Get headers from http response

Question

I am new to elm, I have a login api which returns a JWT token in its hedears

curl  http://localhost:4000/api/login?email=bob@example&password=1234

response:

HTTP/1.1 200 OK
authorization: Bearer eyJhbGciOiJIUzUxMiIsInR5cCI6IkpXyLp0aSI6ImefP2GOWEFYWM47ig2W6nrhw
x-expires: 1499255103
content-type: text/plain; charset=utf-8

success

now Im trying to write a function that will send request and return the token from the headers in elm

authUser =
    Http.send "http://localhost:4000/api/login?email=bob@example&password=1234"

how do I do this in a simple way?

Answer 1

In order to extract a header from a response, you will have to use Http.request along with the expectStringResponse function, which includes the full response including headers.

The expectStringResponse function takes a Http.Response a value, so we can create a function that accepts a header name and a response, then returns Ok headerValue or Err msg depending on whether the header was found:

extractHeader : String -> Http.Response String -> Result String String
extractHeader name resp =
    Dict.get name resp.headers
        |> Result.fromMaybe ("header " ++ name ++ " not found")

This could be used by a request builder like so:

getHeader : String -> String -> Http.Request String
getHeader name url =
    Http.request
        { method = "GET"
        , headers = []
        , url = url
        , body = Http.emptyBody
        , expect = Http.expectStringResponse (extractHeader name)
        , timeout = Nothing
        , withCredentials = False
        }

Here is an example on ellie-app.com which returns the value of content-type as an example. You can substitute "authorization" for your purposes.