3. HTTP Status Codes and Errors
An HTTP request can fail because of a network error or because
of problems encountered while the request is executing on the web server.
3.1 Network Errors
If a network error occurs while transmitting a request message,
error information is available from the underlying network component; e.g.
Windows Sockets or WinInet. Monitoring tools like HttpWatch can display error
codes for situations such as:
- The
host name could not be converted into an IP address, perhaps because an
invalid host name was used or because no DNS lookup service is available.
- The
browser could not connect to the web server. This may happen if the web
server is not running or is listening on the wrong port.
- The
network connection may be broken while transmitting the request message,
perhaps because a physical network connection has been interrupted, e.g. a
network cable has been unplugged.
3.2 Status Codes
HTTP status codes are returned by web servers to describe if and
how a request was processed. The codes are grouped by the first digit:
1xx - Informational
Any code starting with '1' is an intermediate response and
indicates that the server has received the request but has not finished processing
it. For example, IIS initially replies with 100 Continue when
it receives a POST request and then with 200 OK once it has
been processed
2xx - Successful
These codes are used when a request has been successfully
processed. For example, the value 200 is used when the
requested resource is being returned to the HTTP client in the body of the
response message.
3xx - Redirection
Codes starting with a '3' indicate that the request was
processed, but the browser should get the resource from another location. Some
examples are:
302
|
The
requested resource has been temporarily moved and the browser should
issue a request to the URL supplied in the Location response
header.
|
||||||||||
304
|
The
requested resource has not been modified and the browser should read from its
local cache instead. The Content-Length header will be zero
or absent because content is never returned with a 304 response
|
||||||||||
|
4xx - Client Error
The server returns these codes when they is a problem with the
client's request. Here are some examples:
401
|
Anonymous
clients are not authorized to view the requested content and must provide
authentication information in the WWW-Authenticate request header.
|
404
|
The
requested resource does not exist on the server
|
5xx - Server Error
A status code starting with the digit 5 indicates that an error
occurred on the server while processing the request. For example:
500
|
An
internal error occurred on the server. This may be because of an application
error or configuration problem
|
503
|
The
service is currently unavailable, perhaps because of essential maintenance or
overloading
|
HTTP Status Codes and Errors
Reviewed by Admin
on
September 25, 2014
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