From d52846203f9f7db0626188ae50934f098b943897 Mon Sep 17 00:00:00 2001
From: Johannes Rieken <johannes.rieken@gmail.com>
Date: Wed, 26 Jun 2019 11:24:42 +0200
Subject: [PATCH] fix #76076

---
 src/vs/base/common/buffer.ts                  |  7 +++-
 .../base/test/{common => node}/buffer.test.ts | 38 +++++++++++++++++++
 2 files changed, 43 insertions(+), 2 deletions(-)
 rename src/vs/base/test/{common => node}/buffer.test.ts (90%)

diff --git a/src/vs/base/common/buffer.ts b/src/vs/base/common/buffer.ts
index cf34296e74c..7b4e9cc8d66 100644
--- a/src/vs/base/common/buffer.ts
+++ b/src/vs/base/common/buffer.ts
@@ -78,7 +78,10 @@ export class VSBuffer {
 	}
 
 	slice(start?: number, end?: number): VSBuffer {
-		return new VSBuffer(this.buffer.slice(start, end));
+		// IMPORTANT: use subarray instead of slice because TypedArray#slice
+		// creates shallow copy and NodeBuffer#slice doesn't. The use of subarray
+		// ensures the same, performant, behaviour.
+		return new VSBuffer(this.buffer.subarray(start!/*bad lib.d.ts*/, end));
 	}
 
 	set(array: VSBuffer, offset?: number): void {
@@ -437,4 +440,4 @@ class VSBufferWriteableStreamImpl implements VSBufferWriteableStream {
 			this.listeners.end.length = 0;
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/src/vs/base/test/common/buffer.test.ts b/src/vs/base/test/node/buffer.test.ts
similarity index 90%
rename from src/vs/base/test/common/buffer.test.ts
rename to src/vs/base/test/node/buffer.test.ts
index c5a3cd676ee..65f84a66ddf 100644
--- a/src/vs/base/test/common/buffer.test.ts
+++ b/src/vs/base/test/node/buffer.test.ts
@@ -364,4 +364,42 @@ suite('Buffer', () => {
 		assert.equal(ended, false);
 		assert.equal(errors.length, 0);
 	});
+
+	test('Performance issue with VSBuffer#slice #76076', function () {
+		// Buffer#slice creates a view
+		{
+			const buff = Buffer.from([10, 20, 30, 40]);
+			const b2 = buff.slice(1, 3);
+			assert.equal(buff[1], 20);
+			assert.equal(b2[0], 20);
+
+			buff[1] = 17; // modify buff AND b2
+			assert.equal(buff[1], 17);
+			assert.equal(b2[0], 17);
+		}
+
+		// TypedArray#slice creates a copy
+		{
+			const unit = new Uint8Array([10, 20, 30, 40]);
+			const u2 = unit.slice(1, 3);
+			assert.equal(unit[1], 20);
+			assert.equal(u2[0], 20);
+
+			unit[1] = 17; // modify unit, NOT b2
+			assert.equal(unit[1], 17);
+			assert.equal(u2[0], 20);
+		}
+
+		// TypedArray#subarray creates a view
+		{
+			const unit = new Uint8Array([10, 20, 30, 40]);
+			const u2 = unit.subarray(1, 3);
+			assert.equal(unit[1], 20);
+			assert.equal(u2[0], 20);
+
+			unit[1] = 17; // modify unit AND b2
+			assert.equal(unit[1], 17);
+			assert.equal(u2[0], 17);
+		}
+	});
 });
-- 
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