fix: support string encoding parameter in readFile

__test__/read_file.spec.ts

@@ -36,6 +36,21 @@ test('readFile: async should throw on non-existent file', async (t) => {
   await t.throwsAsync(async () => await readFile('./no-such-file'), { message: /ENOENT/ })
 })
 
+test('readFile: async should return string with encoding as string param', async (t) => {
+  const result = await readFile('./package.json', 'utf-8')
+  t.is(typeof result, 'string')
+})
+
+test('readFile: async should return string with encoding as options object', async (t) => {
+  const result = await readFile('./package.json', { encoding: 'utf-8' })
+  t.is(typeof result, 'string')
+})
+
+test('readFile: async should return Buffer with no encoding', async (t) => {
+  const result = await readFile('./package.json')
+  t.true(Buffer.isBuffer(result))
+})
+
 test('dual-run: readFileSync Buffer should match node:fs byte-for-byte', (t) => {
   const nodeResult = nodeFs.readFileSync('./package.json')
   const hyperResult = readFileSync('./package.json') as Buffer

src/read_file.rs

@@ -66,15 +66,28 @@ pub struct ReadFileOptions {
   pub flag: Option<String>,
 }
 
+fn normalize_read_file_options(
+  options: Option<Either<String, ReadFileOptions>>,
+) -> ReadFileOptions {
+  match options {
+    Some(Either::A(encoding)) => ReadFileOptions {
+      encoding: Some(encoding),
+      flag: None,
+    },
+    Some(Either::B(opts)) => opts,
+    None => ReadFileOptions {
+      encoding: None,
+      flag: None,
+    },
+  }
+}
+
 fn read_file_impl(
   path_str: String,
-  options: Option<ReadFileOptions>,
+  options: Option<Either<String, ReadFileOptions>>,
 ) -> Result<Either<String, Buffer>> {
   let path = Path::new(&path_str);
-  let opts = options.unwrap_or(ReadFileOptions {
-    encoding: None,
-    flag: None,
-  });
+  let opts = normalize_read_file_options(options);
 
   let flag = opts.flag.as_deref().unwrap_or("r");
 
@@ -142,7 +155,7 @@ fn read_file_impl(
 #[napi(js_name = "readFileSync")]
 pub fn read_file_sync(
   path: String,
-  options: Option<ReadFileOptions>,
+  options: Option<Either<String, ReadFileOptions>>,
 ) -> Result<Either<String, Buffer>> {
   read_file_impl(path, options)
 }
@@ -151,7 +164,7 @@ pub fn read_file_sync(
 
 pub struct ReadFileTask {
   pub path: String,
-  pub options: Option<ReadFileOptions>,
+  pub options: Option<Either<String, ReadFileOptions>>,
 }
 
 impl Task for ReadFileTask {
@@ -168,6 +181,9 @@ impl Task for ReadFileTask {
 }
 
 #[napi(js_name = "readFile")]
-pub fn read_file(path: String, options: Option<ReadFileOptions>) -> AsyncTask<ReadFileTask> {
+pub fn read_file(
+  path: String,
+  options: Option<Either<String, ReadFileOptions>>,
+) -> AsyncTask<ReadFileTask> {
   AsyncTask::new(ReadFileTask { path, options })
 }