simple tcp server

Author: akshaykmr

.vscode/launch.json

@@ -0,0 +1,29 @@
+{
+  // Use IntelliSense to learn about possible attributes.
+  // Hover to view descriptions of existing attributes.
+  // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+  "version": "0.2.0",
+  "configurations": [
+    {
+      "type": "mix_task",
+      "name": "mix (Default task)",
+      "request": "launch",
+      "projectDir": "${workspaceRoot}"
+    },
+    {
+      "type": "mix_task",
+      "name": "mix test",
+      "request": "launch",
+      "task": "test",
+      "taskArgs": [
+        "--trace"
+      ],
+      "startApps": true,
+      "projectDir": "${workspaceRoot}",
+      "requireFiles": [
+        "test/**/test_helper.exs",
+        "test/**/*_test.exs"
+      ]
+    }
+  ]
+}

lib/redex_server.ex

@@ -1,4 +1,5 @@
 defmodule Redex.Server do
+  require Logger
   @moduledoc """
   A naive redis-server
   """
@@ -12,7 +13,45 @@ defmodule Redex.Server do
       {:ok, #PID<0.102.0>}
 
   """
-  def start_link do
-    {:ok, self()}
+  def start_link args do
+    Task.start_link(fn -> Redex.Server.accept(args) end)
+  end
+
+  def accept(args) do
+    # The options below mean:
+    #
+    # 1. `:binary` - receives data as binaries (instead of lists)
+    # 2. `packet: :line` - receives data line by line
+    # 3. `active: false` - blocks on `:gen_tcp.recv/2` until data is available
+    # 4. `reuseaddr: true` - allows us to reuse the address if the listener crashes
+    #
+    port = Keyword.get(args, :port, 6379)
+    {:ok, socket} =
+      :gen_tcp.listen(port, [:binary, packet: :line, active: false, reuseaddr: true])
+    Logger.info("Accepting connections on port #{port}")
+    loop_acceptor(socket)
+  end
+
+  defp loop_acceptor(socket) do
+    {:ok, client} = :gen_tcp.accept(socket)
+    serve(client)
+    loop_acceptor(socket)
+  end
+
+  defp serve(socket) do
+    socket
+    |> read_line()
+    |> write_line(socket)
+
+    serve(socket)
+  end
+
+  defp read_line(socket) do
+    {:ok, data} = :gen_tcp.recv(socket, 0)
+    data
+  end
+
+  defp write_line(line, socket) do
+    :gen_tcp.send(socket, line)
   end
 end

lib/test_utils.ex

@@ -0,0 +1,18 @@
+defmodule Redex.TestUtils do
+  def wait_for_server(retries \\ 5) do
+    case :gen_tcp.connect('localhost', 6379, []) do
+      {:ok, socket} ->
+        :gen_tcp.close(socket)
+      {:error, reason} ->
+        cond do
+          retries > 0 ->
+            :timer.sleep(100)
+            wait_for_server(retries - 1)
+          :true ->
+            Mix.raise "Cannot connect to Redis" <>
+                  " (http://localhost:6379):" <>
+                  " #{:inet.format_error(reason)}"
+        end
+    end
+  end
+end

test/redex_test.exs

@@ -4,63 +4,72 @@ defmodule RedexServerTest do
 
   setup do
     IO.puts "starting server"
-    {:ok, server} = Redex.Server.start_link()
+    {:ok, server} = Redex.Server.start_link([])
     %{pid: server}
   end
 
+  setup context do
+    Redex.TestUtils.wait_for_server()
+    context
+  end
+
   test "it starts", %{pid: pid} do
     assert Process.alive?(pid)
   end
+
+  test "it responds to ping", %{pid: pid} do
+
+  end
 end
 
 
-defmodule AssertionTest do
-  use ExUnit.Case, async: true
+# defmodule AssertionTest do
+#   use ExUnit.Case, async: true
 
-  # "setup_all" is called once per module before any test runs
-  setup_all do
-    IO.puts "Starting AssertionTest"
+#   # "setup_all" is called once per module before any test runs
+#   setup_all do
+#     IO.puts "Starting AssertionTest"
 
-    # Context is not updated here
-    :ok
-  end
+#     # Context is not updated here
+#     :ok
+#   end
 
-  # "setup" is called before each test
-  setup do
-    IO.puts "This is a setup callback for #{inspect self()}"
+#   # "setup" is called before each test
+#   setup do
+#     IO.puts "This is a setup callback for #{inspect self()}"
 
-    on_exit fn ->
-      IO.puts "This is invoked once the test is done. Process: #{inspect self()}"
-    end
+#     on_exit fn ->
+#       IO.puts "This is invoked once the test is done. Process: #{inspect self()}"
+#     end
 
-    # Returns extra metadata to be merged into context
-    [hello: "world"]
+#     # Returns extra metadata to be merged into context
+#     [hello: "world"]
 
-    # Similarly, any of the following would work:
-    #   {:ok, [hello: "world"]}
-    #   %{hello: "world"}
-    #   {:ok, %{hello: "world"}}
-  end
+#     # Similarly, any of the following would work:
+#     #   {:ok, [hello: "world"]}
+#     #   %{hello: "world"}
+#     #   {:ok, %{hello: "world"}}
+#   end
 
-  # Same as above, but receives the context as argument
-  setup context do
-    IO.puts "Setting up: #{context.test}"
-    :ok
-  end
+#   # Same as above, but receives the context as argument
+#   setup context do
+#     IO.puts "Setting up: #{context.test}"
+#     :ok
+#   end
 
-  # Setups can also invoke a local or imported function that returns a context
-  setup :invoke_local_or_imported_function
+#   # Setups can also invoke a local or imported function that returns a context
+#   setup :invoke_local_or_imported_function
 
-  test "always pass" do
-    assert true
-  end
+#   test "always pass" do
+#     assert true
+#   end
 
-  test "uses metadata from setup", context do
-    assert context[:hello] == "world"
-    assert context[:from_named_setup] == true
-  end
+#   test "uses metadata from setup", context do
+#     assert context[:hello] == "world"
+#     assert context[:from_named_setup] == true
+#   end
 
-  defp invoke_local_or_imported_function(context) do
-    [from_named_setup: true]
-  end
-end
+#   defp invoke_local_or_imported_function(context) do
+#     [from_named_setup: true]
+#   end
+# end