/*
 *
 * Copyright 2017 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package test

import (
	"context"
	"fmt"
	"io"
	"net"
	"sync"
	"testing"
	"time"

	"google.golang.org/grpc"

	"google.golang.org/grpc/internal/envconfig"
	testpb "google.golang.org/grpc/test/grpc_testing"
)

type delayListener struct {
	net.Listener
	closeCalled  chan struct{}
	acceptCalled chan struct{}
	allowCloseCh chan struct{}
	cc           *delayConn
	dialed       bool
}

func (d *delayListener) Accept() (net.Conn, error) {
	select {
	case <-d.acceptCalled:
		// On the second call, block until closed, then return an error.
		<-d.closeCalled
		<-d.allowCloseCh
		return nil, fmt.Errorf("listener is closed")
	default:
		close(d.acceptCalled)
		conn, err := d.Listener.Accept()
		// Allow closing of listener only after accept.
		// Note: Dial can return successfully, yet Accept
		// might now have finished.
		d.allowClose()
		return conn, err
	}
}

func (d *delayListener) allowClose() {
	close(d.allowCloseCh)
}
func (d *delayListener) Close() error {
	close(d.closeCalled)
	go func() {
		<-d.allowCloseCh
		d.Listener.Close()
	}()
	return nil
}

func (d *delayListener) allowClientRead() {
	d.cc.allowRead()
}

func (d *delayListener) Dial(ctx context.Context) (net.Conn, error) {
	if d.dialed {
		// Only hand out one connection (net.Dial can return more even after the
		// listener is closed).  This is not thread-safe, but Dial should never be
		// called concurrently in this environment.
		return nil, fmt.Errorf("no more conns")
	}
	d.dialed = true
	c, err := (&net.Dialer{}).DialContext(ctx, "tcp", d.Listener.Addr().String())
	if err != nil {
		return nil, err
	}
	d.cc = &delayConn{Conn: c, blockRead: make(chan struct{})}
	return d.cc, nil
}

type delayConn struct {
	net.Conn
	blockRead chan struct{}
}

func (d *delayConn) allowRead() {
	close(d.blockRead)
}

func (d *delayConn) Read(b []byte) (n int, err error) {
	<-d.blockRead
	return d.Conn.Read(b)
}

func (s) TestGracefulStop(t *testing.T) {
	// Set default behavior and restore current setting after test.
	old := envconfig.RequireHandshake
	envconfig.RequireHandshake = envconfig.RequireHandshakeOff
	defer func() { envconfig.RequireHandshake = old }()

	// This test ensures GracefulStop cannot race and break RPCs on new
	// connections created after GracefulStop was called but before
	// listener.Accept() returns a "closing" error.
	//
	// Steps of this test:
	// 1. Start Server
	// 2. GracefulStop() Server after listener's Accept is called, but don't
	//    allow Accept() to exit when Close() is called on it.
	// 3. Create a new connection to the server after listener.Close() is called.
	//    Server will want to send a GoAway on the new conn, but we delay client
	//    reads until 5.
	// 4. Send an RPC on the new connection.
	// 5. Allow the client to read the GoAway.  The RPC should complete
	//    successfully.

	lis, err := net.Listen("tcp", "localhost:0")
	if err != nil {
		t.Fatalf("Error listenening: %v", err)
	}
	dlis := &delayListener{
		Listener:     lis,
		acceptCalled: make(chan struct{}),
		closeCalled:  make(chan struct{}),
		allowCloseCh: make(chan struct{}),
	}
	d := func(ctx context.Context, _ string) (net.Conn, error) { return dlis.Dial(ctx) }
	serverGotReq := make(chan struct{})

	ss := &stubServer{
		fullDuplexCall: func(stream testpb.TestService_FullDuplexCallServer) error {
			close(serverGotReq)
			_, err := stream.Recv()
			if err != nil {
				return err
			}
			return stream.Send(&testpb.StreamingOutputCallResponse{})
		},
	}
	s := grpc.NewServer()
	testpb.RegisterTestServiceServer(s, ss)

	// 1. Start Server
	wg := sync.WaitGroup{}
	wg.Add(1)
	go func() {
		s.Serve(dlis)
		wg.Done()
	}()

	// 2. GracefulStop() Server after listener's Accept is called, but don't
	//    allow Accept() to exit when Close() is called on it.
	<-dlis.acceptCalled
	wg.Add(1)
	go func() {
		s.GracefulStop()
		wg.Done()
	}()

	// 3. Create a new connection to the server after listener.Close() is called.
	//    Server will want to send a GoAway on the new conn, but we delay it
	//    until 5.

	<-dlis.closeCalled // Block until GracefulStop calls dlis.Close()

	// Now dial.  The listener's Accept method will return a valid connection,
	// even though GracefulStop has closed the listener.
	ctx, dialCancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer dialCancel()
	cc, err := grpc.DialContext(ctx, "", grpc.WithInsecure(), grpc.WithBlock(), grpc.WithContextDialer(d))
	if err != nil {
		dlis.allowClientRead()
		t.Fatalf("grpc.Dial(%q) = %v", lis.Addr().String(), err)
	}
	client := testpb.NewTestServiceClient(cc)
	defer cc.Close()

	// 4. Send an RPC on the new connection.
	// The server would send a GOAWAY first, but we are delaying the server's
	// writes for now until the client writes more than the preface.
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	stream, err := client.FullDuplexCall(ctx)
	if err != nil {
		t.Fatalf("FullDuplexCall= _, %v; want _, <nil>", err)
	}
	go func() {
		// 5. Allow the client to read the GoAway.  The RPC should complete
		//    successfully.
		<-serverGotReq
		dlis.allowClientRead()
	}()
	if err := stream.Send(&testpb.StreamingOutputCallRequest{}); err != nil {
		t.Fatalf("stream.Send(_) = %v, want <nil>", err)
	}
	if _, err := stream.Recv(); err != nil {
		t.Fatalf("stream.Recv() = _, %v, want _, <nil>", err)
	}
	if _, err := stream.Recv(); err != io.EOF {
		t.Fatalf("stream.Recv() = _, %v, want _, io.EOF", err)
	}
	// 5. happens above, then we finish the call.
	cancel()
	wg.Wait()
}