feat(core): transactions for the wasm reader

Signed-off-by: Florian Hartung <[email protected]>

src/core/reader/mod.rs

@@ -7,6 +7,7 @@ pub mod types;
 /// A struct for managing and reading WASM bytecode
 ///
 /// Its purpose is to abstract parsing basic WASM values from the bytecode.
+#[derive(Clone)]
 pub struct WasmReader<'a> {
     /// Entire WASM binary as slice
     pub full_wasm_binary: &'a [u8],
@@ -148,9 +149,30 @@ impl<'a> WasmReader<'a> {
     pub fn into_inner(self) -> &'a [u8] {
         self.full_wasm_binary
     }
+
+    /// A wrapper function for reads with transaction-like behavior.
+    ///
+    /// The provided closure will be called with `&mut self` and its result will be returned.
+    /// However if the closure returns `Err(_)`, `self` will be reset as if the closure was never called.
+    #[allow(unused)]
+    pub fn handle_transaction<R>(
+        &mut self,
+        f: impl FnOnce(&mut WasmReader) -> Result<R>,
+    ) -> Result<R> {
+        let original = self.clone();
+        f(self).map_err(|err| {
+            *self = original;
+            err
+        })
+    }
 }
 
 pub trait WasmReadable: Sized {
+    /// Reads a new [`Self`] from given [`WasmReader`].
+    ///
+    /// Note that if this function returns `Err(_)`, the [`WasmReader`] may still have been advanced,
+    /// which may lead to unexpected behaviour.
+    /// To avoid this consider using the [`WasmReader::handle_transaction`] method to wrap this function call.
     fn read(wasm: &mut WasmReader) -> Result<Self>;
     fn read_unvalidated(wasm: &mut WasmReader) -> Self;
 }