All about APIs

As per the official definition by Mozilla

An HTTP header is a field of an HTTP request or response that passes additional context and metadata about the request or response.

In a simple term client and server can pass the extra bit of information(contextual/meta data) with the request and response using the http headers.

These are further divided into four parts;

• Request headers
  These are use to send information while making a client to
  sever call.

• Response headers
  Contrary to the first one, these are use to send information
  while sending the response back to the client from the
  server.

• Representation headers
  This holds the information about the body of the response.

• Payload headers
  This is used to hold the information about the payload data.

Commonly used headers

1. Accept
   Media types/data types are accepted by the server.

2. Content-type
   This can be used both by clients and servers to identify
   the format of the data in their request or response.

3. Accept-encoding
   This provides meta-information such as the encoding method
   client can understand.

4. Host
   It specifies the domain name. This means information such
   as the host and the port.

5. Authorization
   This is used to pass the credentials (such as information,
   keys or tokens) primarily to let the server authenticate
   the request.

6. Access-control-allow-origin
   This is to restrict the origin which tries to fetch the
   resource.

7. Accept-language
   Helps in determining the detail that client is accepting
   the response in the mentioned language.

8. Access-control-allow-methods
   This helps in knowing which methods are allowed to access
   the cross origin resources.

Http Request Methods

1. Get
   The Get method is the most common of all these request
   methods. It is used to fetch the resources from the
   server.

2. Post
   The Post method is used to submit the information to the
   server. Since, we are submitting the data the post method
   often changes the state of the server.

3. Put
   The put method is used to change data already present in
   the resource collection.

4. Patch
   Contrary to put, the patch request method is used to
   modify only the necessary part of the data or response.
   Simply stating it never modifies the entire response.

5. Delete
   As per its name, delete request method is used to delete
   the specific resource. It requests that the origin server
   delete the resource identified the request URL.

**Resources are datasets in the above statements.