fix(std/node): Buffer.copy doesn't work as expected (#8125)

std/node/buffer.ts

@@ -163,10 +163,16 @@ export default class Buffer extends Uint8Array {
       }
     }
 
-    const buffer = new Buffer(totalLength);
+    const buffer = Buffer.allocUnsafe(totalLength);
     let pos = 0;
-    for (const buf of list) {
-      buffer.set(buf, pos);
+    for (const item of list) {
+      let buf: Buffer;
+      if (!(item instanceof Buffer)) {
+        buf = Buffer.from(item);
+      } else {
+        buf = item;
+      }
+      buf.copy(buffer, pos);
       pos += buf.length;
     }
 
@@ -247,7 +253,12 @@ export default class Buffer extends Uint8Array {
     sourceStart = 0,
     sourceEnd = this.length,
   ): number {
-    const sourceBuffer = this.subarray(sourceStart, sourceEnd);
+    const sourceBuffer = this
+      .subarray(sourceStart, sourceEnd)
+      .subarray(0, Math.max(0, targetBuffer.length - targetStart));
+
+    if (sourceBuffer.length === 0) return 0;
+
     targetBuffer.set(sourceBuffer, targetStart);
     return sourceBuffer.length;
   }

std/node/buffer_test.ts

@@ -260,10 +260,15 @@ Deno.test({
 Deno.test({
   name: "Two Buffers are concatenated",
   fn() {
-    const buffer1 = Buffer.alloc(1);
-    const buffer2 = Buffer.alloc(2);
+    const data1 = [1, 2, 3];
+    const data2 = [4, 5, 6];
+
+    const buffer1 = Buffer.from(data1);
+    const buffer2 = Buffer.from(data2);
+
     const resultBuffer = Buffer.concat([buffer1, buffer2]);
-    assertEquals(resultBuffer.length, 3, "Buffer length should be 3");
+    const expectedBuffer = Buffer.from([...data1, ...data2]);
+    assertEquals(resultBuffer, expectedBuffer);
   },
 });
 
@@ -285,27 +290,95 @@ Deno.test({
 });
 
 Deno.test({
-  name: "concat respects totalLenght parameter",
+  name: "Buffer concat respects totalLenght parameter",
   fn() {
+    const maxLength1 = 10;
     const buffer1 = Buffer.alloc(2);
     const buffer2 = Buffer.alloc(2);
-    const resultBuffer = Buffer.concat([buffer1, buffer2], 10);
-    assertEquals(resultBuffer.length, 10, "Buffer length should be 10");
+    assertEquals(
+      Buffer.concat([buffer1, buffer2], maxLength1).length,
+      maxLength1,
+    );
+
+    const maxLength2 = 3;
+    const buffer3 = Buffer.alloc(2);
+    const buffer4 = Buffer.alloc(2);
+    assertEquals(
+      Buffer.concat([buffer3, buffer4], maxLength2).length,
+      maxLength2,
+    );
   },
 });
 
 Deno.test({
-  name: "concat totalLenght throws if is lower than the size of the buffers",
+  name: "Buffer copy works as expected",
   fn() {
-    const buffer1 = Buffer.alloc(2);
-    const buffer2 = Buffer.alloc(2);
-    assertThrows(
-      () => {
-        Buffer.concat([buffer1, buffer2], 3);
+    const data1 = new Uint8Array([1, 2, 3]);
+    const data2 = new Uint8Array([4, 5, 6]);
+
+    const buffer1 = Buffer.from(data1);
+    const buffer2 = Buffer.from(data2);
+
+    //Mutates data_1
+    data1.set(data2);
+    //Mutates buffer_1
+    buffer2.copy(buffer1);
+
+    assertEquals(
+      data1,
+      buffer1,
+    );
   },
-      RangeError,
-      "offset is out of bounds",
-      "should throw on negative numbers",
+});
+
+Deno.test({
+  name: "Buffer copy respects the starting point for copy",
+  fn() {
+    const buffer1 = Buffer.from([1, 2, 3]);
+    const buffer2 = Buffer.alloc(8);
+
+    buffer1.copy(buffer2, 5);
+
+    const expected = Buffer.from([0, 0, 0, 0, 0, 1, 2, 3]);
+
+    assertEquals(
+      buffer2,
+      expected,
+    );
+  },
+});
+
+Deno.test({
+  name: "Buffer copy doesn't throw on offset but copies until offset reached",
+  fn() {
+    const buffer1 = Buffer.from([1, 2, 3]);
+    const buffer2 = Buffer.alloc(8);
+
+    const writtenBytes1 = buffer1.copy(buffer2, 6);
+
+    assertEquals(
+      writtenBytes1,
+      2,
+    );
+
+    assertEquals(
+      buffer2,
+      Buffer.from([0, 0, 0, 0, 0, 0, 1, 2]),
+    );
+
+    const buffer3 = Buffer.from([1, 2, 3]);
+    const buffer4 = Buffer.alloc(8);
+
+    const writtenBytes2 = buffer3.copy(buffer4, 8);
+
+    assertEquals(
+      writtenBytes2,
+      0,
+    );
+
+    assertEquals(
+      buffer4,
+      Buffer.from([0, 0, 0, 0, 0, 0, 0, 0]),
     );
   },
 });