Introduction to HTTP

 Introduction to HTTP

Introduction to HTTP



- Hypertext Transfer Protocol (HTTP) is a protocol that provides a standardized way for computers to communicate with each other. 

- It has been the foundation for data communication over the internet since 1990 and is integral to understanding how client-server communication functions.

- HTTP is a protocol that allows the fetching of resources, such as HTML documents.

- It is the foundation of any data exchange on the Web and it is a client-server protocol, which means requests are initiated by the recipient, usually the Web browser. 

- A complete document is reconstructed from the different sub-documents fetched, for instance, text, layout description, images, videos, scripts, and more.


Features:


Connectionless: When a request is sent, the client opens the connection; once a response is received, the client closes the connection.
- The client and server only maintain a connection during the response and request.
- Future responses are made on a new connection.

Stateless: There is no dependency between successive requests.

Not Sessionless: Utilizing headers and cookies, sessions can be created to allow each HTTP request to share the same context.

Media Independent: Any type of data can be sent over HTTP as long as both the client and server know how to handle the data format.


Elements:

Universal Resource Identifiers (URIs): 
- An example URI is http://www.example.com/tasks/term=homework. 

It has certain components:

Scheme: specifies the protocol used to access the resource, HTTP or HTTPS. In our example HTTP.

Host: specifies the host that holds the resources. 
- In our example www.example.com.

Path: specifies the specific resource being requested. 
- In our example, /tasks.

Query: an optional component, the query string provides information the resource can use for some purpose such as a search parameter. 
- In our example, /term=homework.


Side Note: URI vs URL:

- You may be unsure what the difference is between a URI (Universal Resource Identifier) and a URL (Universal Resource Locator). 

- These terms tend to get confused a lot, and are even frequently used interchangeably—but there is a distinction.

- The term URI can refer to any identifier for a resource—for example, it could be either the name of a resource or the address of a resource (since both the name and address are identifiers of that resource).

- In contrast, URL only refers to the location of a resource—in other words, it only ever refers to an address.

- So, "URI" could refer to a name or an address, while "URL" only refers to an address. 

- Thus, URLs are a specific type of URI that is used to locate a resource on the internet when a client makes a request to a server.


HTTP Requests: 

- HTTP requests are sent from the client to the server to initiate some operation.
- In addition to the URL, HTTP requests have other elements to specify the requested resource.


Elements:

Method: Defines the operation to be performed.

Path: The URL of the resource to be fetched, excluding the scheme and host.

HTTP Version: HTTP/2.0 

Headers: optional information, success as Accept-Language.

Body: optional information, usually for methods such as POST and PATCH, which contain the resource being sent to the server.


Request Methods:

- Different request methods indicate different operations to be performed.
- It's essential to attend to this to correctly format your requests and properly structure an API.


Methods:

GET: ONLY retrieves information for the requested resource of the given URI.

POST: Send data to the server to create a new resource.

PUT: Replaces all of the representation of the target resource with the request data.

PATCH: Partially modifies the representation of the target resource with the request data.

DELETE: Removes all of the representation of the resource specified by the URI.

OPTIONS: Sends the communication options for the requested resource.



HTTP Responses:

- After the request has been received by the server and processed, the server returns an HTTP response message to the client. 

- The response informs the client of the outcome of the requested operation.


Elements:

Status Code & Status Message.

HTTP Version.

Headers: similar to the request headers, provides information about the response and resource representation. 
Some common headers include:
- Date
- Content-Type: the media type of the body of the request

Body: optional data containing the requested resource.


Status Codes:

- As an API developer, it's important to send the correct status code. 

- As a developer using an API, the status codes—particularly the error codes—are important for understanding what caused an error and how to proceed.

Codes fall into five categories:

- 100 Informational
- 200 Success
- 300 Redirection
- 400 Client Error
- 500 Server Error

Common Codes:

- 200: OK
- 201: Created
- 304: Not Modified
- 400: Bad Request
- 401: Unauthorized
- 404: Not Found
- 405: Method Not Allowed
- 500: Internal Server Error



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