HTTP Requests

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1. HTTP Overview
2. HTTP Parameters
3. HTTP Messages
4. HTTP Requests
5. HTTP Responses
6. HTTP Method
7. HTTP Status Codes
8. HTTP Header Fields
9. HTTP Caching
10. HTTP URL Encoding
11. HTTP Security
12. HTTP Message Examples

An HTTP client  sends an HTTP request to a server in the form of a request message which includes following format:

• A Request-line
• Zero or more header (General|Request|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 entities used in an HTTP request message.

Request-Line

The Request-Line begins with a method token, followed by the Request-URI and the protocol version, and ending with CRLF. The elements are separated by space SP characters.

Request-Line = Method SP Request-URI SP HTTP-Version CRLF

Let's discuss each of the parts mentioned in the Request-Line.

Request Method

The request method indicates the method to be perform on the resource identified by the given Request-URI. The method is case-sensitive and should always be mentioned in uppercase. The following table lists all the supported methods in HTTP/ 1.1

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 it transfers the status line and the 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 the current representation of the target resource with the uploaded content.
5	DELETE Removes all the current representations of the target resource given by URI.
6	CONNECT Establishes a tunnel to the server identified by a given URI.
7	OPTIONS Describe the communication options for the target resource.
8	TRACE Perform a message loop back test along with the path to the target resource.

Request-URI

The Request-URI is a Uniform Resource Identifier and identifies the resource upon which to apply the request. Following are the most commonly used forms to specify an URI:

Request-URI = "*" | absolutURI | abs_path | authority

S.N.	Method and Description
1	The asterisk * is used when an HTTP request does not apply to a particular resource, but not the server itself, and is only allowed when the method used does not necessarily apply to a resource. For example: OPTIONS * HTTP/1.1
2	The absoluteURI is used when an HTTP request is being made to a proxy. The proxy is request to forward the request or service from a valid cache, and return the response. For example: GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
3	The most common form of Request-URI is that used to identify a resource on an origin server or gateway. For example, a client wishing to retrieve a resource directly from the origin server would create a TCP connection to port 80 of the host "www.w3.org" and send the following lines: GET /pub/WWW/TheProject.html HTTP/1.1 Host: www.w3.org Note that the absolute path cannot be empty; if none is present in the original URI, it MUST be given as "/" (the server root).

Request 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 Request header fields are.

 The request-header fields allow the client to pass additional information about the request, and about the client itself, to the server. These fields act as request modifiers. Here is a list of some important Request-header fields that can be used based on the requirement:

• Accept-Charset
• Accept-Encoding
• Accept-Language
• Authorization
• Expect
• From
• Host
• If-Match
• If-Modified-Since
• If-None-Match
• If-Range
• If-Unmodified-Since
• Max-Forwards
• Proxy-Authorization
• Range
• Referer
• TE
• User-Agent

You can introduce your custom fields in case you are going to write your own custom Client and Web Server.

Example of Request Message

Now let's put it all together to form an HTTP request to fetch hello.htm page from the web server running on tutorialspoint.com

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

Here we are not sending any request data to the server because we are fetching a plain HTML page from the server. Connection is a general-header, and the rest of the headers are request headers. The following example shows how to send form data to the server using request message body:

POST /cgi-bin/process.cgi HTTP/1.1

User-Agent: Mozilla/4.0 (compatible; MSIE5.01; Windows NT)

Host: www.tutorialspoint.com

Content-Type: application/x-www-form-urlencoded

Content-Length: length

Accept-Language: en-us

Accept-Encoding: gzip, deflate

Connection: Keep-Alive

licenseID=string&content=string&/paramsXML=string

Here the given URL /cgi-bin/process.cgi will be used to process the passed data and accordingly, a response will be returned. Here content-type tells the server that the passed data is a simple web form data and length will be the actual length to the data put in the message body. The following example shows how you can pass plain XML to your web server:

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: length

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>

Tham khảo: Tutorialspoint.com 

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HTTP Messages

1. HTTP Overview
2. HTTP Parameters
3. HTTP Messages
4. HTTP Requests
5. HTTP Responses
6. HTTP Method
7. HTTP Status Codes
8. HTTP Header Fields
9. HTTP Caching
10. HTTP URL Encoding
11. HTTP Security
12. HTTP Message Examples

    HTTP is based on the client-server architecture model and a stateless request/response protocol that operates by (điều hành bởi) exchanging messages across a reliable(xác thực/tin cậy) 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 Infomation Services IIS, etc. ) that accepts connections in order to serve HTTP request by sending HTTP response messages.

    HTTP make 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 [RFC3522] 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 response use a generic message format consists of (bao gồm) 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 (một cách tương đối). For now, let's see the examples of start line in case of the 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 header:

• 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 fields consists of a name followed by a colon (:) and the fields value as follows:

message-header = field-name ":" [field-value]

Following are the examples of various header fields:

User-Agent: curl/7.16.3 OpenSSL/0.9.71 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: Web, 22 Jul 2009 19:15:56 GMT

ETag: "34aa234-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(liên kết) 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 from 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.

Tham khảo: https://www.tutorialspoint.com/

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HTTP Parameters

    

1. HTTP Overview
2. HTTP Parameters
3. HTTP Messages
4. HTTP Requests
5. HTTP Responses
6. HTTP Method
7. HTTP Status Codes
8. HTTP Header Fields
9. HTTP Caching
10. HTTP URL Encoding
11. HTTP Security
12. HTTP Message Examples

    This chapter is going to list down few of the important HTTP protocol parameters and their syntax the way they are used in the communication. For example, format for date, format for URL, etc. This will help you in constructing your request and response message while writing HTTP client or server programs. You will see the complete usage of these parameters subsequent chapters while learning the message structure for HTTP requests and responses.

HTTP Version

HTTP uses a <major>.<minor> numbering scheme to indicate version of the protocol. The version of an HTTP message is indicated by the HTTP-Version field in the first line. Here is the general syxtax of specifying HTTP version number:

HTTP-Version = "HTTP" "/" 1*DIGIT "." 1*DIGIT

Example

HTTP/1.0 or HTTP/1.1

Uniform Resource Identifiers

Uniform Resource Identifiers (URI) are simply formatted, case-insensitive string containing name, location, ect. to identify a resource, for example, a website, a web service, etc. A general syntax of URI used for HTTP is as follows:

URI = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]

Here if the port is empty or not given, port 80 is assumed for HTTP and an empty abs_path is equivalent to an abs_path of "/".The characters other than those in the reserved and unsafe sets are equivalent to their ""%" HEX HEX" encoding.

Example

The following three URIs are equivalent:

http://abc.com:80/~smith/home.html

http://ABC.com/%7Esmith/home.html

http://ABC.com:/%7esmith/home.html

Date/Time Formats

All HTTP date/time stamps MUST be represented in Greenwich Mean Time (GMT), without exception. HTTP applications are allowed to use any of the following three representations of date/time stamps:

Sun,  06 Nov 1994 08:49:37 GMT   ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT  ; RFC 850, obsoleted by RFC 1036
Sun Nov    6 08:49:37 1994              ; ANSI C's asctime() format

Character Sets

We use character sets to specify the character sets that the client prefers. Multiple character sets can be listed separated by commas. If a value is not specified, the default is the US-ASCII.

Example

Following are the calid character sets:

US-ASCII or ISO-8859-1 or ISO-8859-7

Content Encodings

A content encoding value indicates that an encoding algorithm has been used to encode the content before passing it over the network. Content coding are primarily used to allow a document to be compressed or otherwise usefully transformed without losing the identity.

All content-encoding values are case-insensitive. HTTP/1.1 uses content encoding values in the Accept-Encoding and Content-Encoding header fields which we will see in the subsequent chapters.

Example

Following are the valid encoding schemes:

Accept-encoding: gzip or compress or deflate

Media Type

HTTP uses Internet Media Types in the Content-Type and Accept header fields in order to provide open and extensible data typing and type negotiation. All the Media-type values are registered with the Internet Assigned Number Authority (IANA). The general syntax to specify media type is as follows:

media-type   = type "/" subtype *(";" parameter )

The type, subtype, and parameter attribute names are case-insensitive.

Example

Accept: image/gif

Language Tags

HTTP uses language tags within the Accept-language and Content-Language fields. A language tag is composed of one or more parts: a primary language tag and a possibly empty series of subtags:

language-tag = primary-tag *("-" subtag )

White spaces are not allowed within the tag and all tags are case-insensitive.

Example

Example tags include:

en, en-US, en-cockney, i-cherokee, x-pig-latin

where any two-letter primary-tag is an ISO-639 language abbreviation and any two-letter initial subtag is an ISO-3166 contry code.

Tham khảo: https://www.tutorialspoint.com/ 

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HTTP Overview

Vừa học kiến thức, vừa rèn luyện tiếng anh! Còn gì tuyệt vời hơn nữa 😊😊😋 

1. HTTP Overview
2. HTTP Parameters
3. HTTP Messages
4. HTTP Requests
5. HTTP Responses
6. HTTP Method
7. HTTP Status Codes
8. HTTP Header Fields
9. HTTP Caching
10. HTTP URL Encoding
11. HTTP Security
12. HTTP Message Examples

    The HyperText Transfer Protocol (HTTP) is an application-level protocol for distributed (phân phối), collaborative (cộng tác), hyper-media information systems. This is the foundation for data communication for World Wide Web (i.e. internet) since 1990. HTTP is a generic and stateless (phi trạng thái) protocol which can be used for other purposes as well using extensions of its request methods, error codes and headers.

    Basically, HTTP is a TCP/IP based communicate protocol, that used to deliver (phân phối) data (HTML files, image files, query results, ect.) on the WWW. The default port is TCP 80, but other ports can be used as well. It provides a standardized way for computers to communicate with each other. HTTP specification specifies how clients' data will be constructed and send to the server, and how to the servers response  these requests.

Basic features:

   There are three features that make HTTP a simple but powerful protocol:

• HTTP is a connectionless (kết nối không liên tục): The HTTP client, i.e., a browser initiates an HTTP request and after a request is made,  the client disconnects from the server and waits for a response. The server processes the request and re-establishes  (thiết lập lại) the connection with the client to send a response back. 
• HTTP is media independent (phương tiện độc lập): It means, any type of data can be sent by HTTP as long as both the client and the server know how to handle the data content. It's required for the client as well as the server specify the content type using appropriate (thích hợp) MIME-type.
• HTTP is a stateless: As mentioned above, HTTP is connectionless and it's a direct result HTTP being a stateless protocol. The client and the server are aware of each other during a current request. Afterwards, both of them forget about each other. Due to this nature of the protocol, neither the client nor the server can retain (ghi nhớ) information between different requests across the web pages.

Note: HTTP/1.0 uses a new connection for each request/response exchange (trao đổi) where as HTTP/1.1 may be used for one or more request/response exchanges.

Basic Architecture:

    The following diagram shows a basic architecture of a web application and depicts (miêu tả) where HTTP sits:

    The HTTP is a request/response protocol based on the client/server based architecture where web browsers, robots, search engines,  ect., act like HTTP clients and the Web server acts like servers.

Client

    The HTTP client sends  a request to the server in the form of a request method, URI, and protocol version followed by a MIME-like message containing the request modifiers, client information, and possible body content over a TCP/IP connection.

Server

    The HTTP server responds with a status line, including the message's protocol version and a success or error code followed by a MIME-like message containing server information, entity meta information , and possible entity-body content.

Tham khảo: tutorialspoint.com

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