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Scout Absinthe (GraphQL) Instrumentation
defmodule ScoutApm.Absinthe.Plug do
alias ScoutApm.Internal.Layer
def init(default), do: default
def call(conn, _default) do
ScoutApm.TrackedRequest.start_layer("Controller", action_name(conn))
conn
|> Plug.Conn.register_before_send(&before_send/1)
end
def before_send(conn) do
full_name = action_name(conn)
uri = "#{conn.request_path}"
ScoutApm.TrackedRequest.stop_layer(fn layer ->
layer
|> Layer.update_name(full_name)
|> Layer.update_uri(uri)
end
)
conn
end
# Takes a connection, extracts the phoenix controller & action, then manipulates & cleans it up.
# Returns a string like "PageController#index"
defp action_name(conn) do
action_name = conn.params["operationName"]
"GraphQL##{action_name}"
end
end

In case anyone is interested, the plug shown is dependent on the operationName being set for the GraphQL queries. For the project I'm working on, we don't name the queries/mutations we send to Absinthe, but limit each query/mutation to a single field per request. In this case, using the code above results in all GraphQL requests being labelled "GraphQL" in Scout. I needed a way to extract the first field so that queries/mutations like the one below show up as "GraphQL#firstField" in Scout.

query {
  firstField(id: 1) {
    id
  }
}

Here's what I arrived at: https://gist.github.com/pgrunwald/6dd1d9132855b0372785e75df4a26669

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