Added Channel bounds.

Fortune for comfork's current commit: Half blessing − 半吉

Cargo.toml

@@ -12,3 +12,4 @@ cfg-if = "1.0.0"
 libc = "0.2.99"
 once_cell = "1.8.0"
 serde = { version = "1.0.129", features = ["derive"] }
+serde_cbor = "0.11.2"

src/channel.rs

@@ -1,16 +1,41 @@
 //! `Channel<T>`: Move objects between parent and child processes.
 use super::*;
-use bytes::Buf;
+use bytes::{
+    Buf,
+    BufMut,
+    Bytes,
+};
 use std::marker::PhantomData;
 use std::{fmt, error};
 use std::io::{
     self,
     Read,
     Write,
+    Cursor,
+};
+use serde::{
+    Serialize,
+    de::DeserializeOwned,
 };
 
 use sys::pipe;
 
+/// A value that can be sent through a serial `Channel`
+///
+/// Bitwise channels can take `ChannelBitwiseValue` objects.
+pub trait ChannelSerialValue: Serialize + DeserializeOwned{}
+
+impl<T: ?Sized> ChannelSerialValue for T
+where T: Serialize + DeserializeOwned{}
+
+/// A value that can be sent through a bitwise `Channel`
+///
+/// Serial channels require `ChannelSerialValue`.
+pub trait ChannelBitwiseValue: Send + Unpin{}
+
+impl<T: ?Sized> ChannelBitwiseValue for T
+where T: Send + Unpin{}
+
 //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.
@@ -24,6 +49,10 @@ pub trait TransferMethod
     /// This can be set to `()`.
     type State;
 
+    /// Error for the send/recv conversion.
+    /// Must be able to convert into `channel::Error`.
+    type Error: Into<Error>;
+
     /// 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.
@@ -38,7 +67,16 @@ pub struct TransferSerial;
 
 impl TransferMethod for TransferSerial
 {
-    
+    type Buffer = Cursor<Vec<u8>>;
+    type State = ();
+    type Error = Error;
+
+    fn send<T>(_: &mut Self::State, obj: &T) -> Result<Self::Buffer, Error> {
+	todo!()
+    }
+    fn recv<T, B: Buf>(_: &mut Self::State, buffer: B) -> Result<T, Error> {
+	todo!()
+    }
 }
 
 /// Send objects through the stream as bitwise copied (unsafe.)
@@ -47,7 +85,29 @@ pub struct TransferBitwise;
 
 impl TransferMethod for TransferBitwise
 {
-    
+    type Buffer = Bytes;
+    type State = ();
+    type Error = std::convert::Infallible;
+
+    fn send<T>(_: &mut Self::State, obj: &T) -> Result<Self::Buffer, Error> {
+	let bytes = unsafe {
+	    std::slice::from_raw_parts(obj as *const T as *const _, std::mem::size_of::<T>())
+	};
+	Ok(bytes.into())
+    }
+    fn recv<T, B: Buf>(_: &mut Self::State, mut buffer: B) -> Result<T, Error> {
+	use std::mem::{
+	    self,
+	    MaybeUninit,
+	};
+	let mut value: MaybeUninit<T> = MaybeUninit::uninit();
+	unsafe {
+	    let slice = std::slice::from_raw_parts_mut(&mut value as *mut MaybeUninit<T> as *mut _, mem::size_of::<T>());
+	    buffer.copy_to_slice(slice);
+
+	    Ok(value.assume_init())
+	}
+    }
 }
 
 /// Send objects of type `T` through parent-child streams.
@@ -75,18 +135,19 @@ pub struct Receiver<T, M: ?Sized + TransferMethod = TransferSerial>
     _mathod: PhantomData<M>,
 }
 
-#[inline] pub fn pair<T>() -> (Sender<T, TransferSerial>, Receiver<T, TransferSerial>)
+#[inline] pub fn pair<T: ChannelSerialValue>() -> (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>)
+#[inline] pub unsafe fn pair_bitwise<T: ChannelBitwiseValue>() -> (Sender<T, TransferBitwise>, Receiver<T, TransferBitwise>)
 {
     Sender::<_, TransferBitwise>::new()
 }
 
-impl<T> Sender<T, TransferBitwise>
+// TODO: What bounds should we have on this, if any? Send? Unpin? Maybe even restricted to Copy.
+impl<T: ChannelBitwiseValue> Sender<T, TransferBitwise>
 {
     // TODO: TransferBitwise is very unsafe, document that here.
     pub unsafe fn new() -> (Self, Receiver<T, TransferBitwise>)
@@ -95,16 +156,56 @@ impl<T> Sender<T, TransferBitwise>
     }
 }
 
-impl<T> Sender<T, TransferSerial>
+impl<T: ChannelSerialValue> 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: ...
+
+/// The kind of channel error
+#[derive(Debug)]
+#[non_exhaustive]
+pub enum ErrorKind
+{
+    Unknown,
+    
+    Serialisation(serde_cbor::Error),
+    Deserialisation(serde_cbor::Error),
+    
+    IO(io::Error),
+}
+
+/// An error in a channel operation.
+#[derive(Debug)]
+pub struct Error(Box<(ErrorKind, Option<bool>)>);
+
+impl From<(ErrorKind, bool)> for Error
+{
+    #[inline] fn from((k, s): (ErrorKind, bool)) -> Self
+    {
+	let from = (k, Some(s));
+	Self(Box::new(from))
+    }
+}
+
+impl From<ErrorKind> for Error
+{
+    fn from(from: ErrorKind) -> Self
+    {
+	Self(Box::new((from, None)))
+    }
+}
+
+impl From<std::convert::Infallible> for Error
+{
+    #[inline] fn from(from: std::convert::Infallible) -> Self
+    {
+	match from{}
+    }
+}
+
 remove! {
     /// The kind of channel error
     #[derive(Debug)]