Move Linux client & common packages into a public repo.

safesocket/unixsocket.go

@@ -0,0 +1,61 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build !windows
+
+package safesocket
+
+import (
+	"fmt"
+	"net"
+	"os"
+)
+
+func path(vendor, name string) string {
+	return fmt.Sprintf("%s-%s.sock", vendor, name)
+}
+
+func ConnCloseRead(c net.Conn) error {
+	return c.(*net.UnixConn).CloseRead()
+}
+
+func ConnCloseWrite(c net.Conn) error {
+	return c.(*net.UnixConn).CloseWrite()
+}
+
+// TODO(apenwarr): handle magic cookie auth
+func Connect(cookie, vendor, name string, port uint16) (net.Conn, error) {
+	pipe, err := net.Dial("unix", path(vendor, name))
+	if err != nil {
+		return nil, err
+	}
+	return pipe, err
+}
+
+// TODO(apenwarr): handle magic cookie auth
+func Listen(cookie, vendor, name string, port uint16) (net.Listener, uint16, error) {
+	// Unix sockets hang around in the filesystem even after nobody
+	// is listening on them. (Which is really unfortunate but long-
+	// entrenched semantics.) Try connecting first; if it works, then
+	// the socket is still live, so let's not replace it. If it doesn't
+	// work, then replace it.
+	//
+	// Note that there's a race condition between these two steps. A
+	// "proper" daemon usually uses a dance involving pidfiles to first
+	// ensure that no other instances of itself are running, but that's
+	// beyond the scope of our simple socket library.
+	p := path(vendor, name)
+	c, err := net.Dial("unix", p)
+	if err == nil {
+		c.Close()
+		return nil, 0, fmt.Errorf("%v: address already in use", p)
+	}
+	_ = os.Remove(p)
+	pipe, err := net.Listen("unix", p)
+	if err != nil {
+		return nil, 0, err
+	}
+	os.Chmod(p, 0666)
+	return pipe, 0, err
+}