From 0b930665a8dd6fc607dbd1fe19cf36c10fe00a02 Mon Sep 17 00:00:00 2001
From: Yiyu He <dead_horse@qq.com>
Date: Thu, 12 Jul 2018 14:10:12 +0800
Subject: [PATCH] perf: avoid stringify when set header (#1220)

---
 lib/response.js         | 4 ++--
 test/response/header.js | 3 ++-
 test/response/set.js    | 8 +++++++-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/lib/response.js b/lib/response.js
index e42506f..8092c7a 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -439,8 +439,8 @@ module.exports = {
     if (this.headerSent) return;
 
     if (2 == arguments.length) {
-      if (Array.isArray(val)) val = val.map(String);
-      else val = String(val);
+      if (Array.isArray(val)) val = val.map(v => typeof v === 'string' ? v : String(v));
+      else if (typeof val !== 'string') val = String(val);
       this.res.setHeader(field, val);
     } else {
       for (const key in field) {
diff --git a/test/response/header.js b/test/response/header.js
index b78c405..b7ccfc1 100644
--- a/test/response/header.js
+++ b/test/response/header.js
@@ -10,7 +10,8 @@ describe('res.header', () => {
   it('should return the response header object', () => {
     const res = response();
     res.set('X-Foo', 'bar');
-    assert.deepEqual(res.header, { 'x-foo': 'bar' });
+    res.set('X-Number', 200);
+    assert.deepEqual(res.header, { 'x-foo': 'bar', 'x-number': '200' });
   });
 
   it('should use res.getHeaders() accessor when available', () => {
diff --git a/test/response/set.js b/test/response/set.js
index 8a21a05..710b458 100644
--- a/test/response/set.js
+++ b/test/response/set.js
@@ -11,12 +11,18 @@ describe('ctx.set(name, val)', () => {
     assert.equal(ctx.response.header['x-foo'], 'bar');
   });
 
-  it('should coerce to a string', () => {
+  it('should coerce number to string', () => {
     const ctx = context();
     ctx.set('x-foo', 5);
     assert.equal(ctx.response.header['x-foo'], '5');
   });
 
+  it('should coerce undefined to string', () => {
+    const ctx = context();
+    ctx.set('x-foo', undefined);
+    assert.equal(ctx.response.header['x-foo'], 'undefined');
+  });
+
   it('should set a field value of array', () => {
     const ctx = context();
     ctx.set('x-foo', ['foo', 'bar']);