Json endpoint #5
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| defmodule Provider.Cache do | ||
| @moduledoc """ | ||
| Defines a behaviour for cache implementations to follow | ||
| """ | ||
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| @callback set(mod :: module(), key :: atom(), value :: term()) :: :ok | ||
| @callback get(mod :: module(), key :: atom()) :: {:ok, term()} | {:error, :not_found} | ||
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| @spec set(module(), atom(), term()) :: :ok | ||
| def set(mod, key, value) do | ||
| impl().set(mod, key, value) | ||
| end | ||
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| @spec get(module(), atom()) :: {:ok, term()} | {:error, :not_found} | ||
| def get(mod, key) do | ||
| impl().get(mod, key) | ||
| end | ||
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| defp impl do | ||
| Application.get_env(:provider, :cache, Provider.Cache.ETS) | ||
| end | ||
| end |
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| defmodule Provider.Cache.ETS do | ||
| @moduledoc """ | ||
| An ets based cache implementation | ||
| """ | ||
| @behaviour Provider.Cache | ||
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| use GenServer | ||
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| @spec start_link(Keyword.t()) :: GenServer.server() | ||
| def start_link(_opts) do | ||
| GenServer.start_link(__MODULE__, :ok, name: __MODULE__) | ||
| end | ||
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| @impl Provider.Cache | ||
| def set(module, key, value) do | ||
| GenServer.call(__MODULE__, {:set, module, key, value}) | ||
| end | ||
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| @impl Provider.Cache | ||
| def get(module, key) do | ||
| case :ets.lookup(__MODULE__, {module, key}) do | ||
| [{{^module, ^key}, value}] -> {:ok, value} | ||
| [] -> {:error, :not_found} | ||
| end | ||
| end | ||
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| @impl GenServer | ||
| def init(:ok) do | ||
| state = :ets.new(__MODULE__, [:named_table]) | ||
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| {:ok, state} | ||
| end | ||
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| @impl GenServer | ||
| def handle_call({:set, module, key, value}, _from, state) do | ||
| :ets.insert(state, {{module, key}, value}) | ||
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| {:reply, :ok, state} | ||
| end | ||
| end |
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| @@ -0,0 +1,15 @@ | ||
| defmodule Provider.Application do | ||
| @moduledoc false | ||
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| use Application | ||
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| @impl true | ||
| def start(_type, _args) do | ||
| children = [ | ||
| Provider.Cache.ETS | ||
| ] | ||
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| opts = [strategy: :one_for_one, name: Provider.Supervisor] | ||
| Supervisor.start_link(children, opts) | ||
| end | ||
| end |
| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,52 @@ | ||
| defmodule Provider.JsonEndpoint do | ||
| @moduledoc """ | ||
| Provider source which retrieves values from a JSON endpoint. | ||
| The following options are accepted. | ||
| * :endpoint - This is the URL where the JSON configuration can be found. | ||
| """ | ||
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| @behaviour Provider.Source | ||
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| require Logger | ||
| alias Provider.Source | ||
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| @impl Source | ||
| def display_name(param_name, spec), do: Map.get(spec, :source, to_string(param_name)) | ||
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| @impl Source | ||
| def values(params, opts) do | ||
| endpoint = Keyword.fetch!(opts, :endpoint) | ||
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| response = | ||
| [{Tesla.Middleware.BaseUrl, endpoint}, Tesla.Middleware.JSON] | ||
| |> Tesla.client() | ||
| |> Tesla.get("") | ||
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Collaborator
There was a problem hiding this comment. I'd probably use req (as an optional dep), and alternatively allow the client to supply the |
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| case response do | ||
| {:ok, response} -> | ||
| Enum.map(params, fn {k, spec} -> | ||
| response.body[display_name(k, spec)] | ||
| end) | ||
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| {:error, reason} -> | ||
| Logger.warning("#{__MODULE__} unable to retrieve values - #{reason}") | ||
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| Enum.map(params, fn {_k, _spec} -> | ||
| nil | ||
| end) | ||
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Collaborator
There was a problem hiding this comment. Is this actually what we want? Shouldn't we raise in this case? I see you mention in the commit desc that
But, I don't think dev convenience justifies this default which can lead to weird prod bugs. If the clients don't want to use a JSON server locally in dev, they could use a different source in dev. Or alternatively, start a mock server (for which we could support a convenience helper function, something like
Owner
Author
There was a problem hiding this comment.
This is very true. There is no reason we could not have someone do something like defmodule MyConfig do
use Provider,
source: Application.compile_env(:my_app, :my_config_source)
endin order to do something slightly different between dev and prod-like deployments. |
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| end | ||
| end | ||
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| @impl Source | ||
| def template(params) do | ||
| params | ||
| |> Enum.map(fn {k, spec} -> | ||
| {display_name(k, spec), spec.default} | ||
| end) | ||
| |> Map.new() | ||
| |> Jason.encode!() | ||
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Collaborator
There was a problem hiding this comment. Could we use the stock Erlang's json (https://www.erlang.org/doc/apps/stdlib/json.html) instead? Note that in this case we'd only support OTP 27+.
Owner
Author
There was a problem hiding this comment. I would prefer not to as of right now. I would reconsider it once OTP 28 is released. |
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| |> Jason.Formatter.pretty_print() | ||
| end | ||
| end | ||
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These opts are passed to the source, right? It would be good to document that somewhere.