Remove heap top setting

Previously the SDK would set the heap top before each evaluation. This
could lead to memory leaks if repeated calls to grow() allocated new
memory (repeated calls to grow() would occur because the heap top was
being reset on each evaluation.)

This addresses the same issue as
open-policy-agent/golang-opa-wasm#5 in the
golang-opa-wasm SDK.

Signed-off-by: Torin Sandall <[email protected]>

src/opa.js

@@ -19,8 +19,8 @@ function stringDecoder(mem) {
 
 /**
  * Stringifies and loads an object into OPA's Memory
- * @param {WebAssembly.Instance} wasmInstance 
- * @param {WebAssembly.Memory} memory 
+ * @param {WebAssembly.Instance} wasmInstance
+ * @param {WebAssembly.Memory} memory
  * @param {any} value
  * @returns {number}
  */
@@ -47,9 +47,9 @@ function _loadJSON(wasmInstance, memory, value) {
 
 /**
  * Dumps and parses a JSON object from OPA's Memory
- * @param {WebAssembly.Instance} wasmInstance 
- * @param {WebAssembly.Memory} memory 
- * @param {number} addr 
+ * @param {WebAssembly.Instance} wasmInstance
+ * @param {WebAssembly.Memory} memory
+ * @param {number} addr
  * @returns {object}
  */
 function _dumpJSON(wasmInstance, memory, addr) {
@@ -71,8 +71,8 @@ const builtinFuncs = builtIns;
 /**
  * _builtinCall dispatches the built-in function. The built-in function
  * arguments are loaded from Wasm and back in using JSON serialization.
- * @param {WebAssembly.Instance} wasmInstance 
- * @param {WebAssembly.Memory} memory 
+ * @param {WebAssembly.Instance} wasmInstance
+ * @param {WebAssembly.Memory} memory
  * @param {{ [builtinId: number]: string }} builtins
  * @param {string} builtin_id
  */
@@ -109,8 +109,8 @@ function _builtinCall(wasmInstance, memory, builtins, builtin_id) {
  * It will return a Promise, depending on the input type the promise
  * resolves to both a compiled WebAssembly.Module and its first WebAssembly.Instance
  * or to the WebAssemblyInstance.
- * @param {BufferSource | WebAssembly.Module} policy_wasm 
- * @param {WebAssembly.Memory} memory 
+ * @param {BufferSource | WebAssembly.Module} policy_wasm
+ * @param {WebAssembly.Memory} memory
  * @returns {Promise<WebAssembly.WebAssemblyInstantiatedSource | WebAssembly.Instance>}
  */
 async function _loadPolicy(policy_wasm, memory) {
@@ -195,8 +195,8 @@ async function _loadPolicy(policy_wasm, memory) {
 class LoadedPolicy {
  /**
  * Loads and initializes a compiled Rego policy.
- * @param {WebAssembly.WebAssemblyInstantiatedSource} policy 
- * @param {WebAssembly.Memory} memory 
+ * @param {WebAssembly.WebAssemblyInstantiatedSource} policy
+ * @param {WebAssembly.Memory} memory
  */
  constructor(policy, memory) {
  this.mem = memory;
@@ -208,9 +208,7 @@ class LoadedPolicy {
 
  this.dataAddr = _loadJSON(this.wasmInstance, this.mem, {});
  this.baseHeapPtr = this.wasmInstance.exports.opa_heap_ptr_get();
- this.baseHeapTop = this.wasmInstance.exports.opa_heap_top_get();
  this.dataHeapPtr = this.baseHeapPtr;
- this.dataHeapTop = this.baseHeapTop;
  }
 
  /**
@@ -222,7 +220,6 @@ class LoadedPolicy {
  evaluate(input) {
  // Reset the heap pointer before each evaluation
  this.wasmInstance.exports.opa_heap_ptr_set(this.dataHeapPtr);
- this.wasmInstance.exports.opa_heap_top_set(this.dataHeapTop);
 
  // Load the input data
  const inputAddr = _loadJSON(this.wasmInstance, this.mem, input);
@@ -255,14 +252,12 @@ class LoadedPolicy {
 
  /**
  * Loads data for use in subsequent evaluations.
- * @param {object} data 
+ * @param {object} data
  */
  setData(data) {
  this.wasmInstance.exports.opa_heap_ptr_set(this.baseHeapPtr);
- this.wasmInstance.exports.opa_heap_top_set(this.baseHeapTop);
  this.dataAddr = _loadJSON(this.wasmInstance, this.mem, data);
  this.dataHeapPtr = this.wasmInstance.exports.opa_heap_ptr_get();
- this.dataHeapTop = this.wasmInstance.exports.opa_heap_top_get();
  }
 }