我的浏览器没有为 PHP 生成的内容发回 If-Modified-Since 标头
在我的脚本发送的第一个请求中：
(Status-Line) HTTP/1.1 200 OK
Date Thu, 21 Jan 2010 08:55:25 GMT
Server Apache/2.2.11 (Win32) PHP/5.2.9-1
X-Powered-By PHP/5.2.9-1
Pragma no-cache
x-ua-compatible IE=8;FF=3;OtherUA=4
Last-Modfied Sat, 02 Jan 2010 02:02:20 GMT
Content-Length 28453
Etag b98e0795b509be20146f58e06fbb624f
Keep-Alive timeout=5, max=90
Connection Keep-Alive
Content-Type image/png
它在它发送的第二个请求中：
(Request-Line) GET /kincumberunitingchurch/banner_image.php?id=1 HTTP/1.1
Host localhost
User-Agent Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.0.17) Gecko/2009122116 Firefox/3.0.17
Accept image/png,image/*;q=0.8,*/*;q=0.5
Accept-Language en-us,en;q=0.5
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300
Connection keep-alive
Referer http://localhost/kincumberunitingchurch/index.php?sid=tgl9jq3f71nau3cj9vps6pna03
Cookie sid=tgl9jq3f71nau3cj9vps6pna03; PHPSESSID=m0jvven6d7l65pl6odm9ecfnt4
If-None-Match b98e0795b509be20146f58e06fbb624f
Cache-Control max-age=0
对于服务器首先发送的其他文件：
(Status-Line) HTTP/1.1 200 OK
Date Thu, 21 Jan 2010 08:55:25 GMT
Server Apache/2.2.11 (Win32) PHP/5.2.9-1
Last-Modified Wed, 30 Dec 2009 02:40:58 GMT
Etag "1000000013d35-40d9-47be9117f6280"
Accept-Ranges bytes
Content-Length 16601
Keep-Alive timeout=5, max=84
Connection Keep-Alive
Content-Type image/png
我的浏览器在下一个请求中发送以下内容：
(Request-Line) GET /kincumberunitingchurch/img/cbuttons.png HTTP/1.1
Host localhost
User-Agent Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.0.17) Gecko/2009122116 Firefox/3.0.17
Accept image/png,image/*;q=0.8,*/*;q=0.5
Accept-Language en-us,en;q=0.5
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300
Connection keep-alive
Referer http://localhost/kincumberunitingchurch/mystyle.css
Cookie sid=tgl9jq3f71nau3cj9vps6pna03; PHPSESSID=m0jvven6d7l65pl6odm9ecfnt4
If-Modified-Since Wed, 30 Dec 2009 02:40:58 GMT
If-None-Match "1000000013d35-40d9-47be9117f6280"
Cache-Control max-age=0
为什么它会发送 If-Modified-Since 标头