Plug to help unwrap headers and fields from the message body

This can be helpful if your broker doesn’t support message headers natively.

By default this plug expects the body to be a map containing 3 string keys:

• "headers" - will be put into the message headers
• "fields" - will be put into the messages fields (i.e. :message_id, :correlation_id, etc.)
• "body" - will replace the current wrapper body

If you want a different wrapping structure for the message, you can pass the the :unwrap_fn option. The wrap function should accept a message and return a message.

Examples

iex> alias Conduit.Message
iex> defmodule MyPipeline do
iex>   use Conduit.Plug.Builder
iex>   plug Conduit.Plug.Unwrap
iex> end
iex>
iex> message =
iex>   %Message{}
iex>   |> Message.put_body(%{
iex>     "body" => %{},
iex>     "headers" => %{"foo" => "bar"},
iex>     "fields" => %{"correlation_id" => "1"}
iex>   })
iex>   |> MyPipeline.run()
iex> message.body
%{}
iex> Message.get_header(message, "foo")
"bar"
iex> message.correlation_id
"1"

iex> alias Conduit.Message
iex> defmodule MyOtherPipeline do
iex>   use Conduit.Plug.Builder
iex>   plug Conduit.Plug.Unwrap, unwrap_fn: fn message ->
iex>     body = Map.drop(message.body, ["meta"])
iex>     fields = Map.drop(message.body["meta"], ["headers"])
iex>     headers = message.body["meta"]["headers"]
iex>
iex>     message
iex>     |> Conduit.Message.put_body(body)
iex>     |> Conduit.Message.put_headers(Map.merge(message.headers, headers))
iex>     |> Conduit.Message.put_content_encoding(fields["content_encoding"])
iex>     |> Conduit.Message.put_content_type(fields["content_type"])
iex>     |> Conduit.Message.put_correlation_id(fields["correlation_id"])
iex>     |> Conduit.Message.put_created_at(fields["created_at"])
iex>     |> Conduit.Message.put_created_by(fields["created_by"])
iex>     |> Conduit.Message.put_message_id(fields["message_id"])
iex>     |> Conduit.Message.put_user_id(fields["user_id"])
iex>   end
iex> end
iex>
iex> message =
iex>   %Message{}
iex>   |> Message.put_body(%{
iex>     "meta" => %{
iex>       "correlation_id" => "1",
iex>       "headers" => %{
iex>         "foo" => "bar"
iex>       },
iex>     }
iex>   })
iex>   |> MyOtherPipeline.run()
iex> message.body
%{}
iex> Message.get_header(message, "foo")
"bar"
iex> message.correlation_id
"1"