2.2.1 Shared Message Header (SHARED_MSG_HEADER)

Every packet in this extension contains a common header.<1>

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InterfaceId																														Mask
MessageId
FunctionId (optional)
messagePayload (variable)
...

InterfaceId (30 bits): A 30-bit field that represents the common identifier for the interface. Some interfaces have predefined default IDs. If the message uses a default interface ID, the message is interpreted for the associated interface. All other values MUST be retrieved either from a Query Interface response (QI_RSP) ([MS-RDPEXPS] section 2.2.2.1.2) or from responses that contain interface IDs. The highest two bits of the NetInterfaceId field in a QI_RSP message MUST be ignored.

This interface ID is valid until it is sent or received in an Interface Release (IFACE_RELEASE) message ([MS-RDPEXPS] section 2.2.2.2). After an IFACE_RELEASE message is processed, the ID is considered invalid.

Mask (2 bits): The 2 bits of the Mask field MUST be set to one of the following values.

Value	Meaning
STREAM_ID_STUB 0x2	Indicates that the SHARED_MSG_HEADER is being used in a response message.
STREAM_ID_PROXY 0x1	Indicates that the SHARED_MSG_HEADER is not being used in a response message.
STREAM_ID_NONE 0x0	Indicates that the SHARED_MSG_HEADER is being used for interface manipulation capabilities exchange as specified in section 2.2.3. This value MUST NOT be used for any other messages.

MessageId (4 bytes): A 32-bit unsigned integer. A unique ID for the request or response pair. Requests and responses are matched based on this ID coupled with the InterfaceId.

FunctionId (4 bytes): A 32-bit unsigned integer. This field MUST be present in all packets except response packets. Its value is either used in interface manipulation messages or defined for a specific interface. The following values are categorized by the interface for which they are defined.

Common IDs for all interfaces are as follows.

Value	Meaning
RIMCALL_RELEASE 0x00000001	Release the given interface ID.
RIMCALL_QUERYINTERFACE 0x00000002	Query for a new interface.

Capabilities Negotiator Interface IDs are as follows.

Value	Meaning
RIM_EXCHANGE_CAPABILITY_REQUEST 0x00000100	The server sends the Interface Manipulation Exchange Capabilities Request message.

Client Request Completion Interface IDs are as follows.

Value	Meaning
IOCONTROL_COMPLETION 0x00000100	The client sends the IO Control Completion message.
URB_COMPLETION 0x00000101	The client sends the URB Completion message.
URB_COMPLETION_NO_DATA 0x00000102	The client sends the URB Completion No Data message.

Server USB Device Interface IDs are as follows.

Value	Meaning
CANCEL_REQUEST 0x00000100	The server sends the Cancel Request message.
REGISTER_REQUEST_CALLBACK 0x00000101	The server sends the Register Request Callback message.
IO_CONTROL 0x00000102	The server sends the IO Control message.
INTERNAL_IO_CONTROL 0x00000103	The server sends the Internal IO Control message.
QUERY_DEVICE_TEXT 0x00000104	The server sends the Query Device Text message.
TRANSFER_IN_REQUEST 0x00000105	The server sends the Transfer In Request message.
TRANSFER_OUT_REQUEST 0x00000106	The server sends the Transfer Out Request message.
RETRACT_DEVICE 0x00000107	The server sends the Retract Device message.

Client Device Sink Interface IDs are as follows.

Value	Meaning
ADD_VIRTUAL_CHANNEL 0x00000100	The client sends the Add Virtual Channel message.
ADD_DEVICE 0x00000101	The client sends the Add Device message.

Channel Notification Interface IDs are as follows.

Value	Meaning
CHANNEL_CREATED 0x00000100	The server and the client send the Channel Created message.

messagePayload (variable): An array of unsigned 8-bit integers. The remainder of the message is interpreted based on the interface for which the packet is sent. This field is optional based on the packet length.