[pkg] go mod vendor to build debian/ubuntu packages

6 files changed, 860 insertions, 0 deletions

diff --git a/vendor/github.com/apparentlymart/go-openvpn-mgmt/demux/demuxer.go b/vendor/github.com/apparentlymart/go-openvpn-mgmt/demux/demuxer.go
new file mode 100644
index 0000000..c57964e
--- /dev/null
+++ b/vendor/github.com/apparentlymart/go-openvpn-mgmt/demux/demuxer.go
@@ -0,0 +1,63 @@
+package demux
+
+import (
+	"bufio"
+	"io"
+)
+
+var readErrSynthEvent = []byte("FATAL:Error reading from OpenVPN")
+
+// Demultiplex reads from the given io.Reader, assumed to be the client
+// end of an OpenVPN Management Protocol connection, and splits it into
+// distinct messages from OpenVPN.
+//
+// It then writes the raw message buffers into either replyCh or eventCh
+// depending on whether each message is a reply to a client command or
+// an asynchronous event notification.
+//
+// The buffers written to replyCh are entire raw message lines (without the
+// trailing newlines), while the buffers written to eventCh are the raw
+// event strings with the prototcol's leading '>' indicator omitted.
+//
+// The caller should usually provide buffered channels of sufficient buffer
+// depth so that the reply channel will not be starved by slow event
+// processing.
+//
+// Once the io.Reader signals EOF, eventCh will be closed, then replyCh
+// will be closed, and then this function will return.
+//
+// As a special case, if a non-EOF error occurs while reading from the
+// io.Reader then a synthetic "FATAL" event will be written to eventCh
+// before the two buffers are closed and the function returns. This
+// synthetic message will have the error message "Error reading from OpenVPN".
+func Demultiplex(r io.Reader, replyCh, eventCh chan<- []byte) {
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		buf := scanner.Bytes()
+
+		if len(buf) < 1 {
+			// Should never happen but we'll be robust and ignore this,
+			// rather than crashing below.
+			continue
+		}
+
+		// Asynchronous messages always start with > to differentiate
+		// them from replies.
+		if buf[0] == '>' {
+			// Trim off the > when we post the message, since it's
+			// redundant after we've demuxed.
+			eventCh <- buf[1:]
+		} else {
+			replyCh <- buf
+		}
+	}
+
+	if err := scanner.Err(); err != nil {
+		// Generate a synthetic FATAL event so that the caller can
+		// see that the connection was not gracefully closed.
+		eventCh <- readErrSynthEvent
+	}
+
+	close(eventCh)
+	close(replyCh)
+}
diff --git a/vendor/github.com/apparentlymart/go-openvpn-mgmt/demux/doc.go b/vendor/github.com/apparentlymart/go-openvpn-mgmt/demux/doc.go
new file mode 100644
index 0000000..263a267
--- /dev/null
+++ b/vendor/github.com/apparentlymart/go-openvpn-mgmt/demux/doc.go
@@ -0,0 +1,12 @@
+// Package demux implements low-level demultiplexing of the stream of
+// messages sent from OpenVPN on the management channel.
+//
+// OpenVPN's protocol includes two different kinds of message from the OpenVPN
+// process: replies to commands sent by the management client, and asynchronous
+// event notifications.
+//
+// This package's purpose is to split these messages into two separate streams,
+// so that functions executing command/response sequences can just block
+// on the reply channel while an event loop elsewhere deals with any async
+// events that might show up.
+package demux
diff --git a/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/client.go b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/client.go
new file mode 100644
index 0000000..7768004
--- /dev/null
+++ b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/client.go
@@ -0,0 +1,303 @@
+package openvpn
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"strconv"
+	"time"
+
+	"github.com/apparentlymart/go-openvpn-mgmt/demux"
+)
+
+var newline = []byte{'\n'}
+var successPrefix = []byte("SUCCESS: ")
+var errorPrefix = []byte("ERROR: ")
+var endMessage = []byte("END")
+
+type MgmtClient struct {
+	wr      io.Writer
+	replies <-chan []byte
+}
+
+// NewClient creates a new MgmtClient that communicates via the given
+// io.ReadWriter and emits events on the given channel.
+//
+// eventCh should be a buffered channel with a sufficient buffer depth
+// such that it cannot be filled under the expected event volume. Event
+// volume depends on which events are enabled and how they are configured;
+// some of the event-enabling functions have further discussion how frequently
+// events are likely to be emitted, but the caller should also factor in
+// how long its own event *processing* will take, since slow event
+// processing will create back-pressure that could cause this buffer to
+// fill faster.
+//
+// It probably goes without saying given the previous paragraph, but the
+// caller *must* constantly read events from eventCh to avoid its buffer
+// becoming full. Events and replies are received on the same channel
+// from OpenVPN, so if writing to eventCh blocks then this will also block
+// responses from the client's various command methods.
+//
+// eventCh will be closed to signal the closing of the client connection,
+// whether due to graceful shutdown or to an error. In the case of error,
+// a FatalEvent will be emitted on the channel as the last event before it
+// is closed. Connection errors may also concurrently surface as error
+// responses from the client's various command methods, should an error
+// occur while we await a reply.
+func NewClient(conn io.ReadWriter, eventCh chan<- Event) *MgmtClient {
+	replyCh := make(chan []byte)
+	rawEventCh := make(chan []byte) // not buffered because eventCh should be
+
+	go demux.Demultiplex(conn, replyCh, rawEventCh)
+
+	// Get raw events and upgrade them into proper event types before
+	// passing them on to the caller's event channel.
+	go func() {
+		for raw := range rawEventCh {
+			eventCh <- upgradeEvent(raw)
+		}
+		close(eventCh)
+	}()
+
+	return &MgmtClient{
+		// replyCh acts as the reader for our ReadWriter, so we only
+		// need to retain the io.Writer for it, so we can send commands.
+		wr:      conn,
+		replies: replyCh,
+	}
+}
+
+// Dial is a convenience wrapper around NewClient that handles the common
+// case of opening an TCP/IP socket to an OpenVPN management port and creating
+// a client for it.
+//
+// See the NewClient docs for discussion about the requirements for eventCh.
+//
+// OpenVPN will create a suitable management port if launched with the
+// following command line option:
+//
+//    --management <ipaddr> <port>
+//
+// Address may an IPv4 address, an IPv6 address, or a hostname that resolves
+// to either of these, followed by a colon and then a port number.
+//
+// When running on Unix systems it's possible to instead connect to a Unix
+// domain socket. To do this, pass an absolute path to the socket as
+// the target address, having run OpenVPN with the following options:
+//
+//    --management /path/to/socket unix
+//
+func Dial(addr string, eventCh chan<- Event) (*MgmtClient, error) {
+	proto := "tcp"
+	if len(addr) > 0 && addr[0] == '/' {
+		proto = "unix"
+	}
+	conn, err := net.Dial(proto, addr)
+	if err != nil {
+		return nil, err
+	}
+
+	return NewClient(conn, eventCh), nil
+}
+
+// HoldRelease instructs OpenVPN to release any management hold preventing
+// it from proceeding, but to retain the state of the hold flag such that
+// the daemon will hold again if it needs to reconnect for any reason.
+//
+// OpenVPN can be instructed to activate a management hold on startup by
+// running it with the following option:
+//
+//     --management-hold
+//
+// Instructing OpenVPN to hold gives your client a chance to connect and
+// do any necessary configuration before a connection proceeds, thus avoiding
+// the problem of missed events.
+//
+// When OpenVPN begins holding, or when a new management client connects while
+// a hold is already in effect, a HoldEvent will be emitted on the event
+// channel.
+func (c *MgmtClient) HoldRelease() error {
+	_, err := c.simpleCommand("hold release")
+	return err
+}
+
+// SetStateEvents either enables or disables asynchronous events for changes
+// in the OpenVPN connection state.
+//
+// When enabled, a StateEvent will be emitted from the event channel each
+// time the connection state changes. See StateEvent for more information
+// on the event structure.
+func (c *MgmtClient) SetStateEvents(on bool) error {
+	var err error
+	if on {
+		_, err = c.simpleCommand("state on")
+	} else {
+		_, err = c.simpleCommand("state off")
+	}
+	return err
+}
+
+// SetEchoEvents either enables or disables asynchronous events for "echo"
+// commands sent from a remote server to our managed OpenVPN client.
+//
+// When enabled, an EchoEvent will be emitted from the event channel each
+// time the server sends an echo command. See EchoEvent for more information.
+func (c *MgmtClient) SetEchoEvents(on bool) error {
+	var err error
+	if on {
+		_, err = c.simpleCommand("echo on")
+	} else {
+		_, err = c.simpleCommand("echo off")
+	}
+	return err
+}
+
+// SetByteCountEvents either enables or disables ongoing asynchronous events
+// for information on OpenVPN bandwidth usage.
+//
+// When enabled, a ByteCountEvent will be emitted at given time interval,
+// (which may only be whole seconds) describing how many bytes have been
+// transferred in each direction See ByteCountEvent for more information.
+//
+// Set the time interval to zero in order to disable byte count events.
+func (c *MgmtClient) SetByteCountEvents(interval time.Duration) error {
+	msg := fmt.Sprintf("bytecount %d", int(interval.Seconds()))
+	_, err := c.simpleCommand(msg)
+	return err
+}
+
+// SendSignal sends a signal to the OpenVPN process via the management
+// channel. In effect this causes the OpenVPN process to send a signal to
+// itself on our behalf.
+//
+// OpenVPN accepts a subset of the usual UNIX signal names, including
+// "SIGHUP", "SIGTERM", "SIGUSR1" and "SIGUSR2". See the OpenVPN manual
+// page for the meaning of each.
+//
+// Behavior is undefined if the given signal name is not entirely uppercase
+// letters. In particular, including newlines in the string is likely to
+// cause very unpredictable behavior.
+func (c *MgmtClient) SendSignal(name string) error {
+	msg := fmt.Sprintf("signal %q", name)
+	_, err := c.simpleCommand(msg)
+	return err
+}
+
+// LatestState retrieves the most recent StateEvent from the server. This
+// can either be used to poll the state or it can be used to determine the
+// initial state after calling SetStateEvents(true) but before the first
+// state event is delivered.
+func (c *MgmtClient) LatestState() (*StateEvent, error) {
+	err := c.sendCommand([]byte("state"))
+	if err != nil {
+		return nil, err
+	}
+
+	payload, err := c.readCommandResponsePayload()
+	if err != nil {
+		return nil, err
+	}
+
+	if len(payload) != 1 {
+		return nil, fmt.Errorf("Malformed OpenVPN 'state' response")
+	}
+
+	return &StateEvent{
+		body: payload[0],
+	}, nil
+}
+
+// Pid retrieves the process id of the connected OpenVPN process.
+func (c *MgmtClient) Pid() (int, error) {
+	raw, err := c.simpleCommand("pid")
+	if err != nil {
+		return 0, err
+	}
+
+	if !bytes.HasPrefix(raw, []byte("pid=")) {
+		return 0, fmt.Errorf("malformed response from OpenVPN")
+	}
+
+	pid, err := strconv.Atoi(string(raw[4:]))
+	if err != nil {
+		return 0, fmt.Errorf("error parsing pid from OpenVPN: %s", err)
+	}
+
+	return pid, nil
+}
+
+func (c *MgmtClient) sendCommand(cmd []byte) error {
+	_, err := c.wr.Write(cmd)
+	if err != nil {
+		return err
+	}
+	_, err = c.wr.Write(newline)
+	return err
+}
+
+// sendCommandPayload can be called after sendCommand for
+// commands that expect a multi-line input payload.
+//
+// The buffer given in 'payload' *must* end with a newline,
+// or else the protocol will be broken.
+func (c *MgmtClient) sendCommandPayload(payload []byte) error {
+	_, err := c.wr.Write(payload)
+	if err != nil {
+		return err
+	}
+	_, err = c.wr.Write(endMessage)
+	if err != nil {
+		return err
+	}
+	_, err = c.wr.Write(newline)
+	return err
+}
+
+func (c *MgmtClient) readCommandResult() ([]byte, error) {
+	reply, ok := <-c.replies
+	if !ok {
+		return nil, fmt.Errorf("connection closed while awaiting result")
+	}
+
+	if bytes.HasPrefix(reply, successPrefix) {
+		result := reply[len(successPrefix):]
+		return result, nil
+	}
+
+	if bytes.HasPrefix(reply, errorPrefix) {
+		message := reply[len(errorPrefix):]
+		return nil, ErrorFromServer(message)
+	}
+
+	return nil, fmt.Errorf("malformed result message")
+}
+
+func (c *MgmtClient) readCommandResponsePayload() ([][]byte, error) {
+	lines := make([][]byte, 0, 10)
+
+	for {
+		line, ok := <-c.replies
+		if !ok {
+			// We'll give the caller whatever we got before the connection
+			// closed, in case it's useful for debugging.
+			return lines, fmt.Errorf("connection closed before END recieved")
+		}
+
+		if bytes.Equal(line, endMessage) {
+			break
+		}
+
+		lines = append(lines, line)
+	}
+
+	return lines, nil
+}
+
+func (c *MgmtClient) simpleCommand(cmd string) ([]byte, error) {
+	err := c.sendCommand([]byte(cmd))
+	if err != nil {
+		return nil, err
+	}
+	return c.readCommandResult()
+}
diff --git a/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/error.go b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/error.go
new file mode 100644
index 0000000..554e2ef
--- /dev/null
+++ b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/error.go
@@ -0,0 +1,11 @@
+package openvpn
+
+type ErrorFromServer []byte
+
+func (err ErrorFromServer) Error() string {
+	return string(err)
+}
+
+func (err ErrorFromServer) String() string {
+	return string(err)
+}
diff --git a/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/event.go b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/event.go
new file mode 100644
index 0000000..66625f3
--- /dev/null
+++ b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/event.go
@@ -0,0 +1,299 @@
+package openvpn
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+)
+
+var eventSep = []byte(":")
+var fieldSep = []byte(",")
+var byteCountEventKW = []byte("BYTECOUNT")
+var byteCountCliEventKW = []byte("BYTECOUNT_CLI")
+var clientEventKW = []byte("CLIENT")
+var echoEventKW = []byte("ECHO")
+var fatalEventKW = []byte("FATAL")
+var holdEventKW = []byte("HOLD")
+var infoEventKW = []byte("INFO")
+var logEventKW = []byte("LOG")
+var needOkEventKW = []byte("NEED-OK")
+var needStrEventKW = []byte("NEED-STR")
+var passwordEventKW = []byte("PASSWORD")
+var stateEventKW = []byte("STATE")
+
+type Event interface {
+	String() string
+}
+
+// UnknownEvent represents an event of a type that this package doesn't
+// know about.
+//
+// Future versions of this library may learn about new event types, so a
+// caller should exercise caution when making use of events of this type
+// to access unsupported behavior. Backward-compatibility is *not*
+// guaranteed for events of this type.
+type UnknownEvent struct {
+	keyword []byte
+	body    []byte
+}
+
+func (e *UnknownEvent) Type() string {
+	return string(e.keyword)
+}
+
+func (e *UnknownEvent) Body() string {
+	return string(e.body)
+}
+
+func (e *UnknownEvent) String() string {
+	return fmt.Sprintf("%s: %s", e.keyword, e.body)
+}
+
+// MalformedEvent represents a message from the OpenVPN process that is
+// presented as an event but does not comply with the expected event syntax.
+//
+// Events of this type should never be seen but robust callers will accept
+// and ignore them, possibly generating some kind of debugging message.
+//
+// One reason for potentially seeing events of this type is when the target
+// program is actually not an OpenVPN process at all, but in fact this client
+// has been connected to a different sort of server by mistake.
+type MalformedEvent struct {
+	raw []byte
+}
+
+func (e *MalformedEvent) String() string {
+	return fmt.Sprintf("Malformed Event %q", e.raw)
+}
+
+// HoldEvent is a notification that the OpenVPN process is in a management
+// hold and will not continue connecting until the hold is released, e.g.
+// by calling client.HoldRelease()
+type HoldEvent struct {
+	body []byte
+}
+
+func (e *HoldEvent) String() string {
+	return string(e.body)
+}
+
+// StateEvent is a notification of a change of connection state. It can be
+// used, for example, to detect if the OpenVPN connection has been interrupted
+// and the OpenVPN process is attempting to reconnect.
+type StateEvent struct {
+	body []byte
+
+	// bodyParts is populated only on first request, giving us the
+	// separate comma-separated elements of the message. Not all
+	// fields are populated for all states.
+	bodyParts [][]byte
+}
+
+func (e *StateEvent) RawTimestamp() string {
+	parts := e.parts()
+	return string(parts[0])
+}
+
+func (e *StateEvent) NewState() string {
+	parts := e.parts()
+	return string(parts[1])
+}
+
+func (e *StateEvent) Description() string {
+	parts := e.parts()
+	return string(parts[2])
+}
+
+// LocalTunnelAddr returns the IP address of the local interface within
+// the tunnel, as a string that can be parsed using net.ParseIP.
+//
+// This field is only populated for events whose NewState returns
+// either ASSIGN_IP or CONNECTED.
+func (e *StateEvent) LocalTunnelAddr() string {
+	parts := e.parts()
+	return string(parts[3])
+}
+
+// RemoteAddr returns the non-tunnel IP address of the remote
+// system that has connected to the local OpenVPN process.
+//
+// This field is only populated for events whose NewState returns
+// CONNECTED.
+func (e *StateEvent) RemoteAddr() string {
+	parts := e.parts()
+	return string(parts[4])
+}
+
+func (e *StateEvent) String() string {
+	newState := e.NewState()
+	switch newState {
+	case "ASSIGN_IP":
+		return fmt.Sprintf("%s: %s", newState, e.LocalTunnelAddr())
+	case "CONNECTED":
+		return fmt.Sprintf("%s: %s", newState, e.RemoteAddr())
+	default:
+		desc := e.Description()
+		if desc != "" {
+			return fmt.Sprintf("%s: %s", newState, desc)
+		} else {
+			return newState
+		}
+	}
+}
+
+func (e *StateEvent) parts() [][]byte {
+	if e.bodyParts == nil {
+		// State messages currently have only five segments, but
+		// we'll ask for 5 so any additional fields that might show
+		// up in newer versions will gather in an element we're
+		// not actually using.
+		e.bodyParts = bytes.SplitN(e.body, fieldSep, 6)
+
+		// Prevent crash if the server has sent us a malformed
+		// status message. This should never actually happen if
+		// the server is behaving itself.
+		if len(e.bodyParts) < 5 {
+			expanded := make([][]byte, 5)
+			copy(expanded, e.bodyParts)
+			e.bodyParts = expanded
+		}
+	}
+	return e.bodyParts
+}
+
+// EchoEvent is emitted by an OpenVPN process running in client mode when
+// an "echo" command is pushed to it by the server it has connected to.
+//
+// The format of the echo message is free-form, since this message type is
+// intended to pass application-specific data from the server-side config
+// into whatever client is consuming the management prototcol.
+//
+// This event is emitted only if the management client has turned on events
+// of this type using client.SetEchoEvents(true)
+type EchoEvent struct {
+	body []byte
+}
+
+func (e *EchoEvent) RawTimestamp() string {
+	sepIndex := bytes.Index(e.body, fieldSep)
+	if sepIndex == -1 {
+		return ""
+	}
+	return string(e.body[:sepIndex])
+}
+
+func (e *EchoEvent) Message() string {
+	sepIndex := bytes.Index(e.body, fieldSep)
+	if sepIndex == -1 {
+		return ""
+	}
+	return string(e.body[sepIndex+1:])
+}
+
+func (e *EchoEvent) String() string {
+	return fmt.Sprintf("ECHO: %s", e.Message())
+}
+
+// ByteCountEvent represents a periodic snapshot of data transfer in bytes
+// on a VPN connection.
+//
+// For OpenVPN *servers*, events are emitted for each client and the method
+// ClientId identifies thet client.
+//
+// For other OpenVPN modes, events are emitted only once per interval for the
+// single connection managed by the target process, and ClientId returns
+// the empty string.
+type ByteCountEvent struct {
+	hasClient bool
+	body      []byte
+
+	// populated on first call to parts()
+	bodyParts [][]byte
+}
+
+func (e *ByteCountEvent) ClientId() string {
+	if !e.hasClient {
+		return ""
+	}
+
+	return string(e.parts()[0])
+}
+
+func (e *ByteCountEvent) BytesIn() int {
+	index := 0
+	if e.hasClient {
+		index = 1
+	}
+	str := string(e.parts()[index])
+	val, _ := strconv.Atoi(str)
+	// Ignore error, since this should never happen if OpenVPN is
+	// behaving itself.
+	return val
+}
+
+func (e *ByteCountEvent) BytesOut() int {
+	index := 1
+	if e.hasClient {
+		index = 2
+	}
+	str := string(e.parts()[index])
+	val, _ := strconv.Atoi(str)
+	// Ignore error, since this should never happen if OpenVPN is
+	// behaving itself.
+	return val
+}
+
+func (e *ByteCountEvent) String() string {
+	if e.hasClient {
+		return fmt.Sprintf("Client %s: %d in, %d out", e.ClientId(), e.BytesIn(), e.BytesOut())
+	} else {
+		return fmt.Sprintf("%d in, %d out", e.BytesIn(), e.BytesOut())
+	}
+}
+
+func (e *ByteCountEvent) parts() [][]byte {
+	if e.bodyParts == nil {
+		e.bodyParts = bytes.SplitN(e.body, fieldSep, 4)
+
+		wantCount := 2
+		if e.hasClient {
+			wantCount = 3
+		}
+
+		// Prevent crash if the server has sent us a malformed
+		// message. This should never actually happen if the
+		// server is behaving itself.
+		if len(e.bodyParts) < wantCount {
+			expanded := make([][]byte, wantCount)
+			copy(expanded, e.bodyParts)
+			e.bodyParts = expanded
+		}
+	}
+	return e.bodyParts
+}
+
+func upgradeEvent(raw []byte) Event {
+	splitIdx := bytes.Index(raw, eventSep)
+	if splitIdx == -1 {
+		// Should never happen, but we'll handle it robustly if it does.
+		return &MalformedEvent{raw}
+	}
+
+	keyword := raw[:splitIdx]
+	body := raw[splitIdx+1:]
+
+	switch {
+	case bytes.Equal(keyword, stateEventKW):
+		return &StateEvent{body: body}
+	case bytes.Equal(keyword, holdEventKW):
+		return &HoldEvent{body}
+	case bytes.Equal(keyword, echoEventKW):
+		return &EchoEvent{body}
+	case bytes.Equal(keyword, byteCountEventKW):
+		return &ByteCountEvent{hasClient: false, body: body}
+	case bytes.Equal(keyword, byteCountCliEventKW):
+		return &ByteCountEvent{hasClient: true, body: body}
+	default:
+		return &UnknownEvent{keyword, body}
+	}
+}
diff --git a/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/server.go b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/server.go
new file mode 100644
index 0000000..d7defd4
--- /dev/null
+++ b/vendor/github.com/apparentlymart/go-openvpn-mgmt/openvpn/server.go
@@ -0,0 +1,172 @@
+package openvpn
+
+import (
+	"net"
+	"time"
+)
+
+// MgmtListener accepts incoming connections from OpenVPN.
+//
+// The primary way to instantiate this type is via the function Listen.
+// See its documentation for more information.
+type MgmtListener struct {
+	l net.Listener
+}
+
+// NewMgmtListener constructs a MgmtListener from an already-established
+// net.Listener. In most cases it will be more convenient to use
+// the function Listen.
+func NewMgmtListener(l net.Listener) *MgmtListener {
+	return &MgmtListener{l}
+}
+
+// Listen opens a listen port and awaits incoming connections from OpenVPN
+// processes.
+//
+// OpenVPN will behave in this manner when launched with the following options:
+//
+//    --management ipaddr port --management-client
+//
+// Note that in this case the terminology is slightly confusing, since from
+// the standpoint of TCP/IP it is OpenVPN that is the client and our program
+// that is the server, but once the connection is established the channel
+// is indistinguishable from the situation where OpenVPN exposed a management
+// *server* and we connected to it. Thus we still refer to our program as
+// the "client" and OpenVPN as the "server" once the connection is established.
+//
+// When running on Unix systems it's possible to instead listen on a Unix
+// domain socket. To do this, pass an absolute path to the socket as
+// the listen address, and then run OpenVPN with the following options:
+//
+//    --management /path/to/socket unix --management-client
+//
+func Listen(laddr string) (*MgmtListener, error) {
+	proto := "tcp"
+	if len(laddr) > 0 && laddr[0] == '/' {
+		proto = "unix"
+	}
+	listener, err := net.Listen(proto, laddr)
+	if err != nil {
+		return nil, err
+	}
+
+	return NewMgmtListener(listener), nil
+}
+
+// Accept waits for and returns the next connection.
+func (l *MgmtListener) Accept() (*IncomingConn, error) {
+	conn, err := l.l.Accept()
+	if err != nil {
+		return nil, err
+	}
+
+	return &IncomingConn{conn}, nil
+}
+
+// Close closes the listener. Any blocked Accept operations
+// will be blocked and each will return an error.
+func (l *MgmtListener) Close() error {
+	return l.l.Close()
+}
+
+// Addr returns the listener's network address.
+func (l *MgmtListener) Addr() net.Addr {
+	return l.l.Addr()
+}
+
+// Serve will await new connections and call the given handler
+// for each.
+//
+// Serve does not return unless the listen port is closed; a non-nil
+// error is always returned.
+func (l *MgmtListener) Serve(handler IncomingConnHandler) error {
+	defer l.Close()
+
+	var tempDelay time.Duration
+
+	for {
+		incoming, err := l.Accept()
+		if err != nil {
+			if ne, ok := err.(net.Error); ok && ne.Temporary() {
+				if tempDelay == 0 {
+					tempDelay = 5 * time.Millisecond
+				} else {
+					tempDelay *= 2
+				}
+				if max := 1 * time.Second; tempDelay > max {
+					tempDelay = max
+				}
+
+				// Wait a while before we try again.
+				time.Sleep(tempDelay)
+				continue
+			} else {
+				// Listen socket is permanently closed or errored,
+				// so it's time for us to exit.
+				return err
+			}
+		}
+
+		// always reset our retry delay once we successfully read
+		tempDelay = 0
+
+		go handler.ServeOpenVPNMgmt(*incoming)
+	}
+}
+
+type IncomingConn struct {
+	conn net.Conn
+}
+
+// Open initiates communication with the connected OpenVPN process,
+// and establishes the channel on which events will be delivered.
+//
+// See the documentation for NewClient for discussion about the requirements
+// for eventCh.
+func (ic IncomingConn) Open(eventCh chan<- Event) *MgmtClient {
+	return NewClient(ic.conn, eventCh)
+}
+
+// Close abruptly closes the socket connected to the OpenVPN process.
+//
+// This is a rather abrasive way to close the channel, intended for rejecting
+// unwanted incoming clients that may or may not speak the OpenVPN protocol.
+//
+// Once communication is accepted and established, it is generally better
+// to close the connection gracefully using commands on the client returned
+// from Open.
+func (ic IncomingConn) Close() error {
+	return ic.conn.Close()
+}
+
+type IncomingConnHandler interface {
+	ServeOpenVPNMgmt(IncomingConn)
+}
+
+// IncomingConnHandlerFunc is an adapter to allow the use of ordinary
+// functions as connection handlers.
+//
+// Given a function with the appropriate signature, IncomingConnHandlerFunc(f)
+// is an IncomingConnHandler that calls f.
+type IncomingConnHandlerFunc func(IncomingConn)
+
+func (f IncomingConnHandlerFunc) ServeOpenVPNMgmt(i IncomingConn) {
+	f(i)
+}
+
+// ListenAndServe creates a MgmtListener for the given listen address
+// and then calls AcceptAndServe on it.
+//
+// This is just a convenience wrapper. See the AcceptAndServe method for
+// more details. Just as with AcceptAndServe, this function does not return
+// except on error; in addition to the error cases handled by AcceptAndServe,
+// this function may also fail if the listen socket cannot be established
+// in the first place.
+func ListenAndServe(laddr string, handler IncomingConnHandler) error {
+	listener, err := Listen(laddr)
+	if err != nil {
+		return err
+	}
+
+	return listener.Serve(handler)
+}