Allow configurable Mint adapter

README.md

@@ -205,6 +205,26 @@ iex> {:ok, channel} = GRPC.Stub.connect("localhost:50051", interceptors: [GRPC.C
 
 Check the [examples](examples) and [interop](interop) directories in the project's source code for some examples.
 
+## Client Adapter and Configuration
+
+The default adapter used by `GRPC.Stub.connect/2` is `GRPC.Client.Adapter.Gun`. Another option is to use `GRPC.Client.Adapters.Mint` instead, like so:
+
+```
+GRPC.Stub.connect("localhost:50051",
+  # Use Mint adapter instead of default Gun
+  adapter: GRPC.Client.Adapters.Mint
+)
+```
+
+The `GRPC.Client.Adapters.Mint` adapter accepts custom configuration. To do so, you can configure it from your mix application via:
+
+```
+// File: your application's config file.
+config :grpc, GRPC.Client.Adapters.Mint, custom_opts
+```
+
+The accepted options for configuration are the ones listed on [Mint.HTTP.connect/4](https://hexdocs.pm/mint/Mint.HTTP.html#connect/4-options)
+
 ## Features
 
 - Various kinds of RPC:

lib/grpc/client/adapters/mint.ex

@@ -15,7 +15,12 @@ defmodule GRPC.Client.Adapters.Mint do
 
   @impl true
   def connect(%{host: host, port: port} = channel, opts \\ []) do
-    opts = Keyword.merge(@default_connect_opts, connect_opts(channel, opts))
+    # Added :config_options to facilitate testing.
+    {config_opts, opts} = Keyword.pop(opts, :config_options, [])
+    module_opts = Application.get_env(:grpc, __MODULE__, config_opts)
+
+    opts = connect_opts(channel, opts) |> merge_opts(module_opts)
+
     Process.flag(:trap_exit, true)
 
     channel
@@ -122,6 +127,11 @@ defmodule GRPC.Client.Adapters.Mint do
     [transport_opts: Keyword.merge(@default_transport_opts, transport_opts)]
   end
 
+  defp merge_opts(opts, module_opts) do
+    opts = Keyword.merge(opts, module_opts)
+    Keyword.merge(@default_connect_opts, opts)
+  end
+
   defp mint_scheme(%Channel{scheme: "https"} = _channel), do: :https
   defp mint_scheme(_channel), do: :http
 

test/grpc/client/adapters/mint_test.exs

@@ -15,14 +15,14 @@ defmodule GRPC.Client.Adapters.MintTest do
     end
 
     test "connects insecurely (default options)", %{port: port} do
-      channel = build(:channel, port: port, host: "localhost")
+      channel = build(:channel, adapter: Mint, port: port, host: "localhost")
 
       assert {:ok, result} = Mint.connect(channel, [])
       assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
     end
 
     test "connects insecurely (custom options)", %{port: port} do
-      channel = build(:channel, port: port, host: "localhost")
+      channel = build(:channel, adapter: Mint, port: port, host: "localhost")
 
       assert {:ok, result} = Mint.connect(channel, transport_opts: [ip: :loopback])
       assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
@@ -32,5 +32,20 @@ defmodule GRPC.Client.Adapters.MintTest do
 
       assert message == "Error while opening connection: {:error, :badarg}"
     end
+
+    test "accepts config_options for application specific configuration", %{port: port} do
+      channel = build(:channel, adapter: Mint, port: port, host: "localhost")
+
+      assert {:ok, result} =
+               Mint.connect(channel, config_options: [transport_opts: [ip: :loopback]])
+
+      assert %{channel | adapter_payload: %{conn_pid: result.adapter_payload.conn_pid}} == result
+
+      # Ensure that changing one of the options via config_options also breaks things
+      assert {:error, message} =
+               Mint.connect(channel, config_options: [transport_opts: [ip: "256.0.0.0"]])
+
+      assert message == "Error while opening connection: {:error, :badarg}"
+    end
   end
 end