refactor (controller): Use a grpc server for the grpc-gateway (#1576)

* refactor (controller): Use a grpc server for the grpc-gateway

This starts a grpc server for the grpc-gateway.  The new gateway
server uses an in-memory listener which also supports "dialing", so
the http proxy can connect to the in-memory listener.

This change allows us to use all grpc server features and was in part
motivated by a need for an interceptor of inbound requests.  With that
said, having a "proper" grpc server for the gateway will provide a lot
more flexibility and capabilities moving forward.

The request context will still be verified via middleware in the
http proxy (see wrapHandlerWithCommonFuncs).  This verified context
will be serialized into a protobuf and sent along to the grpc-gateway
via metadata where an interceptor will add the verified request
info to the request's context (see requestCtxInterceptor).  The
interceptor will verify the serialized request info via a shared ticket
with it's companion in-memory http proxy.  FYI: the ticket is simply
random base62 string (see db.NewPrivateId).

This change also necessitated a minor change to services.  We need to
return an empty response instead of nil, nil when there are no errors
and the response is empty.

* refactor (handlers): Rename gRPC Gateway filter

Originally, this was called an OutgoingInterceptor, which is an
unfortunate name since it's not an interceptor.  Now that we're
refactoring the gateway stuff and have proper interceptors, renaming
this should remove ambiguity

* refactor: Rework how 204 with empty msg is handled

Recent changes to grpc gateway has necessitated a change to how
204s are handled by the gateway

* tests (bats): Check status codes for delete operations

internal/servers/controller/testing.go

@@ -10,6 +10,7 @@ import (
 	"testing"
 	"time"
 
+	grpc_middleware "github.com/grpc-ecosystem/go-grpc-middleware"
 	"github.com/hashicorp/boundary/api"
 	"github.com/hashicorp/boundary/api/authmethods"
 	"github.com/hashicorp/boundary/api/authtokens"
@@ -18,6 +19,7 @@ import (
 	"github.com/hashicorp/boundary/internal/cmd/config"
 	"github.com/hashicorp/boundary/internal/db"
 	"github.com/hashicorp/boundary/internal/db/schema"
+	"github.com/hashicorp/boundary/internal/gen/testing/interceptor"
 	"github.com/hashicorp/boundary/internal/iam"
 	"github.com/hashicorp/boundary/internal/intglobals"
 	"github.com/hashicorp/boundary/internal/kms"
@@ -27,6 +29,9 @@ import (
 	wrapping "github.com/hashicorp/go-kms-wrapping"
 	"github.com/hashicorp/go-secure-stdlib/base62"
 	"github.com/hashicorp/go-secure-stdlib/strutil"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/test/bufconn"
 )
 
 const (
@@ -716,3 +721,39 @@ func (tc *TestController) WaitForNextWorkerStatusUpdate(workerId string) error {
 	event.WriteSysEvent(ctx, op, "waiting for next status report from worker received successfully", "worker", workerId)
 	return nil
 }
+
+// startTestGreeterService is intended to facilitate the testing of
+// interceptors.  You provide a greeter service that produces appropriate
+// responses to test your interceptor(s).  This test function will start up a
+// test greeter service wrapped with the  specified interceptors and return an
+// initialized client for the service. The test service will be stopped/cleaned
+// up after the test (or subtests) have completed.
+func startTestGreeterService(t *testing.T, greeter interceptor.GreeterServiceServer, interceptors ...grpc.UnaryServerInterceptor) interceptor.GreeterServiceClient {
+	t.Helper()
+	require := require.New(t)
+	dialCtx := context.Background()
+
+	buffer := 1024 * 1024
+	listener := bufconn.Listen(buffer)
+
+	s := grpc.NewServer(
+		grpc.UnaryInterceptor(grpc_middleware.ChainUnaryServer(interceptors...)),
+	)
+	interceptor.RegisterGreeterServiceServer(s, greeter)
+	go func() {
+		err := s.Serve(listener)
+		require.NoError(err)
+	}()
+
+	conn, _ := grpc.DialContext(dialCtx, "", grpc.WithContextDialer(func(context.Context, string) (net.Conn, error) {
+		return listener.Dial()
+	}), grpc.WithInsecure())
+
+	t.Cleanup(func() {
+		listener.Close()
+		s.Stop()
+	})
+
+	client := interceptor.NewGreeterServiceClient(conn)
+	return client
+}