Use bytes for reading Region from wasm memory

packages/vm/src/memory.rs

@@ -1,4 +1,4 @@
-use std::mem::MaybeUninit;
+use std::mem::{size_of, MaybeUninit};
 
 use wasmer::{ValueType, WasmPtr};
 
@@ -25,6 +25,35 @@ pub struct Region {
     /// The number of bytes used in this region
     pub length: u32,
 }
+type RegionBytes = [u8; size_of::<Region>()];
+
+impl Region {
+    fn from_wasm_bytes(bytes: RegionBytes) -> Self {
+        let offset = u32::from_le_bytes(bytes[0..4].try_into().unwrap());
+        let capacity = u32::from_le_bytes(bytes[4..8].try_into().unwrap());
+        let length = u32::from_le_bytes(bytes[8..12].try_into().unwrap());
+        Region {
+            offset,
+            capacity,
+            length,
+        }
+    }
+
+    fn into_wasm_bytes(self) -> RegionBytes {
+        let Region {
+            offset,
+            capacity,
+            length,
+        } = self;
+
+        let mut bytes = [0u8; 12];
+        // wasm is little endian
+        bytes[0..4].copy_from_slice(&offset.to_le_bytes());
+        bytes[4..8].copy_from_slice(&capacity.to_le_bytes());
+        bytes[8..12].copy_from_slice(&length.to_le_bytes());
+        bytes
+    }
+}
 
 unsafe impl ValueType for Region {
     fn zero_padding_bytes(&self, _bytes: &mut [MaybeUninit<u8>]) {
@@ -91,10 +120,10 @@ pub fn write_region(memory: &wasmer::MemoryView, ptr: u32, data: &[u8]) -> VmRes
 
 /// Reads in a Region at offset in Wasm memory and returns a copy of it
 fn get_region(memory: &wasmer::MemoryView, offset: u32) -> CommunicationResult<Region> {
-    let wptr = WasmPtr::<Region>::new(offset);
-    let region = wptr.deref(memory).read().map_err(|_err| {
+    let wptr = WasmPtr::<RegionBytes>::new(offset);
+    let region = Region::from_wasm_bytes(wptr.deref(memory).read().map_err(|_err| {
         CommunicationError::deref_err(offset, "Could not dereference this pointer to a Region")
-    })?;
+    })?);
     validate_region(&region)?;
     Ok(region)
 }
@@ -122,10 +151,12 @@ fn validate_region(region: &Region) -> RegionValidationResult<()> {
 
 /// Overrides a Region at offset in Wasm memory
 fn set_region(memory: &wasmer::MemoryView, offset: u32, data: Region) -> CommunicationResult<()> {
-    let wptr = WasmPtr::<Region>::new(offset);
-    wptr.deref(memory).write(data).map_err(|_err| {
-        CommunicationError::deref_err(offset, "Could not dereference this pointer to a Region")
-    })?;
+    let wptr = WasmPtr::<RegionBytes>::new(offset);
+    wptr.deref(memory)
+        .write(data.into_wasm_bytes())
+        .map_err(|_err| {
+            CommunicationError::deref_err(offset, "Could not dereference this pointer to a Region")
+        })?;
     Ok(())
 }