From 15260cc5e6cb44a538c0c41cff3215d9fd9d9931 Mon Sep 17 00:00:00 2001
From: ilbertt <luca.bertelli@dfinity.org>
Date: Tue, 11 Nov 2025 13:28:05 +0100
Subject: [PATCH] fix: handle offset views in encode

---
 src/encode/encode.spec.ts | 42 +++++++++++++++++++++++++++++++++++++++
 src/encode/encode.ts      | 18 ++++++++++++++---
 2 files changed, 57 insertions(+), 3 deletions(-)

diff --git a/src/encode/encode.spec.ts b/src/encode/encode.spec.ts
index 2381128..a4525a5 100644
--- a/src/encode/encode.spec.ts
+++ b/src/encode/encode.spec.ts
@@ -255,6 +255,48 @@ describe('encode', () => {
     expect(bytesToHexString(results[1])).toEqual('A2616303616404'); // { "c": 3, "d": 4 }
     expect(bytesToHexString(results[2])).toEqual('A2616505616606'); // { "e": 5, "f": 6 }
   });
+
+  it('should handle Uint8Array with non-zero byteOffset', () => {
+    // Create a larger buffer and take a view at an offset
+    const largeBuffer = new ArrayBuffer(10);
+    const view = new Uint8Array(largeBuffer, 5, 3);
+    view[0] = 1;
+    view[1] = 2;
+    view[2] = 3;
+
+    const result = encode(view);
+
+    expect(bytesToHexString(result)).toEqual('43010203'); // byte string [1, 2, 3]
+  });
+
+  it('should handle encoding large data that triggers buffer resizing', () => {
+    // Create a large string that will trigger buffer resizing in encode
+    const largeString = new Array(5000).fill('a').join('');
+    const result = encode(largeString);
+
+    // Should not throw RangeError and should produce valid CBOR
+    expect(result).toBeInstanceOf(Uint8Array);
+    expect(result.length).toBeGreaterThan(5000);
+  });
+
+  it('should handle nested objects with offset Uint8Array views', () => {
+    const buffer = new ArrayBuffer(20);
+    const view1 = new Uint8Array(buffer, 0, 5);
+    const view2 = new Uint8Array(buffer, 10, 5);
+    view1.set([1, 2, 3, 4, 5]);
+    view2.set([6, 7, 8, 9, 10]);
+
+    const value = {
+      first: view1,
+      second: view2,
+    };
+
+    const result = encode(value);
+
+    expect(bytesToHexString(result)).toEqual(
+      'A2656669727374450102030405667365636F6E6445060708090A',
+    ); // { "first": [1,2,3,4,5], "second": [6,7,8,9,10] }
+  });
 });
 
 describe('encodeWithSelfDescribedTag', () => {
diff --git a/src/encode/encode.ts b/src/encode/encode.ts
index 12c3286..36f7782 100644
--- a/src/encode/encode.ts
+++ b/src/encode/encode.ts
@@ -27,7 +27,11 @@ function encodeMajorType(majorType: CborMajorType): number {
 }
 
 let target = new Uint8Array(INITIAL_BUFFER_SIZE);
-let targetView = new DataView(target.buffer);
+let targetView = new DataView(
+  target.buffer,
+  target.byteOffset,
+  target.byteLength,
+);
 let bytesOffset = 0;
 let mapEntries: [string, CborValue][] = [];
 
@@ -100,7 +104,11 @@ export function encodeWithSelfDescribedTag<T = any>(
 function encodeItem(item: CborValue, replacer?: Replacer): void {
   if (bytesOffset > target.length - SAFE_BUFFER_END_OFFSET) {
     target = resizeUint8Array(target, target.length * 2);
-    targetView = new DataView(target.buffer);
+    targetView = new DataView(
+      target.buffer,
+      target.byteOffset,
+      target.byteLength,
+    );
   }
 
   if (item === false || item === true || item === null || item === undefined) {
@@ -241,7 +249,11 @@ function encodeBytes(majorType: CborMajorType, value: Uint8Array): void {
 
   if (bytesOffset > target.length - value.length) {
     target = resizeUint8Array(target, target.length + value.length);
-    targetView = new DataView(target.buffer);
+    targetView = new DataView(
+      target.buffer,
+      target.byteOffset,
+      target.byteLength,
+    );
   }
   target.set(value, bytesOffset);
   bytesOffset += value.length;