fix: multi-byte character corruption when converting Buffers to strings (#3100)

* add tests for multi-byte character buffer
* support multi-byte characters when decoding buffers

fixes: #2993

Author: brb3

packages/client/lib/RESP/decoder.spec.ts

@@ -226,6 +226,11 @@ describe('RESP Decoder', () => {
       toWrite: Buffer.from('+OK\r\n'),
       replies: [Buffer.from('OK')]
     });
+
+    test("'é'", {
+      toWrite: Buffer.from('+é\r\n'),
+      replies: ['é']
+    });
   });
 
   describe('BlobString', () => {
@@ -251,6 +256,11 @@ describe('RESP Decoder', () => {
       toWrite: Buffer.from('$2\r\nOK\r\n'),
       replies: [Buffer.from('OK')]
     });
+
+    test("'é'", {
+      toWrite: Buffer.from('$2\r\né\r\n'),
+      replies: ['é']
+    });
   });
 
   describe('VerbatimString', () => {
@@ -279,6 +289,11 @@ describe('RESP Decoder', () => {
       toWrite: Buffer.from('=6\r\ntxt:OK\r\n'),
       replies: [Buffer.from('OK')]
     });
+
+    test("'é'", {
+      toWrite: Buffer.from('=6\r\ntxt:é\r\n'),
+      replies: ['é']
+    });
   });
 
   test('SimpleError', {

packages/client/lib/RESP/decoder.ts

@@ -506,9 +506,8 @@ export class Decoder {
     }
 
     chunks.push(chunk.subarray(start, crlfIndex));
-    return type === Buffer ?
-      Buffer.concat(chunks) :
-      chunks.join('');
+    const buffer = Buffer.concat(chunks);
+    return type === Buffer ? buffer : buffer.toString();
   }
 
   #decodeBlobString(type, chunk) {
@@ -578,9 +577,8 @@ export class Decoder {
 
     chunks.push(chunk.subarray(this.#cursor, end));
     this.#cursor = end + skip;
-    return type === Buffer ?
-      Buffer.concat(chunks) :
-      chunks.join('');
+    const buffer = Buffer.concat(chunks);
+    return type === Buffer ? buffer : buffer.toString();
   }
 
   #decodeBlobStringWithLength(length, type, chunk) {