chore: grpc configuration (momentohq#35)

* feat: add transport strategy / grpc config to configuration

This commit attempts to bulid out the first few bits of the configuration
API. It creates a module for transport strategy and grpc config,
and adds them to the configuration struct.

---------

Co-authored-by: Chris Price <[email protected]>

src/integration-test/momento/integration_test_utils.exs

@@ -2,7 +2,9 @@ defmodule Momento.IntegrationTestUtils do
   use ExUnit.Case
 
   alias Momento.CacheClient
-  alias Momento.Configuration
+  alias Momento.Config.Transport.GrpcConfiguration
+  alias Momento.Config.Transport.TransportStrategy
+  alias Momento.Config.Configuration
   alias Momento.Auth.CredentialProvider
 
   def initialize_cache_client() do
@@ -13,7 +15,15 @@ defmodule Momento.IntegrationTestUtils do
     end
 
     credential_provider = CredentialProvider.from_env_var!("TEST_AUTH_TOKEN")
-    config = %Configuration{}
+
+    config = %Configuration{
+      transport_strategy: %TransportStrategy{
+        grpc_config: %GrpcConfiguration{
+          deadline_millis: 5000
+        }
+      }
+    }
+
     cache_client = CacheClient.create!(config, credential_provider)
     [cache_name: cache_name, cache_client: cache_client]
   end

src/lib/momento/cache_client.ex

@@ -1,8 +1,8 @@
 defmodule Momento.CacheClient do
   alias Momento.Auth.CredentialProvider
-  alias Momento.Configuration
   alias Momento.Internal.ScsControlClient
   alias Momento.Internal.ScsDataClient
+  alias Momento.Config.Configuration, as: Configuration
 
   require Logger
 
@@ -43,7 +43,7 @@ defmodule Momento.CacheClient do
   - A `%Momento.CacheClient{}` struct representing the connected client.
   """
   @spec create!(
-          config :: Momento.Configuration.t(),
+          config :: Configuration.t(),
           credential_provider :: CredentialProvider.t()
         ) :: t()
   def create!(config, credential_provider) do

src/lib/momento/config/configuration.ex

@@ -0,0 +1,19 @@
+defmodule Momento.Config.Configuration do
+  @moduledoc """
+  Configuration for Momento CacheClient
+  """
+  @enforce_keys[:transport_strategy]
+  defstruct [:transport_strategy]
+
+  @opaque t() :: %__MODULE__{
+            transport_strategy: Momento.Config.Transport.TransportStrategy.t()
+          }
+
+  @spec with_transport_strategy(
+          config :: Momento.Config.Configuration.t(),
+          transport_strategy :: Momento.Config.Transport.TransportStrategy.t()
+        ) :: Momento.Config.Configuration.t()
+  def with_transport_strategy(config, transport_strategy) do
+    %{config | transport_strategy: transport_strategy}
+  end
+end

src/lib/momento/config/transport/grpc_configuration.ex

@@ -0,0 +1,11 @@
+defmodule Momento.Config.Transport.GrpcConfiguration do
+  @moduledoc """
+  Encapsulates gRPC configuration tunables.
+  """
+  @enforce_keys [:deadline_millis]
+  defstruct [:deadline_millis]
+
+  @opaque t() :: %__MODULE__{
+            deadline_millis: number()
+          }
+end

src/lib/momento/config/transport/transport_strategy.ex

@@ -0,0 +1,27 @@
+defmodule Momento.Config.Transport.TransportStrategy do
+  alias Momento.Config.Transport.TransportStrategy, as: TransportStrategy
+  alias Momento.Config.Transport.GrpcConfiguration, as: GrpcConfiguration
+
+  @moduledoc """
+  Configuration for the low-level Momento transport layer
+  """
+  @enforce_keys [:grpc_config]
+  defstruct [:grpc_config]
+
+  @opaque t() :: %__MODULE__{
+            grpc_config: GrpcConfiguration.t()
+          }
+
+  @doc """
+  Copy constructor for overriding the gRPC configuration
+  """
+  @spec with_grpc_config(
+          transport_strategy :: TransportStrategy.t(),
+          grpc_config :: GrpcConfiguration.t()
+        ) :: TransportStrategy.t()
+  def with_grpc_config(transport_strategy, grpc_config) do
+    %TransportStrategy{
+      grpc_config: grpc_config
+    }
+  end
+end

src/test/momento/config/configuration_test.exs

@@ -0,0 +1,40 @@
+defmodule Momento.Config.ConfigurationTest do
+  alias Momento.Config.Transport.TransportStrategy, as: TransportStrategy
+  alias Momento.Config.Transport.GrpcConfiguration, as: GrpcConfiguration
+
+  use ExUnit.Case
+  doctest Momento.Config.Configuration
+
+  @test_grpc_configuration %GrpcConfiguration{
+    deadline_millis: 90210
+  }
+
+  @test_transport_strategy %TransportStrategy{
+    grpc_config: @test_grpc_configuration
+  }
+
+  @test_configuration %Momento.Config.Configuration{
+    transport_strategy: @test_transport_strategy
+  }
+
+  describe "Constructing Configuration" do
+    test "overriding transport strategy" do
+      new_grpc_configuration = %GrpcConfiguration{
+        deadline_millis: 424_242
+      }
+
+      new_transport_strategy = %TransportStrategy{
+        grpc_config: new_grpc_configuration
+      }
+
+      new_config =
+        Momento.Config.Configuration.with_transport_strategy(
+          @test_configuration,
+          new_transport_strategy
+        )
+
+      assert new_config.transport_strategy == new_transport_strategy
+      assert new_config.transport_strategy.grpc_config == new_grpc_configuration
+    end
+  end
+end