Properly handle multiple missing headers.

Author: DevL

README.md

@@ -66,14 +66,29 @@ end
 If the header is missing or set to `nil` the status code, a status code of 400
 (bad request) will be returned before the plug pipeline is halted. Notice that
 the function specified as a callback needs to be a public function as it'll be
-invoked from another module.
+invoked from another module. Also notice that the callback must return a `Plug.Conn` struct.
 
 Lastly, it's possible to extract multiple headers at the same time.
-
 ```elixir
   plug PlugRequireHeader, headers: [api_key: "x-api-key", magic: "x-magic"]
 ```
 
+If extracting multiple headers _and_ specifying an `:on_missing` callback, be aware
+that the callback will be invoked once for each missing header. Be careful to not send
+a response as you can easily run into raising a `Plug.Conn.AlreadySentError`. A way of
+avoiding this is to have your callback function pattern match on the state of the `conn`.
+```elixir
+  plug PlugRequireHeader, headers: [api_key: "x-api-key", secret: "x-secret"], on_missing: {__MODULE__, :handle_missing_header}
+
+  def handle_missing_header(%Plug.Conn{state: :sent} = conn, _), do: conn
+  def handle_missing_header(conn, missing_header_key) do
+    conn
+    |> send_resp(Status.code(:bad_request), "Missing header: #{missing_header_key}")
+    |> halt
+  end
+```
+This example will only send a response for the first missing header.
+
 ## Planned features
 
 * Make the action taken when a required header is missing more configurable.

lib/plug_require_header.ex

@@ -2,7 +2,7 @@ defmodule PlugRequireHeader do
   import Plug.Conn
   alias Plug.Conn.Status
 
-  @vsn "0.3.1"
+  @vsn "0.3.2"
   @doc false
   def version, do: @vsn
 
@@ -71,6 +71,7 @@ defmodule PlugRequireHeader do
     conn |> assign(key, value)
   end
 
+  defp halt_connection(%Plug.Conn{halted: true} = conn, _), do: conn
   defp halt_connection(conn, _) do
     conn
     |> send_resp(Status.code(:forbidden), "")

mix.exs

@@ -4,7 +4,7 @@ defmodule PlugRequireHeader.Mixfile do
   def project do
     [
       app: :plug_require_header,
-      version: "0.3.1",
+      version: "0.3.2",
       name: "PlugRequireHeader",
       source_url: "https://github.com/DevL/plug_require_header",
       elixir: "~> 1.0",

test/plug_require_header_test.exs

@@ -49,18 +49,35 @@ defmodule PlugRequireHeaderTest do
     connection = conn(:get, "/")
     |> put_req_header("x-api-key", "12345")
     |> put_req_header("x-secret", "handshake")
-    response = TestAppWithCallbackAndMultipleRequiredHeaders.call(connection, [])
+    response = TestAppWithMultipleRequiredHeaders.call(connection, [])
 
     assert response.status == Status.code(:ok)
     assert response.resp_body == "API key: 12345 and the secret handshake"
   end
 
+  test "block request missing one of several required headers" do
+    connection = conn(:get, "/")
+    |> put_req_header("x-api-key", "12345")
+    response = TestAppWithMultipleRequiredHeaders.call(connection, [])
+
+    assert response.status == Status.code(:forbidden)
+    assert response.resp_body == ""
+  end
+
+  test "block request missing multiple required headers" do
+    connection = conn(:get, "/")
+    response = TestAppWithMultipleRequiredHeaders.call(connection, [])
+
+    assert response.status == Status.code(:forbidden)
+    assert response.resp_body == ""
+  end
+
   test "invoke a callback function if any of the required headers are missing" do
     connection = conn(:get, "/")
     |> put_req_header("x-api-key", "12345")
     response = TestAppWithCallbackAndMultipleRequiredHeaders.call(connection, [])
 
-    assert response.status == Status.code(:bad_request)
-    assert response.resp_body == "Missing header: x-secret"
+    assert response.status == Status.code(:ok)
+    assert response.resp_body == "API key: 12345 and the secret is missing"
   end
 end

test/test_helper.exs

@@ -35,16 +35,26 @@ defmodule TestAppWithCallback do
   end
 end
 
+defmodule TestAppWithMultipleRequiredHeaders do
+  use AppMaker, headers: [api_key: "x-api-key", secret: "x-secret"]
+
+  get "/" do
+    send_resp(conn, Status.code(:ok), "API key: #{conn.assigns[:api_key]} and the secret #{conn.assigns[:secret]}")
+  end
+end
+
 defmodule TestAppWithCallbackAndMultipleRequiredHeaders do
   use AppMaker, headers: [api_key: "x-api-key", secret: "x-secret"], on_missing: {__MODULE__, :callback}
 
   get "/" do
     send_resp(conn, Status.code(:ok), "API key: #{conn.assigns[:api_key]} and the secret #{conn.assigns[:secret]}")
   end
 
-  def callback(conn, missing_header_key) do
-    conn
-    |> send_resp(Status.code(:bad_request), "Missing header: #{missing_header_key}")
-    |> halt
+  def callback(conn, "x-api-key") do
+    conn |> assign :api_key, "not available"
+  end
+
+  def callback(conn, "x-secret") do
+    conn |> assign :secret, "is missing"
   end
 end