Use ssmarshal to generate the response data

Previously, we manually constructed the data to sent with a Get_Report
response.  This patch introduces the Response struct which can be
serialized using ssmarshal.

As Serialize is only implemented for arrays with a length up to 32, we
have to use the serde-big-array crate for the data field.  As the
command ID might not be recognized by us, we use a raw u8 value instead
of the CommandId enum.

1 files changed, 36 insertions, 26 deletions

diff --git a/src/device.rs b/src/device.rs
index 300ce56..5fd0aed 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -1,6 +1,8 @@
 // Copyright 2019 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: GPL-3.0-or-later
 
+use serde::Serialize;
+use serde_big_array::big_array;
 use usb_device::bus::{UsbBus, UsbBusAllocator};
 use usb_device::device::{UsbDevice, UsbDeviceBuilder, UsbVidPid};
 
@@ -20,6 +22,8 @@ const REPORT_DESCRIPTOR: &[u8] = &[
     0x75, 0x08, 0x95, 0x40, 0xB1, 0x02, 0xC0,
 ];
 
+big_array! { BigArray; COMMAND_LEN, }
+
 enum_u8! {
     #[derive(Clone, Copy, Debug, PartialEq)]
     pub enum DeviceStatus {
@@ -47,6 +51,30 @@ enum_u8! {
     }
 }
 
+#[derive(Serialize)]
+struct Response {
+    pub device_status: DeviceStatus,
+    pub command_id: u8,
+    pub last_crc: [u8; 4],
+    pub command_status: CommandStatus,
+    #[serde(with = "BigArray")]
+    pub data: [u8; COMMAND_LEN],
+    pub crc: u32,
+}
+
+impl Response {
+    fn new(device_status: DeviceStatus, command_id: u8) -> Response {
+        Response {
+            device_status,
+            command_id,
+            last_crc: [0; 4],
+            command_status: CommandStatus::NotSupported,
+            data: [0; COMMAND_LEN],
+            crc: 0,
+        }
+    }
+}
+
 pub struct Nitrokey {
     buf: [u8; REPORT_LEN],
 }
@@ -77,36 +105,18 @@ impl HidDevice for Nitrokey {
             return Err(());
         }
 
-        const PREFIX_LEN: usize = 7;
-        const SUFFIX_LEN: usize = 4;
-        const PREFIX_END: usize = PREFIX_LEN;
-        const SUFFIX_START: usize = REPORT_LEN - SUFFIX_LEN;
-        let mut buf = [0; COMMAND_LEN];
-
-        let device_status = DeviceStatus::Ok;
-        let command_id = self.buf[0];
-        let command_status = if let Ok(command_id) = CommandId::try_from(command_id) {
-            command_id.execute(&self.buf[1..60], &mut buf)
+        let mut response = Response::new(DeviceStatus::Ok, self.buf[0]);
+        response.last_crc = [self.buf[60], self.buf[61], self.buf[62], self.buf[63]];
+        response.command_status = if let Ok(command_id) = CommandId::try_from(response.command_id) {
+            command_id.execute(&self.buf[1..60], &mut response.data)
         } else {
             CommandStatus::UnknownCommand
         };
+        // TODO: calculate actual CRC
+        response.crc = 1; // libnitrokey accepts any non-zero value
 
-        let pre_data: [u8; PREFIX_LEN] = [
-            device_status.into(), // device status
-            command_id,           // command_id
-            self.buf[60],
-            self.buf[61],
-            self.buf[62],
-            self.buf[63],          // last_command_crc
-            command_status.into(), // last_command_status
-        ];
-        let post_data: [u8; SUFFIX_LEN] = [
-            0x00, 0x00, 0x00, 0x01, // crc -- libnitrokey accepts any non-zero value
-        ];
-
-        self.buf[..PREFIX_END].copy_from_slice(&pre_data);
-        self.buf[PREFIX_END..SUFFIX_START].copy_from_slice(&buf);
-        self.buf[SUFFIX_START..].copy_from_slice(&post_data);
+        let len = ssmarshal::serialize(&mut self.buf, &response).map_err(|_| ())?;
+        assert!(len == REPORT_LEN);
         Ok(&self.buf)
     }