Factor out WebSocket upgrade validation to its own module & refactor

lib/bandit/websocket/README.md

@@ -17,14 +17,14 @@ The HTTP request containing the upgrade request is first passed to the user's
 application as a standard Plug call. After inspecting the request and deeming it
 a suitable upgrade candidate (via whatever policy the application dictates), the
 user indicates a desire to upgrade the connection to a WebSocket by calling
-`Plug.Conn.upgrade_adapter/3` (this is most commonly done by calling
-`WebSockAdapter.upgrade/4`, which wraps this underlying call in
-a server-agnostic manner). At the conclusion of the `Plug.call/2` callback, 
-`Bandit.Pipeline` will then attempy to upgrade the underlying connection. As
-part of this upgrade process, `Bandit.DelegatingHandler` will switch the
-Handler for the connection to be `Bandit.WebSocket.Handler`. This will cause any
-future communication after the upgrade process to be handled directly by
-Bandit's WebSocket stack.
+`WebSockAdapter.upgrade/4`, which checks that the request is a valid WebSocket
+upgrade request, and then calls `Plug.Conn.upgrade_adapter/3` to signal to
+Bandit that the connection should be upgraded at the conclusion of the request.
+At the conclusion of the `Plug.call/2` callback, `Bandit.Pipeline` will then
+attempt to upgrade the underlying connection. As part of this upgrade process,
+`Bandit.DelegatingHandler` will switch the Handler for the connection to be
+`Bandit.WebSocket.Handler`. This will cause any future communication after the
+upgrade process to be handled directly by Bandit's WebSocket stack.
 
 ## Process model
 
@@ -41,7 +41,7 @@ modeled by the `Bandit.WebSocket.Connection` struct and module.
 
 All data subsequently received by the underlying [Thousand
 Island](https://github.com/mtrudel/thousand_island) library will result in
-a call to `Bandit.WebSocket.Handler.handle_data/3`, which will then attmept to
+a call to `Bandit.WebSocket.Handler.handle_data/3`, which will then attempt to
 parse the data into one or more WebSocket frames. Once a frame has been
 constructed, it is them passed through to the configured `WebSock` handler by
 way of the underlying `Bandit.WebSocket.Connection`.

lib/bandit/websocket/handshake.ex

@@ -6,37 +6,10 @@ defmodule Bandit.WebSocket.Handshake do
 
   @type extensions :: [{String.t(), [{String.t(), String.t() | true}]}]
 
-  @spec valid_upgrade?(Plug.Conn.t()) :: boolean()
-  def valid_upgrade?(%Plug.Conn{} = conn) do
-    validate_upgrade(conn) == :ok
-  end
-
-  @spec validate_upgrade(Plug.Conn.t()) :: :ok | {:error, String.t()}
-  defp validate_upgrade(conn) do
-    # Cases from RFC6455§4.2.1
-    with {:http_version, :"HTTP/1.1"} <- {:http_version, get_http_protocol(conn)},
-         {:method, "GET"} <- {:method, conn.method},
-         {:host_header, header} when header != [] <- {:host_header, get_req_header(conn, "host")},
-         {:upgrade_header, true} <-
-           {:upgrade_header, header_contains(conn, "upgrade", "websocket")},
-         {:connection_header, true} <-
-           {:connection_header, header_contains(conn, "connection", "upgrade")},
-         {:sec_websocket_key_header, true} <-
-           {:sec_websocket_key_header,
-            match?([<<_::binary>>], get_req_header(conn, "sec-websocket-key"))},
-         {:sec_websocket_version_header, ["13"]} <-
-           {:sec_websocket_version_header, get_req_header(conn, "sec-websocket-version")} do
-      :ok
-    else
-      {step, detail} ->
-        {:error, "WebSocket upgrade failed: error in #{step} check: #{inspect(detail)}"}
-    end
-  end
-
   @spec handshake(Plug.Conn.t(), keyword(), keyword()) ::
           {:ok, Plug.Conn.t(), Keyword.t()} | {:error, String.t()}
   def handshake(%Plug.Conn{} = conn, opts, websocket_opts) do
-    with :ok <- validate_upgrade(conn) do
+    with :ok <- Bandit.WebSocket.UpgradeValidation.validate_upgrade(conn) do
       do_handshake(conn, opts, websocket_opts)
     end
   end
@@ -126,19 +99,4 @@ defmodule Bandit.WebSocket.Handshake do
 
     put_resp_header(conn, "sec-websocket-extensions", extensions)
   end
-
-  @spec header_contains(Plug.Conn.t(), field :: String.t(), value :: String.t()) ::
-          true | binary()
-  defp header_contains(conn, field, value) do
-    downcase_value = String.downcase(value, :ascii)
-    header = get_req_header(conn, field)
-
-    header
-    |> Enum.flat_map(&Plug.Conn.Utils.list/1)
-    |> Enum.any?(&(String.downcase(&1, :ascii) == downcase_value))
-    |> case do
-      true -> true
-      false -> "Did not find '#{value}' in '#{header}'"
-    end
-  end
 end

lib/bandit/websocket/upgrade_validation.ex

@@ -0,0 +1,65 @@
+defmodule Bandit.WebSocket.UpgradeValidation do
+  @moduledoc false
+  # Provides validation of WebSocket upgrade requests as described in RFC6455§4.2
+
+  # Validates that the request satisfies the requirements to issue a WebSocket upgrade response.
+  # Validations are performed based on the clauses laid out in RFC6455§4.2
+  #
+  # This function does not actually perform an upgrade or change the connection in any way
+  #
+  # Returns `:ok` if the connection satisfies the requirements for a WebSocket upgrade, and
+  # `{:error, reason}` if not
+  #
+  @spec validate_upgrade(Plug.Conn.t()) :: :ok | {:error, String.t()}
+  def validate_upgrade(conn) do
+    case Plug.Conn.get_http_protocol(conn) do
+      :"HTTP/1.1" -> validate_upgrade_http1(conn)
+      other -> {:error, "HTTP version #{other} unsupported"}
+    end
+  end
+
+  # Validate the conn per RFC6455§4.2.1
+  defp validate_upgrade_http1(conn) do
+    with :ok <- assert_method(conn, "GET"),
+         :ok <- assert_header_nonempty(conn, "host"),
+         :ok <- assert_header_contains(conn, "connection", "upgrade"),
+         :ok <- assert_header_contains(conn, "upgrade", "websocket"),
+         :ok <- assert_header_nonempty(conn, "sec-websocket-key"),
+         :ok <- assert_header_equals(conn, "sec-websocket-version", "13") do
+      :ok
+    end
+  end
+
+  defp assert_method(conn, verb) do
+    case conn.method do
+      ^verb -> :ok
+      other -> {:error, "HTTP method #{other} unsupported"}
+    end
+  end
+
+  defp assert_header_nonempty(conn, header) do
+    case Plug.Conn.get_req_header(conn, header) do
+      [] -> {:error, "Header #{header} is absent"}
+      _ -> :ok
+    end
+  end
+
+  defp assert_header_equals(conn, header, value) do
+    case Plug.Conn.get_req_header(conn, header) |> Enum.map(&String.downcase(&1, :ascii)) do
+      [^value] -> :ok
+      header_value -> {:error, "Header #{header} #{inspect(header_value)} not equal to #{value}"}
+    end
+  end
+
+  defp assert_header_contains(conn, header, value) do
+    header_value = Plug.Conn.get_req_header(conn, header)
+
+    header_value
+    |> Enum.flat_map(&Plug.Conn.Utils.list/1)
+    |> Enum.any?(&(String.downcase(&1, :ascii) == value))
+    |> case do
+      true -> :ok
+      false -> {:error, "Header #{header} #{inspect(header_value)} does not contain #{value}"}
+    end
+  end
+end

test/bandit/http1/request_test.exs

@@ -638,13 +638,12 @@ defmodule HTTP1RequestTest do
           )
 
           assert SimpleHTTP1Client.recv_reply(client)
-                 ~> {:ok, "400 Bad Request", list(),
-                  "WebSocket upgrade failed: error in method check: \"POST\""}
+                 ~> {:ok, "400 Bad Request", list(), "HTTP method POST unsupported"}
 
           Process.sleep(100)
         end)
 
-      assert errors =~ "WebSocket upgrade failed: error in method check: \\\"POST\\\""
+      assert errors =~ "HTTP method POST unsupported"
     end
 
     test "returns a 400 and errors loudly in cases where an upgrade is indicated but upgrade header is incorrect",
@@ -668,13 +667,12 @@ defmodule HTTP1RequestTest do
 
           assert SimpleHTTP1Client.recv_reply(client)
                  ~> {:ok, "400 Bad Request", list(),
-                  "WebSocket upgrade failed: error in upgrade_header check: \"Did not find 'websocket' in 'NOPE'\""}
+                  "Header upgrade [\"NOPE\"] does not contain websocket"}
 
           Process.sleep(100)
         end)
 
-      assert errors =~
-               "WebSocket upgrade failed: error in upgrade_header check: \\\"Did not find 'websocket' in 'NOPE'\\\""
+      assert errors =~ "Header upgrade [\\\"NOPE\\\"] does not contain websocket"
     end
 
     test "returns a 400 and errors loudly in cases where an upgrade is indicated but connection header is incorrect",
@@ -698,13 +696,12 @@ defmodule HTTP1RequestTest do
 
           assert SimpleHTTP1Client.recv_reply(client)
                  ~> {:ok, "400 Bad Request", list(),
-                  "WebSocket upgrade failed: error in connection_header check: \"Did not find 'upgrade' in 'NOPE'\""}
+                  "Header connection [\"NOPE\"] does not contain upgrade"}
 
           Process.sleep(100)
         end)
 
-      assert errors =~
-               "WebSocket upgrade failed: error in connection_header check: \\\"Did not find 'upgrade' in 'NOPE'\\\""
+      assert errors =~ "Header connection [\\\"NOPE\\\"] does not contain upgrade"
     end
 
     test "returns a 400 and errors loudly in cases where an upgrade is indicated but key header is incorrect",
@@ -726,13 +723,12 @@ defmodule HTTP1RequestTest do
           )
 
           assert SimpleHTTP1Client.recv_reply(client)
-                 ~> {:ok, "400 Bad Request", list(),
-                  "WebSocket upgrade failed: error in sec_websocket_key_header check: false"}
+                 ~> {:ok, "400 Bad Request", list(), "Header sec-websocket-key is absent"}
 
           Process.sleep(100)
         end)
 
-      assert errors =~ "WebSocket upgrade failed: error in sec_websocket_key_header check: false"
+      assert errors =~ "Header sec-websocket-key is absent"
     end
 
     test "returns a 400 and errors loudly in cases where an upgrade is indicated but version header is incorrect",
@@ -756,13 +752,12 @@ defmodule HTTP1RequestTest do
 
           assert SimpleHTTP1Client.recv_reply(client)
                  ~> {:ok, "400 Bad Request", list(),
-                  "WebSocket upgrade failed: error in sec_websocket_version_header check: [\"99\"]"}
+                  "Header sec-websocket-version [\"99\"] not equal to 13"}
 
           Process.sleep(100)
         end)
 
-      assert errors =~
-               "WebSocket upgrade failed: error in sec_websocket_version_header check: [\\\"99\\\"]"
+      assert errors =~ "Header sec-websocket-version [\\\"99\\\"] not equal to 13"
     end
 
     test "returns a 400 and errors loudly if websocket support is not enabled", context do

test/bandit/websocket/autobahn_test.exs

@@ -16,10 +16,7 @@ defmodule WebsocketAutobahnTest do
 
   @impl Plug
   def call(conn, _opts) do
-    case Bandit.WebSocket.Handshake.valid_upgrade?(conn) do
-      true -> Plug.Conn.upgrade_adapter(conn, :websocket, {EchoWebSock, :ok, compress: true})
-      false -> Plug.Conn.send_resp(conn, 204, <<>>)
-    end
+    Plug.Conn.upgrade_adapter(conn, :websocket, {EchoWebSock, :ok, compress: true})
   end
 
   @tag capture_log: true