rpc rewrite: control RPCs using gRPC + separate RPC for data transfer

transport/ssh: update go-netssh to new version
    => supports CloseWrite and Deadlines
    => build: require Go 1.11 (netssh requires it)

transport/transport.go

@@ -0,0 +1,84 @@
+// Package transport defines a common interface for
+// network connections that have an associated client identity.
+package transport
+
+import (
+	"context"
+	"errors"
+	"net"
+	"syscall"
+
+	"github.com/zrepl/zrepl/logger"
+	"github.com/zrepl/zrepl/rpc/dataconn/timeoutconn"
+	"github.com/zrepl/zrepl/zfs"
+)
+
+type AuthConn struct {
+	Wire
+	clientIdentity string
+}
+
+var _ timeoutconn.SyscallConner = AuthConn{}
+
+func (a AuthConn) SyscallConn() (rawConn syscall.RawConn, err error) {
+	scc, ok := a.Wire.(timeoutconn.SyscallConner)
+	if !ok {
+		return nil, timeoutconn.SyscallConnNotSupported
+	}
+	return scc.SyscallConn()
+}
+
+func NewAuthConn(conn Wire, clientIdentity string) *AuthConn {
+	return &AuthConn{conn, clientIdentity}
+}
+
+func (c *AuthConn) ClientIdentity() string {
+	if err := ValidateClientIdentity(c.clientIdentity); err != nil {
+		panic(err)
+	}
+	return c.clientIdentity
+}
+
+// like net.Listener, but with an AuthenticatedConn instead of net.Conn
+type AuthenticatedListener interface {
+	Addr() net.Addr
+	Accept(ctx context.Context) (*AuthConn, error)
+	Close() error
+}
+
+type AuthenticatedListenerFactory func() (AuthenticatedListener, error)
+
+type Wire = timeoutconn.Wire
+
+type Connecter interface {
+	Connect(ctx context.Context) (Wire, error)
+}
+
+// A client identity must be a single component in a ZFS filesystem path
+func ValidateClientIdentity(in string) (err error) {
+	path, err := zfs.NewDatasetPath(in)
+	if err != nil {
+		return err
+	}
+	if path.Length() != 1 {
+		return errors.New("client identity must be a single path comonent (not empty, no '/')")
+	}
+	return nil
+}
+
+type contextKey int
+
+const contextKeyLog contextKey = 0
+
+type Logger = logger.Logger
+
+func WithLogger(ctx context.Context, log Logger) context.Context {
+	return context.WithValue(ctx, contextKeyLog, log)
+}
+
+func GetLogger(ctx context.Context) Logger {
+	if log, ok := ctx.Value(contextKeyLog).(Logger); ok {
+		return log
+	}
+	return logger.NewNullLogger()
+}