experiment: zync: an rsync-like tool for ZFS datasets (re-uses zrepl abstractions)

Local sync and sync over SSH seems to work.
The sshdirect transport might be interesting / re-usable for zrepl as well, although we'd still need some kind of locking in that case.

zync/transport/sshdirect/error.go

@@ -0,0 +1,48 @@
+package sshdirect
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+)
+
+type timeouter interface {
+	Timeout() bool
+}
+
+var _ timeouter = &os.PathError{}
+
+type IOError struct {
+	Cause error
+}
+
+var _ net.Error = &IOError{}
+
+func (e IOError) GoString() string {
+	return fmt.Sprintf("ServeConnIOError:%#v", e.Cause)
+}
+
+func (e IOError) Error() string {
+	// following case found by experiment
+	if pathErr, ok := e.Cause.(*os.PathError); ok {
+		if pathErr.Err == syscall.EPIPE {
+			return fmt.Sprintf("netssh %s: %s (likely: connection reset by peer)",
+				pathErr.Op, pathErr.Err,
+			)
+		}
+		return fmt.Sprintf("netssh: %s: %s", pathErr.Op, pathErr.Err)
+	}
+	return fmt.Sprintf("netssh: %s", e.Cause.Error())
+}
+
+func (e IOError) Timeout() bool {
+	if to, ok := e.Cause.(timeouter); ok {
+		return to.Timeout()
+	}
+	return false
+}
+
+func (e IOError) Temporary() bool {
+	return false
+}