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Rest Service and HTTP

Representational State Transfer (REST) defines a set of architectural principles by which you can design Web services that focus on a system's resources, including how resource states are addressed and transferred over HTTP by a wide range of clients written in different languages. REST is a style of architecture based on a set of principles that describe how networked resources are defined and addressed.
Many developers found SOAP cumbersome and hard to use. For example, working with SOAP in JavaScript means writing a ton of code to perform extremely simple tasks because you must create the required XML structure absolutely every time. REST provides a lighter weight alternative. Instead of using XML to make a request, REST relies on a simple URL in many cases. In some situations you must provide additional information in special ways, but most Web services using REST rely exclusively on obtaining the needed information using the URL approach. REST can use four different HTTP 1.1 verbs (GET, POST, PUT, and DELETE) to perform tasks.
Unlike SOAP, REST doesn't have to use XML to provide the response. You can find REST-based Web services that output the data in Command Separated Value (CSV), JavaScript Object Notation (JSON) and Really Simple Syndication (RSS). The point is that you can obtain the output you need in a form that's easy to parse within the language you need for your application. REST architecture describes six constraints.

  • Uniform Interface - Resources are manipulated via CRUD (create, read, update, delete) operations. CRUD operations are managed via PUT, GET, POST, and DELETE request methods.
  • Stateless - In REST the state is contained within the request itself, or as part of the URI, query-string parameters, body or in the headers. After processing the request, the state may be communicated back via the headers, status or response body.
  • Cacheable - Responses from the web service to its clients are explicitly labeled as cacheable or non-cacheable. This way, the service, the consumer, or one of the intermediary middleware components can cache the response for reuse in later requests.
  • Client Server - This is a key constraint, as it based on separations of concerns. The client/server requirement ensures that a distributed environment exists. It requires the client, that sends requests and a server component that receives the requests. After processing the request, the server may return a response to the client.
  • Layered System - A client should may not be able to tell whether it is connected directly to the end server, or to an intermediary along the way. Intermediary servers may add security policies, or improve scalability.
  • Code On Demand - This is an optional constraint. It allows a client to have logic locally via the ability to download and execute code from a remote server.

Rest Principle

  • Give every thing its own ID
  • Link things together (HATEOAS)
  • Use standard HTTP methods
  • Resources can have mulitple representations
  • Communicate statelessly
  • Support Caching

HTTP is the protocol that allows for sending documents back and forth on the web. A protocol is a set of rules that determines which messages can be exchanged, and which messages are appropriate replies to others. In HTTP, there are two different roles: server and client. In general, the client always initiates the conversation; the server replies. HTTP is text based; that is, messages are essentially bits of text, although the message body can also contain other media. Text usage makes it easy to monitor an HTTP exchange.
HTTP messages are made of a header and a body. The body can often remain empty; it contains data that you want to transmit over the network, in order to use it according to the instructions in the header. The header contains metadata, such as encoding information; but, in the case of a request, it also contains the important HTTP methods. In the REST style, you will find that header data is often more significant than the body.


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