Http Status 304 Error
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response. 10.1 Informational 1xx This class of status code indicates a provisional response, consisting only of the Status-Line and optional headers, and is terminated by an empty line. There are no required headers http response example for this class of status code. Since HTTP/1.0 did not define any 1xx
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status codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client except under experimental conditions. A client MUST http 404 be prepared to accept one or more 1xx status responses prior to a regular response, even if the client does not expect a 100 (Continue) status message. Unexpected 1xx status responses MAY be ignored
Http 403
by a user agent. Proxies MUST forward 1xx responses, unless the connection between the proxy and its client has been closed, or unless the proxy itself requested the generation of the 1xx response. (For example, if a proxy adds a "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding 100 (Continue) response(s).) 10.1.1 100 Continue The client SHOULD continue with its request. http status codes cheat sheet This interim response is used to inform the client that the initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server MUST send a final response after the request has been completed. See section 8.2.3 for detailed discussion of the use and handling of this status code. 10.1.2 101 Switching Protocols The server understands and is willing to comply with the client's request, via the Upgrade message header field (section 14.42), for a change in the application protocol being used on this connection. The server will switch protocols to those defined by the response's Upgrade header field immediately after the empty line which terminates the 101 response. The protocol SHOULD be switched only when it is advantageous to do so. For example, switching to a newer version of HTTP is advantageous over older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use such features. 10.2 Successful 2xx This class of status code indicates that the client's request was successfully received, understood, and accepted.
be returned if allowed by the client (e.g. your Web browser or our CheckUpDown robot). The client specifies this in the HTTP data stream sent to the Web server e.g. via If_Modified_Since headers in the request. Systems that cache or index
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Web resources (such as search engines) often use the 304 response to determine if the information
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they previously gathered for a particular URL is now out-of-date. Fixing 304 errors - general You should never see this error in your Web http error wordpress browser. It should simply present the Web page from its cache - because it believes the page has not changed since it was last cached. If your client is not a Web browser, then it should equally be able to present https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html the page from a cache. If unable to do so, it is not using the If_Modified_Since or related headers correctly. Fixing 304 errors - CheckUpDown You should never see this error at all for the CheckUpDown service. It indicates defective programming by us or the developers of the Web server software. Either we or they are not respecting HTTP protocols completely. The 304 status code should only be returned if we allow it in the HTTP data stream we send to http://www.checkupdown.com/status/E304.html the Web server. Because we keep no records of the actual content of your URL Web page, we specifically disallow the 304 response in the HTTP data stream we send. So if the Web server implements the HTTP protocol properly, it should never send an 304 status code back to us. This response is not what we expect, so we actively report it as an error even though it does not necessarily mean that the Web site is down. Please contact us directly (email preferred) whenever you encounter 304 errors. Only we can resolve them for you. Unfortunately this may take some time, because we have to analyse the underlying HTTP data streams and may have to liaise with your ISP and the vendor of the Web server software to agree the exact source of the error. 304 errors in the HTTP cycle Any client (e.g. your Web browser or our CheckUpDown robot) goes through the following cycle when it communicates with the Web server: Obtain an IP address from the IP name of the site (the site URL without the leading 'http://'). This lookup (conversion of IP name to IP address) is provided by domain name servers (DNSs). Open an IP socket connection to that IP address. Write an HTTP data stream through that socket. Receive an HTTP data stream back from the Web server in response. This data stream contains status codes whose values are determined by the HTT
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more http://stackoverflow.com/questions/2603595/why-am-i-getting-304-not-modified-error-on-some-links-when-using-httpwebrequ about Stack Overflow the company Business Learn more about hiring developers or posting ads https://httpstatuses.com/304 with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up Why am I getting “(304) Not Modified” error on some links when http status using HttpWebRequest? up vote 18 down vote favorite 7 Any ideas why on some links that I try to access using HttpWebRequest I am getting "The remote server returned an error: (304) Not Modified." in the code? The code I'm using is from Jeff's post here (the page seems to have disappeared, see an archive copy at the Wayback Machine). Note the concept of the code is a simple proxy http status 304 server, so I'm pointing my browser at this locally running piece of code, which gets my browsers request, and then proxies it on by creating a new HttpWebRequest, as you'll see in the code. It works great for most sites/links, but for some this error comes up. You will see one key bit in the code is where it seems to copy the http header settings from the browser request to it's request out to the site, and it copies in the header attributes. Not sure if the issue is something to do with how it mimics this aspect of the request and then what happens as the result comes back? case "If-Modified-Since": request.IfModifiedSince = DateTime.Parse(listenerContext.Request.Headers[key]); break; I get the issue for example from http://en.wikipedia.org/wiki/Main_Page PS. UPDATE HERE Still can't work this out. Basically I can identify 1 link which has an issue, and it seems to work fine, 2nd time it gets the error, 3rd time OK, 4th time gets the error, 5th time OK etc. As if there is some state not getting cleared or something in the code. I've tried to clean up the code a bit using "using" type statements etc. Here's the code. If anyone can spot why every 2nd
false. In other words, there is no need for the server to transfer a representation of the target resource because the request indicates that the client, which made the request conditional, already has a valid representation; the server is therefore redirecting the client to make use of that stored representation as if it were the payload of a 200 OK response. The server generating a 304 response MUST generate any of the following header fields that would have been sent in a 200 OK response to the same request: Cache-Control, Content-Location, Date, ETag, Expires, and Vary. Since the goal of a 304 response is to minimize information transfer when the recipient already has one or more cached representations, a sender SHOULD NOT generate representation metadata other than the above listed fields unless said metadata exists for the purpose of guiding cache updates (e.g., Last-Modified might be useful if the response does not have an ETag field). Requirements on a cache that receives a 304 response are defined in Section 4.3.4 of RFC7234. If the conditional request originated with an outbound client, such as a user agent with its own cache sending a conditional GET to a shared proxy, then the proxy SHOULD forward the 304 response to that client. A 304 response cannot contain a message-body; it is always terminated by the first empty line after the header fields. Source: RFC7232 Section 4.1 304 Code References Rails HTTP Status Symbol :not_modified Go HTTP Status Constant http.StatusNotModified Symfony HTTP Status Constant Response::HTTP_NOT_MODIFIED Python2 HTTP Status Constant httplib.NOT_MODIFIED Python3+ HTTP Status Constant http.client.NOT_MODIFIED Python3.5+ HTTP Status Constant http.HTTPStatus.NOT_MODIFIED← Return to httpstatuses.com