dispatch: Make Dispatch generic over buffer size

The fixed buffer size can be problematic for some use cases, see:
- https://github.com/trussed-dev/ctaphid-dispatch/pull/15

To avoid adding support for different buffer sizes to the crate, we can
just make the dispatch implementation generic over the buffer size.  For
simple cases, a type alias is provided using the old buffer size.

dispatch/CHANGELOG.md

@@ -5,7 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
--
+
+- Make `Dispatch` generic over the buffer size, rename `MESSAGE_SIZE` to `DEFAULT_MESSAGE_SIZE`, remove the `Message` type and add a `DefaultDispatch` type alias for `Dispatch<_, _, DEFAULT_MESSAGE_SIZE>`.
 
 ## [0.2.0] - 2025-01-08
 

dispatch/src/dispatch.rs

@@ -1,18 +1,19 @@
 use core::sync::atomic::Ordering;
 
-use crate::types::{InterchangeResponse, Message, Responder, MESSAGE_SIZE};
+use crate::types::{InterchangeResponse, Responder};
 
 use ctaphid_app::{App, Command, Error};
+use heapless_bytes::Bytes;
 use ref_swap::OptionRefSwap;
 use trussed_core::InterruptFlag;
 
-pub struct Dispatch<'pipe, 'interrupt> {
-    responder: Responder<'pipe>,
+pub struct Dispatch<'pipe, 'interrupt, const N: usize> {
+    responder: Responder<'pipe, N>,
     interrupt: Option<&'interrupt OptionRefSwap<'interrupt, InterruptFlag>>,
 }
 
-impl<'pipe> Dispatch<'pipe, '_> {
-    pub fn new(responder: Responder<'pipe>) -> Self {
+impl<'pipe, const N: usize> Dispatch<'pipe, '_, N> {
+    pub fn new(responder: Responder<'pipe, N>) -> Self {
         Dispatch {
             responder,
             interrupt: None,
@@ -20,9 +21,9 @@ impl<'pipe> Dispatch<'pipe, '_> {
     }
 }
 
-impl<'pipe, 'interrupt> Dispatch<'pipe, 'interrupt> {
+impl<'pipe, 'interrupt, const N: usize> Dispatch<'pipe, 'interrupt, N> {
     pub fn with_interrupt(
-        responder: Responder<'pipe>,
+        responder: Responder<'pipe, N>,
         interrupt: Option<&'interrupt OptionRefSwap<'interrupt, InterruptFlag>>,
     ) -> Self {
         Dispatch {
@@ -33,8 +34,8 @@ impl<'pipe, 'interrupt> Dispatch<'pipe, 'interrupt> {
 
     fn find_app<'a, 'b>(
         command: Command,
-        apps: &'a mut [&'b mut dyn App<'interrupt, MESSAGE_SIZE>],
-    ) -> Option<&'a mut &'b mut dyn App<'interrupt, MESSAGE_SIZE>> {
+        apps: &'a mut [&'b mut dyn App<'interrupt, N>],
+    ) -> Option<&'a mut &'b mut dyn App<'interrupt, N>> {
         apps.iter_mut()
             .find(|app| app.commands().contains(&command))
     }
@@ -53,7 +54,7 @@ impl<'pipe, 'interrupt> Dispatch<'pipe, 'interrupt> {
         self.reply_or_cancel(InterchangeResponse(Err(error)))
     }
 
-    fn reply_or_cancel(&mut self, response: InterchangeResponse) {
+    fn reply_or_cancel(&mut self, response: InterchangeResponse<N>) {
         if self.responder.respond(response).is_ok() {
             return;
         }
@@ -62,6 +63,7 @@ impl<'pipe, 'interrupt> Dispatch<'pipe, 'interrupt> {
             panic!("Unexpected state: {:?}", self.responder.state());
         }
     }
+
     fn send_reply_or_cancel(&mut self) {
         if self.responder.send_response().is_ok() {
             return;
@@ -73,12 +75,7 @@ impl<'pipe, 'interrupt> Dispatch<'pipe, 'interrupt> {
     }
 
     #[inline(never)]
-    fn call_app(
-        &mut self,
-        app: &mut dyn App<'interrupt, MESSAGE_SIZE>,
-        command: Command,
-        request: &Message,
-    ) {
+    fn call_app(&mut self, app: &mut dyn App<'interrupt, N>, command: Command, request: &Bytes<N>) {
         let response_buffer = self
             .responder
             .response_mut()
@@ -109,9 +106,9 @@ impl<'pipe, 'interrupt> Dispatch<'pipe, 'interrupt> {
     }
 
     #[inline(never)]
-    pub fn poll(&mut self, apps: &mut [&mut dyn App<'interrupt, MESSAGE_SIZE>]) -> bool {
+    pub fn poll(&mut self, apps: &mut [&mut dyn App<'interrupt, N>]) -> bool {
         // We could call take_request directly, but for some reason this doubles stack usage.
-        let mut message_buffer = Message::new();
+        let mut message_buffer = Bytes::new();
         if let Ok((command, message)) = self.responder.request() {
             // info_now!("cmd: {}", u8::from(command));
             // info_now!("cmd: {:?}", command);

dispatch/src/lib.rs

@@ -19,4 +19,6 @@ mod types;
 pub use ctaphid_app as app;
 
 pub use dispatch::Dispatch;
-pub use types::{Channel, InterchangeResponse, Message, Requester, Responder, MESSAGE_SIZE};
+pub use types::{Channel, InterchangeResponse, Requester, Responder, DEFAULT_MESSAGE_SIZE};
+
+pub type DefaultDispatch<'pipe, 'interrupt> = Dispatch<'pipe, 'interrupt, DEFAULT_MESSAGE_SIZE>;

dispatch/src/types.rs

@@ -1,31 +1,32 @@
 use ctaphid_app::{Command, Error};
 use heapless_bytes::Bytes;
 
-pub const MESSAGE_SIZE: usize = 7609;
-
-pub type Message = Bytes<MESSAGE_SIZE>;
+pub const DEFAULT_MESSAGE_SIZE: usize = 7609;
 
 /// Wrapper struct that implements [`Default`][] to be able to use [`response_mut`](interchange::Responder::response_mut)
-pub struct InterchangeResponse(pub Result<Message, Error>);
+pub struct InterchangeResponse<const N: usize>(pub Result<Bytes<N>, Error>);
 
-impl Default for InterchangeResponse {
+impl<const N: usize> Default for InterchangeResponse<N> {
     fn default() -> Self {
-        InterchangeResponse(Ok(Message::new()))
+        InterchangeResponse(Ok(Default::default()))
     }
 }
 
-impl From<Result<Message, Error>> for InterchangeResponse {
-    fn from(value: Result<Message, Error>) -> Self {
+impl<const N: usize> From<Result<Bytes<N>, Error>> for InterchangeResponse<N> {
+    fn from(value: Result<Bytes<N>, Error>) -> Self {
         Self(value)
     }
 }
 
-impl From<InterchangeResponse> for Result<Message, Error> {
-    fn from(value: InterchangeResponse) -> Self {
+impl<const N: usize> From<InterchangeResponse<N>> for Result<Bytes<N>, Error> {
+    fn from(value: InterchangeResponse<N>) -> Self {
         value.0
     }
 }
 
-pub type Responder<'pipe> = interchange::Responder<'pipe, (Command, Message), InterchangeResponse>;
-pub type Requester<'pipe> = interchange::Requester<'pipe, (Command, Message), InterchangeResponse>;
-pub type Channel = interchange::Channel<(Command, Message), InterchangeResponse>;
+pub type Responder<'pipe, const N: usize> =
+    interchange::Responder<'pipe, (Command, Bytes<N>), InterchangeResponse<N>>;
+pub type Requester<'pipe, const N: usize> =
+    interchange::Requester<'pipe, (Command, Bytes<N>), InterchangeResponse<N>>;
+pub type Channel<const N: usize> =
+    interchange::Channel<(Command, Bytes<N>), InterchangeResponse<N>>;