Set content-length when decompressing

lib/req/steps.ex

@@ -861,6 +861,9 @@ defmodule Req.Steps do
   | zstd          | `:ezstd.decompress/1` (if [ezstd] is installed) |
   | _other_       | Returns data as is                              |
 
+  This step updates the following headers to reflect the changes:
+  - `content-length` is set to the length of the decompressed body
+
   ## Options
 
     * `:raw` - if set to `true`, disables response body decompression. Defaults to `false`.
@@ -902,7 +905,14 @@ defmodule Req.Steps do
       {request, response}
     else
       compression_algorithms = get_content_encoding_header(response.headers)
-      {request, update_in(response.body, &decompress_body(&1, compression_algorithms))}
+      decompressed_body = decompress_body(response.body, compression_algorithms)
+      decompressed_content_length = decompressed_body |> byte_size() |> to_string()
+
+      response =
+        %Req.Response{response | body: decompressed_body}
+        |> Req.Response.put_header("content-length", decompressed_content_length)
+
+      {request, response}
     end
   end
 

test/req/steps_test.exs

@@ -370,6 +370,24 @@ defmodule Req.StepsTest do
 
       assert Req.head!(c.url).body == ""
     end
+
+    test "recalculate content-length when decompressing", c do
+      body = "foo"
+      gzipped_body = :zlib.gzip(body)
+
+      assert byte_size(body) != byte_size(gzipped_body)
+
+      Bypass.expect(c.bypass, "GET", "/", fn conn ->
+        conn
+        |> Plug.Conn.put_resp_header("content-encoding", "gzip")
+        |> Plug.Conn.put_resp_header("content-length", gzipped_body |> byte_size() |> to_string())
+        |> Plug.Conn.send_resp(200, gzipped_body)
+      end)
+
+      response = Req.get!(c.url)
+      [content_length] = Req.Response.get_header(response, "content-length")
+      assert String.to_integer(content_length) == byte_size(body)
+    end
   end
 
   describe "output" do