source: code/trunk/conn.go@ 819

package suika

import (
        "context"
        "fmt"
        "io"
        "net"
        "strings"
        "sync"
        "time"
        "unicode"

        "golang.org/x/time/rate"
        "gopkg.in/irc.v3"
        "nhooyr.io/websocket"
)

// ircConn is a generic IRC connection. It's similar to net.Conn but focuses on
// reading and writing IRC messages.
type ircConn interface {
        ReadMessage() (*irc.Message, error)
        WriteMessage(*irc.Message) error
        Close() error
        SetReadDeadline(time.Time) error
        SetWriteDeadline(time.Time) error
        RemoteAddr() net.Addr
        LocalAddr() net.Addr
}

func newNetIRCConn(c net.Conn) ircConn {
        type netConn net.Conn
        return struct {
                *irc.Conn
                netConn
        }{irc.NewConn(c), c}
}

type websocketIRCConn struct {
        conn                        *websocket.Conn
        readDeadline, writeDeadline time.Time
        remoteAddr                  string
}

func newWebsocketIRCConn(c *websocket.Conn, remoteAddr string) ircConn {
        return &websocketIRCConn{conn: c, remoteAddr: remoteAddr}
}

func (wic *websocketIRCConn) ReadMessage() (*irc.Message, error) {
        ctx := context.Background()
        if !wic.readDeadline.IsZero() {
                var cancel context.CancelFunc
                ctx, cancel = context.WithDeadline(ctx, wic.readDeadline)
                defer cancel()
        }
        _, b, err := wic.conn.Read(ctx)
        if err != nil {
                switch websocket.CloseStatus(err) {
                case websocket.StatusNormalClosure, websocket.StatusGoingAway:
                        return nil, io.EOF
                default:
                        return nil, err
                }
        }
        return irc.ParseMessage(string(b))
}

func (wic *websocketIRCConn) WriteMessage(msg *irc.Message) error {
        b := []byte(strings.ToValidUTF8(msg.String(), string(unicode.ReplacementChar)))
        ctx := context.Background()
        if !wic.writeDeadline.IsZero() {
                var cancel context.CancelFunc
                ctx, cancel = context.WithDeadline(ctx, wic.writeDeadline)
                defer cancel()
        }
        return wic.conn.Write(ctx, websocket.MessageText, b)
}

func isErrWebSocketClosed(err error) bool {
        return err != nil && strings.HasSuffix(err.Error(), "failed to close WebSocket: already wrote close")
}

func (wic *websocketIRCConn) Close() error {
        err := wic.conn.Close(websocket.StatusNormalClosure, "")
        // TODO: remove once this PR is merged:
        // https://github.com/nhooyr/websocket/pull/303
        if isErrWebSocketClosed(err) {
                return nil
        }
        return err
}

func (wic *websocketIRCConn) SetReadDeadline(t time.Time) error {
        wic.readDeadline = t
        return nil
}

func (wic *websocketIRCConn) SetWriteDeadline(t time.Time) error {
        wic.writeDeadline = t
        return nil
}

func (wic *websocketIRCConn) RemoteAddr() net.Addr {
        return websocketAddr(wic.remoteAddr)
}

func (wic *websocketIRCConn) LocalAddr() net.Addr {
        // Behind a reverse HTTP proxy, we don't have access to the real listening
        // address
        return websocketAddr("")
}

type websocketAddr string

func (websocketAddr) Network() string {
        return "ws"
}

func (wa websocketAddr) String() string {
        return string(wa)
}

type connOptions struct {
        Logger         Logger
        RateLimitDelay time.Duration
        RateLimitBurst int
}

type conn struct {
        conn   ircConn
        srv    *Server
        logger Logger

        lock     sync.Mutex
        outgoing chan<- *irc.Message
        closed   bool
        closedCh chan struct{}
}

func newConn(srv *Server, ic ircConn, options *connOptions) *conn {
        outgoing := make(chan *irc.Message, 64)
        c := &conn{
                conn:     ic,
                srv:      srv,
                outgoing: outgoing,
                logger:   options.Logger,
                closedCh: make(chan struct{}),
        }

        go func() {
                ctx, cancel := c.NewContext(context.Background())
                defer cancel()

                rl := rate.NewLimiter(rate.Every(options.RateLimitDelay), options.RateLimitBurst)
                for msg := range outgoing {
                        if err := rl.Wait(ctx); err != nil {
                                break
                        }

                        c.logger.Debugf("sent: %v", msg)
                        c.conn.SetWriteDeadline(time.Now().Add(writeTimeout))
                        if err := c.conn.WriteMessage(msg); err != nil {
                                c.logger.Printf("failed to write message: %v", err)
                                break
                        }
                }
                if err := c.conn.Close(); err != nil && !isErrClosed(err) {
                        c.logger.Printf("failed to close connection: %v", err)
                } else {
                        c.logger.Debugf("connection closed")
                }
                // Drain the outgoing channel to prevent SendMessage from blocking
                for range outgoing {
                        // This space is intentionally left blank
                }
        }()

        c.logger.Debugf("new connection")
        return c
}

func (c *conn) isClosed() bool {
        c.lock.Lock()
        defer c.lock.Unlock()
        return c.closed
}

// Close closes the connection. It is safe to call from any goroutine.
func (c *conn) Close() error {
        c.lock.Lock()
        defer c.lock.Unlock()

        if c.closed {
                return fmt.Errorf("connection already closed")
        }

        err := c.conn.Close()
        c.closed = true
        close(c.outgoing)
        close(c.closedCh)
        return err
}

func (c *conn) ReadMessage() (*irc.Message, error) {
        msg, err := c.conn.ReadMessage()
        if isErrClosed(err) {
                return nil, io.EOF
        } else if err != nil {
                return nil, err
        }

        c.logger.Debugf("received: %v", msg)
        return msg, nil
}

// SendMessage queues a new outgoing message. It is safe to call from any
// goroutine.
//
// If the connection is closed before the message is sent, SendMessage silently
// drops the message.
func (c *conn) SendMessage(ctx context.Context, msg *irc.Message) {
        c.lock.Lock()
        defer c.lock.Unlock()

        if c.closed {
                return
        }

        select {
        case c.outgoing <- msg:
                // Success
        case <-ctx.Done():
                c.logger.Printf("failed to send message: %v", ctx.Err())
        }
}

func (c *conn) RemoteAddr() net.Addr {
        return c.conn.RemoteAddr()
}

func (c *conn) LocalAddr() net.Addr {
        return c.conn.LocalAddr()
}

// NewContext returns a copy of the parent context with a new Done channel. The
// returned context's Done channel is closed when the connection is closed,
// when the returned cancel function is called, or when the parent context's
// Done channel is closed, whichever happens first.
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete.
func (c *conn) NewContext(parent context.Context) (context.Context, context.CancelFunc) {
        ctx, cancel := context.WithCancel(parent)

        go func() {
                defer cancel()

                select {
                case <-ctx.Done():
                        // The parent context has been cancelled, or the caller has called
                        // cancel()
                case <-c.closedCh:
                        // The connection has been closed
                }
        }()

        return ctx, cancel
}