The objective of this technique is to help users locate themselves in a document by providing running headers and footers via pagination artifacts. This is. Jun 1, methods, error codes and headers . A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built. See How to force files to open in browser instead of download (pdf)? which has an answer from ColinM that tells you exactly what the headers.
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HTTP header fields provide required information about the request or response, An HTTP client or server can use the Cache-control general header to specify. Nov 6, Can't guarantee this, but it's taken from our PDF generation classes. Try un- commenting the Content-Disposition: inline; header, and use the correct. Mar 26, In a multipart/form-data body, the HTTP Content-Disposition general header is a header that can be used on the subpart of a multipart body to.
The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2. The objective of this technique is to help users locate themselves in a document by providing running headers and footers via pagination artifacts. This is normally accomplished using a tool for authoring PDF. Running headers and footers help make content easier to use and understandable by providing repeated information in a consistent and predictable way. The content of headers and footers will vary widely depending on the document scope and content, the audience, and design decisions. Some examples of location information that may be used in headers and footers are listed below.
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That is, you have to explicitly turn on MultiViews. The directive LanguagePriority can be used to specify the language preference in case of a tie during content negotiation or if the client does not express a preference. For example:.
A client can use the request header Accept-Charset to negotiate with the server for the character set it prefers. The commonly encountered character sets include: Similarly, the AddCharset directive is used to associate the file extension with the character set. A client can use the Accept-Encoding header to tell the server the type of encoding it supports. The common encoding schemes are: Similarly, the AddEncoding directive is used to associate the file extension with the an encoding scheme.
That is, each TCP connection services only one request. If you download a page containing 5 inline images, the browser has to establish TCP connection 6 times to the same server. The client can negotiate with the server and ask the server not to close the connection after delivering the response, so that another request can be sent through the same connection. This is known as persistent connection or keep-alive connection. Persistent connections greatly enhance the efficiency of the network.
To ask for persistent connection, the client must include a request header " Connection: Keep-alive " in the request message to negotiate with the server. The client do not have to sent the " Connection: Keep-alive " header. Instead, the client may wish to send the header " Connection: Close " to ask the server to close the connection after delivering the response. Persistent connection is extremely useful for web pages with many small inline images and other associated data, as all these can be downloaded using the same connection.
The benefits for persistent connection are:. The KeepAlive directive decides whether to support persistent connections. This takes value of either On or Off. The MaxKeepAliveRequests directive sets the maximum number of requests that can be sent through a persistent connection. You can set to 0 to allow unlimited number of requests. It is recommended to set to a high number for better performance and network efficiency.
The KeepAliveTimeOut directive set the time out in seconds for a persistent connection to wait for the next request. The client can send a request header " Cache-control: You could include both headers in your request.
Latest version tested: HTTP 1. October 20, HTTP is an asymmetric request-response client-server protocol as illustrated. HTTP is a stateless protocol. In other words, the current request does not know what has been done in the previous requests.
HTTP permits negotiating of data type and representation, so as to allow systems to be built independently of the data being transferred. Quoting from the RFC It is a generic, stateless, protocol which can be used for many tasks beyond its use for hypertext, such as name servers and distributed object management systems, through extension of its request methods, error codes and headers.
This process is illustrated below: URL has the following syntax: The application-level protocol used by the client and server, e. The DNS domain name e. The TCP port number that the server is listening for incoming requests from the clients. The name and location of the requested resource, under the server document base directory. Other examples of URL are: Singapore telnet: The server interprets the request received, maps the request into a file under the server's document directory, and returns the file requested to the client.
The server interprets the request received, maps the request into a program kept in the server, executes the program, and returns the output of the program to the client.
The request cannot be satisfied, the server returns an error message. An example of the HTTP response message is as shown: Sun, 18 Oct Sat, 20 Nov An HTTP message consists of a message header and an optional message body , separated by a blank line , as illustrated below: Request Line The first line of the header is called the request line , followed by optional request headers.
The request line has the following syntax: HTTP protocol defines a set of request methods, e.
The client can use one of these methods to send a request to the server. Two versions are currently in use: Examples of request line are: Examples of request headers are: Keep-Alive Accept: Status Line The first line is called the status line , followed by optional response header s.
The status line has the following syntax: The HTTP version used in this session. Examples of status line are: Examples of response headers are: Keep-Alive Keep-Alive: Example The following shows a sample response message: The methods are: A client can use the GET request to get a web resource from the server. Since the header contains the last-modified date of the data, this can be used to check against the local cache copy. Used to post data up to the web server.
Ask the server to store the data. Ask the server to delete the data. Ask the server to return a diagnostic trace of the actions it takes. Ask the server to return the list of request methods it supports. Used to tell a proxy to make a connection to another host and simply reply the content, without attempting to parse or cache it. This is often used to make SSL connection through the proxy.
Other extension methods. A GET request message takes the following syntax: This client negotiates the protocol to be used for the current session.
The client uses the optional request headers such as Accept , Accept-Language , and etc to negotiate with the server and ask the server to deliver the preferred contents e. GET request message has an optional request body which contains the query string to be explained later. Telnet "Telnet" is a very useful networking utility. HTTP response message The request method name "GET" is case sensitive, and must be in uppercase.
If the request method name was incorrectly spelt, the server would return an error message " Method Not Implemented". If the request method name is not allowed, the server will return an error message " Method Not Allowed".
Otherwise, the server would return an error message " Bad Request". If you use telnet to connect to the server, the message "Connection to host lost" appears immediately after the response body is received.
You could use an optional request header " Connection: Keep-Alive " to request for a persistent or keep-alive connection, so that another request can be sent through the same TCP connection to achieve better network efficiency. Response Status Code The first line of the response message i. The status code is a 3-digit number: Request received, server is continuing the process. The request was successfully received, understood, accepted and serviced.
Further action must be taken in order to complete the request. The request contains bad syntax or cannot be understood. The server failed to fulfill an apparently valid request.
Some commonly encountered status codes are: The server received the request and in the process of giving the response. The request is fulfilled. The resource requested for has been permanently moved to a new location. The URL of the new location is given in the response header called Location.
The client should issue a new request to the new location. Application should update all references to this new location. Same as , but the new location is temporarily in nature. The client should issue a new request, but applications need not update the references. In response to the If-Modified-Since conditional GET request, the server notifies that the resource requested has not been modified.
Server could not interpret or understand the request, probably syntax error in the request message.
Server refuses to supply the resource, regardless of identity of client. The requested resource cannot be found in the server. The request method used, e. However, the server does not allow that method for the resource requested. Server is confused, often caused by an error in the server-side program responding to the request.
The request method used is invalid could be caused by a typing error, e. Proxy or Gateway indicates that it receives a bad response from the upstream server. Server cannot response due to overloading or maintenance. The client can try again later. Proxy or Gateway indicates that it receives a timeout from an upstream server. Sun, 08 Feb GET test.
Keep-Alive Content-Type: The message "Connection to host lost" for telnet appears after " keep-alive " timeout Before the "Connection to host lost" message appears i.
The header " Connection: Keep-alive " is not case sensitive. The space is optional. If an optional header is misspelled or invalid, it will be ignored by the server. The conditional request headers include: If-Modified-Since check for response status code " Not Modified".
GET Request for Directory Suppose that a directory called " testdir " is present in the document base directory " htdocs ". Otherwise, the server returns the directory listing, if directory listing is enabled in the server configuration. Otherwise, the server returns " Page Not Found". GET http: Fri, 27 Feb The syntax of the HEAD request is as follows: Sometimes, HEAD is not listed.
TRACE request takes the following syntax: TRACE http: The types of field include: Text Box: Password Box: Radio Button: Text Area: Submit Button: Reset Button: Hidden Field: The amount of data you could append behind request-URI is limited. If this amount exceed a server-specific threshold, the server would return an error " Request URI too Large". The URL-encoded query string would appear on the address box of the browser.
The following GET request is: Keep-Alive Note that although the password that you enter does not show on the screen, it is shown clearly in the address box of the browser. The application-layer protocol used by the client and server, e. URL rewriting for session management, e. The POST request takes the following syntax: Keep-Alive Cache-Control: The amount of data that can be posted is unlimited, as they are kept in the request body, which is often sent to the server in a separate data stream.
The query string is not shown on the address box of the browser. An example of the POST message for file upload is as follows: The message trace is shown: Sun, 29 Feb Wed, 21 Feb Fri, 20 Feb For Example: AddLanguage en. A message trace is as follows: For example: AddCharset ISO AddEncoding x-compress.
Z AddEncoding x-gzip.