fix: preserve empty string cookie values

index.js

@@ -154,18 +154,27 @@ function Cookie(name, value, attrs) {
     throw new TypeError('argument name is invalid');
   }
 
-  if (value && (!fieldContentRegExp.test(value) || RESTRICTED_VALUE_CHARS_REGEXP.test(value))) {
-    throw new TypeError('argument value is invalid');
+  this.name = name
+
+  var isNullValue = value == null
+
+  if (value == null) {
+    this.value = ''
+    this.maxAge = null
+    this.expires = new Date(0)
+  } else {
+    this.value = String(value)
   }
 
-  this.name = name
-  this.value = value || ""
+  if (this.value && (!fieldContentRegExp.test(this.value) || RESTRICTED_VALUE_CHARS_REGEXP.test(this.value))) {
+    throw new TypeError('argument value is invalid');
+  }
 
   for (var name in attrs) {
     this[name] = attrs[name]
   }
 
-  if (!this.value) {
+  if (isNullValue) {
     this.expires = new Date(0)
     this.maxAge = null
   }
@@ -208,7 +217,7 @@ Cookie.prototype.toString = function() {
 Cookie.prototype.toHeader = function() {
   var header = this.toString()
 
-  if (this.maxAge) this.expires = new Date(Date.now() + this.maxAge);
+  if (this.maxAge != null) this.expires = new Date(Date.now() + this.maxAge);
 
   if (this.path     ) header += "; path=" + this.path
   if (this.expires  ) header += "; expires=" + this.expires.toUTCString()

test/cookie.js

@@ -8,6 +8,16 @@ describe('new Cookie(name, value, [options])', function () {
     assert.equal(cookie.constructor, cookies.Cookie)
   })
 
+  it('should preserve zero value', function () {
+    var cookie = new cookies.Cookie('foo', 0)
+    assert.strictEqual(cookie.toHeader(), 'foo=0; path=/; httponly')
+  })
+
+  it('should preserve empty value', function () {
+    var cookie = new cookies.Cookie('foo', '')
+    assert.strictEqual(cookie.toHeader(), 'foo=; path=/; httponly')
+  })
+
   it('should throw on invalid name', function () {
     assert.throws(function () {
       new cookies.Cookie('foo\n', 'bar')
@@ -79,6 +89,23 @@ describe('new Cookie(name, value, [options])', function () {
           new cookies.Cookie('foo', 'bar', { maxAge: NaN })
         }, /option maxAge is invalid/)
       })
+
+      it('should set expires for zero maxAge', function () {
+        var before = Date.now()
+        var cookie = new cookies.Cookie('foo', 'bar', { maxAge: 0 })
+        var header = cookie.toHeader()
+        var parts = header.split('; ')
+        var expiresPart = parts.filter(function (part) {
+          return part.indexOf('expires=') === 0
+        })[0]
+        assert.ok(expiresPart, 'should include expires attribute')
+
+        var match = /expires=(.+)/.exec(expiresPart)
+        var expires = Date.parse(match[1])
+
+        assert.ok(match)
+        assert.ok(expires >= (before - 1000))
+      })
     })
 
     describe('partitioned', function () {

test/test.js

@@ -200,6 +200,24 @@ describe('new Cookies(req, res, [options])', function () {
         .end(done)
     })
 
+    it('should set numeric zero value', function (done) {
+      request(createServer(setCookieHandler('foo', 0)))
+        .get('/')
+        .expect(200)
+        .expect(shouldSetCookieToValue('foo', '0'))
+        .end(done)
+    })
+
+    it('should set empty string value', function (done) {
+      request(createServer(setCookieHandler('foo', '')))
+        .get('/')
+        .expect(200)
+        .expect(shouldSetCookieCount(1))
+        .expect(shouldSetCookieToValue('foo', ''))
+        .expect(shouldSetCookieWithoutAttribute('foo', 'expires'))
+        .end(done)
+    })
+
     describe('when value is falsy', function () {
       it('should delete cookie', function (done) {
         request(createServer(setCookieHandler('foo', null)))