How to get current request url full query params (as a keyword list if possible) inside a phoenix template?

Kurisu · May 7, 2019, 2:09pm

For example for a current url like
http://localhost:4000/cosmetic/products?_utf8=✓&query=perfume&page=2,
I would like to get:

[_utf8: “✓”, query: “perfume”, page: “2”]

I tought I could use @conn.assigns.params but I realized it may contain other stuff that I don’t need here. I just want only the params present in the url after the ?.

awestbro · May 7, 2019, 2:19pm

I think this will do what you want

https://hexdocs.pm/plug/Plug.Conn.html#fetch_query_params/2

NobbZ · May 7, 2019, 2:25pm

This triggers parsing them if they haven’t been parsed yet.

To actually get the params from the query string, one could just do conn.query_params IIRC. They will return as a map though, not as a keywordlist (which would be dangerous anyway as it would open your system for atom overflow attacks)

Kurisu · May 7, 2019, 2:45pm

Thanks for the warning. When converting the Map to a Keyword List, I will then match only the allowed query param keys. I think this will avoid atom overflow attacks.

awestbro · May 7, 2019, 2:47pm

Ah you’re right!

github.com

elixir-plug/plug/blob/5ac4858d80fa5235a8aae2a5eed3c0c97ef14d31/lib/plug/conn.ex#L965-L981


def fetch_query_params(%Conn{query_params: %Unfetched{}} = conn, opts) do
  %{params: params, query_string: query_string} = conn
  Plug.Conn.Utils.validate_utf8!(query_string, InvalidQueryError, "query string")
  length = Keyword.get(opts, :length, 1_000_000)


  if byte_size(query_string) > length do
    raise InvalidQueryError,
          "maximum query string length is #{length}, got a query with #{byte_size(query_string)} bytes"
  end


  query_params = Plug.Conn.Query.decode(query_string)


  case params do
    %Unfetched{} -> %{conn | query_params: query_params, params: query_params}
    %{} -> %{conn | query_params: query_params, params: Map.merge(query_params, params)}
  end
end