RemoteInputProtocol

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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. This message, sent by the remote input client, specifies a capability category of the remote input device. To enable event capabilities in a category, the category itself must first be enabled. The server must ensure that the input device instantiated is capable of receiving events of this category type.
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Capability Type; 4; Unsigned Integer; See table below
Capability Code; 2; Unsigned Integer; Capability code, specific to capability type, see linux/input.h header file for values		 Capability Category; 2; Unsigned Integer; See rinput.h for values
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==== Capability Types ====
There a seven capability event categories. To enable event capabilities in a category, the category itself must be enabled. This is accomplished by using the Input Event Capability Category type and the category's type value as defined in linux/input.h. After enabling a capability category, event capabilities may be set. This is accomplished by using the event capability type value listed in the table below with the capability code listed in linux/input.h.

/!\ '''Note: The category type values in linux/input.h may or may not equal the category type value specified in the table below.'''		 ==== Capability Categories ====
The following capability categories are specified for version 1 of the remote input message protocol. Values are provided in rinput.h header file.
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Description; Value
Input Event Capability Category; 0
Key Event; 1
Relative Event; 2
Absolute Event; 3
Miscellaneous Event; 4
Switch Event; 5
LED Output Event; 17
Sound Output Event; 18		 Value; Description
EV_SYN; Synthesis messages, not usually useful for remote input devices
EV_KEY; Key and button presses that have on/off states, i.e. keyboard keys and mouse buttons
EV_REL; Relative value events, i.e. mouse pointer movements
EV_ABS; Absolute value events, i.e. track pad event locations
EV_MSC; Miscellaneous input events, not generally useful for remote input devices
EV_SW; Switches that generally have two states, i.e. lid switch
EV_LED; Output event sent from server to client, has on/off state
EV_SND; Output event sent from server to client, momentary trigger
EV_REP; Auto-repeat settings
EV_PWR; Power switch
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=== Input Device Set Capability Event Message ===
This message, sent by the remote input client, specifies a capability event of the remote input device. The server must ensure that the input device instantiated is capable of receiving events of this type.

{{{#!CSV
Field; Bytes; Type; Value
Message Type; 4; Unsigned Integer; 2
Capability Category; 2; Unsigned Integer; See capability categories above
Capability Code; 2; Unsigned Integer; Capability code, specific to capability type, see rinput.h header file for values
}}}
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Message Type; 4; Unsigned Integer; 2 Message Type; 4; Unsigned Integer; 3
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Message Type; 4; Unsigned Integer; 3 Message Type; 4; Unsigned Integer; 4
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Message Type; 4; Unsigned Integer; 4
Input Event Type; 2; Unsigned Integer; Input event category type, see linux/input.h for values
Input Event Code; 2; Unsigned Integer; Input event code specific to input event category, see linux/input.h for values		 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
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/!\ '''Note: The input event category type value used in this message must conform to the values in linux/input.h, which may or may not equal the category values used during the set capability message'''
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Message Type; 4; Unsigned Integer; 5 Message Type; 4; Unsigned Integer; 6
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After the remote input device has been initialized, the client may send input device event messages. These event messages must match the format expected by the Linux input device subsystem. There is no documentation on the values allowed, but they can be inferred from linux/input.h. 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.

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

Contents

  1. Security
  2. Authentication
  3. Remote Input Message Protocol
    1. Remote Input Protocol Version Message
    2. Input Device Set Capability Message
    3. Input Device Set Capability Event Message
    4. Input Device Create Message
    5. Input Device Destroy Message
    6. Input Device Event Message
    7. Input Device Error Message
  4. Input Device Initialization
    1. Receive remote input protocol version message from server
    2. Set input device capabilities
    3. Create input device
  5. Input Device Events

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 category of the remote input device. To enable event capabilities in a category, the category itself must first be enabled. The server must ensure that the input device instantiated is capable of receiving events of this category type.

Field Bytes Type Value
Message Type 4 Unsigned Integer 1
Capability Category 2 Unsigned Integer See rinput.h for values

Capability Categories

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

Value Description
EV_SYN Synthesis messages, not usually useful for remote input devices
EV_KEY Key and button presses that have on/off states, i.e. keyboard keys and mouse buttons
EV_REL Relative value events, i.e. mouse pointer movements
EV_ABS Absolute value events, i.e. track pad event locations
EV_MSC Miscellaneous input events, not generally useful for remote input devices
EV_SW Switches that generally have two states, i.e. lid switch
EV_LED Output event sent from server to client, has on/off state
EV_SND Output event sent from server to client, momentary trigger
EV_REP Auto-repeat settings
EV_PWR Power switch

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 Capability Event Message

This message, sent by the remote input client, specifies a capability event 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 2
Capability Category 2 Unsigned Integer See capability categories above
Capability Code 2 Unsigned Integer Capability code, specific to capability type, see rinput.h header file for values

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.

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 remote input server that the remote input client had an input event.

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 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 Code 4 Unsigned Integer Error code value

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 Code Server closes connnection
Internal error causing premature termination of service of not matching any other error defined below 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 No
Capability type invalid After client sends an input device set capability message 3 No
Capability set operation failed After client sends an input device set capability message 4 No
Input device creation failed After client sends an input device create message 5 Yes
Input device event message failed After server receives input device event message 6 No

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 allowed 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. First, it must send messages enabling input event category types. Then, it must send messages enabling specific capabilities for each enabled category type.

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:

Message Type Capability Type (From Remote Input Set Capability Message Capability Types) Capability Code (From linux/input.h)
1 0 (Input Event Capability Category) EV_KEY (Enable button capability for mouse button)
1 0 (Input Event Capability Category) EV_REL (Enable relative capability for mouse movement)
1 1 (Key Event Capability Category) BTN_MOUSE
1 2 (Relative Event Capability Category) REL_X
1 2 (Relative Event Capability Category) REL_Y

Create input device

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

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.

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.

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 cpe-75-180-27-10)