PLT-7407: Back-end plugin mechanism (#7177)

* begin backend plugin wip

* flesh out rpcplugin. everything done except for minor supervisor stubs

* done with basic plugin infrastructure

* simplify tests

* remove unused test lines

plugin/rpcplugin/muxer_test.go

@@ -0,0 +1,169 @@
+package rpcplugin
+
+import (
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMuxer(t *testing.T) {
+	r1, w1 := io.Pipe()
+	r2, w2 := io.Pipe()
+
+	alice := NewMuxer(NewReadWriteCloser(r1, w2), false)
+	defer func() { assert.NoError(t, alice.Close()) }()
+
+	bob := NewMuxer(NewReadWriteCloser(r2, w1), true)
+	defer func() { assert.NoError(t, bob.Close()) }()
+
+	id1, alice1 := alice.Serve()
+	defer func() { assert.NoError(t, alice1.Close()) }()
+
+	id2, bob2 := bob.Serve()
+	defer func() { assert.NoError(t, bob2.Close()) }()
+
+	done1 := make(chan bool)
+	done2 := make(chan bool)
+
+	go func() {
+		bob1 := bob.Connect(id1)
+		defer func() { assert.NoError(t, bob1.Close()) }()
+
+		n, err := bob1.Write([]byte("ping1.0"))
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+
+		n, err = bob1.Write([]byte("ping1.1"))
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+	}()
+
+	go func() {
+		alice2 := alice.Connect(id2)
+		defer func() { assert.NoError(t, alice2.Close()) }()
+
+		n, err := alice2.Write([]byte("ping2.0"))
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+
+		buf := make([]byte, 20)
+		n, err = alice2.Read(buf)
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+		assert.Equal(t, []byte("pong2.0"), buf[:n])
+
+		done2 <- true
+	}()
+
+	go func() {
+		buf := make([]byte, 7)
+		n, err := io.ReadFull(alice1, buf)
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+		assert.Equal(t, []byte("ping1.0"), buf[:n])
+
+		n, err = alice1.Read(buf)
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+		assert.Equal(t, []byte("ping1.1"), buf[:n])
+
+		done1 <- true
+	}()
+
+	go func() {
+		buf := make([]byte, 20)
+		n, err := bob2.Read(buf)
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+		assert.Equal(t, []byte("ping2.0"), buf[:n])
+
+		n, err = bob2.Write([]byte("pong2.0"))
+		require.NoError(t, err)
+		assert.Equal(t, n, 7)
+	}()
+
+	<-done1
+	<-done2
+}
+
+// Closing a muxer during a read should unblock, but return an error.
+func TestMuxer_CloseDuringRead(t *testing.T) {
+	r1, w1 := io.Pipe()
+	r2, w2 := io.Pipe()
+
+	alice := NewMuxer(NewReadWriteCloser(r1, w2), false)
+
+	bob := NewMuxer(NewReadWriteCloser(r2, w1), true)
+	defer func() { assert.NoError(t, bob.Close()) }()
+
+	_, s := alice.Serve()
+
+	go alice.Close()
+	buf := make([]byte, 20)
+	n, err := s.Read(buf)
+	assert.Equal(t, 0, n)
+	assert.NotNil(t, err)
+	assert.NotEqual(t, io.EOF, err)
+}
+
+// Closing a stream during a read should unblock and return io.EOF since this is the way to
+// gracefully close a connection.
+func TestMuxer_StreamCloseDuringRead(t *testing.T) {
+	r1, w1 := io.Pipe()
+	r2, w2 := io.Pipe()
+
+	alice := NewMuxer(NewReadWriteCloser(r1, w2), false)
+	defer func() { assert.NoError(t, alice.Close()) }()
+
+	bob := NewMuxer(NewReadWriteCloser(r2, w1), true)
+	defer func() { assert.NoError(t, bob.Close()) }()
+
+	_, s := alice.Serve()
+
+	go s.Close()
+	buf := make([]byte, 20)
+	n, err := s.Read(buf)
+	assert.Equal(t, 0, n)
+	assert.Equal(t, io.EOF, err)
+}
+
+// Closing a muxer during a write should unblock, but return an error.
+func TestMuxer_CloseDuringWrite(t *testing.T) {
+	r1, w1 := io.Pipe()
+	r2, w2 := io.Pipe()
+
+	alice := NewMuxer(NewReadWriteCloser(r1, w2), false)
+
+	// Don't connect bob to let writes will block forever.
+	defer r2.Close()
+	defer w1.Close()
+
+	_, s := alice.Serve()
+
+	go alice.Close()
+	buf := make([]byte, 20)
+	n, err := s.Write(buf)
+	assert.Equal(t, 0, n)
+	assert.NotNil(t, err)
+	assert.NotEqual(t, io.EOF, err)
+}
+
+func TestMuxer_ReadWrite(t *testing.T) {
+	r1, w1 := io.Pipe()
+	r2, w2 := io.Pipe()
+
+	alice := NewMuxer(NewReadWriteCloser(r1, w2), false)
+	defer func() { assert.NoError(t, alice.Close()) }()
+
+	bob := NewMuxer(NewReadWriteCloser(r2, w1), true)
+	defer func() { assert.NoError(t, bob.Close()) }()
+
+	go alice.Write([]byte("hello"))
+	buf := make([]byte, 20)
+	n, err := bob.Read(buf)
+	assert.Equal(t, 5, n)
+	assert.Nil(t, err)
+	assert.Equal(t, []byte("hello"), buf[:n])
+}