Move protocol-specific user presence checking code from Env to CTAP library (#501)

* Common duration type for ctap library independent of TockOS

* Implement Env-specific ctap-hid channels for I/O
Common I/O Status, Error and Result types

* Move common user presence checking code to ctap library

* Move CtapHidChannel and UserPresence traits, with their accompanying
types to separate API mods. Remove Default implementations of methods
in these traits, to keep all implementation details inside of concrete
Env types.

Rename methods in UserPresence trait, for better readability.

Remove duplicate code for finding appropriate HID channel for given
transport.

Rework check_user_presence() function so that there's no more need for
quick_check() method in UserPresence trait. To short-circuit user
presence check, Env implementation may use wait_with_timeout() method.

* Fix button press wait with zero timeout for TockEnv

* Fix formatting

* Remove type for duration, use embedded_time::duration::Milliseconds
directly, for better readability.

Treat any unconfirmed result of user presence check as an error, which
maps more naturally to CTAP spec status codes.

Remove unneeded underscores in trait definition.

Store usb endpoint directly, in TockEnv channels, to avoid unneeded
conversions.

* No need for separate error type for send_keepalive_up_needed()

* Document UserPresence trait and types.

Remove unused parameters in UserPresence trait's methods.

Add conversion function from UserPresence errors to Ctap2 status codes.

Do not check button status when tock user presence wait is called with
zero timeout.

* Make test environment always report success sending data

* Rename CtapHidChannel to HidConnection, rename *_hid_channel ->
*_hid_connection, for clarity. Use "Channel" to refer to the logical
connection from authenticator to one client, and use "Connection" to
refer to physical connection of authenticator to platform, on which
clients run.

Remove channel parameter from user presence API, it's not needed.

* Remove duplicate comments.

Co-authored-by: kaczmarczyck <43844792+kaczmarczyck@users.noreply.github.com>

src/api/connection.rs

@@ -0,0 +1,34 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::clock::ClockInt;
+use embedded_time::duration::Milliseconds;
+
+pub enum SendOrRecvStatus {
+    Timeout,
+    Sent,
+    Received,
+}
+
+pub struct SendOrRecvError;
+
+pub type SendOrRecvResult = Result<SendOrRecvStatus, SendOrRecvError>;
+
+pub trait HidConnection {
+    fn send_or_recv_with_timeout(
+        &mut self,
+        buf: &mut [u8; 64],
+        timeout: Milliseconds<ClockInt>,
+    ) -> SendOrRecvResult;
+}

src/api/mod.rs

@@ -3,6 +3,8 @@
 //! The [environment](crate::env::Env) is split into components. Each component has an API described
 //! by a trait. This module gathers the API of those components.
 
+pub mod connection;
 pub mod customization;
 pub mod firmware_protection;
 pub mod upgrade_storage;
+pub mod user_presence;

src/api/user_presence.rs

@@ -0,0 +1,44 @@
+// Copyright 2022 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use crate::clock::ClockInt;
+use embedded_time::duration::Milliseconds;
+
+pub enum UserPresenceError {
+    /// User explicitly declined user presence check.
+    Declined,
+    /// User presence check was canceled by User Agent.
+    Canceled,
+    /// User presence check timed out.
+    Timeout,
+}
+
+pub type UserPresenceResult = Result<(), UserPresenceError>;
+
+pub trait UserPresence {
+    /// Initializes for a user presence check.
+    ///
+    /// Must eventually be followed by a call to [`Self::check_complete`].
+    fn check_init(&mut self);
+
+    /// Waits until user presence is confirmed, rejected, or the given timeout expires.
+    ///
+    /// Must be called between calls to [`Self::check_init`] and [`Self::check_complete`].
+    fn wait_with_timeout(&mut self, timeout: Milliseconds<ClockInt>) -> UserPresenceResult;
+
+    /// Finalizes a user presence check.
+    ///
+    /// Must be called after [`Self::check_init`].
+    fn check_complete(&mut self);
+}