Packages

  • package root
    Definition Classes
    root
  • package com
    Definition Classes
    root
  • package twitter

    Start with com.twitter.finagle.

    Definition Classes
    com
  • package finagle

    Finagle is an extensible RPC system.

    Finagle is an extensible RPC system.

    Services are represented by class com.twitter.finagle.Service. Clients make use of com.twitter.finagle.Service objects while servers implement them.

    Finagle contains a number of protocol implementations; each of these implement Client and/or com.twitter.finagle.Server. For example, Finagle's HTTP implementation, com.twitter.finagle.Http (in package finagle-http), exposes both.

    Thus a simple HTTP server is built like this:

    import com.twitter.finagle.{Http, Service}
    import com.twitter.finagle.http.{Request, Response}
    import com.twitter.util.{Await, Future}
    
    val service = new Service[Request, Response] {
      def apply(req: Request): Future[Response] =
        Future.value(Response())
    }
    val server = Http.server.serve(":8080", service)
    Await.ready(server)

    We first define a service to which requests are dispatched. In this case, the service returns immediately with a HTTP 200 OK response, and with no content.

    This service is then served via the Http protocol on TCP port 8080. Finally we wait for the server to stop serving.

    We can now query our web server:

    % curl -D - localhost:8080
    HTTP/1.1 200 OK

    Building an HTTP client is also simple. (Note that type annotations are added for illustration.)

    import com.twitter.finagle.{Http, Service}
    import com.twitter.finagle.http.{Request, Response}
    import com.twitter.util.{Future, Return, Throw}
    
    val client: Service[Request, Response] = Http.client.newService("localhost:8080")
    val f: Future[Response] = client(Request()).respond {
      case Return(rep) =>
        printf("Got HTTP response %s\n", rep)
      case Throw(exc) =>
        printf("Got error %s\n", exc)
    }

    Http.client.newService("localhost:8080") constructs a new com.twitter.finagle.Service instance connected to localhost TCP port 8080. We then issue a HTTP/1.1 GET request to URI "/". The service returns a com.twitter.util.Future representing the result of the operation. We listen to this future, printing an appropriate message when the response arrives.

    The Finagle homepage contains useful documentation and resources for using Finagle.

    Definition Classes
    twitter
  • package postgresql
    Definition Classes
    finagle
  • package machine
    Definition Classes
    postgresql
  • CloseMachine
  • ExecuteMachine
  • HandshakeMachine
  • PrepareMachine
  • Runner
  • SimpleQueryMachine
  • StateMachine

trait StateMachine[+R <: Response] extends AnyRef

A StateMachine is responsible for managing the connection state and expose a Request => Future[Response] regardless of the number of actual request / response cycles required with a backend server.

That is, for any particular client request / response cycle, multiple request / response cycles are usually required with the postgresql backend. This requires coordinating state with the backend which is what is encapsulated in StateMachine implementations.

StateMachines have a public type parameter to represent the response type that it will eventually produce. They also have an internal type parameter to represent its internal state representation.

StateMachine only encapsulates the state transitions, not the state itself, which must be maintained externally (i.e.: in some kind of runner). That is, implementations provide a starting state and a way to transition to another state. The "current state" must be maintained in whatever is encapsulating the connection (specifically, in com.twitter.finagle.postgresql.ClientDispatcher for the finagle client.)

StateMachines are responsible for eventually producing the response to the client's request as well as eventually reaching a completion state which leaves the connection ready for a new client request. Note that responding to the client with the response does not necessarily occur at the same time the state machine completing. That is, the client response may be produced while the state machine still exchanges messages with the backend on the connection.

R

The type of client response eventually produced by the state machine implementation.

See also

com.twitter.finagle.postgresql.ClientDispatcher

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Type Members

  1. abstract type State

Abstract Value Members

  1. abstract def receive(state: State, msg: BackendMessage): TransitionResult[State, R]

    Given the current state and a message from the backend server, this method will produce the appropriate transition to execute.

    Given the current state and a message from the backend server, this method will produce the appropriate transition to execute.

    Specifically, this may be additional messages to send to the backend, a response to send to the client, etc.

    state

    the current state of the connection previously returned by a call to start or receive.

    msg

    the message received from the backend server

    returns

    the transition to execute to realize the new state

  2. abstract def start: TransitionResult[State, R]

    The initial transition to execute upon starting this particular machine.

    The initial transition to execute upon starting this particular machine. Normally, this will contain Send actions to send messages to the Postgres backend.

    returns

    the initial transition to execute upon starting the machine.

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