Allow atom header keys in inform/3

[rodrigues]

Hello plug team!

I've got an issue after upgrading plug, latest plug with latest bandit (1.12.0):

  ** (ArgumentError) errors were found at the given arguments:
    * 1st argument: not a binary
      (stdlib 7.3) :binary.match(:upgrade, [":", "\n", "\r", <<0>>])
      (plug 1.20.0) lib/plug/conn.ex:1994: Plug.Conn.validate_header_key_value!/2
      (plug 1.20.0) lib/plug/conn.ex:1440: anonymous fn/2 in Plug.Conn.adapter_inform/3
      (plug 1.20.0) lib/plug/conn.ex:1393: Plug.Conn.inform/3
      (bandit 1.12.0) lib/bandit/websocket/handshake.ex:28: Bandit.WebSocket.Handshake.do_handshake/3
      (bandit 1.12.0) lib/bandit/pipeline.ex:150: Bandit.Pipeline.maybe_upgrade!/1

Bandit websocket handshake calls Plug.Conn.inform(conn, 101, [{:upgrade, "websocket"}, ...]), passing the header key as an atom. Newest plug on validate_header_key_value!/2 calls :binary.match/2 on the key without coercion to binary, so atoms blow up.

Thank you!

[Fudoshiki]

Same error

[error] ** (ArgumentError) errors were found at the given arguments:

  * 1st argument: not a binary

    (stdlib 8.0.1) :binary.match(:upgrade, [":", "\n", "\r", <<0>>])
    (plug 1.20.0) lib/plug/conn.ex:1994: Plug.Conn.validate_header_key_value!/2
    (plug 1.20.0) lib/plug/conn.ex:1440: anonymous fn/2 in Plug.Conn.adapter_inform/3
    (elixir 1.20.2) lib/enum.ex:2622: Enum."-reduce/3-lists^foldl/2-0-"/3
    (plug 1.20.0) lib/plug/conn.ex:1439: Plug.Conn.adapter_inform/3
    (plug 1.20.0) lib/plug/conn.ex:1393: Plug.Conn.inform/3
    (bandit 1.12.0) lib/bandit/websocket/handshake.ex:28: Bandit.WebSocket.Handshake.do_handshake/3
    (bandit 1.12.0) lib/bandit/pipeline.ex:150: Bandit.Pipeline.maybe_upgrade!/1
    (bandit 1.12.0) lib/bandit/pipeline.ex:43: Bandit.Pipeline.run/5
    (bandit 1.12.0) lib/bandit/http1/handler.ex:13: Bandit.HTTP1.Handler.handle_data/3
    (bandit 1.12.0) lib/bandit/delegating_handler.ex:18: Bandit.DelegatingHandler.handle_data/3
    (bandit 1.12.0) lib/bandit/delegating_handler.ex:8: Bandit.DelegatingHandler.handle_continue/2
    (stdlib 8.0.1) gen_server.erl:2424: :gen_server.try_handle_continue/3
    (stdlib 8.0.1) gen_server.erl:2291: :gen_server.loop/4
    (stdlib 8.0.1) proc_lib.erl:333: :proc_lib.init_p_do_apply/3

[josevalim]

Nowhere in Plug we assume headers can be atoms and I am not sure we should carve an exception here. :(

[josevalim]

Ignore me, we document it as a keyword list.

[josevalim]

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