Assert maximum size for command request and response structs

The request and response structs for a command should not be bigger than
the buffer they are read from or written to.  Therefore we add
assertions that enforce this property at compile time.

3 files changed, 18 insertions, 3 deletions

diff --git a/src/commands.rs b/src/commands.rs
index 99e049f..66851c1 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -34,6 +34,8 @@ struct GetStatusResponse {
     config_delete_user_password: u8,
 }
 
+assert_maximum_size!(GetStatusResponse; GetStatusResponse, crate::device::RESPONSE_DATA_LEN);
+
 #[derive(Debug, Default)]
 struct GetStatusCommand {}
 
@@ -53,11 +55,15 @@ struct ReadSlotNameRequest {
     internal_slot_number: u8,
 }
 
+assert_maximum_size!(ReadSlotNameRequest; ReadSlotNameRequest, crate::device::REQUEST_DATA_LEN);
+
 #[derive(Debug, Default, Serialize)]
 struct ReadSlotNameResponse {
     slot_name: [u8; 15],
 }
 
+assert_maximum_size!(ReadSlotNameResponse; ReadSlotNameResponse, crate::device::RESPONSE_DATA_LEN);
+
 #[derive(Debug, Default)]
 struct ReadSlotNameCommand {}
 
diff --git a/src/device.rs b/src/device.rs
index 8f6f6ef..9f3d1a7 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -15,9 +15,9 @@ use crate::util::TryFrom;
 const VID_CLAY_LOGIC: u16 = 0x20a0;
 const PID_NITROKEY_PRO: u16 = 0x4108;
 
-const REPORT_LEN: usize = 64;
-const REQUEST_DATA_LEN: usize = REPORT_LEN - 5;
-const RESPONSE_DATA_LEN: usize = REPORT_LEN - 11;
+pub const REPORT_LEN: usize = 64;
+pub const REQUEST_DATA_LEN: usize = REPORT_LEN - 5;
+pub const RESPONSE_DATA_LEN: usize = REPORT_LEN - 11;
 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,
diff --git a/src/util.rs b/src/util.rs
index c86d047..7b12afb 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -77,6 +77,15 @@ macro_rules! enum_u8 {
     };
 }
 
+macro_rules! assert_maximum_size {
+    ($i:ident; $t:ident, $e: expr) => {
+        ::static_assertions::const_assert!(
+            $i;
+            ::core::mem::size_of::<$t>() <= $e
+        );
+    }
+}
+
 pub trait TryFrom<T>: Sized {
     fn try_from(val: T) -> Result<Self, ()>;
 }