Ensure headers are downcased (#227)

lib/req.ex

@@ -59,12 +59,11 @@ defmodule Req do
         * atom header names are turned into strings, replacing `_` with `-`. For example,
           `:user_agent` becomes `"user-agent"`.
 
-        * string header names are left as is. Because header keys are case-insensitive
-          in both HTTP/1.1 and HTTP/2, it is recommended for header keys to be in
-          lowercase, to avoid sending duplicate keys in a request.
+        * string header names are downcased.
 
-        * `DateTime` header values are encoded as "HTTP date". Otherwise,
-          the header value is encoded with `String.Chars.to_string/1`.
+        * `%DateTime{}` header values are encoded as "HTTP date".
+
+        * other header values are encoded with `String.Chars.to_string/1`.
 
       If you set `:headers` options both in `Req.new/1` and `request/2`, the header lists are merged.
 
@@ -948,10 +947,10 @@ defmodule Req do
       name =
         case name do
           atom when is_atom(atom) ->
-            atom |> Atom.to_string() |> String.replace("_", "-")
+            atom |> Atom.to_string() |> String.replace("_", "-") |> String.downcase(:ascii)
 
           binary when is_binary(binary) ->
-            binary
+            String.downcase(binary, :ascii)
         end
 
       value =
@@ -998,4 +997,14 @@ defmodule Req do
       body: Keyword.get(options, :body, "")
     }
   end
+
+  def __ensure_header_downcase__(name) do
+    downcased = String.downcase(name, :ascii)
+
+    if name != downcased do
+      IO.warn("header names should be downcased, got: #{name}")
+    end
+
+    downcased
+  end
 end

lib/req/request.ex

@@ -56,13 +56,13 @@ defmodule Req.Request do
 
   Public fields are:
 
-    * `:method` - the HTTP request method
+    * `:method` - the HTTP request method.
 
-    * `:url` - the HTTP request URL
+    * `:url` - the HTTP request URL.
 
-    * `:headers` - the HTTP request headers
+    * `:headers` - the HTTP request headers. The header names must be downcased.
 
-    * `:body` - the HTTP request body
+    * `:body` - the HTTP request body.
 
       Can be one of:
 
@@ -304,7 +304,7 @@ defmodule Req.Request do
                [:with_body]
              ) do
           {:ok, status, headers, body} ->
-            headers = for {name, value} <- headers, do: {String.downcase(name), value}
+            headers = for {name, value} <- headers, do: {String.downcase(name, :ascii), value}
             response = %Req.Response{status: status, headers: headers, body: body}
             {request, response}
 
@@ -647,7 +647,7 @@ defmodule Req.Request do
   end
 
   @doc """
-  Returns the values of the header specified by `key`.
+  Returns the values of the header specified by `name`.
 
   ## Examples
 
@@ -657,21 +657,15 @@ defmodule Req.Request do
 
   """
   @spec get_header(t(), binary()) :: [binary()]
-  def get_header(%Req.Request{} = request, key) when is_binary(key) do
-    for {^key, value} <- request.headers, do: value
+  def get_header(%Req.Request{} = request, name) when is_binary(name) do
+    name = Req.__ensure_header_downcase__(name)
+    for {^name, value} <- request.headers, do: value
   end
 
   @doc """
-  Adds a new request header (`key`) if not present, otherwise replaces the
+  Adds a new request header `name` if not present, otherwise replaces the
   previous value of that header with `value`.
 
-  Because header keys are case-insensitive in both HTTP/1.1 and HTTP/2,
-  it is recommended for header keys to be in lowercase, to avoid sending
-  duplicate keys in a request.
-
-  Additionally, requests with mixed-case headers served over HTTP/2 are not
-  considered valid by common clients, resulting in dropped requests.
-
   ## Examples
 
       iex> req = Req.new()
@@ -681,9 +675,10 @@ defmodule Req.Request do
 
   """
   @spec put_header(t(), binary(), binary()) :: t()
-  def put_header(%Req.Request{} = request, key, value)
-      when is_binary(key) and is_binary(value) do
-    %{request | headers: List.keystore(request.headers, key, 0, {key, value})}
+  def put_header(%Req.Request{} = request, name, value)
+      when is_binary(name) and is_binary(value) do
+    name = Req.__ensure_header_downcase__(name)
+    %{request | headers: List.keystore(request.headers, name, 0, {name, value})}
   end
 
   @doc """
@@ -700,13 +695,13 @@ defmodule Req.Request do
   """
   @spec put_headers(t(), [{binary(), binary()}]) :: t()
   def put_headers(%Req.Request{} = request, headers) do
-    for {key, value} <- headers, reduce: request do
-      acc -> put_header(acc, key, value)
+    for {name, value} <- headers, reduce: request do
+      acc -> put_header(acc, name, value)
     end
   end
 
   @doc """
-  Adds a request header (`key`) unless already present.
+  Adds a request header `name` unless already present.
 
   See `put_header/3` for more information.
 
@@ -720,11 +715,11 @@ defmodule Req.Request do
       [{"accept", "application/json"}]
   """
   @spec put_new_header(t(), binary(), binary()) :: t()
-  def put_new_header(%Req.Request{} = request, key, value)
-      when is_binary(key) and is_binary(value) do
-    case get_header(request, key) do
+  def put_new_header(%Req.Request{} = request, name, value)
+      when is_binary(name) and is_binary(value) do
+    case get_header(request, name) do
       [] ->
-        put_header(request, key, value)
+        put_header(request, name, value)
 
       _ ->
         request

lib/req/response.ex

@@ -4,11 +4,11 @@ defmodule Req.Response do
 
   Fields:
 
-    * `:status` - the HTTP status code
+    * `:status` - the HTTP status code.
 
-    * `:headers` - the HTTP response headers
+    * `:headers` - the HTTP response headers. The header names must be downcased.
 
-    * `:body` - the HTTP response body
+    * `:body` - the HTTP response body.
 
     * `:private` - a map reserved for libraries and frameworks to use.
       Prefix the keys with the name of your project to avoid any future
@@ -114,32 +114,34 @@ defmodule Req.Response do
   end
 
   @doc """
-  Returns the values of the header specified by `key`.
+  Returns the values of the header specified by `name`.
 
   ## Examples
 
       iex> Req.Response.get_header(response, "content-type")
       ["application/json"]
   """
   @spec get_header(t(), binary()) :: [binary()]
-  def get_header(%Req.Response{} = response, key) when is_binary(key) do
-    for {^key, value} <- response.headers, do: value
+  def get_header(%Req.Response{} = response, name) when is_binary(name) do
+    name = Req.__ensure_header_downcase__(name)
+    for {^name, value} <- response.headers, do: value
   end
 
   @doc """
-  Adds a new response header (`key`) if not present, otherwise replaces the
+  Adds a new response header `name` if not present, otherwise replaces the
   previous value of that header with `value`.
 
   ## Examples
 
-      iex> Req.Response.put_header(response, "content-type", "application/json").headers
+      iex> resp = Req.Response.put_header(resp, "content-type", "application/json")
+      iex> resp.headers
       [{"content-type", "application/json"}]
-
   """
   @spec put_header(t(), binary(), binary()) :: t()
-  def put_header(%Req.Response{} = response, key, value)
-      when is_binary(key) and is_binary(value) do
-    %{response | headers: List.keystore(response.headers, key, 0, {key, value})}
+  def put_header(%Req.Response{} = response, name, value)
+      when is_binary(name) and is_binary(value) do
+    name = Req.__ensure_header_downcase__(name)
+    %{response | headers: List.keystore(response.headers, name, 0, {name, value})}
   end
 
   @doc """
@@ -156,13 +158,15 @@ defmodule Req.Response do
       []
 
   """
-  def delete_header(%Req.Response{} = response, key) when is_binary(key) do
+  def delete_header(%Req.Response{} = response, name) when is_binary(name) do
+    name_to_delete = Req.__ensure_header_downcase__(name)
+
     %Req.Response{
       response
       | headers:
           for(
             {name, value} <- response.headers,
-            String.downcase(name) != String.downcase(key),
+            name != name_to_delete,
             do: {name, value}
           )
     }