&mut self) -> Result<(), Self::Error> {
Ok(())
}
}
// Shared between embedded-io 0.6 and embedded-io-async 0.6 as the latter uses a re-export
#[cfg(feature = "embedded_io_0_6")]
impl<'a> embedded_io_0_6::ErrorType for WindowedInfinity<'a> {
type Error = core::convert::Infallible;
}
#[cfg(feature = "with_embedded_io_0_6")]
impl<'a> embedded_io_0_6::Write for WindowedInfinity<'a> {
fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
self.write(buf);
Ok(buf.len())
}
fn flush(&mut self) -> Result<(), Self::Error> {
Ok(())
}
}
#[cfg(feature = "with_embedded_io_async_0_6")]
impl<'a> embedded_io_async_0_6::Write for WindowedInfinity<'a> {
async fn write(&mut self, buf: &[u8]) -> Result<usize, core::convert::Infallible> {
self.write(buf);
Ok(buf.len())
}
}
#[cfg(test)]
mod tests {
use super::WindowedInfinity;
#[test]
fn zero_length() {
let mut data: [u8; 0] = [];
let mut writer = WindowedInfinity::new(&mut data, -10);
writer.write(&[42; 20]);
assert_eq!(writer.cursor(), 10);
assert_eq!(writer.written(), &[]);
}
#[test]
fn single_write() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
writer.write(&[42; 20]);
assert_eq!(writer.cursor(), 10);
assert_eq!(writer.written(), &[42; 5]);
assert_eq!(data, [42; 5]);
}
#[test]
fn small_chunks() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
for i in 0..10 {
writer.write(&[i as u8; 2]);
assert_eq!(writer.cursor(), -10 + (i + 1) * 2);
if i == 5 {
assert_eq!(writer.written(), &[5; 2]);
}
}
assert_eq!(writer.written(), [5, 5, 6, 6, 7]);
assert_eq!(data, [5, 5, 6, 6, 7]);
}
#[cfg(feature = "std")]
#[test]
fn single_write_std() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
std::io::Write::write(&mut writer, &[42; 20]).unwrap();
assert_eq!(writer.cursor(), 10);
}
#[cfg(feature = "with_serde_cbor")]
#[test]
fn single_write_cbor() {
use serde::ser::Serialize;
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
let cbordata = ["Hello World"];
cbordata
.serialize(&mut serde_cbor::ser::Serializer::new(&mut writer))
.unwrap();
assert_eq!(writer.cursor(), 3);
}
#[cfg(feature = "with_minicbor")]
#[test]
fn single_write_minicbor() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
minicbor::encode(["Hello World"], &mut writer).unwrap();
assert_eq!(writer.cursor(), 3);
}
#[cfg(feature = "with_minicbor_0_19")]
#[test]
fn single_write_minicbor_0_19() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
minicbor_0_19::encode(["Hello World"], &mut writer).unwrap();
assert_eq!(writer.cursor(), 3);
}
#[cfg(feature = "with_minicbor_0_24")]
#[test]
fn single_write_minicbor_0_24() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
minicbor_0_24::encode(["Hello World"], &mut writer).unwrap();
assert_eq!(writer.cursor(), 3);
}
#[cfg(feature = "with_minicbor_0_25")]
#[test]
fn single_write_minicbor_0_25() {
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
minicbor_0_25::encode(["Hello World"], &mut writer).unwrap();
assert_eq!(writer.cursor(), 3);
}
#[cfg(feature = "with_ciborium")]
#[test]
fn single_write_cborium() {
use ciborium_ll;
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
let mut encoder = ciborium_ll::Encoder::from(&mut writer);
encoder.push(ciborium_ll::Header::Array(Some(1))).unwrap();
encoder.text("Hello World", None).unwrap();
assert_eq!(writer.cursor(), 3);
}
#[cfg(feature = "with_embedded_io_0_4")]
#[test]
fn write_embedded_io_blocking() {
use embedded_io::blocking::Write;
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
writer.write_all(b"Hello ").unwrap();
writer.flush().unwrap();
writer.write_fmt(format_args!("Worl{}", "d")).unwrap();
// It's 3 in other places b/c they encode a CBOR array and a string header, and we're just
// writing the text.
assert_eq!(writer.cursor(), 1);
}
#[cfg(feature = "with_embedded_io_0_6")]
#[test]
fn write_embedded_io_0_6() {
use embedded_io_0_6::Write;
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
writer.write_all(b"Hello ").unwrap();
writer.flush().unwrap();
writer.write_fmt(format_args!("Worl{}", "d")).unwrap();
// It's 3 in other places b/c they encode a CBOR array and a string header, and we're just
// writing the text.
assert_eq!(writer.cursor(), 1);
}
#[cfg(feature = "with_embedded_io_async_0_6")]
#[tokio::test]
async fn write_embedded_io_async_0_6() {
use embedded_io_async_0_6::Write;
let mut data: [u8; 5] = [0; 5];
let mut writer = WindowedInfinity::new(&mut data, -10);
writer.write_all(b"Hello World").await.unwrap();
writer.flush().await.unwrap();
// It's 3 in other places b/c they encode a CBOR array and a string header, and we're just
// writing the text.
assert_eq!(writer.cursor(), 1);
}
}