From 9b5149cb0c175b164baa89c985eaf12f071e072b Mon Sep 17 00:00:00 2001
From: Siim Kallas <siimkallas@gmail.com>
Date: Mon, 22 Aug 2022 18:15:41 +0300
Subject: [PATCH] perf: improve hexToBase64 (#3178)

Co-authored-by: Daniel Dyla <dyladan@users.noreply.github.com>
---
 CHANGELOG.md                                  |  1 +
 .../src/platform/node/hex-to-base64.ts        | 40 +++++++++++++++----
 .../test/platform/hex-to-base64.test.ts       |  8 +++-
 3 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 66f4e5d119..bd1372e254 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,7 @@ All notable changes to this project will be documented in this file.
 
 ### :rocket: (Enhancement)
 
+* perf(opentelemetry-core): improve hexToBase64 performance [#3178](https://github.com/open-telemetry/opentelemetry-js/pull/3178)
 * feat(sdk-trace-base): move Sampler declaration into sdk-trace-base [#3088](https://github.com/open-telemetry/opentelemetry-js/pull/3088) @legendecas
 * fix(grpc-instrumentation): added grpc attributes in instrumentation [#3127](https://github.com/open-telemetry/opentelemetry-js/pull/3127) @andrewzenkov
 * feat: support latest `@opentelemetry/api` [#3177](https://github.com/open-telemetry/opentelemetry-js/pull/3177) @dyladan
diff --git a/packages/opentelemetry-core/src/platform/node/hex-to-base64.ts b/packages/opentelemetry-core/src/platform/node/hex-to-base64.ts
index 9330aaa91f..66d4ad0fe9 100644
--- a/packages/opentelemetry-core/src/platform/node/hex-to-base64.ts
+++ b/packages/opentelemetry-core/src/platform/node/hex-to-base64.ts
@@ -13,14 +13,40 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+function intValue(charCode: number): number {
+  // 0-9
+  if (charCode >= 48 && charCode <= 57) {
+    return charCode - 48;
+  }
+
+  // a-f
+  if (charCode >= 97 && charCode <= 102) {
+    return charCode - 87;
+  }
+
+  // A-F
+  return charCode - 55;
+}
+
+const buf8 = Buffer.alloc(8);
+const buf16 = Buffer.alloc(16);
+
 export function hexToBase64(hexStr: string): string {
-  const hexStrLen = hexStr.length;
-  let hexAsciiCharsStr = '';
-  for (let i = 0; i < hexStrLen; i += 2) {
-    const hexPair = hexStr.substring(i, i + 2);
-    const hexVal = parseInt(hexPair, 16);
-    hexAsciiCharsStr += String.fromCharCode(hexVal);
+  let buf;
+  if (hexStr.length === 16) {
+    buf = buf8;
+  } else if (hexStr.length === 32) {
+    buf = buf16;
+  } else {
+    buf = Buffer.alloc(hexStr.length / 2);
+  }
+  let offset = 0;
+
+  for (let i = 0; i < hexStr.length; i += 2) {
+    const hi = intValue(hexStr.charCodeAt(i));
+    const lo = intValue(hexStr.charCodeAt(i + 1));
+    buf.writeUInt8((hi << 4) | lo, offset++);
   }
 
-  return Buffer.from(hexAsciiCharsStr, 'ascii').toString('base64');
+  return buf.toString('base64');
 }
diff --git a/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts b/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts
index 7f78ded3ef..d73409fc09 100644
--- a/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts
+++ b/packages/opentelemetry-core/test/platform/hex-to-base64.test.ts
@@ -20,8 +20,12 @@ import { hexToBase64 } from '../../src/platform';
 describe('hexToBase64', () => {
   it('convert hex to base64', () => {
     const id1 = '7deb739e02e44ef2';
-    const id2 = '46cef837b919a16ff26e608c8cf42c80';
+    const id2 = '12abc034d567e89ff26e608c8cf42c80';
+    const id3 = id2.toUpperCase();
     assert.strictEqual(hexToBase64(id1), 'fetzngLkTvI=');
-    assert.strictEqual(hexToBase64(id2), 'Rs74N7kZoW/ybmCMjPQsgA==');
+    assert.strictEqual(hexToBase64(id2), 'EqvANNVn6J/ybmCMjPQsgA==');
+    assert.strictEqual(hexToBase64(id3), 'EqvANNVn6J/ybmCMjPQsgA==');
+    // Don't use the preallocated path
+    assert.strictEqual(hexToBase64(id2.repeat(2)), 'EqvANNVn6J/ybmCMjPQsgBKrwDTVZ+if8m5gjIz0LIA=');
   });
 });