sahilpaudel
Destructuring the conn object
my headers
[
{"accept", "*/*"},
{"accept-encoding", "gzip, deflate, br"},
{"authorization",
"eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjo2LCJzYWx0IjozMzQ4Mjd9.RtWI9w8uuxBue9Byi0tlZm6EUlN83HC1Ed9UzhPHpN4"},
{"cache-control", "no-cache"},
{"connection", "keep-alive"},
{"content-length", "136"},
{"content-type", "application/json"},
{"experiment_data",
"8Qd7CiAgICAiZXhwZXJpbWVudHMiOiBbFQAAAgACHwAEAgD1ByJuYW1lIjogIlZlcnNpb25UZXN0IiwtAAACADAiaWQhABxCFwCLcmVzdWx0IjpSAAACAPoFInhnLWRlbGl2ZXJ5LXgxIjogMjBVAAACAAomAF8yIjogNSYADmkzIjogMzCgABV9DgAWfWQACpQAD+YAATxPbmXSAA/pAJeACiAgICBdCn0="},
{"host", "localhost:4000"},
{"postman-token", "af95e65d-1261-4471-8191-b3f29b634254"},
{"user-agent", "PostmanRuntime/7.26.5"}
]
def evaluate(%{req_headers: [%{"experiment_data"=> experiment_data}]} = conn, _) do
IO.inspect("===============")
IO.inspect(experiment_data)
IO.inspect("===============")
conn
|> render_json_response(%{})
end
I want the evaluate function to be called only when the experiment_data is present in the header and process it else go to other fallback function.
I tried all possible goggling stuff but couldn’t find the solution.
Thanks.
Marked As Solved
und0ck3d
The req_headers is a list of 2-elem tuples and your matcher on evaluate is trying to match a map inside the list.
My suggestion is that on the function you are calling evaluate you use the Plug.Conn.get_req_header/2 function, that returns a list of values for that header and pattern match against that:
def call(%{req_headers: headers} = conn, _) do
conn |> Plug.Conn.get_req_header("experiment_data") |> List.first() |> evaluate(conn)
end
def evaluate(nil, conn), do: conn
def evaluate(value, conn) do
# do something with value
end
Bear in mind it’s possible to pattern match against list’s values:
ExampleA:
def evaluate(%{req_headers: [{"experiment_data", experiment_data} | _]}) do
...
end
Example B:
def evaluate(%{req_headers: [{"experiment_data", experiment_data}]}) do
...
end
But example A would only work if the {"experiment_data", "value"} tuple was the first element of the list and example B would only work if the list only had one element and that tuple was that element.
Hope I clarified your question 
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