Add static assertions for Request and Response size

The Request and Response types have to have a size of 64 bytes.
Previously, we only verified this property by visual inspection.
Accidental changes to the size could lead to runtime errors.  This patch
adds static assertions using the static_assertions crate to enforce this
property at compile time.

3 files changed, 13 insertions, 0 deletions

diff --git a/Cargo.lock b/Cargo.lock
index bb5177b..76dc8ef 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -80,6 +80,7 @@ dependencies = [
  "serde 1.0.88 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde-big-array 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "ssmarshal 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "static_assertions 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "stm32f103xx-usb 0.1.0 (git+https://github.com/mvirkkunen/stm32f103xx-usb?rev=57d23751367461bec5f39322727bdd65e5c2aa30)",
  "stm32f1xx-hal 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "usb-device 0.2.0 (git+https://github.com/mvirkkunen/usb-device?rev=e58e30f3b9c9bf4aab00ea039d129b964a3fd2d3)",
@@ -190,6 +191,11 @@ dependencies = [
 ]
 
 [[package]]
+name = "static_assertions"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "stm32f1"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -288,6 +294,7 @@ dependencies = [
 "checksum serde-big-array 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "dbd629249ae3007dac9632aa92334c5ba9c8a4dbe0a6263e546121dd1c57394a"
 "checksum serde_derive 1.0.88 (registry+https://github.com/rust-lang/crates.io-index)" = "beed18e6f5175aef3ba670e57c60ef3b1b74d250d962a26604bff4c80e970dd4"
 "checksum ssmarshal 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "f3e6ad23b128192ed337dfa4f1b8099ced0c2bf30d61e551b65fda5916dbb850"
+"checksum static_assertions 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "389ce475f424f267dbed6479cbd8f126c5e1afb053b0acdaa019c74305fc65d1"
 "checksum stm32f1 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "48763f6f093674476399efbd8d2e52349dc32c3bbf57657234cbb15d309cd8a3"
 "checksum stm32f103xx-usb 0.1.0 (git+https://github.com/mvirkkunen/stm32f103xx-usb?rev=57d23751367461bec5f39322727bdd65e5c2aa30)" = "<none>"
 "checksum stm32f1xx-hal 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "f410543fc282d51e181e3cf5c8adff303d9e5ae8b9eb731e6a07f58a4cec4265"
diff --git a/Cargo.toml b/Cargo.toml
index b5f2c65..0d773d8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -15,6 +15,7 @@ cortex-m-rt = "0.6.7"
 embedded-hal = "0.2.2"
 panic-halt = "0.2.0"
 serde-big-array = "0.1.4"
+static_assertions = "0.3.1"
 stm32f103xx-usb = { git = "https://github.com/mvirkkunen/stm32f103xx-usb", rev = "57d23751367461bec5f39322727bdd65e5c2aa30" }
 usb-device = { git = "https://github.com/mvirkkunen/usb-device", rev = "e58e30f3b9c9bf4aab00ea039d129b964a3fd2d3" }
 
diff --git a/src/device.rs b/src/device.rs
index b25cfb7..8f6f6ef 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -3,6 +3,7 @@
 
 use serde::{Deserialize, Serialize};
 use serde_big_array::big_array;
+use static_assertions::assert_eq_size;
 use usb_device::bus::{UsbBus, UsbBusAllocator};
 use usb_device::device::{UsbDevice, UsbDeviceBuilder, UsbVidPid};
 
@@ -65,6 +66,8 @@ struct Request {
     pub crc: u32,
 }
 
+assert_eq_size!(request; [u8; REPORT_LEN], Request);
+
 #[derive(Serialize)]
 struct Response {
     pub device_status: DeviceStatus,
@@ -76,6 +79,8 @@ struct Response {
     pub crc: u32,
 }
 
+assert_eq_size!(response; [u8; REPORT_LEN], Response);
+
 impl Response {
     fn new(device_status: DeviceStatus, command_id: u8, last_crc: u32) -> Response {
         Response {