feat: add API for decoding stake instructions

web3.js/src/instruction.js

@@ -25,3 +25,23 @@ export function encodeData(type: InstructionType, fields: Object): Buffer {
   type.layout.encode(layoutFields, data);
   return data;
 }
+
+/**
+ * Decode instruction data buffer using an InstructionType
+ */
+export function decodeData(type: InstructionType, buffer: Buffer): Object {
+  let data;
+  try {
+    data = type.layout.decode(buffer);
+  } catch (err) {
+    throw new Error('invalid instruction; ' + err);
+  }
+
+  if (data.instruction !== type.index) {
+    throw new Error(
+      `invalid instruction; instruction index mismatch ${data.instruction} != ${type.index}`,
+    );
+  }
+
+  return data;
+}