feat: improve decompression middleware

closes #598

lib/tesla/middleware.ex

@@ -16,11 +16,11 @@ defmodule Tesla.Middleware do
       Tesla.client([{Tesla.Middleware.BaseUrl, "https://example.com"}])
       
   ## Ordering
-  
+
   The order in which middleware is defined matters. Note that the order when _sending_ the request
   matches the order the middleware was defined in, but the order when _receiving_ the response
   is reversed.
-  
+
   For example, `Tesla.Middleware.DecompressResponse` must come _after_ `Tesla.Middleware.JSON`,
   otherwise the response isn't decompressed before it reaches the JSON parser.
 

lib/tesla/middleware/compression.ex

@@ -61,8 +61,19 @@ defmodule Tesla.Middleware.Compression do
   def decompress({:error, reason}), do: {:error, reason}
 
   def decompress(env) do
+    body = decompress_body(env.body, Tesla.get_header(env, "content-encoding"))
+
+    content_length =
+      body
+      |> byte_size()
+      |> to_string()
+
     env
-    |> Tesla.put_body(decompress_body(env.body, Tesla.get_header(env, "content-encoding")))
+    |> Tesla.put_body(body)
+    # what should happen if the content-encoding is not supported and the body
+    # is not decompressed?
+    |> Tesla.delete_header("content-encoding")
+    |> Tesla.put_header("content-length", content_length)
   end
 
   defp decompress_body(<<31, 139, 8, _::binary>> = body, "gzip"), do: :zlib.gunzip(body)

lib/tesla/middleware/json.ex

@@ -164,6 +164,8 @@ defmodule Tesla.Middleware.DecodeJson do
   """
   @moduledoc since: "1.8.0"
 
+  @behaviour Tesla.Middleware
+
   @impl Tesla.Middleware
   def call(env, next, opts) do
     opts = opts || []
@@ -180,6 +182,8 @@ defmodule Tesla.Middleware.EncodeJson do
   """
   @moduledoc since: "1.8.0"
 
+  @behaviour Tesla.Middleware
+
   @impl Tesla.Middleware
   def call(env, next, opts) do
     opts = opts || []

test/support/test_support.ex

@@ -0,0 +1,7 @@
+defmodule TestSupport do
+  def gzip_headers(env) do
+    env.headers
+    |> Enum.map_join("|", fn {key, value} -> "#{key}: #{value}" end)
+    |> :zlib.gzip()
+  end
+end

test/tesla/middleware/compression_test.exs

@@ -67,8 +67,14 @@ defmodule Tesla.Middleware.CompressionTest do
     end
   end
 
+  test "decompress response body update the headers correctly" do
+    assert {:ok, env} = CompressionResponseClient.get("/response-gzip")
+    assert env.headers == [{"content-type", "text/plain"}, {"content-length", "17"}]
+  end
+
   test "decompress response body (gzip)" do
     assert {:ok, env} = CompressionResponseClient.get("/response-gzip")
+    assert env.headers == [{"content-type", "text/plain"}, {"content-length", "17"}]
     assert env.body == "decompressed gzip"
   end
 
@@ -114,7 +120,8 @@ defmodule Tesla.Middleware.CompressionTest do
       {status, headers, body} =
         case env.url do
           "/" ->
-            {200, [{"content-type", "text/plain"}, {"content-encoding", "gzip"}], env.headers}
+            {200, [{"content-type", "text/plain"}, {"content-encoding", "gzip"}],
+             TestSupport.gzip_headers(env)}
         end
 
       {:ok, %{env | status: status, headers: headers, body: body}}
@@ -123,7 +130,7 @@ defmodule Tesla.Middleware.CompressionTest do
 
   test "Compression headers" do
     assert {:ok, env} = CompressionHeadersClient.get("/")
-    assert env.body == [{"accept-encoding", "gzip, deflate"}]
+    assert env.body == "accept-encoding: gzip, deflate"
   end
 
   defmodule DecompressResponseHeadersClient do
@@ -135,7 +142,8 @@ defmodule Tesla.Middleware.CompressionTest do
       {status, headers, body} =
         case env.url do
           "/" ->
-            {200, [{"content-type", "text/plain"}, {"content-encoding", "gzip"}], env.headers}
+            {200, [{"content-type", "text/plain"}, {"content-encoding", "gzip"}],
+             TestSupport.gzip_headers(env)}
         end
 
       {:ok, %{env | status: status, headers: headers, body: body}}
@@ -144,7 +152,7 @@ defmodule Tesla.Middleware.CompressionTest do
 
   test "Decompress response headers" do
     assert {:ok, env} = DecompressResponseHeadersClient.get("/")
-    assert env.body == [{"accept-encoding", "gzip, deflate"}]
+    assert env.body == "accept-encoding: gzip, deflate"
   end
 
   defmodule CompressRequestHeadersClient do