Endpoints and handlers

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Endpoints

When a web service request is received by your application, the first step for Granitic is to see if there is an endpoint defined for the request. An endpoint is defined as the combination of the path element of the HTTP request and the HTTP method

For example:

  /artist GET
  /artist POST
  /status HEAD 

are three different endpoints.

Components that provide endpoints for requests implement the httpendpoint.Provider interface.

Regular expressions

The path that is associated with the endpoint is not expressed as a static string, instead it is specified as a Go regular expression.

Using regular expression serves two purposes: firstly it allows the endpoint to be less brittle - the regular expression can be crafted to support mixed-cases or trailing slashes in paths. Secondly, and more importantly, it allows capture groups to be defined to allow meaningful information to be extracted from the request path. This is vital for REST-like APIs where IDs are often included as part of paths.

Handlers

Once Granitic has found an component that defines an endpoint matching the request, it calls the ServeHTTP method on that component. Depending on the implementation of httpendpoint.Provider in use, that method may be fully implemented by the component in question, or it might defer it to another component.

Whatever the arrangement, Granitic refers to the component which performs the mechanical parts of web service processing (parsing, validating, error handling etc) as a handler.

For some non-standard endpoints (serving binary data, for example), you may write your own handler, but the vast majority of handler components you create will use Granitic’s built-in handler.WsHandler

WsHandler

WsHandler supports the bulk of Granitic’s web processing phases. It also implements httpendpoint.Provider

A component using WsHandler as a type requires:

  • A regex to match a path
  • An HTTP method
  • A reference to (or an inline definition of) a logic component that implements the interesting work that your web service performs

For example, a minimal component definition might look like:

"artistHandler": {
  "type": "handler.WsHandler",
  "PathPattern": "^/artist"
  "HTTPMethod": "GET",
  "Logic": {
    "type": "artist.GetLogic"
  }
}

WsHandler has a number of fields which are used to customise its behaviour and the remainder of this section will explain how to use them.


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