From b9128eba4bd7d3b283cf0ac9745e38b64dfa5a3d Mon Sep 17 00:00:00 2001
From: Avril <flanchan@cumallover.me>
Date: Sat, 28 Aug 2021 16:54:46 +0100
Subject: [PATCH] Start: `Channel<T>`: Typed pipes.
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Fortune for comfork's current commit: Curse − 凶
---
 Cargo.toml     |   2 +
 src/channel.rs | 166 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs     |   2 +
 3 files changed, 170 insertions(+)
 create mode 100644 src/channel.rs

diff --git a/Cargo.toml b/Cargo.toml
index 405373d..42f6536 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,8 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+bytes = "1.0.1"
 cfg-if = "1.0.0"
 libc = "0.2.99"
 once_cell = "1.8.0"
+serde = { version = "1.0.129", features = ["derive"] }
diff --git a/src/channel.rs b/src/channel.rs
new file mode 100644
index 0000000..e579e73
--- /dev/null
+++ b/src/channel.rs
@@ -0,0 +1,166 @@
+//! `Channel<T>`: Move objects between parent and child processes.
+use super::*;
+use bytes::Buf;
+use std::marker::PhantomData;
+use std::{fmt, error};
+use std::io::{
+    self,
+    Read,
+    Write,
+};
+
+use sys::pipe;
+
+//TODO: We can create a non-stream version of this using a memory mapped ring-buffer on an fd shared between parent and child. (i.e: map two pages, the first and second one pointing to the start of the file). But that might be unneeded or too much work for this project's scope.
+
+/// Controls how objects are sent through the streams.
+pub trait TransferMethod
+{
+    /// The returned buffer that is build from `send`.
+    ///
+    /// `recv` takes any `impl Buf` object.
+    type Buffer: Buf;
+    /// An optional internal state object to hold any additional data needed.
+    /// This can be set to `()`.
+    type State;
+
+    /// Serialise the object `T` to a byte buffer for sending.
+    fn send<T>(state: &mut Self::State, obj: &T) -> Result<Self::Buffer, Error>;
+    /// Read the object `T` from a byte buffer that was read from the pipe.
+    ///
+    /// The buffer's size is handled by the channel.
+    fn recv<T, B: Buf>(state: &mut Self::State, buffer: B) -> Result<T, Error>;
+}
+
+/// Serialize objects deeply to send them.
+#[derive(Debug)]
+pub struct TransferSerial;
+
+impl TransferMethod for TransferSerial
+{
+    
+}
+
+/// Send objects through the stream as bitwise copied (unsafe.)
+#[derive(Debug)]
+pub struct TransferBitwise;
+
+impl TransferMethod for TransferBitwise
+{
+    
+}
+
+/// Send objects of type `T` through parent-child streams.
+#[derive(Debug)]
+pub struct Sender<T, M: ?Sized + TransferMethod = TransferSerial>
+{
+    tx: pipe::WriteHalf,
+
+    state: M::State,
+    
+    _data: PhantomData<Vec<T>>,
+    _method: PhantomData<M>,
+}
+
+
+/// Receive objects of type `T` from a parent-child stream.
+#[derive(Debug)]
+pub struct Receiver<T, M: ?Sized + TransferMethod = TransferSerial>
+{
+    rx: pipe::ReadHalf,
+    
+    state: M::State,
+
+    _data: PhantomData<Vec<T>>,
+    _mathod: PhantomData<M>,
+}
+
+#[inline] pub fn pair<T>() -> (Sender<T, TransferSerial>, Receiver<T, TransferSerial>)
+{
+    Sender::<_, TransferSerial>::new()
+}
+
+// TODO: TransferBitwise is very unsafe, document that here.
+#[inline] pub unsafe fn pair_bitwise<T>() -> (Sender<T, TransferBitwise>, Receiver<T, TransferBitwise>)
+{
+    Sender::<_, TransferBitwise>::new()
+}
+
+impl<T> Sender<T, TransferBitwise>
+{
+    // TODO: TransferBitwise is very unsafe, document that here.
+    pub unsafe fn new() -> (Self, Receiver<T, TransferBitwise>)
+    {
+	todo!()
+    }
+}
+
+impl<T> Sender<T, TransferSerial>
+{
+    pub fn new() -> (Self, Receiver<T, TransferSerial>)
+    {
+	todo!()
+    }
+}
+//TODO: Re-do. Do not use generics on the Error type...
+// It does NOT need to hold the type information or value.
+pub struct Error; //TODO: ...
+remove! {
+    /// The kind of channel error
+    #[derive(Debug)]
+    #[non_exhaustive]
+    pub enum ErrorKind
+    {
+	IO(io::Error),
+	
+	Unknown,
+    }
+
+    /// An error on a channel operation
+    #[derive(Debug)]
+    pub struct Error<T>(Box<(ErrorKind, bool, Option<T>)>);
+
+    impl fmt::Display for ErrorKind
+    {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+	{
+	    todo!()
+	}
+    }
+
+
+    impl<T: fmt::Debug> fmt::Display for Error<T>
+    {
+	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+	{
+	    write!(f, "channel<{}>: failed to ", std::any::type_name::<T>())?;
+	    match (self.0.1, self.0.2.as_ref()) {
+		(true, None) => write!(f, "send"),
+		(false, None) => write!(f, "recv"),
+		(true, Some(val)) => write!(f, "send (value [{:?}])", val),
+		(false, Some(val)) => write!(f, "recv (value [{:?}])", val),
+	    }?;
+	    write!(f, ": {}", self.0.0)
+	}
+    }
+
+    impl<T> Error<T>
+    {
+	pub fn recv(kind: ErrorKind, value: Option<T>) -> Self
+	{
+	    Self(Box::new((
+		kind,
+		false,
+		value
+	    )))
+	}
+	pub fn send(kind: ErrorKind, value: Option<T>) -> Self
+	{
+	    Self(Box::new((
+		kind,
+		true,
+		value
+	    )))
+	}
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 9136015..034db3d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,11 +1,13 @@
 #![allow(dead_code)]
 
 #[macro_use] extern crate cfg_if;
+#[macro_use] extern crate serde;
 
 use std::convert::{TryFrom, TryInto};
 
 #[macro_use] mod ext; use ext::*;
 mod sys;
+pub mod channel;
 
 #[cfg(test)]
 mod tests {