memory stuff

index.js

@@ -6,6 +6,21 @@ const runWasm = async () => {
     const result = rustWasm.de_iavascriptis(0, 1);
     console.log("Should be undefined: ", rustWasm.add_integer_with_constant);
     document.body.textContent = `Gamarjoba! result: ${result}`;
+
+    const NUMBER = 257;
+
+    console.log("Write in WASM, read in JS");
+    rustWasm.store_value_in_wasm_mem_idx_0(NUMBER);
+    let wasmMemory = new Uint8Array(rustWasm.memory.buffer);
+    let ptr = rustWasm.get_wasm_mem_buffer_pointer();
+    console.log("Pointer from rust: ", ptr);
+
+    console.log(wasmMemory[ptr+0]); // should be NUMBER, wrapped around 256
+
+    console.log("Write in JS, read in wasm");
+    wasmMemory[ptr+1] = 15;
+    console.log(rustWasm.read_wasm_mem_buffer_idx_1()); // should be 15
+
 };
 
 runWasm();

src/lib.rs

@@ -15,3 +15,33 @@ const CONSTANT: i32 = 94;
 fn add_integer_with_constant(a: i32, b: i32) -> i32 {
     a + b + CONSTANT
 }
+
+// Linear memory example - see
+// https://wasmbyexample.dev/examples/webassembly-linear-memory/webassembly-linear-memory.rust.en-us.html
+
+const WASM_MEMORY_BUF_SIZE: usize = 2;
+static mut WASM_MEMORY_BUFFER: [u8; WASM_MEMORY_BUF_SIZE] = [0; WASM_MEMORY_BUF_SIZE];
+
+#[wasm_bindgen]
+pub fn store_value_in_wasm_mem_idx_0(value: u8) {
+    unsafe {
+        WASM_MEMORY_BUFFER[0] = value;
+    }
+}
+
+#[wasm_bindgen]
+pub fn get_wasm_mem_buffer_pointer() -> *const u8 {
+    let ptr: * const u8 = unsafe {
+        WASM_MEMORY_BUFFER.as_ptr()
+    };
+    ptr
+}
+
+
+#[wasm_bindgen]
+pub fn read_wasm_mem_buffer_idx_1() -> u8 {
+    let value = unsafe {
+        WASM_MEMORY_BUFFER[1]
+    };
+    value
+}