feat: sse implementation for events beacon API

config/config.exs

@@ -52,3 +52,13 @@ if System.get_env("RUSTLER_SKIP_COMPILE") do
   config :lambda_ethereum_consensus, Snappy, skip_compilation?: true
   config :lambda_ethereum_consensus, Ssz, skip_compilation?: true
 end
+
+config :sse,
+  keep_alive: {:system, "SSE_KEEP_ALIVE_IN_MS", 55000}
+
+config :event_bus,
+  topics: [:finalized_checkpoint, :block]
+
+config :mime, :types, %{
+  "text/event-stream" => ["sse"]
+}

config/runtime.exs

@@ -150,7 +150,9 @@ config :lambda_ethereum_consensus, EngineApi,
 # Beacon API
 config :lambda_ethereum_consensus, BeaconApi.Endpoint,
   server: enable_beacon_api,
-  http: [port: beacon_api_port || 4000],
+  # We use an infinit idle timeout to avoid closing sse connections, if needed we can
+  # create a separate endpoint for them.
+  http: [port: beacon_api_port || 4000, protocol_options: [idle_timeout: :infinity]],
   url: [host: "localhost"],
   render_errors: [
     formats: [json: BeaconApi.ErrorJSON],

lib/beacon_api/controllers/v1/events_controller.ex

@@ -0,0 +1,55 @@
+defmodule BeaconApi.V1.EventsController do
+  use BeaconApi, :controller
+
+  alias BeaconApi.ApiSpec
+  alias BeaconApi.EventPubSub
+
+  require Logger
+
+  def open_api_operation(:subscribe),
+    do: ApiSpec.spec().paths["/eth/v1/events"].get
+
+  @spec subscribe(Plug.Conn.t(), any) :: Plug.Conn.t()
+  def subscribe(conn, %{"topics" => topics}) do
+    case parse_topics(topics) do
+      {:ok, topics} ->
+        EventPubSub.sse_subscribe(conn, topics)
+
+      {:error, error} ->
+        send_chunked_error(conn, error)
+    end
+  end
+
+  def subscribe(conn, _params) do
+    error =
+      Jason.encode!(%{
+        code: 400,
+        message: "Missing field topics"
+      })
+
+    send_chunked_error(conn, error)
+  end
+
+  defp parse_topics(topics_string) do
+    # topics is a string list in the form of: "finalized_checkpoint, block" we need to split it
+    topics = topics_string |> String.split(",") |> Enum.map(&String.trim/1)
+    not_implemented_topics = Enum.reject(topics, &EventPubSub.implemented_topic?/1)
+
+    if Enum.empty?(not_implemented_topics) do
+      {:ok, topics}
+    else
+      {:error,
+       "Invalid topic/s #{inspect(not_implemented_topics)}. For now, only #{inspect(EventPubSub.implemented_topics())} are supported."}
+    end
+  end
+
+  defp send_chunked_error(conn, error) do
+    conn
+    |> Plug.Conn.send_chunked(400)
+    |> Plug.Conn.chunk(error)
+    |> case do
+      {:ok, conn} -> Plug.Conn.halt(conn)
+      {:error, _reason} -> Plug.Conn.halt(conn)
+    end
+  end
+end

lib/beacon_api/event_pubsub.ex

@@ -0,0 +1,84 @@
+defmodule BeaconApi.EventPubSub do
+  @moduledoc """
+  Event listener for aggregating and sending events for SSE subscribers.
+
+  TODO: (#1368) This depends on `event_bus` and `sse`, but it could be easily switched later:
+  - `event_bus` we could move to phoenix pubsub
+  - `sse` we could just implement it ourselves using Plug.Conn.chunk and Plug.Conn.send_chunked
+
+  The idea is to have a single place to publish events, and then a method for a connection to subscribe to them.
+  """
+
+  require Logger
+  alias EventBus.Model.Event
+  alias LambdaEthereumConsensus.Store
+  alias SSE.Chunk
+  alias Types.StateInfo
+
+  @type topic() :: String.t() | atom()
+  @type topics() :: list(topic())
+  @type event_data() :: any()
+
+  # This is also dependant on the already needed event_bus compile time config,
+  # we maintain them as strings for convienience
+  @implemented_topics Application.compile_env!(:event_bus, :topics) |> Enum.map(&Atom.to_string/1)
+
+  @spec implemented_topics() :: topics()
+  def implemented_topics(), do: @implemented_topics
+
+  @spec implemented_topic?(topic()) :: boolean()
+  def implemented_topic?(topic) when is_atom(topic), do: implemented_topic?(Atom.to_string(topic))
+  def implemented_topic?(topic) when is_binary(topic), do: topic in @implemented_topics
+
+  @doc """
+  Publish an event to the event bus.
+
+  TODO: We might want a noop if there are no subscribers for a topic.
+  """
+  @spec publish(topic(), event_data()) :: :ok | {:error, atom()}
+  def publish(:finalized_checkpoint = topic, %{root: block_root, epoch: epoch}) do
+    case Store.BlockStates.get_state_info(block_root) do
+      %StateInfo{root: state_root} ->
+        data = %{
+          block: BeaconApi.Utils.hex_encode(block_root),
+          state: BeaconApi.Utils.hex_encode(state_root),
+          epoch: Integer.to_string(epoch),
+          # TODO: this is a placeholder, we need to get if the execution is optimistic or not
+          execution_optimistic: false
+        }
+
+        chunk = %Chunk{event: topic, data: [Jason.encode!(data)]}
+        event = %Event{id: UUID.uuid4(), data: chunk, topic: topic}
+
+        EventBus.notify(event)
+
+      nil ->
+        Logger.error("State not available for block", root: block_root)
+
+        {:error, :state_not_available}
+    end
+  end
+
+  def publish(:block = topic, %{root: block_root, slot: slot}) do
+    data = %{
+      block: BeaconApi.Utils.hex_encode(block_root),
+      slot: Integer.to_string(slot),
+      # TODO: this is a placeholder, we need to get if the execution is optimistic or not
+      execution_optimistic: false
+    }
+
+    chunk = %Chunk{event: topic, data: [Jason.encode!(data)]}
+    event = %Event{id: UUID.uuid4(), data: chunk, topic: topic}
+
+    EventBus.notify(event)
+  end
+
+  def publish(_topic, _event_data), do: {:error, :unsupported_topic}
+
+  @doc """
+  Subscribe to a topic for stream events in an sse connection.
+  """
+  @spec sse_subscribe(Plug.Conn.t(), topics()) :: Plug.Conn.t()
+  def sse_subscribe(conn, topics) when is_list(topics),
+    do: SSE.stream(conn, {topics, %Chunk{data: []}})
+end

lib/beacon_api/router.ex

@@ -2,7 +2,7 @@ defmodule BeaconApi.Router do
   use BeaconApi, :router
 
   pipeline :api do
-    plug(:accepts, ["json"])
+    plug(:accepts, ["json", "sse"])
     plug(OpenApiSpex.Plug.PutApiSpec, module: BeaconApi.ApiSpec)
   end
 
@@ -22,6 +22,10 @@ defmodule BeaconApi.Router do
       get("/identity", NodeController, :identity)
       get("/version", NodeController, :version)
     end
+
+    scope "/events" do
+      get("/", EventsController, :subscribe)
+    end
   end
 
   # Ethereum API Version 2

lib/lambda_ethereum_consensus/fork_choice/fork_choice.ex

@@ -4,6 +4,7 @@ defmodule LambdaEthereumConsensus.ForkChoice do
   """
 
   require Logger
+  alias BeaconApi.EventPubSub
   alias LambdaEthereumConsensus.Execution.ExecutionChain
   alias LambdaEthereumConsensus.ForkChoice.Handlers
   alias LambdaEthereumConsensus.ForkChoice.Head
@@ -65,6 +66,7 @@ defmodule LambdaEthereumConsensus.ForkChoice do
         |> tap(fn store ->
           StoreDb.persist_store(store)
           Logger.info("[Fork choice] Added new block", slot: slot, root: block_root)
+          EventPubSub.publish(:block, %{root: block_root, slot: slot})
 
           Logger.info("[Fork choice] Recomputed head",
             slot: store.head_slot,

lib/lambda_ethereum_consensus/fork_choice/handlers.ex

@@ -4,6 +4,7 @@ defmodule LambdaEthereumConsensus.ForkChoice.Handlers do
   """
   require Logger
 
+  alias BeaconApi.EventPubSub
   alias LambdaEthereumConsensus.Execution.ExecutionClient
   alias LambdaEthereumConsensus.ForkChoice
   alias LambdaEthereumConsensus.StateTransition
@@ -281,7 +282,11 @@ defmodule LambdaEthereumConsensus.ForkChoice.Handlers do
     |> if_then_update(
       finalized_checkpoint.epoch > store.finalized_checkpoint.epoch,
       # Update finalized checkpoint
-      &%Store{&1 | finalized_checkpoint: finalized_checkpoint}
+      fn store ->
+        EventPubSub.publish(:finalized_checkpoint, finalized_checkpoint)
+
+        %Store{store | finalized_checkpoint: finalized_checkpoint}
+      end
     )
   end
 

mix.exs

@@ -64,7 +64,10 @@ defmodule LambdaEthereumConsensus.MixProject do
       {:sentry, "~> 10.8.0"},
       {:prom_ex, "~> 1.11.0"},
       {:flama, git: "https://github.com/lambdaclass/ht1223_tracer"},
-      {:uuid, "~> 1.1"}
+      {:uuid, "~> 1.1"},
+      # TODO: (#1368) We might want to use phoenix_pubsub instead and do our implementation of SSE.
+      {:sse, "~> 0.4"},
+      {:event_bus, ">= 1.6.0"}
     ]
   end
 

mix.lock

@@ -19,6 +19,7 @@
   "elixir_make": {:hex, :elixir_make, "0.8.4", "4960a03ce79081dee8fe119d80ad372c4e7badb84c493cc75983f9d3bc8bde0f", [:mix], [{:castore, "~> 0.1 or ~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:certifi, "~> 2.0", [hex: :certifi, repo: "hexpm", optional: true]}], "hexpm", "6e7f1d619b5f61dfabd0a20aa268e575572b542ac31723293a4c1a567d5ef040"},
   "erlex": {:hex, :erlex, "0.2.7", "810e8725f96ab74d17aac676e748627a07bc87eb950d2b83acd29dc047a30595", [:mix], [], "hexpm", "3ed95f79d1a844c3f6bf0cea61e0d5612a42ce56da9c03f01df538685365efb0"},
   "escape": {:hex, :escape, "0.1.0", "548edab75e6e6938b1e199ef59cb8e504bcfd3bcf83471d4ae9a3c7a7a3c7d45", [:mix], [], "hexpm", "a5d8e92db4677155df54bc1306d401b5233875d570d474201db03cb3047491cd"},
+  "event_bus": {:hex, :event_bus, "1.7.0", "29a36fc09e8c4463c82206b6a300fa1d61cf4baf9a7b4e7cf0c3efb99c73998e", [:mix], [], "hexpm", "e556470f49f53060a0696c4bad81341252685011afc69eda25032c8a3a86eb2e"},
   "ex2ms": {:hex, :ex2ms, "1.7.0", "45b9f523d0b777667ded60070d82d871a37e294f0b6c5b8eca86771f00f82ee1", [:mix], [], "hexpm", "2589eee51f81f1b1caa6d08c990b1ad409215fe6f64c73f73c67d36ed10be827"},
   "exleveldb": {:hex, :exleveldb, "0.14.0", "8e9353bbce38482d6971d254c6b98ceb50f3f179c94732b5d17db1be426fca18", [:mix], [{:eleveldb, "~> 2.2.20", [hex: :eleveldb, repo: "hexpm", optional: false]}], "hexpm", "803cd3b4c826a1e17e7e28f6afe224837a743b475e1a48336f186af3dd8636ad"},
   "expo": {:hex, :expo, "0.5.2", "beba786aab8e3c5431813d7a44b828e7b922bfa431d6bfbada0904535342efe2", [:mix], [], "hexpm", "8c9bfa06ca017c9cb4020fabe980bc7fdb1aaec059fd004c2ab3bff03b1c599c"},
@@ -68,6 +69,7 @@
   "sentry": {:hex, :sentry, "10.8.1", "aa45309785e1521416225adb16e0b4d8b957578804527f3c7babb6fefbc5e456", [:mix], [{:hackney, "~> 1.8", [hex: :hackney, repo: "hexpm", optional: true]}, {:jason, "~> 1.1", [hex: :jason, repo: "hexpm", optional: true]}, {:nimble_options, "~> 1.0", [hex: :nimble_options, repo: "hexpm", optional: false]}, {:nimble_ownership, "~> 0.3.0 or ~> 1.0", [hex: :nimble_ownership, repo: "hexpm", optional: false]}, {:phoenix, "~> 1.6", [hex: :phoenix, repo: "hexpm", optional: true]}, {:phoenix_live_view, "~> 0.20 or ~> 1.0", [hex: :phoenix_live_view, repo: "hexpm", optional: true]}, {:plug, "~> 1.6", [hex: :plug, repo: "hexpm", optional: true]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: true]}], "hexpm", "495b3cdadad90ba72eef973aa3dec39b3b8b2a362fe87e2f4ef32133ac3b4097"},
   "snappyer": {:hex, :snappyer, "1.2.10", "023e9ae00e969b0997208b5de7d3b12bb46ec6bc5411e8dc53e7b3f435b8f0fd", [:rebar3], [], "hexpm", "f55bd9ed147e7163cb3acd1e431a7ff2c9e31ceacbb8308786094fb64551c284"},
   "sourceror": {:hex, :sourceror, "1.5.0", "3e65d5fbb1a8e2864ad6411262c8018fee73474f5789dda12285c82999253d5d", [:mix], [], "hexpm", "4a32b5d189d8453f73278c15712f8731b89e9211e50726b798214b303b51bfc7"},
+  "sse": {:hex, :sse, "0.4.0", "f17affacbc4618bac07590eec7bff849aa27d1f71bb3d41da3fd3cb255d16910", [:mix], [{:event_bus, ">= 1.6.0", [hex: :event_bus, repo: "hexpm", optional: false]}, {:plug, ">= 1.4.5", [hex: :plug, repo: "hexpm", optional: false]}], "hexpm", "2dfb9923725b9d5292763c3de9b7798713f5771522823e961a250204917d7efb"},
   "ssl_verify_fun": {:hex, :ssl_verify_fun, "1.1.7", "354c321cf377240c7b8716899e182ce4890c5938111a1296add3ec74cf1715df", [:make, :mix, :rebar3], [], "hexpm", "fe4c190e8f37401d30167c8c405eda19469f34577987c76dde613e838bbc67f8"},
   "statistex": {:hex, :statistex, "1.0.0", "f3dc93f3c0c6c92e5f291704cf62b99b553253d7969e9a5fa713e5481cd858a5", [:mix], [], "hexpm", "ff9d8bee7035028ab4742ff52fc80a2aa35cece833cf5319009b52f1b5a86c27"},
   "stream_data": {:hex, :stream_data, "1.1.2", "05499eaec0443349ff877aaabc6e194e82bda6799b9ce6aaa1aadac15a9fdb4d", [:mix], [], "hexpm", "129558d2c77cbc1eb2f4747acbbea79e181a5da51108457000020a906813a1a9"},

network_params.yaml

@@ -1,9 +1,12 @@
 participants:
   - el_type: geth
+    el_image: ethereum/client-go:v1.14.12
     cl_type: lighthouse
+    cl_image: sigp/lighthouse:v5.3.0
     count: 2
     validator_count: 32
   - el_type: geth
+    el_image: ethereum/client-go:v1.14.12
     cl_type: lambda
     cl_image: lambda_ethereum_consensus:latest
     use_separate_vc: false

test/unit/beacon_api/beacon_api_v1_test.exs

@@ -158,6 +158,8 @@ defmodule Unit.BeaconApiTest.V1 do
   test "node identity" do
     alias LambdaEthereumConsensus.Libp2pPort
     alias LambdaEthereumConsensus.P2P.Metadata
+
+    patch(BeaconApi.EventPubSub, :publish, fn _, _ -> :ok end)
     patch(ForkChoice, :get_fork_version, fn -> ChainSpec.get("DENEB_FORK_VERSION") end)
 
     start_link_supervised!({Libp2pPort, genesis_time: :os.system_time(:second), store: %Store{}})

test/unit/fork_choice/handlers_test.exs

@@ -1,6 +1,8 @@
 defmodule Unit.ForkChoice.HandlersTest do
   use ExUnit.Case
 
+  use Patch
+
   alias LambdaEthereumConsensus.ForkChoice.Handlers
   alias LambdaEthereumConsensus.Utils.Diff
   alias Types.Store
@@ -44,6 +46,8 @@ defmodule Unit.ForkChoice.HandlersTest do
     end
 
     test "upgrades unrealized checkpoints" do
+      patch(BeaconApi.EventPubSub, :publish, fn _, _ -> :ok end)
+
       start_time = 0
       end_time = start_time + ChainSpec.get("SECONDS_PER_SLOT") * ChainSpec.get("SLOTS_PER_EPOCH")