Barrier client protocol — QEMU documentation

# Barrier client protocol

QEMU’s `input-barrier` device implements the client end of the KVM (Keyboard-Video-Mouse) software Barrier.

This document briefly describes the protocol as we implement it.

## Message format

Message format between the server and client is in two parts:

1. the payload length, a 32bit integer in network endianness

2. the payload

The payload starts with a 4byte string (without NUL) which is the command. The first command between the server and the client is the only command not encoded on 4 bytes (“Barrier”). The remaining part of the payload is decoded according to the command.

## Protocol Description

This comes from `barrier/src/lib/barrier/protocol_types.h`.

### barrierCmdHello “Barrier”

Direction:

  server -> client

Parameters:

  `{ int16_t minor, int16_t major }`

Description:

  Say hello to client

  `minor` = protocol major version number supported by server

  `major` = protocol minor version number supported by server

### barrierCmdHelloBack “Barrier”

Direction:

  client ->server

Parameters:

  `{ int16_t minor, int16_t major, char *name}`

Description:

  Respond to hello from server

  `minor` = protocol major version number supported by client

  `major` = protocol minor version number supported by client

  `name` = client name

### barrierCmdDInfo “DINF”

Direction:

  client ->server

Parameters:

  `{ int16_t x_origin, int16_t y_origin, int16_t width, int16_t height, int16_t x, int16_t y}`

Description:

  The client screen must send this message in response to the barrierCmdQInfo message. It must also send this message when the screen’s resolution changes. In this case, the client screen should ignore any barrierCmdDMouseMove messages until it receives a barrierCmdCInfoAck in order to prevent attempts to move the mouse off the new screen area.

### barrierCmdCNoop “CNOP”

Direction:

  client -> server

Parameters:

  None

Description:

  No operation

### barrierCmdCClose “CBYE”

Direction:

  server -> client

Parameters:

  None

Description:

  Close connection

### barrierCmdCEnter “CINN”

Direction:

  server -> client

Parameters:

  `{ int16_t x, int16_t y, int32_t seq, int16_t modifier }`

Description:

  Enter screen.

  `x`, `y` = entering screen absolute coordinates

  `seq` = sequence number, which is used to order messages between screens. the secondary screen must return this number with some messages

  `modifier` = modifier key mask. this will have bits set for each toggle modifier key that is activated on entry to the screen. the secondary screen should adjust its toggle modifiers to reflect that state.

### barrierCmdCLeave “COUT”

Direction:

  server -> client

Parameters:

  None

Description:

  Leaving screen. the secondary screen should send clipboard data in response to this message for those clipboards that it has grabbed (i.e. has sent a barrierCmdCClipboard for and has not received a barrierCmdCClipboard for with a greater sequence number) and that were grabbed or have changed since the last leave.

### barrierCmdCClipboard “CCLP”

Direction:

  server -> client

Parameters:

  `{ int8_t id, int32_t seq }`

Description:

  Grab clipboard. Sent by screen when some other app on that screen grabs a clipboard.

  `id` = the clipboard identifier

  `seq` = sequence number. Client must use the sequence number passed in the most recent barrierCmdCEnter. the server always sends 0.

### barrierCmdCScreenSaver “CSEC”

Direction:

  server -> client

Parameters:

  `{ int8_t started }`

Description:

  Screensaver change.

  `started` = Screensaver on primary has started (1) or closed (0)

### barrierCmdCResetOptions “CROP”

Direction:

  server -> client

Parameters:

  None

Description:

  Reset options. Client should reset all of its options to their defaults.

### barrierCmdCInfoAck “CIAK”

Direction:

  server -> client

Parameters:

  None

Description:

  Resolution change acknowledgment. Sent by server in response to a client screen’s barrierCmdDInfo. This is sent for every barrierCmdDInfo, whether or not the server had sent a barrierCmdQInfo.

### barrierCmdCKeepAlive “CALV”

Direction:

  server -> client

Parameters:

  None

Description:

  Keep connection alive. Sent by the server periodically to verify that connections are still up and running. clients must reply in kind on receipt. if the server gets an error sending the message or does not receive a reply within a reasonable time then the server disconnects the client. if the client doesn’t receive these (or any message) periodically then it should disconnect from the server. the appropriate interval is defined by an option.

### barrierCmdDKeyDown “DKDN”

Direction:

  server -> client

Parameters:

  `{ int16_t keyid, int16_t modifier [,int16_t button] }`

Description:

  Key pressed.

  `keyid` = X11 key id

  `modified` = modified mask

  `button` = X11 Xkb keycode (optional)

### barrierCmdDKeyRepeat “DKRP”

Direction:

  server -> client

Parameters:

  `{ int16_t keyid, int16_t modifier, int16_t repeat [,int16_t button] }`

Description:

  Key auto-repeat.

  `keyid` = X11 key id

  `modified` = modified mask

  `repeat` = number of repeats

  `button` = X11 Xkb keycode (optional)

### barrierCmdDKeyUp “DKUP”

Direction:

  server -> client

Parameters:

  `{ int16_t keyid, int16_t modifier [,int16_t button] }`

Description:

  Key released.

  `keyid` = X11 key id

  `modified` = modified mask

  `button` = X11 Xkb keycode (optional)

### barrierCmdDMouseDown “DMDN”

Direction:

  server -> client

Parameters:

  `{ int8_t button }`

Description:

  Mouse button pressed.

  `button` = button id

### barrierCmdDMouseUp “DMUP”

Direction:

  server -> client

Parameters:

  `{ int8_t button }`

Description:

  Mouse button release.

  `button` = button id

### barrierCmdDMouseMove “DMMV”

Direction:

  server -> client

Parameters:

  `{ int16_t x, int16_t y }`

Description:

  Absolute mouse moved.

  `x`, `y` = absolute screen coordinates

### barrierCmdDMouseRelMove “DMRM”

Direction:

  server -> client

Parameters:

  `{ int16_t x, int16_t y }`

Description:

  Relative mouse moved.

  `x`, `y` = r relative screen coordinates

### barrierCmdDMouseWheel “DMWM”

Direction:

  server -> client

Parameters:

  `{ int16_t x , int16_t y }` or `{ int16_t y }`

Description:

  Mouse scroll. The delta should be +120 for one tick forward (away from the user) or right and -120 for one tick backward (toward the user) or left.

  `x` = x delta

  `y` = y delta

### barrierCmdDClipboard “DCLP”

Direction:

  server -> client

Parameters:

  `{ int8_t id, int32_t seq, int8_t mark, char *data }`

Description:

  Clipboard data.

  `id` = clipboard id

  `seq` = sequence number. The sequence number is 0 when sent by the server. Client screens should use the/ sequence number from the most recent barrierCmdCEnter.

### barrierCmdDSetOptions “DSOP”

Direction:

  server -> client

Parameters:

  `{ int32 t nb, { int32_t id, int32_t val }[] }`

Description:

  Set options. Client should set the given option/value pairs.

  `nb` = numbers of `{ id, val }` entries

  `id` = option id

  `val` = option new value

### barrierCmdDFileTransfer “DFTR”

Direction:

  server -> client

Parameters:

  `{ int8_t mark, char *content }`

Description:

  Transfer file data.

  - `mark` = 0 means the content followed is the file size

  - 1 means the content followed is the chunk data

  - 2 means the file transfer is finished

### barrierCmdDDragInfo “DDRG”

Direction:

  server -> client

Parameters:

  `{ int16_t nb, char *content }`

Description:

  Drag information.

  `nb` = number of dragging objects

  `content` = object’s directory

### barrierCmdQInfo “QINF”

Direction:

  server -> client

Parameters:

  None

Description:

  Query screen info

  Client should reply with a barrierCmdDInfo

### barrierCmdEIncompatible “EICV”

Direction:

  server -> client

Parameters:

  `{ int16_t nb, major *minor }`

Description:

  Incompatible version.

  `major` = major version

  `minor` = minor version

### barrierCmdEBusy “EBSY”

Direction:

  server -> client

Parameters:

  None

Description:

  Name provided when connecting is already in use.

### barrierCmdEUnknown “EUNK”

Direction:

  server -> client

Parameters:

  None

Description:

  Unknown client. Name provided when connecting is not in primary’s screen configuration map.

### barrierCmdEBad “EBAD”

Direction:

  server -> client

Parameters:

  None

Description:

  Protocol violation. Server should disconnect after sending this message.