RemoteInputProtocol

Warning /!\ This protocol is a work in progress and is not complete.

The remote input server uses an open protocol with encryption and authentication to communicate between the clients and the server.

Security

When the client connects to the server, an SSL connection must be initiated immediately. Most remote input server installations use self-signed certificates, so the client should be able to verify the server through the SSL certificate fingerprint. The fingerprint is a digest (usually SHA1) of the DER form of the SSL certificate. It may be determined on the server by running:

$ openssl x509 -noout -in <certificate file> -fingerprint

If the client cannot verify the certificate through the certificate authority chain or by fingerprint verification it must close the connection immediately.

Authentication

After the SSL connection has been created, the client must send authentication credentials to the server. The credentials have the following form:

Field Bytes Type
Credentials Length 1 Unsigned Integer
NULL 1
Username Indeterminate UTF-8 Null-Terminated String
Password Indeterminate UTF-8 Null-Terminated String

The credentials length field specifies the total size of the following fields. The NULL field must be set to 0. These fields put two limits on the username and password:

  1. The combined length of the username and password, not including the null terminator, must be less than 253.
  2. The username and the password may not include the null character.

The server must validate the credentials. The server sends a one byte message to the client indicating whether the credentials are valid:

Result Value Character
Authenticated 97 'a'
Invalid 105 'i'

If the result was invalid, the server must immediately close all communication with the client after sending the credential validation result. If the client was authenticated, the client should begin the input device initialization process.

Remote Input Message Protocol

All communication after the channel has been secured and authenticated must follow the Remote Input Message Protocol. The remote input client may terminate the connection with the server at any point, and the server must immediately destroy all state associated with the connection. The server must not terminate the connection except after an error message with a type that requires the server to do so. Any other connection termination by the server should be interpreted by the client to be in error.

All messages are padded as necessary to have a length of 12 bytes. All values larger than one byte in length are in network byte order. The first four bytes are an unsigned integer specifying the message type. The following messages are supported in version 1 of the remote input message protocol:

Remote Input Protocol Version Message

This message, sent by the remote input server, specifies the version of the remote input message protocol. This standard defines only version 1 of the protocol, so the value must be 1.

Field Bytes Type Value
Message Type 4 Unsigned Integer 0
Version 4 Unsigned Integer Remote input message protocol version, must be 1 in this standard

Input Device Set Capability Message

This message, sent by the remote input client, specifies a capability of the remote input device. The server must ensure that the input device instantiated is capable of receiving events of this type.

Field Bytes Type Value
Message Type 4 Unsigned Integer 1
Capability Category 2 Unsigned Integer See capability categories below
Capability Code 2 Unsigned Integer Capability code, specific to capability type, see rinput.h header file for values

Capability Categories

The following capability categories are specified for version 1 of the remote input message protocol. Values are provided in the rinput.h header file.

Value Description
RINPUT_EV_KEY Key and button presses that have on/off states, i.e. keyboard keys and mouse buttons
RINPUT_EV_REL Relative value events, i.e. mouse pointer movements
RINPUT_EV_ABS Absolute value events, i.e. track pad event locations
RINPUT_EV_MSC Miscellaneous input events, not generally useful for remote input devices
RINPUT_EV_SW Switches that generally have two states, i.e. lid switch
RINPUT_EV_LED Output event sent from server to client, has on/off state
RINPUT_EV_SND Output event sent from server to client, momentary trigger
RINPUT_EV_UTF8 Unicode character input event

Event capability categories not listed above, such as force feedback events, are not supported in this version of the remote input message protocol.

Input Device Set Absolute Axis Parameter

This message informs the remote input server of special parameters related to absolute input events. The maximum and minimum parameters determine the maximum and minimum values that may be generated in an event on the axis. The fuzz parameter sets a zone around the previous absolute event wherein current event values within the zone are gradually averaged with the previous event. The flat parameter specifies a dead zone around the previous event wherein current event values within the zone are ignored.

All parameter values for all axes default to 0 if no message specifying otherwise is sent.

Field Bytes Type Value
Message Type 4 Unsigned Integer 2
Absolute Axis 2 Unsigned Integer An absolute axis, see rinput.h for possible values
Parameter Type 2 Unsigned Integer An absolute axis parameter, see table below
Value 4 Signed Integer Parameter value

Absolute Axis Parameter Types

The following absolute axis parameter types are specified for version 1 of the remote input message protocol. Values are provided in the rinput.h header file.

Value Description
RINPUT_ABS_PARAM_MAX Maximum possible value of absolute events for the specified axis
RINPUT_ABS_PARAM_MIN Minimum possible value of absolute events for the specified axis
RINPUT_ABS_PARAM_FUZZ Fuzz factor for absolute events for the specified axis
RINPUT_ABS_PARAM_FLAT Dead zone for absolute events for the specified axis

Input Device Create Message

This message informs the remote input server that the full capabilities of the remote input device have been set. The server must then create the input device. After the server creates the input device it must echo the create message back to the client. When the client receives the create message echo it may begin sending input events.

Field Bytes Type Value
Message Type 4 Unsigned Integer 3

Input Device Destroy Message

This message informs the remote input server that the input device must be destroyed.

Field Bytes Type Value
Message Type 4 Unsigned Integer 4

Input Device Event Message

This message informs the receiver of an input event. LED and sound events may only be sent by the server to the client. All other events may only be sent by the client to the receiver.

After all events occurring at a single point in time are sent, the RINPUT_EV_SYN event must be sent. This event tells the server to process the preceding events as though they occurred at the same time. For example, if the mouse pointer moved one point up and to the right, an RINPUT_REL_X and RINPUT_REL_Y relative events would be sent followed by an RINPUT_EV_SYN event. The code and value of syn events are undefined.

Field Bytes Type Value
Message Type 4 Unsigned Integer 5
Input Event Type 2 Unsigned Integer Input event category type, see rinput.h header file for values
Input Event Code 2 Unsigned Integer Input event code specific to input event category, see rinput.h header file for values
Input Event Value 4 Signed Integer Input event value specific to input event code and category type

Input Device UTF-8 event Message

This message informs the remote input server that a key signifying a Unicode character generated an event. It has the same message type as normal input event messages, but the data has a different format.

Field Bytes Type Value
Message Type 4 Unsigned Integer 5
Input Event Type 2 Unsigned Integer RINPUT_EV_UTF8
Input Event Value 2 Signed Integer Input event value specific to input event code and category type
Character 4 Byte Array UTF-8 encoded Unicode character

Input Device Error Message

The remote input server must send an error message to the client if certain errors are encountered.

Field Bytes Type Value
Message Type 4 Unsigned Integer 6
Error Type 4 Unsigned Integer Error type value
Error Code 1 2 Unsigned Integer First error code specific to error type
Error Code 2 2 Unsigned Integer Second error code specific to error type

Error Events and Codes

If any of the following events occurs in the remote input server, it must send the matching event error code to the client. If the error requires the server to close the connection, the server must close the connection immediately after sending the error message.

Error Event When it may occur Error Type Error Code 1 Meaning Error Code 2 Meaning Server closes connection
Internal error causing premature termination of service not matching any other defined error Any time 0 Yes
Input device allocation failed After client connects but before the server processes any input event set capability messages 1 Yes
Message type invalid After client sends a remote input message 2 Received message type No
Capability type invalid After client sends an input device set capability message 3 Received capability type No
Capability set operation failed After client sends an input device set capability message 4 Received capability type Received capability code No
Absolute axis invalid After client sends an input device set absolute axis parameter message 5 Received absolute axis No
Absolute axis parameter type invalid After client sends an input device set absolute axis parameter message 6 Received absolute axis parameter type No
Input device creation failed After client sends an input device create message 7 Yes
Input device event message failed After server receives input device event message 8 Received input event type Received input event code No
Authenticate revoked by server Any time 9 Yes

Input Device Initialization

After the communication channel has been secured and authenticated, the client must begin initializing the input device to be instantiated by the server. All messages after authentication must conform to the remote input message protocol.

At any point the server may send an error message to the client and, if required for the error type, then terminate the connection.

The following initialization steps must be performed by the client in order:

Receive remote input protocol version message from server

The client must receive the protocol version and determine whether to proceed based on whether the client supports the protocol version. If the client does not proceed, it must immediately terminate communication with the server.

Set input device capabilities

The client must send the capabilities of the input device it represents. The client must listen for error messages while setting capabilities. These error messages may indicate capabilities that are unsupported by the server.

Set absolute axis parameter values

The client must send absolute axis parameter values for all axes the device sent capability messages for. All parameters default to 0, so only parameters differing from 0 must be specified.

Example: Simple one button mouse

To set the capabilities for a simple remote mouse with one button and no scroll wheels, send input event set capability messages with the following values (defined in rinput.h header file):

Message Type Capability Category Capability Code
1 RINPUT_EV_KEY RINPUT_BTN_MOUSE
1 RINPUT_EV_REL RINPUT_REL_X
1 RINPUT_EV_REL RINPUT_REL_Y

Create input device

The client must send the input device create message after all the device capabilities have been set.

Receive input device create echo

The client must receive the input device create message echoed back by the server before it may continue.

Input Device Events

After the remote input device has been initialized, the client may send input device event messages. There is no explicit documentation for the values allowed, but they may be inferred from the rinput.h header file. Input events for unset capabilities and/or events for invalid input types or codes will generate error messages from the server.

One special addition to the input protocol is necessary for momentary key presses. When the server receives a key event with value 256 it must immediately propagate two key events with the same code to the input subsystem: the first with value 1 and the second with value 0. In between the two events the server must also pass a syn event to the input subsystem if required for the platform.

After any message, the server may send an error message back. The error message is in reference to a previous remote input event message, but the specific message causing the error is left unspecified.

When the remote input client intends to end the remote input session it must immediately close the communication channel to the remote input server.

RemoteInput/RemoteInputProtocol (last edited 2009-10-12 16:02:52 by chasedouglas)