don't coerce header value to string on set

lib/response.js

@@ -450,22 +450,21 @@ module.exports = {
    *    this.set('Accept', 'application/json');
    *    this.set({ Accept: 'text/plain', 'X-API-Key': 'tobi' });
    *
-   * @param {String|Object|Array} field
-   * @param {String} val
+   * @param {String|{ [k: string]: any }} field
+   * @param {any} [val]
    * @api public
    */
 
   set(field, val) {
-    if (this.headerSent) return;
+    if (this.headerSent || !field) return;
 
-    if (2 === arguments.length) {
-      if (Array.isArray(val)) val = val.map(v => typeof v === 'string' ? v : String(v));
-      else if (typeof val !== 'string') val = String(val);
+    if (typeof field === 'string') {
       this.res.setHeader(field, val);
     } else {
-      for (const key in field) {
-        this.set(key, field[key]);
-      }
+      // it must be an object with header: value
+      Object.keys(field).forEach(
+        header => this.res.setHeader(header, field[header])
+      );
     }
   },
 

test/response/inspect.js

@@ -25,7 +25,7 @@ describe('res.inspect()', () => {
       message: 'OK',
       header: {
         'content-type': 'text/plain; charset=utf-8',
-        'content-length': '5'
+        'content-length': 5
       },
       body: 'hello'
     };

test/response/set.js

@@ -8,19 +8,19 @@ describe('ctx.set(name, val)', () => {
   it('should set a field value', () => {
     const ctx = context();
     ctx.set('x-foo', 'bar');
-    assert.equal(ctx.response.header['x-foo'], 'bar');
+    assert.equal(ctx.response.get('X-foo'), 'bar');
   });
 
-  it('should coerce number to string', () => {
+  it('should not coerce number to string', () => {
     const ctx = context();
     ctx.set('x-foo', 5);
-    assert.equal(ctx.response.header['x-foo'], '5');
+    assert.strictEqual(ctx.response.header['x-foo'], 5);
   });
 
-  it('should coerce undefined to string', () => {
+  it('should not coerce undefined to string', () => {
     const ctx = context();
     ctx.set('x-foo', undefined);
-    assert.equal(ctx.response.header['x-foo'], 'undefined');
+    assert.strictEqual(ctx.response.header['x-foo'], undefined);
   });
 
   it('should set a field value of array', () => {
@@ -35,11 +35,11 @@ describe('ctx.set(object)', () => {
     const ctx = context();
 
     ctx.set({
-      foo: '1',
+      foo: 0,
       bar: '2'
     });
 
-    assert.equal(ctx.response.header.foo, '1');
+    assert.strictEqual(ctx.response.header.foo, 0);
     assert.equal(ctx.response.header.bar, '2');
   });
 });