Management Interface "echo" protocol
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THIS IS A PRELIMINARY VERSION OF THIS DOCUMENT. ALL INFORMATION IN IT
IS SUBJECT TO CHANGE.
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CONTENTS
THE OPENVPN --ECHO OPTION
ENVIRONMENT COMMAND
MESSSAGE COMMANDS
PASSWORD COMMANDS
QUOTING
COMMMAND DETAILS
=========================
THE OPENVPN --ECHO OPTION
=========================
The OpenVPN --echo option causes commands to be sent out through the
management interface, typically to a Graphic User Interface (GUI) such
as "OpenVPN for Android", "Tunnelblick" (for macOS), or "Windows
OpenVPN GUI". It can be included in a configuration file or on a
command line, or can be pushed from the server.
This document describes the commands that can be sent and how they are
interpreted by various GUIs.
* OpenVPN does not process the commands in an --echo option; it only
sends them out through the management interface.
* "echo" commands are processed by the GUI if, as, when, and in the
order they are received. If no GUI is present the processing of
commands may be delayed, the commands may never be processed, or only
some commands may be processed. (That can happen if OpenVPN discards
commands because its buffer for the commands fills up.)
* There is no mechanism for the GUI to acknowledge the receipt,
success, or failure of a command.
* "echo" commands are stored by OpenVPN (within limits, see the next
point) and sent only when the GUI requests them through the management
interface. "echo" commands in the configuration file or the command
line are typically requested and processed at the start of a
connection attempt. "echo" commands that are pushed by the server are
also typically asked for at the start of a connection attempt but can
be sent at any time. They are processed in the middle of a connection
attempt or after a connection is established, as the "push" options
are received by the client from the server.
* OpenVPN's storage for echo commands is limited in size, so a large
number of commands or commands with long messages may require that
some commands be removed from the storage. If that happens, some of
the commands may not be sent through the management interface when a
GUI does connect to it or asks for the "echo" commands.
* On SIGUSR1 and SIGHUP connection restarts, "echo" commands that
were sent through the management interface and have been saved by
OpenVPN are sent again and will be re-processed by the GUI. (The
message commands include a mechanism for muting (skipping) duplicate
messages, see MESSAGE COMMANDS, below.)
* OpenVPN limits the number of separate arguments in each line of a
configuration file. Arguments may be quoted to work around this
limitation, see QUOTING, below.
* OpenVPN limits the size of each "echo" command sent over the
management interface to 255 bytes, including overhead characters. To
allow messages of arbitrary length, several message commands can be
concatenated together before being displayed to the user, see MESSAGE
COMMANDS, below.
* There no indication to the GUI of the source of the command
(configuration file, command line option, or pushed from a server). It
might be possible for the GUI to deduce that a command was pushed from
a server because of timing or other management interface interactions.
===================
ENVIRONMENT COMMAND
===================
Typically, a GUI allows users to specify shell commands (typically
scripts) to run at certain points in the connection/disconnection
process, in addition to those provided by OpenVPN options such as
"--up" and "--down".
The "setenv" command can be used to set environment variables that are
available to the scripts run by the GUI. Each "setenv" command
specifies a value for one environment variable that is available to
the scripts that the GUI runs.
This is similar to Openvpn's "--setenv" option, which specifies an
additional environment variable that is included in the environment
variables that are available to the scripts that OpenVPN runs.
=================
MESSSAGE COMMANDS
=================
Four commands can be used to display a message to the user from the
OpenVPN configuration or server:
msg
msg-n
msg-window
msg-notify
"msg" and "msg-n" commands are concatenated to construct a message.
When a "msg-window"or "msg-notify" command is received the message is
displayed to the user.
Identical messages (same title, text, and destination) received during
one connection may be ignored or muted. Some GUIs may only show the
first message for a connection, or the first message shown in a window
and the first message shown as a notification.
=================
PASSWORD COMMANDS
=================
Three commands can be used to control the GUI's storage of usernames,
passwords, and private keys:
disable-save-passwords
forget-passwords
save-passwords
=======
QUOTING
=======
* In a configuration file, the rest of the line is parsed into
separate arguments and then 'echo' and the arguments are passed, each
separated by a single space, through the management interface. For
example:
echo argument1 argument2
echo " argument1 argument2"
will be sent through the management interface as
>ECHO:timestamp,argument1 argument2
>ECHO:timestamp, argument1 argument2
* In a command line option, the single argument following "--echo" is
parsed similarly, so
--echo argument1 argument2
--echo " argument1 argument2"
will be sent through the management interface as
>ECHO:timestamp,argument1 argument2
>ECHO:timestamp, argument1 argument2
* In a "push" option in a server configuration file, the single
option following "push" is parsed similarly, so
push "echo argument1 argument2 argument3 argument4"
push "echo ' argument1 argument2 argument3 argument4'"
will be sent through the management interface as
>ECHO:timestamp,argument1 argument2 argument3 argument4
>ECHO:timestamp, argument1 argument2 argument3 argument4
================
COMMMAND DETAILS
================
COMMAND -- disable-save-passwords
---------------------------------
Syntax: disable-save-passwords
The GUI is instructed to not allow the user to save passwords or
private keys for the configuration. The user is still allowed to save
usernames. Any passwords or private keys that have been saved will be
forgotten.
This command will be effective at startup only if present in the
configuration file or as a command line option. If pushed from the
server, saving passwords will be disabled in password prompts only
after the initial prompt has been shown to the user.
Android: ??????
Tunnelblick: Planned. This command will disable saving of
passwords or private keys and forget any saved usernames, passwords,
or private keys regardless of the normal (non-forced) global or
per-configuration settings. A computer administrator can "force" this
setting, overriding this command.
Windows OpenVPN GUI: Planned. This command will disable saving of
passwords or private keys and forget any saved usernames, passwords,
or private keys regardless of any global settings.
COMMAND -- forget-passwords
---------------------------
Syntax: forget-passwords
The GUI is instructed to forget any usernames, passwords, and private
keys it has saved for the configuration. Useful when pushed from the
server so that it is processed after authentication.
Android: ??????
Tunnelblick: Planned.
Windows OpenVPN GUI: supported since release 2.4.1 (GUI version 11.5.0)
COMMAND -- msg
--------------
Syntax: msg text
The text is appended to any previous text from "msg" or "msg-n"
commands, and a newline is appended after that.
A trailing newline will be removed from the completed message before
it is displayed to the user.
The text may include any UTF-8 character except a comma (","), CR
(0x0D), LF (0x0A), or NUL (0x00).
The text may not contain percent ("%") except in "percent encoding"
sequences. To display a percent sign, use %25.
The text may not contain commas (",") because of constraints imposed
by OpenVPN. Commas should be encoded using "percent encoding" (URL
encoding): a '%' character followed by two hexadecimal digits, the
high- and then low-nibble of the ASCII code for the character to be
shown. Examples: a comma is encoded as %2C or %2c; a percent sign is
encoded as %25.
Text containing comment characters # and ; must be enclosed in quotes to
survive after option parsing by openvpn.
The insertion of line endings (CR, LF) in the text is discouraged
because it is OS dependent. Instead, use the "msg" command, which
appends a line ending appropriate for the OS on which the GUI is
running.
Android: Planned.
Tunnelblick: Planned.
Windows OpenVPN GUI: supported since release v2.4.11 / v2.5.1
(GUI version v11.22.0)
COMMAND -- msg-n
----------------
Syntax: msg-n text
The text is appended to any previous text from "msg"" or "msg-n""
commands. (Like "msg" except that no newline is appended.)
See "COMMAND -- msg" for details about "text".
Android: Planned.
Tunnelblick: Planned.
Windows OpenVPN GUI: supported since release v2.4.11 / v2.5.1
(GUI version v11.22.0)
COMMAND -- msg-notify
---------------------
Syntax: msg-notify title
The text from previous "msg" and/or "msg-n" commands is displayed to
the user as a notification with title "title" and the previous text is
forgotten.
Android: Planned.
Tunnelblick: Planned.
Windows OpenVPN GUI: supported since release v2.4.11 / v2.5.1
(GUI version v11.22.0)
Note: The max length that will correctly display as a notification
message is OS dependent.
COMMAND -- msg-window title
---------------------------
Syntax: msg-window title
The text from previous "msg" and/or "msg-n" commands is displayed to
the user in a non-modal popup window with title "title" and the
previous text is forgotten. How the title is displayed exactly is left
to the implementation. Could be set as the window title or as a
differently formatted text as the heading of the message, for example.
Android: Planned.
Tunnelblick: Planned.
Windows OpenVPN GUI: supported since release v2.4.11 / v2.5.1
(GUI version v11.22.0)
COMMAND -- save-passwords
-------------------------
Syntax: save-passwords
The GUI is instructed to allow the user to save usernames, passwords
and private keys for the configuration.
This command will be effective at startup only if present in the
configuration file or as a command line option. If pushed from the
server, saving passwords will be allowed in password prompts only
after the initial prompt has been shown to the user.
This command typically has the effect of presenting the password
dialogs to the user with a "save password" checkbox checked. The user
may still uncheck it during the dialog.
Android: ??????
Tunnelblick: Planned. Tunnelblick ignores this command. Usernames,
passwords, and private keys may be saved by default, and this command
will not override the separate Tunnelblick global or per-configuration
settings used to disable saving them.
Windows OpenVPN GUI: Supported since release 2.4.1 (GUI version 11.5.0)
COMMAND -- setenv
-----------------
Syntax: setenv name value
Sets an environment variable that will be available to the scripts run
by the GUI.
This will set environment variable "OPENVPN_name" to value "value" for
the scripts run by the GUI. "name" is changed to "OPENVPN_name" to
prevent overwriting sensitive variables such as PATH. Variables are
set in the order received, with later values replacing earlier ones
for the same "name".
Names may include only alphanumeric characters and underscores. A
"setenv" command with an invalid name will be ignored.
Android: ??????
Tunnelblick: Planned.
Windows OpenVPN GUI: supported since release v2.4.7 (GUI version v11.12.0)
The variables set by "setenv" are merged with those for the process
environment. In case of duplicate names the one in the setenv list is
chosen.