fix: safe buffer alocation

* fixes issue 115

* fixing other case

* Update src/index.ts

Co-authored-by: Nikita Skovoroda <chalkerx@gmail.com>

* added test

---------

Co-authored-by: Nikita Skovoroda <chalkerx@gmail.com>

Author: lemire

src/encoding/ascii.test.ts

@@ -7,3 +7,11 @@ describe('ASCII', () => {
     ).toBe('ASCII');
   });
 });
+
+describe('ASCII', () => {
+  it('should return ASCII', () => {
+    expect(
+      chardet.detectFileSync(__dirname + '/../test/data/encodings/shortascii',  { sampleSize: 32 }),
+    ).toBe('ASCII');
+  });
+});

src/index.ts

@@ -117,10 +117,17 @@ export const detectFile = (
 
     if (opts && opts.sampleSize) {
       fd = fs.openSync(filepath, 'r');
-      const sample: Buffer = Buffer.allocUnsafe(opts.sampleSize);
-
-      fs.read(fd, sample, 0, opts.sampleSize, opts.offset, (err?: Error) => {
-        handler(err, sample);
+      let sample = Buffer.allocUnsafe(opts.sampleSize);
+
+      fs.read(fd, sample, 0, opts.sampleSize, opts.offset, (err: NodeJS.ErrnoException | null, bytesRead: number, buffer: Buffer) => {
+        if (err) {
+          handler(err);
+        } else {
+          if (bytesRead < opts.sampleSize!) {
+            sample = sample.subarray(0, bytesRead);
+          }
+          handler(null, sample);
+        }
       });
       return;
     }
@@ -136,9 +143,12 @@ export const detectFileSync = (
 
   if (opts && opts.sampleSize) {
     const fd = fs.openSync(filepath, 'r');
-    const sample = Buffer.allocUnsafe(opts.sampleSize);
+    let sample = Buffer.allocUnsafe(opts.sampleSize);
 
-    fs.readSync(fd, sample, 0, opts.sampleSize, opts.offset);
+    const bytesRead = fs.readSync(fd, sample, 0, opts.sampleSize, opts.offset);
+    if (bytesRead < opts.sampleSize) {
+      sample = sample.subarray(0, bytesRead);
+    }
     fs.closeSync(fd);
     return detect(sample);
   }

src/test/data/encodings/shortascii

@@ -0,0 +1 @@
+short