Merge pull request #2 from maxohq/feat/reconnect

Feat: graceful reconnection handling

.gitignore

@@ -27,3 +27,6 @@ surrealix-*.tar
 
 # SurrealDB shell history
 history.txt
+
+# SurrealDB data
+data.db/

CHANGELOG.md

@@ -1,3 +1,9 @@
+## v0.1.5 (2023-11-12)
+
+- graceful reconnection handing
+- ability to register on-connect callbacks
+- ability to configure max backoff / step duration for connection retries
+
 ## v0.1.4 (2023-11-11)
 
 - much simpler handling for live query callbacks (https://github.com/maxohq/surrealix/commit/c87fe9b3853d090cb622a2478595b99a213d7fa9)

README.md

@@ -47,6 +47,37 @@ end)
 Surrealix.all_live_queries(pid)
 ```
 
+## Handling reconnection
+
+To properly deal with connection drops, provide an `on_auth`-callback when starting a Surrealix Socket. `on_auth` callbacks should include logic to authenticate the connection and select a namespace / database.
+
+This callback is called in a non-blocking fashion, so it is important to wait until the `on_auth`-callback is finished. This is done via `Surrealix.wait_until_auth_ready(pid)` function, that checks auth status via busy-waiting.
+
+Live queries that were setup via `Surrealix.live_query(pid, sql, callback)` function are registed on SocketState and will be re-established after a successful reconnection.
+
+```elixir
+{:ok, pid} =
+    Surrealix.start(
+      on_auth: fn pid, _state ->
+        IO.puts("PID: #{inspect(pid)}")
+        Surrealix.signin(pid, %{user: "root", pass: "root"}) |> IO.inspect(label: :signin)
+        Surrealix.use(pid, "test", "test") |> IO.inspect(label: :use)
+      end
+    )
+
+# blocks until the `on_auth` callback is executed
+Surrealix.wait_until_auth_ready(pid)
+
+# now we can execute queries, that require auth
+Surrealix.live_query(pid, "LIVE SELECT * FROM user;", fn data, query_id ->
+  IO.inspect({data, query_id}, label: "callback")
+end)
+
+Surrealix.live_query(pid, "LIVE SELECT * FROM person;", fn data, query_id ->
+  IO.inspect({data, query_id}, label: "callback")
+end)
+```
+
 ## Telemetry
 Currently library publishes only 3 events:
 ```elixir
@@ -70,8 +101,9 @@ Surrealix.Telemetry.Logger.setup()
 
 ```elixir
 ## in config.exs / runtime.exs file
-# default 5000
-config :surrealix, timeout: :infinity
+config :surrealix, backoff_max: 2000
+config :surrealix, backoff_step: 50
+config :surrealix, timeout: :infinity # default 5000
 config :surrealix, :conn,
   hostname: "0.0.0.0",
   port: 8000

bin/sur-server.sh

@@ -14,5 +14,4 @@ surreal start \
     --allow-funcs \
     --allow-net \
     --bind 0.0.0.0:8000 \
-    memory
-    ## file:mydatabase.db
+    file:data.db

config/config.exs

@@ -8,6 +8,8 @@ config :logger, :console,
 
   level: :warning
 
+config :surrealix, :timeout, 5000
+
 config :surrealix, :conn,
   hostname: "0.0.0.0",
   port: 8000

gen/src/ApiGenerator.ts

@@ -79,7 +79,7 @@ export class ApiGenerator extends GenBase {
     Show all currently registered live queries (SQL)
     """
     def all_live_queries(pid) do
-      :sys.get_state(pid) |> SocketState.all_lq()
+      :sys.get_state(pid) |> SocketState.all_live_queries()
     end
 
     @doc """
@@ -88,16 +88,14 @@ export class ApiGenerator extends GenBase {
     Params:
         sql: string
         vars: map with variables to interpolate into SQL
-        callback: fn (event, data, config)
+        callback: fn (data, live_query_id)
     """
-    @spec live_query(pid(), String.t(), map(), (any, any, list() -> any)) :: :ok
+    @spec live_query(pid(), String.t(), map(), (any, String.t() -> any)) :: :ok
     def live_query(pid, sql, vars \\\\ %{}, callback) do
       with {:sql_live_check, true} <- {:sql_live_check, Util.is_live_query_stmt(sql)},
-            {:ok, res} <- query(pid, sql, vars),
-            %{"result" => [%{"result" => lq_id}]} <- res do
-        event = [:live_query, lq_id]
-        :ok = Surrealix.Dispatch.attach("#{lq_id}_main", event, callback)
-        :ok = WebSockex.cast(pid, {:register_lq, sql, lq_id})
+          {:ok, res} <- query(pid, sql, vars),
+          %{"result" => [%{"result" => lq_id}]} <- res do
+        :ok = WebSockex.cast(pid, {:register_live_query, sql, lq_id, callback})
         {:ok, res}
       else
         {:sql_live_check, false} -> {:error, "Not a live query: \`#{sql}\`!"}

lib/sand.ex

@@ -0,0 +1,24 @@
+defmodule Sand do
+  def run do
+    {:ok, pid} =
+      Surrealix.start(
+        on_auth: fn pid, _state ->
+          IO.puts("PID: #{inspect(pid)}")
+          Surrealix.signin(pid, %{user: "root", pass: "root"}) |> IO.inspect(label: :signin)
+          Surrealix.use(pid, "test", "test") |> IO.inspect(label: :use)
+        end
+      )
+
+    # blocks until the `on_auth` callback is executed
+    Surrealix.wait_until_auth_ready(pid)
+
+    # now we can execute normal "CRUD" queries
+    Surrealix.live_query(pid, "LIVE SELECT * FROM user;", fn data, query_id ->
+      IO.inspect({data, query_id}, label: "callback")
+    end)
+
+    Surrealix.live_query(pid, "LIVE SELECT * FROM person;", fn data, query_id ->
+      IO.inspect({data, query_id}, label: "callback")
+    end)
+  end
+end

lib/surrealix.ex

@@ -16,6 +16,9 @@ defmodule Surrealix do
   Show all currently registered live queries (SQL)
   """
   defdelegate all_live_queries(pid), to: Api
+  defdelegate reset_live_queries(pid), to: Socket
+  defdelegate set_auth_ready(pid, value), to: Socket
+  defdelegate wait_until_auth_ready(pid), to: Socket
 
   @doc """
   Convenience method, that combines sending an query (live_query) and registering a callback

lib/surrealix/api.ex

@@ -18,7 +18,7 @@ defmodule Surrealix.Api do
   Show all currently registered live queries (SQL)
   """
   def all_live_queries(pid) do
-    :sys.get_state(pid) |> SocketState.all_lq()
+    :sys.get_state(pid) |> SocketState.all_live_queries()
   end
 
   @doc """
@@ -27,14 +27,14 @@ defmodule Surrealix.Api do
   Params:
       sql: string
       vars: map with variables to interpolate into SQL
-      callback: fn (event, data, config)
+      callback: fn (data, live_query_id)
   """
-  @spec live_query(pid(), String.t(), map(), (any, any, list() -> any)) :: :ok
+  @spec live_query(pid(), String.t(), map(), (any, String.t() -> any)) :: :ok
   def live_query(pid, sql, vars \\ %{}, callback) do
     with {:sql_live_check, true} <- {:sql_live_check, Util.is_live_query_stmt(sql)},
          {:ok, res} <- query(pid, sql, vars),
          %{"result" => [%{"result" => lq_id}]} <- res do
-      :ok = WebSockex.cast(pid, {:register_lq, sql, lq_id, callback})
+      :ok = WebSockex.cast(pid, {:register_live_query, sql, lq_id, callback})
       {:ok, res}
     else
       {:sql_live_check, false} -> {:error, "Not a live query: `#{sql}`!"}

lib/surrealix/application.ex

@@ -5,7 +5,9 @@ defmodule Surrealix.Application do
 
   @impl true
   def start(_type, _args) do
-    children = []
+    children = [
+      {Surrealix.RescueProcess, []}
+    ]
 
     opts = [strategy: :one_for_one, name: Surrealix.Supervisor]
     Supervisor.start_link(children, opts)

lib/surrealix/config.ex

@@ -20,5 +20,12 @@ defmodule Surrealix.Config do
   def base_conn_opts, do: @base_connection_opts
 
   @timeout Application.compile_env(:surrealix, :timeout, 5000)
+
+  def default_timeout, do: @timeout
   def task_opts_default, do: [timeout: @timeout]
+
+  @backoff_max Application.compile_env(:surrealix, :backoff_max, 2000)
+  @backoff_step Application.compile_env(:surrealix, :backoff_step, 50)
+  def backoff_max, do: @backoff_max
+  def backoff_step, do: @backoff_step
 end

lib/surrealix/patiently.ex

@@ -0,0 +1,134 @@
+defmodule Surrealix.Patiently do
+  alias Surrealix.Patiently
+  ## https://github.com/dantswain/patiently/blob/main/lib/patiently.ex
+  @moduledoc false
+  @type iteration :: (-> term)
+  @type reducer :: (term -> term)
+  @type predicate :: (term -> boolean)
+  @type condition :: (-> boolean)
+  @type opt :: {:dwell, pos_integer} | {:max_tries, pos_integer}
+  @type opts :: [opt]
+
+  defmodule GaveUp do
+    @moduledoc """
+    Exception raised by Patiently when a condition fails to converge
+    """
+
+    defexception message: nil
+    @type t :: %__MODULE__{__exception__: true}
+
+    @doc false
+    @spec exception({pos_integer, pos_integer}) :: t
+    def exception({dwell, max_tries}) do
+      message =
+        "Gave up waiting for condition after #{max_tries} " <>
+          "iterations waiting #{dwell} msec between tries."
+
+      %Patiently.GaveUp{message: message}
+    end
+  end
+
+  @default_dwell 100
+  @default_tries 10
+
+  @spec wait_for(condition, opts) :: :ok | :error
+  def wait_for(condition, opts \\ []) do
+    wait_while(condition, & &1, opts)
+  end
+
+  @spec wait_for!(condition, opts) :: :ok | no_return
+  def wait_for!(condition, opts \\ []) do
+    ok_or_raise(wait_for(condition, opts), opts)
+  end
+
+  @spec wait_for(iteration, predicate, opts) :: :ok | :error
+  def wait_for(iteration, condition, opts) do
+    wait_while(iteration, condition, opts)
+  end
+
+  @spec wait_for!(iteration, predicate, opts) :: :ok | no_return
+  def wait_for!(iteration, condition, opts) do
+    ok_or_raise(wait_for(iteration, condition, opts), opts)
+  end
+
+  @spec wait_reduce(reducer, predicate, term, opts) :: {:ok, term} | {:error, term}
+  def wait_reduce(reducer, predicate, acc0, opts) do
+    wait_reduce_loop(reducer, predicate, acc0, 0, opts)
+  end
+
+  @spec wait_reduce!(reducer, predicate, term, opts) :: {:ok, term} | no_return
+  def wait_reduce!(reducer, predicate, acc0, opts) do
+    ok_or_raise(wait_reduce_loop(reducer, predicate, acc0, 0, opts), opts)
+  end
+
+  @spec wait_flatten(iteration, predicate | pos_integer, opts) :: {:ok, [term]} | {:error, [term]}
+  def wait_flatten(iteration, predicate, opts \\ [])
+
+  def wait_flatten(iteration, min_length, opts) when is_integer(min_length) and min_length > 0 do
+    wait_flatten(iteration, fn acc -> length(acc) >= min_length end, opts)
+  end
+
+  def wait_flatten(iteration, predicate, opts) when is_function(predicate, 1) do
+    reducer = fn acc -> List.flatten([iteration.() | acc]) end
+    wait_reduce_loop(reducer, predicate, [], 0, opts)
+  end
+
+  @spec wait_flatten!(iteration, predicate | pos_integer, opts) :: {:ok, [term]} | no_return
+  def wait_flatten!(iteration, predicate_or_min_length, opts) do
+    ok_or_raise(wait_flatten(iteration, predicate_or_min_length, opts), opts)
+  end
+
+  @spec wait_for_death(pid, opts) :: :ok | :error
+  def wait_for_death(pid, opts \\ []) do
+    wait_for(fn -> !Process.alive?(pid) end, opts)
+  end
+
+  @spec wait_for_death!(pid, opts) :: :ok | no_return
+  def wait_for_death!(pid, opts \\ []) do
+    ok_or_raise(wait_for_death(pid, opts), opts)
+  end
+
+  defp ok_or_raise(:ok, _), do: :ok
+  defp ok_or_raise({:ok, acc}, _), do: {:ok, acc}
+
+  defp ok_or_raise(:error, opts) do
+    raise Patiently.GaveUp, {dwell(opts), max_tries(opts)}
+  end
+
+  defp ok_or_raise({:error, _}, opts) do
+    raise Patiently.GaveUp, {dwell(opts), max_tries(opts)}
+  end
+
+  defp just_status({:ok, _}), do: :ok
+  defp just_status({:error, _}), do: :error
+
+  defp wait_while(poller, condition, opts) do
+    reducer = fn acc -> [poller.() | acc] end
+    predicate = fn [most_recent | _] -> condition.(most_recent) end
+    ok_or_err = wait_reduce_loop(reducer, predicate, [], 0, opts)
+    just_status(ok_or_err)
+  end
+
+  defp wait_reduce_loop(reducer, predicate, acc, tries, opts) do
+    acc_out = reducer.(acc)
+
+    if predicate.(acc_out) do
+      {:ok, acc_out}
+    else
+      if tries >= max_tries(opts) do
+        {:error, acc_out}
+      else
+        :timer.sleep(dwell(opts))
+        wait_reduce_loop(reducer, predicate, acc_out, tries + 1, opts)
+      end
+    end
+  end
+
+  defp dwell(opts) do
+    Keyword.get(opts, :dwell, @default_dwell)
+  end
+
+  defp max_tries(opts) do
+    Keyword.get(opts, :max_tries, @default_tries)
+  end
+end

lib/surrealix/rescue_process.ex

@@ -0,0 +1,54 @@
+defmodule Surrealix.RescueProcess do
+  @moduledoc """
+  This module is responsible to execute callbacks for on_auth hooks, that happen after a connection is established.
+  This can not be done direcly in the `handle_connect` callback, since then it blocks the execution of the WebSockex process.
+
+  To workaround this issue, we delegate this responsibility to a `RescueProcess`, that executes those callbacks out-of-band.
+  Also we need to use `GenServer.cast`, so that the Socket can properly continue and not be deadlocked.
+  """
+  use GenServer
+  alias Surrealix.SocketState
+
+  def start_link([]) do
+    GenServer.start_link(__MODULE__, [], name: __MODULE__)
+  end
+
+  def execute_callback({socket_pid, state = %SocketState{}}) do
+    GenServer.cast(__MODULE__, {:execute, socket_pid, state})
+  end
+
+  #################
+  # Callbacks
+  #################
+
+  @impl true
+  def init([]) do
+    {:ok, []}
+  end
+
+  @impl true
+  def handle_cast({:execute, socket_pid, socket_state = %SocketState{}}, _state) do
+    if(!is_nil(socket_state.on_auth)) do
+      # set AUTH status to false, so that the busy-waiting does not trigger
+      Surrealix.set_auth_ready(socket_pid, false)
+
+      # on_auth callback used to login / and pick NS / DB
+      socket_state.on_auth.(socket_pid, socket_state)
+
+      # now reconnect live queries
+      queries = SocketState.all_live_queries(socket_state)
+      # we need to reset the current state of live queries, since the connection was dead anyways
+      Surrealix.reset_live_queries(socket_pid)
+
+      # now we re-establish all live queries, that we very listening to before the connection drop.
+      for {sql, callback} <- queries do
+        Surrealix.live_query(socket_pid, sql, callback)
+      end
+
+      # set AUTH status to true, so `Surrealix.wait_until_auth_ready(pid)` unblocks and allows further queries on the authenticated socket.
+      Surrealix.set_auth_ready(socket_pid, true)
+    end
+
+    {:noreply, []}
+  end
+end