<h2>Response Body</h2>
<p>The response body of a 304 status code is empty. The 304 response doesn't contain a message body, it only includes headers.</p>
<p>HTTP 304, "Not Modified", indicates that the resource requested has not been modified since last request.
Server will use <code>If-Modified-Since</code> or <code>If-None-Match</code> headers to determine if the resource requested has been modified since last request.</p>
<h2>If-Modified-Since and Last-modified, If-None-Match and Etag</h2>
<h3>Request Header</h3>
<p>If-Modified-Since
Used by the client to specify that the resource should only be returned if it has been modified since the specified date.
Last-Modified
Used by the server to indicate the date and time at which the resource was last modified.</p>
<h3>Response Header</h3>
<p>If-None-Match
Used by the client to specify that the resource should only be returned if its ETag does not match any of the given ETags.
ETag
Used by the server to provide the current value of the entity tag for the requested resource.</p>
<h2>Example</h2>
<p><strong>Initial request</strong></p>
<pre><code>Client Request:
GET /index.html HTTP/1.1
Host: www.example.com

Server Response:
HTTP/1.1 200 OK
ETag: "1234567890abcdef"
Last-Modified: Wed, 21 Oct 2015 07:30:00 GMT
</code></pre>
<p><strong>Subsequent Conditional Request</strong></p>
<pre><code>Clinet Request:
GET /index.html HTTP/1.1
Host: www.example.com
If-Modified-Since: Wed, 21 Oct 2015 07:30:00 GMT
If-None-Match: "1234567890abcdef"
</code></pre>
<p><strong>Server Response-Not Modified:</strong></p>
<pre><code>HTTP/1.1 304 Not Modified
ETag: "1234567890abcdef"
Last-Modified: Wed, 21 Oct 2015 07:30:00 GMT
</code></pre>
<p><strong>Server Response-Resource Modified:</strong></p>
<pre><code>HTTP/1.1 200 OK
ETag: "fedcba0987654321"
Last-Modified: Wed, 22 Oct 2015 10:00:00 GMT

(Response body with updated resource)
</code></pre>