all: Send Close BEP msg on intentional disconnect (#5440)

This avoids waiting until next ping and timeout until the connection is actually
closed both by notifying the peer of the disconnect and by immediately closing
the local end of the connection after that. As a nice side effect, info level
logging about dropped connections now have the actual reason in it, not a generic
timeout error which looks like a real problem with the connection.

lib/connections/structs.go

@@ -9,7 +9,6 @@ package connections
 import (
 	"crypto/tls"
 	"fmt"
-	"io"
 	"net"
 	"net/url"
 	"time"
@@ -23,7 +22,6 @@ import (
 // that can be closed and has some metadata.
 type Connection interface {
 	protocol.Connection
-	io.Closer
 	Type() string
 	Transport() string
 	RemoteAddr() net.Addr
@@ -39,6 +37,11 @@ type completeConn struct {
 	protocol.Connection
 }
 
+func (c completeConn) Close(err error) {
+	c.Connection.Close(err)
+	c.internalConn.Close()
+}
+
 // internalConn is the raw TLS connection plus some metadata on where it
 // came from (type, priority).
 type internalConn struct {
@@ -82,6 +85,14 @@ func (t connType) Transport() string {
 	}
 }
 
+func (c internalConn) Close() {
+	// *tls.Conn.Close() does more than it says on the tin. Specifically, it
+	// sends a TLS alert message, which might block forever if the
+	// connection is dead and we don't have a deadline set.
+	c.SetWriteDeadline(time.Now().Add(250 * time.Millisecond))
+	c.Conn.Close()
+}
+
 func (c internalConn) Type() string {
 	return c.connType.String()
 }