hare v0.1.9 Hare.Publisher behaviour

A behaviour module for implementing AMQP publisher processes.

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

An example Hare.Publisher process that only sends every other message:

defmodule MyPublisher do
  use Hare.Publisher

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

  def publish(publisher, payload, routing_key) do
    Hare.Publisher.publish(publisher, payload, routing_key)
  end

  def init(:ok) do
    {:ok, %{last_ignored: false}}
  end

  def handle_publication(_payload, _routing_key, _opts, %{last_ignored: false}) do
    {:ignore, %{last_ignored: true}}
  end
  def handle_publication(_payload, _routing_key, _opts, %{last_ignored: true}) do
    {:ok, %{last_ignored: false}}
  end
end

Channel handling

When the Hare.Publisher 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 publisher is to declare its exchange.

Every time a channel is open the context is set up, meaning that the exchange is declared 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

publish(client, payload, routing_key \\ "", opts \\ [])

Publishes a message to an exchange through the Hare.Publisher process

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

Starts a Hare.Publisher process linked to the current process

Callbacks

connected(meta, state)

Called every time the channel has been opened and the exchange declared

handle_info(message, state)

Called when the process receives a message

handle_publication(payload, routing_key, opts, state)

Called before a message will be published to the exchange

init(initial)

Called when the publisher 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

publish(client, payload, routing_key \\ "", opts \\ [])

publish(pid, payload, routing_key, opts) :: :ok

Publishes a message to an exchange through the Hare.Publisher process.

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

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

Starts a Hare.Publisher process linked to the current process.

This function is used to start a Hare.Publisher 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 and the exchange declared.

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

The metadata is a map with a single key :exchange whose value is the Hare.Core.Exchange struct just declared.

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(message, state)

handle_info(message :: term, 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_publication(payload, routing_key, opts, state)

handle_publication(payload, routing_key, opts :: term, state) ::
  {:ok, state} |
  {:ok, payload, routing_key, opts :: term, state} |
  {:ignore, state} |
  {:stop, reason :: term, state}

Called before a message will be published 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 message to be sent with no modification, 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, and enter the main loop with the given state.

Returning {:ignore, state} will ignore that message 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 publisher 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 and declare the exchange. 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.