hare v0.1.9 Hare.RPC.Client behaviour

A behaviour module for implementing AMQP RPC client processes.

The Hare.RPC.Client module provides a way to create processes that hold, monitor, and restart a channel in case of failure, exports a function perform RPC to an exchange and receive the response, and some callbacks to hook into the process lifecycle.

An example Hare.RPC.Client process that performs a RPC request and returns the response, but returns "already_requested" when a request with the same payload has already been performed.

defmodule MyRPCClient do
  use Hare.RPC.Client

  def start_link(conn, config, opts \ []) do
    Hare.RPC.Client.start_link(__MODULE__, conn, config, :ok, opts)
  end

  def init(:ok) do
    {:ok, MapSet.new}
  end

  def handle_request(payload, _routing_key, _opts, state) do
    case MapSet.member?(cache, payload) do
      {:ok, response} -> {:reply, "already_requested", state}
      :error          -> {:ok, MapSet.put(state, payload)}
    end
  end
end

Channel handling

When the Hare.RPC.Client starts with start_link/5 it runs the init/1 callback and responds with {:ok, pid} on success, like a GenServer.

After starting the process it attempts to open a channel on the given connection. It monitors the channel, and in case of failure it tries to reopen again and again on the same connection.

Context setup

The context setup process for a RPC client is to declare the exchange to perform requests to, declare a exclusive server-named queue to receive responses, and consume that server-named queue.

Every time a channel is open the context is set up, meaning that the exchange and a new server-named queue are declared, and the queue is consumed through the new channel based on the given configuration.

The configuration must be a Keyword.t that contains a single key: :exchange whose value is the configuration for the Hare.Context.Action.DeclareExchange. Check it for more detailed information.

Summary

Types

config()

meta()

opts()

payload()

routing_key()

state()

Functions

request(client, payload, routing_key \\ "", opts \\ [], timeout \\ 5000)

Performs a RPC request and blocks until the response arrives

start_link(mod, conn, config, initial, opts \\ [])

Starts a Hare.RPC.Client process linked to the current process

Callbacks

connected(meta, state)

Called every time the channel has been opened, the exchange and the server-named queue declared, and the queue consumed

handle_info(meta, state)

Called when the process receives a message

handle_ready(meta, state)

Called when the AMQP server has registered the process as a consumer of the server-named queue and it will start to receive messages

handle_request(payload, routing_key, opts, state)

Called before a request will be performed to the exchange

init(initial)

Called when the RPC client process is first started. start_link/5 will block until it returns

terminate(reason, state)

This callback is the same as the GenServer equivalent and is called when the process terminates. The first argument is the reason the process is about to exit with

Types

config()

config() :: [{:exchange, Hare.Context.Action.DeclareExchange.config}]

meta()

meta() :: map

opts()

opts() :: Hare.Adapter.opts

payload()

payload() :: Hare.Adapter.payload

routing_key()

routing_key() :: Hare.Adapter.routing_key

state()

state() :: term

Functions

request(client, payload, routing_key \\ "", opts \\ [], timeout \\ 5000)

request(pid, payload, routing_key, opts, timeout) ::
  {:ok, response :: binary} |
  {:error, reason :: term}

Performs a RPC request and blocks until the response arrives.

A timeout bound to the same rules as the GenServer timeout may be specified (5 seconds by default)

start_link(mod, conn, config, initial, opts \\ [])

start_link(module, pid, config, initial :: term, GenServer.options) :: GenServer.on_start

Starts a Hare.RPC.Client process linked to the current process.

This function is used to start a Hare.RPC.Client process in a supervision tree. The process will be started by calling init with the given initial value.

Arguments:

mod - the module that defines the server callbacks (like GenServer)
conn - the pid of a Hare.Core.Conn process
config - the configuration of the publisher (describing the exchange to declare)
initial - the value that will be given to init/1
opts - the GenServer options

Callbacks

connected(meta, state)

connected(meta, state) ::
  {:noreply, state} |
  {:stop, reason :: term, state}

Called every time the channel has been opened, the exchange and the server-named queue declared, and the queue consumed.

It is called with two arguments: some metadata and the process’ internal state.

The metadata is a map with the following fields:

:req_exchange - the Hare.Core.Exchange to issue requests to
:resp_queue - the server-named Hare.Core.Queue to consume the responses from

Returning {:noreply, state} will cause the process to enter the main loop with state as its internal state.

Returning {:stop, reason, state} will terminate the loop and call terminate(reason, state) before the process exists with reason reason.

handle_info(meta, state)

handle_info(meta, state) ::
  {:noreply, state} |
  {:stop, reason :: term, state}

Called when the process receives a message.

Returning {:noreply, state} will causes the process to enter the main loop with the given state.

Returning {:stop, reason, state} will not send the message, terminate the main loop and call terminate(reason, state) before the process exists with reason reason.

handle_ready(meta, state)

handle_ready(meta, state) ::
  {:noreply, state} |
  {:stop, reason :: term, state}

Called when the AMQP server has registered the process as a consumer of the server-named queue and it will start to receive messages.

Returning {:noreply, state} will causes the process to enter the main loop with the given state.

Returning {:stop, reason, state} will not send the message, terminate the main loop and call terminate(reason, state) before the process exists with reason reason.

handle_request(payload, routing_key, opts, state)

handle_request(payload, routing_key, opts :: term, state) ::
  {:ok, state} |
  {:ok, payload, routing_key, opts :: term, state} |
  {:reply, response :: term, state} |
  {:stop, reason :: term, response :: binary, state}

Called before a request will be performed to the exchange.

It receives as argument the message payload, the routing key, the options for that publication and the internal state.

Returning {:ok, state} will cause the request to be performed with no modification, block the client until the response is received, and enter the main loop with the given state.

Returning {:ok, payload, routing_key, opts, state} will cause the given payload, routing key and options to be used instead of the original ones, block the client until the response is received, and enter the main loop with the given state.

Returning {:reply, response, state} will respond the client inmediately without performing the request with the given response, and enter the main loop again with the given state.

Returning {:stop, reason, state} will not send the message, terminate the main loop and call terminate(reason, state) before the process exists with reason reason.

init(initial)

init(initial :: term) ::
  {:ok, state} |
  :ignore |
  {:stop, reason :: term}

Called when the RPC client process is first started. start_link/5 will block until it returns.

It receives as argument the fourth argument given to start_link/5.

Returning {:ok, state} will cause start_link/5 to return {:ok, pid} and attempt to open a channel on the given connection, declare the exchange, declare a server-named queue, and consume it. After that it will enter the main loop with state as its internal state.

Returning :ignore will cause start_link/5 to return :ignore and the process will exit normally without entering the loop, opening a channel or calling terminate/2.

Returning {:stop, reason} will cause start_link/5 to return {:error, reason} and the process will exit with reason reason without entering the loop, opening a channel, or calling terminate/2.

terminate(reason, state)

terminate(reason :: term, state) :: any

This callback is the same as the GenServer equivalent and is called when the process terminates. The first argument is the reason the process is about to exit with.