feat: produce error when source is incorrect

incorrect source could be:
🔸 invalid/not-compilable wasm binary
🔸 wasm code over 4KB when using export mode: instance or module

⚠️ Rust v1.29 and nightly produce ~57KB wasm code, smoke-test need to lock on v1.28
👉 https://developers.google.com/web/updates/2018/04/loading-wasm 👈

Author: DrSensor

.circleci/config.yml

@@ -6,9 +6,9 @@ rustup_nightly: &rustup_nightly
     name: Install Cargo and Rust compiler
     command: |
       echo 'export PATH="$HOME/.cargo/bin:$PATH"' >> $BASH_ENV
-      curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain nightly
+      curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain 1.28.0
       source $BASH_ENV
-      rustup target add wasm32-unknown-unknown --toolchain nightly
+      rustup target add wasm32-unknown-unknown
 
 unit_tests: &unit_tests
   steps:

src/index.ts

@@ -19,7 +19,7 @@ module.exports = function(this: loader.LoaderContext, source: Buffer) {
   });
 
   // if (options.export === 'buffer') return source; /*🤔*/
-  return wasm2js(source, options.export!);
+  return wasm2js(source, options.export!, errMsg => this.emitError(errMsg));
 };
 
 module.exports.raw = true;

src/transform.ts

@@ -1,15 +1,37 @@
 import './__global';
 import wrap from './wrapper';
 
+//#region helpers
+const is = (type: string) => ({
+  oneOf: (types: string[]) => types.some(_ => _ === type)
+});
+function panic(message: string, cb?: (msg: string) => void) {
+  if (cb) cb(message);
+  else throw new Error(message);
+}
+//#endregion
+
 /** Transform WebAssembly binary into JS module
  * @param source - WebAssembly Buffer
+ * @param exportType - what type of export you want to generate
+ * @param {Function} [errorCallback] - callback error in case you want to use your own error reporting
  * @return string of the code
  * @example const code = wasm2js(Buffer.from([0x00, 0x61, 0x73, 0x6d, 0x01, 0, 0, 0]), 'instance')
  */
 export default function(
   source: Buffer,
-  exportType: Export.Type
+  exportType: Export.Type,
+  errorCallback?: (errorMessage: string) => void
 ): string | never {
+  if (WebAssembly.validate(source) === false)
+    panic('Invalid WebAssembly file', errorCallback);
+
+  if (is(exportType).oneOf(['instance', 'module']) && source.byteLength > 4000)
+    panic(
+      `The buffer size is larger than 4KB. Consider using async-${exportType}`,
+      errorCallback
+    );
+
   switch (exportType) {
     case 'buffer':
       return wrap(source).asBuffer;