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Normally we can check the HTTP connection status by $info = curl_getinfo($curl) and
echo out $info['http_code'] in php , for example HTTP 200 OK for request success which
is generated from the server for client request.
But for HTTP 304 status code for curl php program, a little bit confused for me, Just want to know the mechanizm of http 304(not modified) generation. Is the http 304 generated by Broswer like Firefox  when curl_exec()  is sumbitted if previous same webpage is
requested  again ? If so,  browser
will check the cache folder and check  whether the request webpage is existing on client/user computer. If existing, it won't process curl_exec function and just cache the webpage from users' computer  to users and header out http 304 code. IF not exising, browser will let the curl_exec() in php program to continue.
Is that what I said is correct ?

When I output the http_code from getinfo($curl), it will report HTTP 304 when
the firefox cache setting on tool menu and uncheck the stopping cache box and request the same webpage again.  When I disable stopping cache box on Firefox, it means no caching file, HTTP 304 code won't be  generated, the http code is always HTTP200 OK
or HTTP 301 Moved permentantly

Qusetion-1 http 304(not modified) status code is generated by broswers instead of server. ?
Question-2 server can be able to check client's cache setting or ability and header("HTTP1.1 304 Not Modified) in php and echo to header of the webpage if
users requested the webpage is owned by server , Right ?
Please advise
Duncan

Browsers do not use CURL functions.  Automated scripts running on other servers use CURL functions in order to appear to be browsers.  If the automated script acts like a well-behaved client browser, accepting and returning cookies and following redirection instructions, the server will not be able to tell whether the client making the requests is a web browser operated by a human being or a server running CURL functions.

greetings   duncanb7, , the web server response of 304 is not usually sent for an HTTP  standard request for a file, the 304 IS SENT for "information" requests from a browser, or as you use another server request.

Browsers do not change the communication for server CURL functions, as far as I know.

You say that you use -  curl_getinfo(  )  , which is probally the reason for the 304 response, however, as far as I can remember, there should be a request header set to tell the responder what "Date" the information of the file is needed, and if it is the same date, you get the 304 back.  You might look more closely at your setup for using  curl_getinfo(  ) ;

See 10.3.5 304 Not Modified on this page.
http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

The HTTP response codes are generated by the server.  The server cannot check the client cache.  It is the server's responsibility to know what was sent in response to the last identical GET request from a given client, and the server may choose to send the header 304 instead of a message body.  In practice I find this to be rare; the server usually sends the message body.