Category: http

Aug 10

HTTP – Methods

HTTP – Methods ”; Previous Next The set of common methods for HTTP/1.1 is defined below and this set can be expanded based on requirements. These method names are case sensitive and they must be used in uppercase. S.N. Method and Description 1 GET The GET method is used to retrieve information from the given server using a given URI. Requests using GET should only retrieve data and should have no other effect on the data. 2 HEAD Same as GET, but transfers the status line and header section only. 3 POST A POST request is used to send data to the server, for example, customer information, file upload, etc. using HTML forms. 4 PUT Replaces all current representations of the target resource with the uploaded content. 5 DELETE Removes all current representations of the target resource given by a URI. 6 CONNECT Establishes a tunnel to the server identified by a given URI. 7 OPTIONS Describes the communication options for the target resource. 8 TRACE Performs a message loop-back test along the path to the target resource. GET Method A GET request retrieves data from a web server by specifying parameters in the URL portion of the request. This is the main method used for document retrieval. The following example makes use of GET method to fetch hello.htm: GET /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive The server response against the above GET request will be as follows: HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT ETag: “34aa387-d-1568eb00” Vary: Authorization,Accept Accept-Ranges: bytes Content-Length: 88 Content-Type: text/html Connection: Closed <html> <body> <h1>Hello, World!</h1> </body> </html> HEAD Method The HEAD method is functionally similar to GET, except that the server replies with a response line and headers, but no entity-body. The following example makes use of HEAD method to fetch header information about hello.htm: HEAD /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive The server response against the above HEAD request will be as follows: HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT ETag: “34aa387-d-1568eb00″ Vary: Authorization,Accept Accept-Ranges: bytes Content-Length: 88 Content-Type: text/html Connection: Closed You can notice that here server the does not send any data after header. POST Method The POST method is used when you want to send some data to the server, for example, file update, form data, etc. The following example makes use of POST method to send a form data to the server, which will be processed by a process.cgi and finally a response will be returned: POST /cgi-bin/process.cgi HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Content-Type: text/xml; charset=utf-8 Content-Length: 88 Accept-Language: en-us Accept-Encoding: gzip, deflate Connection: Keep-Alive <?xml version=”1.0″ encoding=”utf-8″?> <string xmlns=”http://clearforest.com/”>string</string> The server side script process.cgi processes the passed data and sends the following response: HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT ETag: “34aa387-d-1568eb00” Vary: Authorization,Accept Accept-Ranges: bytes Content-Length: 88 Content-Type: text/html Connection: Closed <html> <body> <h1>Request Processed Successfully</h1> </body> </html> PUT Method The PUT method is used to request the server to store the included entity-body at a location specified by the given URL. The following example requests the server to save the given entity-body in hello.htm at the root of the server: PUT /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Accept-Language: en-us Connection: Keep-Alive Content-type: text/html Content-Length: 182 <html> <body> <h1>Hello, World!</h1> </body> </html> The server will store the given entity-body in hello.htm file and will send the following response back to the client: HTTP/1.1 201 Created Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Content-type: text/html Content-length: 30 Connection: Closed <html> <body> <h1>The file was created.</h1> </body> </html> DELETE Method The DELETE method is used to request the server to delete a file at a location specified by the given URL. The following example requests the server to delete the given file hello.htm at the root of the server: DELETE /hello.htm HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) Host: www.tutorialspoint.com Accept-Language: en-us Connection: Keep-Alive The server will delete the mentioned file hello.htm and will send the following response back to the client: HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Content-type: text/html Content-length: 30 Connection: Closed <html> <body> <h1>URL deleted.</h1> </body> </html> CONNECT Method The CONNECT method is used by the client to establish a network connection to a web server over HTTP. The following example requests a connection with a web server running on the host tutorialspoint.com: CONNECT www.tutorialspoint.com HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) The connection is established with the server and the following response is sent back to the client: HTTP/1.1 200 Connection established Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) OPTIONS Method The OPTIONS method is used by the client to find out the HTTP methods and other options supported by a web server. The client can specify a URL for the OPTIONS method, or an asterisk (*) to refer to the entire server. The following example requests a list of methods supported by a web server running on tutorialspoint.com: OPTIONS * HTTP/1.1 User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) The server will send an information based on the current configuration of the server, for example: HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Allow: GET,HEAD,POST,OPTIONS,TRACE Content-Type: httpd/unix-directory TRACE Method The TRACE method is used to echo the contents of an HTTP Request back to the requester which can be used for debugging purpose at the time of development. The following example shows the usage of TRACE method: TRACE / HTTP/1.1 Host: www.tutorialspoint.com User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT) The server will send the following message in response to the above request: HTTP/1.1 200 OK Date:

Aug 10

HTTP – Responses

HTTP – Responses ”; Previous Next After receiving and interpreting a request message, a server responds with an HTTP response message: A Status-line Zero or more header (General|Response|Entity) fields followed by CRLF An empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header fields Optionally a message-body The following sections explain each of the entities used in an HTTP response message. Message Status-Line A Status-Line consists of the protocol version followed by a numeric status code and its associated textual phrase. The elements are separated by space SP characters. Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF HTTP Version A server supporting HTTP version 1.1 will return the following version information: HTTP-Version = HTTP/1.1 Status Code The Status-Code element is a 3-digit integer where first digit of the Status-Code defines the class of response and the last two digits do not have any categorization role. There are 5 values for the first digit: S.N. Code and Description 1 1xx: Informational It means the request was received and the process is continuing. 2 2xx: Success It means the action was successfully received, understood, and accepted. 3 3xx: Redirection It means further action must be taken in order to complete the request. 4 4xx: Client Error It means the request contains incorrect syntax or cannot be fulfilled. 5 5xx: Server Error It means the server failed to fulfill an apparently valid request. HTTP status codes are extensible and HTTP applications are not required to understand the meaning of all registered status codes. A list of all the status codes has been given in a separate chapter for your reference. Response Header Fields We will study General-header and Entity-header in a separate chapter when we will learn HTTP header fields. For now, let”s check what Response header fields are. The response-header fields allow the server to pass additional information about the response which cannot be placed in the Status- Line. These header fields give information about the server and about further access to the resource identified by the Request-URI. Accept-Ranges Age ETag Location Proxy-Authenticate Retry-After Server Vary WWW-Authenticate You can introduce your custom fields in case you are going to write your own custom Web Client and Server. Examples of Response Message Now let”s put it all together to form an HTTP response for a request to fetch the hello.htm page from the web server running on tutorialspoint.com HTTP/1.1 200 OK Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache/2.2.14 (Win32) Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT Content-Length: 88 Content-Type: text/html Connection: Closed <html> <body> <h1>Hello, World!</h1> </body> </html> The following example shows an HTTP response message displaying error condition when the web server could not find the requested page: HTTP/1.1 404 Not Found Date: Sun, 18 Oct 2012 10:36:20 GMT Server: Apache/2.2.14 (Win32) Content-Length: 230 Connection: Closed Content-Type: text/html; charset=iso-8859-1 <!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”> <html> <head> <title>404 Not Found</title> </head> <body> <h1>Not Found</h1> <p>The requested URL /t.html was not found on this server.</p> </body> </html> Following is an example of HTTP response message showing error condition when the web server encountered a wrong HTTP version in the given HTTP request: HTTP/1.1 400 Bad Request Date: Sun, 18 Oct 2012 10:36:20 GMT Server: Apache/2.2.14 (Win32) Content-Length: 230 Content-Type: text/html; charset=iso-8859-1 Connection: Closed <!DOCTYPE HTML PUBLIC “-//IETF//DTD HTML 2.0//EN”> <html> <head> <title>400 Bad Request</title> </head> <body> <h1>Bad Request</h1> <p>Your browser sent a request that this server could not understand.</p> <p>The request line contained invalid characters following the protocol string.</p> </body> </html> Print Page Previous Next Advertisements ”;

Aug 10

HTTP – Messages

HTTP – Messages ”; Previous Next HTTP is based on the client-server architecture model and a stateless request/response protocol that operates by exchanging messages across a reliable TCP/IP connection. An HTTP “client” is a program (Web browser or any other client) that establishes a connection to a server for the purpose of sending one or more HTTP request messages. An HTTP “server” is a program ( generally a web server like Apache Web Server or Internet Information Services IIS, etc. ) that accepts connections in order to serve HTTP requests by sending HTTP response messages. HTTP makes use of the Uniform Resource Identifier (URI) to identify a given resource and to establish a connection. Once the connection is established, HTTP messages are passed in a format similar to that used by the Internet mail [RFC5322] and the Multipurpose Internet Mail Extensions (MIME) [RFC2045]. These messages include requests from client to server and responses from server to client which will have the following format: HTTP-message = <Request> | <Response> ; HTTP/1.1 messages HTTP requests and HTTP responses use a generic message format of RFC 822 for transferring the required data. This generic message format consists of the following four items. A Start-line Zero or more header fields followed by CRLF An empty line (i.e., a line with nothing preceding the CRLF) indicating the end of the header fields Optionally a message-body In the following sections, we will explain each of the entities used in an HTTP message. Message Start-Line A start-line will have the following generic syntax: start-line = Request-Line | Status-Line We will discuss Request-Line and Status-Line while discussing HTTP Request and HTTP Response messages respectively. For now, let”s see the examples of start line in case of request and response: GET /hello.htm HTTP/1.1 (This is Request-Line sent by the client) HTTP/1.1 200 OK (This is Status-Line sent by the server) Header Fields HTTP header fields provide required information about the request or response, or about the object sent in the message body. There are four types of HTTP message headers: General-header: These header fields have general applicability for both request and response messages. Request-header: These header fields have applicability only for request messages. Response-header: These header fields have applicability only for response messages. Entity-header: These header fields define meta information about the entity-body or, if no body is present, about the resource identified by the request. All the above mentioned headers follow the same generic format and each of the header field consists of a name followed by a colon (:) and the field value as follows: message-header = field-name “:” [ field-value ] Following are the examples of various header fields: User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3 Host: www.example.com Accept-Language: en, mi Date: Mon, 27 Jul 2009 12:28:53 GMT Server: Apache Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT ETag: “34aa387-d-1568eb00″ Accept-Ranges: bytes Content-Length: 51 Vary: Accept-Encoding Content-Type: text/plain Message Body The message body part is optional for an HTTP message but if it is available, then it is used to carry the entity-body associated with the request or response. If entity body is associated, then usually Content-Type and Content-Length headers lines specify the nature of the body associated. A message body is the one which carries the actual HTTP request data (including form data and uploaded, etc.) and HTTP response data from the server ( including files, images, etc.). Shown below is the simple content of a message body: <html> <body> <h1>Hello, World!</h1> </body> </html> Next two chapters will make use of above explained concepts to prepare HTTP Requests and HTTP Responses. Print Page Previous Next Advertisements ”;