feat: improve decompression middleware

closes #598

lib/tesla/middleware/compression.ex

@@ -61,13 +61,30 @@ defmodule Tesla.Middleware.Compression do
   def decompress({:error, reason}), do: {:error, reason}
 
   def decompress(env) do
+    case decompress_body(env.body, Tesla.get_header(env, "content-encoding")) do
+      nil ->
+        env
+
+      body ->
+        put_decompressed_body(env, body)
+    end
+  end
+
+  defp put_decompressed_body(env, body) do
+    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)
+    |> 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)
   defp decompress_body(body, "deflate"), do: :zlib.unzip(body)
-  defp decompress_body(body, _content_encoding), do: body
+  defp decompress_body(_body, _content_encoding), do: nil
 end
 
 defmodule Tesla.Middleware.CompressRequest do

mix.exs

@@ -20,7 +20,8 @@ defmodule Tesla.Mixfile do
         plt_add_apps: [:mix, :inets, :idna, :ssl_verify_fun, :ex_unit],
         plt_add_deps: :project
       ],
-      docs: docs()
+      docs: docs(),
+      preferred_cli_env: [coveralls: :test, "coveralls.html": :test]
     ]
   end
 

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

@@ -69,6 +69,7 @@ defmodule Tesla.Middleware.CompressionTest do
 
   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
 
@@ -80,6 +81,7 @@ defmodule Tesla.Middleware.CompressionTest do
   test "return unchanged response for unsupported content-encoding" do
     assert {:ok, env} = CompressionResponseClient.get("/response-identity")
     assert env.body == "unchanged"
+    assert env.headers == [{"content-type", "text/plain"}, {"content-encoding", "identity"}]
   end
 
   defmodule CompressRequestDecompressResponseClient do
@@ -114,7 +116,8 @@ 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 +126,7 @@ 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 +138,8 @@ 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 +148,7 @@ 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