This content originally appeared on DEV Community and was authored by Mahmoud EL-kariouny
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
This content originally appeared on DEV Community and was authored by Mahmoud EL-kariouny
Mahmoud EL-kariouny | Sciencx (2021-09-05T23:33:15+00:00) Introduction to HTTP. Retrieved from https://www.scien.cx/2021/09/05/introduction-to-http/
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