Merge branch 'hotfix/87'

Close #87
Fixes #26

Author: weierophinney

CHANGELOG.md

@@ -24,7 +24,10 @@ All notable changes to this project will be documented in this file, in reverse
 
 ### Fixed
 
-- Nothing.
+- [#87](https://github.com/zendframework/zend-http/pull/87) fixes the
+  `ContentLength` constructor to test for a non null value (vs a falsy value)
+  before validating the value; this ensures 0 values may be specified for the
+  length.
 
 ## 2.5.4 - 2016-02-04
 

src/Header/ContentLength.php

@@ -40,7 +40,7 @@ public static function fromString($headerLine)
 
     public function __construct($value = null)
     {
-        if ($value) {
+        if (null !== $value) {
             HeaderValue::assertValid($value);
             $this->value = $value;
         }

test/Header/ContentLengthTest.php

@@ -65,4 +65,11 @@ public function testPreventsCRLFAttackViaConstructor()
         $this->setExpectedException('Zend\Http\Header\Exception\InvalidArgumentException');
         $header = new ContentLength("Content-Length: xxx\r\n\r\nevilContent");
     }
+
+    public function testZeroValue()
+    {
+        $contentLengthHeader = new ContentLength(0);
+        $this->assertEquals(0, $contentLengthHeader->getFieldValue());
+        $this->assertEquals('Content-Length: 0', $contentLengthHeader->toString());
+    }
 }