mcs

package
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 Go to latest Published: Mar 29, 2026 License: MIT Imports: 9 Imported by: 0

Documentation

Overview

Package mcs implements the Multipoint Communication Service (T.125) protocol and GCC (Generic Conference Control, T.124) conference structures used in RDP.

This file contains GCC client and server data block types used within MCS Connect Initial/Response PDUs.

Index

Constants

View Source 
const (
	ClientCoreDataType     uint16 = 0xC001
	ClientSecurityDataType uint16 = 0xC002
	ClientNetworkDataType  uint16 = 0xC003
	ClientClusterDataType  uint16 = 0xC004
	ClientMonitorDataType  uint16 = 0xC005
)

GCC data block types — client to server

View Source 
const (
	ServerCoreDataType     uint16 = 0x0C01
	ServerSecurityDataType uint16 = 0x0C02
	ServerNetworkDataType  uint16 = 0x0C03
)

GCC data block types — server to client

View Source 
const (
	VersionRDP4  uint32 = 0x00080001
	VersionRDP5  uint32 = 0x00080004
	VersionRDP10 uint32 = 0x00080005
	VersionRDP61 uint32 = 0x00080006
)

RDP version constants

View Source 
const (
	ColorDepthRNS_UD_COLOR_4BPP  uint16 = 0xCA00
	ColorDepthRNS_UD_COLOR_8BPP  uint16 = 0xCA01
	ColorDepthRNS_UD_COLOR_16BPP uint16 = 0xCA02
	ColorDepthRNS_UD_COLOR_24BPP uint16 = 0xCA03
)

Color depth constants

View Source 
const (
	HighColor4BPP  uint16 = 0x0004
	HighColor8BPP  uint16 = 0x0008
	HighColor15BPP uint16 = 0x000F
	HighColor16BPP uint16 = 0x0010
	HighColor24BPP uint16 = 0x0018
)

High color depth constants

View Source 
const (
	SupportColor24BPP uint16 = 0x0001
	SupportColor16BPP uint16 = 0x0002
	SupportColor15BPP uint16 = 0x0004
	SupportColor32BPP uint16 = 0x0008
)

Supported color depth flags

View Source 
const (
	EarlyCapSupportErrInfoPDU       uint16 = 0x0001
	EarlyCapWant32BPPSession        uint16 = 0x0002
	EarlyCapSupportStatusInfoPDU    uint16 = 0x0004
	EarlyCapStrongAsymmetricKeys    uint16 = 0x0008
	EarlyCapValidConnectionType     uint16 = 0x0020
	EarlyCapSupportMonitorLayout    uint16 = 0x0040
	EarlyCapSupportDynvcGfxProtocol uint16 = 0x0100
)

Early capability flags

View Source 
const (
	KeyboardIBMPC     uint32 = 0x00000001
	KeyboardIBMAT     uint32 = 0x00000002
	KeyboardJapan     uint32 = 0x00000003
	KeyboardEnhanced  uint32 = 0x00000004
	KeyboardNokia1050 uint32 = 0x00000005
	KeyboardNokia9140 uint32 = 0x00000006
	KeyboardJapanese  uint32 = 0x00000007
)

Keyboard types

View Source 
const (
	ConnectionTypeModem      uint8 = 0x01
	ConnectionTypeBroadLow   uint8 = 0x02
	ConnectionTypeSatellite  uint8 = 0x03
	ConnectionTypeBroadHigh  uint8 = 0x04
	ConnectionTypeWAN        uint8 = 0x05
	ConnectionTypeLAN        uint8 = 0x06
	ConnectionTypeAutoDetect uint8 = 0x07
)

Connection type constants

View Source 
const (
	ChannelOptionInitialized  uint32 = 0x80000000
	ChannelOptionEncryptRDP   uint32 = 0x40000000
	ChannelOptionEncryptSC    uint32 = 0x20000000
	ChannelOptionEncryptCS    uint32 = 0x10000000
	ChannelOptionPriHigh      uint32 = 0x08000000
	ChannelOptionPriMed       uint32 = 0x04000000
	ChannelOptionPriLow       uint32 = 0x02000000
	ChannelOptionCompressRDP  uint32 = 0x00800000
	ChannelOptionCompress     uint32 = 0x00400000
	ChannelOptionShowProtocol uint32 = 0x00200000
)

Channel option flags

View Source 
const (
	RedirectionSupported          uint32 = 0x00000001
	RedirectedSessionIDFieldValid uint32 = 0x00000002
	RedirectionVersion5           uint32 = 0x04 // shifted left 2 in flags field
)

Cluster redirection flags (MS-RDPBCGR 2.2.1.3.6)

View Source 
const (
	// BER Application tags for MCS Connect PDUs
	TagConnectInitial  = 101 // Application 101, Constructed
	TagConnectResponse = 102 // Application 102, Constructed

	// PER-encoded MCS domain PDU types (first byte)
	DomainMCSPDUErectDomainRequest          = 0x04
	DomainMCSPDUAttachUserRequest           = 0x28
	DomainMCSPDUAttachUserConfirm           = 0x2C // top 6 bits: 001011, bottom 2 bits vary
	DomainMCSPDUChannelJoinRequest          = 0x38
	DomainMCSPDUChannelJoinConfirm          = 0x3C // top 6 bits: 001111, bottom 2 bits vary
	DomainMCSPDUDisconnectProviderUltimatum = 0x20 // top 6 bits: 001000, bottom 2 bits = reason[2:1]
	DomainMCSPDUSendDataRequest             = 0x64
	DomainMCSPDUSendDataIndication          = 0x68
)

MCS PDU tag constants (Application class, Constructed)

View Source 
const MonitorPrimary uint32 = 0x00000001

MonitorPrimary is the flag indicating the primary monitor in MonitorDef.

View Source 
const SASSequenceRDP uint16 = 0xAA03

SAS (Secure Attention Sequence) constant

Variables

This section is empty.

Functions

func DecodeAttachUserConfirm 

func DecodeAttachUserConfirm(log *slog.Logger, data []byte) (uint16, error)

DecodeAttachUserConfirm parses an MCS Attach User Confirm PDU. Returns the assigned user channel ID.

func DecodeChannelJoinConfirm 

func DecodeChannelJoinConfirm(log *slog.Logger, data []byte) (uint16, error)

DecodeChannelJoinConfirm parses an MCS Channel Join Confirm PDU. Returns the confirmed channel ID.

func DecodeDisconnectProviderUltimatum 

func DecodeDisconnectProviderUltimatum(log *slog.Logger, data []byte) (reason int, err error)

DecodeDisconnectProviderUltimatum parses an MCS Disconnect Provider Ultimatum. Returns the reason code (0=domain-not-hierarchical, 1=user-requested, 2=token-purged, 3=provider-initiated). The DPU is 2 bytes: byte0[1:0] || byte1[7] = 3-bit reason.

func DecodeGCCConferenceCreateResponse 

func DecodeGCCConferenceCreateResponse(data []byte) ([]byte, error)

DecodeGCCConferenceCreateResponse extracts server user data from a GCC Conference Create Response.

func DecodeSendDataIndication 

func DecodeSendDataIndication(log *slog.Logger, data []byte) (channelID uint16, userData []byte, err error)

DecodeSendDataIndication parses an MCS Send Data Indication PDU (PER-encoded). Returns the channel ID and user data payload.

PER layout:

  • Byte 0: type (0x68, top 6 bits = 011010)
  • Bytes 1-2: initiator (uint16 BE, offset by 1001) — skipped
  • Bytes 3-4: channelID (uint16 BE)
  • Byte 5: dataPriority + segmentation
  • Remaining: PER length determinant + user data

func DecodeServerData 

func DecodeServerData(log *slog.Logger, data []byte) (*ServerCoreData, *ServerSecurityData, *ServerNetworkData, error)

DecodeServerData parses GCC server data blocks from the Conference Create Response userData. Returns server core, security, and network data blocks.

func EncodeAttachUserRequest 

func EncodeAttachUserRequest() []byte

EncodeAttachUserRequest builds an MCS Attach User Request PDU (PER-encoded).

func EncodeChannelJoinRequest 

func EncodeChannelJoinRequest(userID, channelID uint16) []byte

EncodeChannelJoinRequest builds an MCS Channel Join Request PDU (PER-encoded).

func EncodeErectDomainRequest 

func EncodeErectDomainRequest() []byte

EncodeErectDomainRequest builds an MCS Erect Domain Request PDU (PER-encoded). subHeight=0, subInterval=0

func EncodeGCCConferenceCreateRequest 

func EncodeGCCConferenceCreateRequest(clientData []byte) []byte

EncodeGCCConferenceCreateRequest builds the GCC Conference Create Request with client data blocks embedded as PER-encoded user data.

func EncodeSendDataRequest 

func EncodeSendDataRequest(userID, channelID uint16, data []byte) []byte

EncodeSendDataRequest builds an MCS Send Data Request PDU header (PER-encoded).

func PDUType 

func PDUType(data []byte) byte

PDUType returns the MCS domain PDU type from the first byte (top 6 bits << 2).

Types

type ChannelDef 

type ChannelDef struct {
	Name    string // 8 bytes, null-padded ASCII
	Options uint32
}

ChannelDef represents a channel definition in the network data.

type ClientClusterData 

type ClientClusterData struct {
	Flags               uint32
	RedirectedSessionID uint32
}

ClientClusterData represents the TS_UD_CS_CLUSTER client data block.

func (*ClientClusterData) Encode 

func (c *ClientClusterData) Encode() []byte

Encode serializes ClientClusterData to bytes (without header).

func (*ClientClusterData) EncodeBlock 

func (c *ClientClusterData) EncodeBlock() []byte

EncodeBlock serializes ClientClusterData with type+length header.

type ClientCoreData 

type ClientCoreData struct {
	Version                uint32
	DesktopWidth           uint16
	DesktopHeight          uint16
	ColorDepth             uint16
	SASSequence            uint16
	KeyboardLayout         uint32
	ClientBuild            uint32
	ClientName             string // max 15 chars, encoded as UTF-16LE (32 bytes)
	KeyboardType           uint32
	KeyboardSubType        uint32
	KeyboardFunctionKey    uint32
	ImeFileName            string // 64 bytes UTF-16LE
	PostBeta2ColorDepth    uint16
	ClientProductID        uint16
	SerialNumber           uint32
	HighColorDepth         uint16
	SupportedColorDepths   uint16
	EarlyCapabilityFlags   uint16
	ClientDigProductID     string // 64 bytes UTF-16LE
	ConnectionType         uint8
	Pad1Octet              uint8
	ServerSelectedProtocol uint32

	// Optional DPI fields (RDP 10.0+, MS-RDPBCGR 2.2.1.3.2).
	// Set DesktopScaleFactor > 0 to include these in the encoded block.
	DesktopPhysicalWidth  uint32 // Physical width in mm
	DesktopPhysicalHeight uint32 // Physical height in mm
	DesktopOrientation    uint16 // 0, 90, 180, or 270
	DesktopScaleFactor    uint32 // 100–500 percent
	DeviceScaleFactor     uint32 // 100, 140, or 180
}

ClientCoreData represents the TS_UD_CS_CORE client data block.

func DefaultClientCoreData 

func DefaultClientCoreData(width, height, depth uint16, selectedProtocol uint32) *ClientCoreData

DefaultClientCoreData returns a ClientCoreData with sensible RDP defaults.

func (*ClientCoreData) Encode 

func (c *ClientCoreData) Encode() []byte

Encode serializes ClientCoreData to bytes (without the block header).

func (*ClientCoreData) EncodeBlock 

func (c *ClientCoreData) EncodeBlock() []byte

EncodeBlock serializes ClientCoreData with type+length header.

type ClientMonitorData 

type ClientMonitorData struct {
	Monitors []MonitorDef
}

ClientMonitorData represents the TS_UD_CS_MONITOR client data block (MS-RDPBCGR 2.2.1.3.6).

func (*ClientMonitorData) Encode 

func (c *ClientMonitorData) Encode() []byte

Encode serializes ClientMonitorData to bytes (without the block header). Wire format: flags(u32) + monitorCount(u32) + monitorDefArray[](20 bytes each)

func (*ClientMonitorData) EncodeBlock 

func (c *ClientMonitorData) EncodeBlock() []byte

EncodeBlock serializes ClientMonitorData with type+length header. Single allocation: header(4) + flags(4) + count(4) + monitors(20*n).

type ClientNetworkData 

type ClientNetworkData struct {
	Channels []ChannelDef
}

ClientNetworkData represents the TS_UD_CS_NET client network data block.

func (*ClientNetworkData) Encode 

func (c *ClientNetworkData) Encode() []byte

Encode serializes ClientNetworkData to bytes (without header).

func (*ClientNetworkData) EncodeBlock 

func (c *ClientNetworkData) EncodeBlock() []byte

EncodeBlock serializes ClientNetworkData with type+length header.

type ClientSecurityData 

type ClientSecurityData struct {
	EncryptionMethods    uint32
	ExtEncryptionMethods uint32
}

ClientSecurityData represents the TS_UD_CS_SEC client security data block.

func (*ClientSecurityData) Encode 

func (c *ClientSecurityData) Encode() []byte

Encode serializes ClientSecurityData to bytes (without header).

func (*ClientSecurityData) EncodeBlock 

func (c *ClientSecurityData) EncodeBlock() []byte

EncodeBlock serializes ClientSecurityData with type+length header.

type ConnectInitial 

type ConnectInitial struct {
	CallingDomainSelector []byte
	CalledDomainSelector  []byte
	UpwardFlag            bool
	TargetParameters      ber.DomainParameters
	MinimumParameters     ber.DomainParameters
	MaximumParameters     ber.DomainParameters
	UserData              []byte // GCC Conference Create Request (encoded)
}

ConnectInitial represents an MCS Connect Initial PDU.

func (*ConnectInitial) Encode 

func (ci *ConnectInitial) Encode() []byte

Encode serializes the MCS Connect Initial as BER with Application 101 tag.

type ConnectResponse 

type ConnectResponse struct {
	Result           int
	CalledConnectID  int
	DomainParameters ber.DomainParameters
	UserData         []byte // GCC Conference Create Response data
}

ConnectResponse represents an MCS Connect Response PDU (parsed from server).

func DecodeConnectResponse 

func DecodeConnectResponse(log *slog.Logger, data []byte) (*ConnectResponse, error)

DecodeConnectResponse parses an MCS Connect Response from BER-encoded data.

type MonitorDef 

type MonitorDef struct {
	Left, Top, Right, Bottom int32
	Flags                    uint32 // MonitorPrimary = 0x01
}

MonitorDef represents a single monitor in TS_MONITOR_DEF (MS-RDPBCGR 2.2.1.3.6).

type ServerCoreData 

type ServerCoreData struct {
	Version              uint32
	ClientRequestedProto uint32
	EarlyCapabilityFlags uint32
}

ServerCoreData represents the TS_UD_SC_CORE server core data block.

type ServerNetworkData 

type ServerNetworkData struct {
	IOChannelID uint16
	ChannelIDs  []uint16
}

ServerNetworkData represents the TS_UD_SC_NET server network data block.

type ServerSecurityData 

type ServerSecurityData struct {
	EncryptionMethod uint32
	EncryptionLevel  uint32
	RawData          []byte // Rest of the data (random, certificate, etc.)
}

ServerSecurityData represents the TS_UD_SC_SEC server security data block.

Source Files

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