Remove support for deflate compression

Closes #215

Per https://zlib.net/zlib_faq.html#faq39

> What's the difference between the "gzip" and "deflate" HTTP 1.1 encodings?
>
> "gzip" is the gzip format, and "deflate" is the zlib format. They
> should probably have called the second one "zlib" instead to avoid
> confusion with the raw deflate compressed data format. While the HTTP
> 1.1 RFC 2616 correctly points to the zlib specification in RFC 1950 for
> the "deflate" transfer encoding, there have been reports of servers and
> browsers that incorrectly produce or expect raw deflate data per the
> deflate specification in RFC 1951, most notably Microsoft. So even
> though the "deflate" transfer encoding using the zlib format would be
> the more efficient approach (and in fact exactly what the zlib format
> was designed for), using the "gzip" transfer encoding is probably more
> reliable due to an unfortunate choice of name on the part of the HTTP
> 1.1 authors.
>
> Bottom line: use the gzip format for HTTP 1.1 encoding.

README.md

@@ -12,7 +12,7 @@ Req is a batteries-included HTTP client for Elixir.
 
   * Extensibility via request, response, and error steps.
 
-  * Request body compression and automatic response body decompression (via [`compress_body`], [`compressed`], and [`decompress_body`] steps). Supports gzip, deflate, brotli and zstd decompression.
+  * Request body compression and automatic response body decompression (via [`compress_body`], [`compressed`], and [`decompress_body`] steps). Supports gzip, brotli, and zstd decompression.
 
   * Request body encoding and automatic response body decoding (via [`encode_body`] and [`decode_body`] steps.)
 

lib/req/request.ex

@@ -218,7 +218,7 @@ defmodule Req.Request do
 
       Req.get!(req, url: "https://httpbin.org/json", print_headers: true).status
       # Outputs:
-      # > accept-encoding: br, gzip, deflate
+      # > accept-encoding: br, gzip
       # > user-agent: req/0.3.0-dev
       # < date: Wed, 11 May 2022 11:10:47 GMT
       # < content-type: application/json
@@ -228,7 +228,7 @@ defmodule Req.Request do
       req = Req.new() |> PrintHeaders.attach(print_headers: true)
       Req.get!(req, url: "https://httpbin.org/json").status
       # Outputs:
-      # > accept-encoding: br, gzip, deflate
+      # > accept-encoding: br, gzip
       # ...
       200
 

lib/req/steps.ex

@@ -190,7 +190,6 @@ defmodule Req.Steps do
   Supported formats:
 
     * `gzip`
-    * `deflate`
     * `br` (if [brotli] is installed)
     * `zstd` (if [ezstd] is installed)
 
@@ -272,7 +271,7 @@ defmodule Req.Steps do
   end
 
   defp supported_accept_encoding do
-    value = "gzip, deflate"
+    value = "gzip"
     value = if brotli_loaded?(), do: "br, " <> value, else: value
     if ezstd_loaded?(), do: "zstd, " <> value, else: value
   end
@@ -812,7 +811,6 @@ defmodule Req.Steps do
   | Format        | Decoder                                         |
   | ------------- | ----------------------------------------------- |
   | gzip, x-gzip  | `:zlib.gunzip/1`                                |
-  | deflate       | `:zlib.unzip/1`                                 |
   | br            | `:brotli.decode/1` (if [brotli] is installed)   |
   | zstd          | `:ezstd.decompress/1` (if [ezstd] is installed) |
   | identity      | Returns data as is                              |
@@ -868,10 +866,6 @@ defmodule Req.Steps do
     :zlib.gunzip(body)
   end
 
-  defp decompress_with_algorithm("deflate", body) do
-    :zlib.unzip(body)
-  end
-
   defp decompress_with_algorithm("br", body) do
     if brotli_loaded?() do
       {:ok, decompressed} = :brotli.decode(body)

test/req/request_test.exs

@@ -244,7 +244,7 @@ defmodule Req.RequestTest do
 
     assert [
              {"user-agent", "req/" <> _},
-             {"accept-encoding", "zstd, br, gzip, deflate"},
+             {"accept-encoding", "zstd, br, gzip"},
              {"authorization", ^authorization}
            ] = request.headers
   end

test/req/steps_test.exs

@@ -242,8 +242,8 @@ defmodule Req.StepsTest do
     test "multiple codecs", c do
       Bypass.expect(c.bypass, "GET", "/", fn conn ->
         conn
-        |> Plug.Conn.put_resp_header("content-encoding", "gzip, deflate")
-        |> Plug.Conn.send_resp(200, "foo" |> :zlib.gzip() |> :zlib.zip())
+        |> Plug.Conn.put_resp_header("content-encoding", "gzip, zstd")
+        |> Plug.Conn.send_resp(200, "foo" |> :zlib.gzip() |> :ezstd.compress())
       end)
 
       assert Req.get!(c.url).body == "foo"
@@ -257,12 +257,12 @@ defmodule Req.StepsTest do
         {:ok, socket} = :gen_tcp.accept(listen_socket)
         assert {:ok, "GET / HTTP/1.1\r\n" <> _} = :gen_tcp.recv(socket, 0)
 
-        body = "foo" |> :zlib.gzip() |> :zlib.zip()
+        body = "foo" |> :zlib.gzip() |> :ezstd.compress()
 
         data = """
         HTTP/1.1 200 OK
         content-encoding: gzip
-        content-encoding: deflate
+        content-encoding: zstd
         content-length: #{byte_size(body)}
 
         #{body}