hid: Add HID and Report descriptors

HID implementations must provide a HID and a Report descriptor.  This
patch adds these descriptors.  The Report descriptor is copied from the
Nitrokey Pro.

As the control_in implementation in usb-device only handles
GET_DESCRIPTOR requests on the device level, we have to change the
control_in method in HidClass to handle GET_DESCRIPTOR on interface
level (required for the Report descriptor).

2 files changed, 75 insertions, 2 deletions

diff --git a/src/device.rs b/src/device.rs
index 31f4293..f71caf0 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -9,6 +9,14 @@ use crate::hid::{HidDevice, Protocol, Subclass};
 const VID_CLAY_LOGIC: u16 = 0x20a0;
 const PID_NITROKEY_PRO: u16 = 0x4108;
 
+const REPORT_DESCRIPTOR: &[u8] = &[
+    0x05, 0x01, 0x09, 0x06, 0xA1, 0x01, 0x05, 0x07, 0x19, 0xE0, 0x29, 0xE7, 0x15, 0x00, 0x25, 0x01,
+    0x75, 0x01, 0x95, 0x08, 0x81, 0x02, 0x95, 0x01, 0x75, 0x08, 0x81, 0x03, 0x95, 0x05, 0x75, 0x01,
+    0x05, 0x08, 0x19, 0x01, 0x29, 0x05, 0x91, 0x02, 0x95, 0x01, 0x75, 0x03, 0x91, 0x03, 0x95, 0x06,
+    0x75, 0x08, 0x15, 0x00, 0x25, 0x65, 0x05, 0x07, 0x19, 0x00, 0x29, 0x65, 0x81, 0x00, 0x09, 0x03,
+    0x75, 0x08, 0x95, 0x40, 0xB1, 0x02, 0xC0,
+];
+
 pub struct Nitrokey {}
 
 impl Nitrokey {
@@ -25,6 +33,10 @@ impl HidDevice for Nitrokey {
     fn protocol(&self) -> Protocol {
         Protocol::Keyboard
     }
+
+    fn report_descriptor(&self) -> &[u8] {
+        REPORT_DESCRIPTOR
+    }
 }
 
 pub fn create_usb_device<B: UsbBus>(alloc: &UsbBusAllocator<B>) -> UsbDevice<'_, B> {
diff --git a/src/hid.rs b/src/hid.rs
index 0bb8a11..a2adeb3 100644
--- a/src/hid.rs
+++ b/src/hid.rs
@@ -3,10 +3,12 @@
 
 use usb_device::bus::{InterfaceNumber, StringIndex, UsbBus, UsbBusAllocator};
 use usb_device::class::{ControlIn, ControlOut, UsbClass};
+use usb_device::control::{Recipient, Request, RequestType};
 use usb_device::descriptor::DescriptorWriter;
 use usb_device::endpoint::{EndpointAddress, EndpointIn};
-use usb_device::Result;
+use usb_device::{Result, UsbError};
 
+const SPECIFICATION_RELEASE: u16 = 0x111;
 const INTERFACE_CLASS_HID: u8 = 0x03;
 
 enum_u8! {
@@ -26,10 +28,21 @@ enum_u8! {
     }
 }
 
+enum_u8! {
+    #[derive(Debug, Clone, Copy)]
+    pub enum DescriptorType {
+        Hid = 0x21,
+        Report = 0x22,
+        Physical = 0x23,
+    }
+}
+
 pub trait HidDevice {
     fn subclass(&self) -> Subclass;
 
     fn protocol(&self) -> Protocol;
+
+    fn report_descriptor(&self) -> &[u8];
 }
 
 pub struct HidClass<'a, B: UsbBus, D: HidDevice> {
@@ -48,6 +61,21 @@ impl<B: UsbBus, D: HidDevice> HidClass<'_, B, D> {
             expect_interrupt_in_complete: false,
         }
     }
+
+    fn get_report_descriptor(&self, index: u8, buf: &mut [u8]) -> Result<usize> {
+        if index == 0 {
+            let report_descriptor = self.device.report_descriptor();
+            let len = report_descriptor.len();
+            if len > buf.len() {
+                Err(UsbError::BufferOverflow)
+            } else {
+                buf[0..len].copy_from_slice(report_descriptor);
+                Ok(len)
+            }
+        } else {
+            Err(UsbError::InvalidState)
+        }
+    }
 }
 
 impl<B: UsbBus, D: HidDevice> UsbClass<B> for HidClass<'_, B, D> {
@@ -64,6 +92,27 @@ impl<B: UsbBus, D: HidDevice> UsbClass<B> for HidClass<'_, B, D> {
             self.device.subclass().into(),
             self.device.protocol().into(),
         )?;
+
+        let report_descriptor = self.device.report_descriptor();
+        let descriptor_len = report_descriptor.len();
+        if descriptor_len > u16::max_value() as usize {
+            return Err(UsbError::InvalidState);
+        }
+        let descriptor_len = (descriptor_len as u16).to_le_bytes();
+        let specification_release = SPECIFICATION_RELEASE.to_le_bytes();
+        writer.write(
+            DescriptorType::Hid.into(),
+            &[
+                specification_release[0],      // bcdHID.lower
+                specification_release[1],      // bcdHID.upper
+                0,                             // bCountryCode: 0 = not supported
+                1,                             // bNumDescriptors
+                DescriptorType::Report.into(), // bDescriptorType
+                descriptor_len[0],             // bDescriptorLength.lower
+                descriptor_len[1],             // bDescriptorLength.upper
+            ],
+        )?;
+
         writer.endpoint(&self.endpoint_interrupt_in)?;
 
         Ok(())
@@ -85,7 +134,19 @@ impl<B: UsbBus, D: HidDevice> UsbClass<B> for HidClass<'_, B, D> {
 
     fn endpoint_out(&mut self, _addr: EndpointAddress) {}
 
-    fn control_in(&mut self, _xfer: ControlIn<B>) {}
+    fn control_in(&mut self, xfer: ControlIn<B>) {
+        let req = xfer.request();
+        if req.request_type == RequestType::Standard
+            && req.recipient == Recipient::Interface
+            && req.request == Request::GET_DESCRIPTOR
+        {
+            let (dtype, index) = req.descriptor_type_index();
+            if dtype == DescriptorType::Report.into() {
+                xfer.accept(|mut buf| self.get_report_descriptor(index, &mut buf))
+                    .ok();
+            }
+        }
+    }
 
     fn control_out(&mut self, _xfer: ControlOut<B>) {}
 }