Protocols/MSNP/MSNC/Binary Headers

MSNP Protocol

MSNC

Overview • MSNObject

Client Capabilities

P2P protocol

Transports • MSNSLP

Headers

P2Pv1 Binary headers

P2Pv2 Binary headers

Transfers

Display Pictures

Custom Emoticons

File Transfer

Overview

Introduction • Terms • Clients

Reference

Error List • Commands • Relying Party Suite • Spotlife

Services

XMPP • HTTP Gateway • Tabs • Activities

Documentation

Development Tools • MSNP Grid

Polygamy • URLs used by MSN

Documents

Protocol Versions

Version 21

Version 18

Version 16

Version 15

Version 14

Version 13

Version 12

Version 11

Version 9

Version 8

Version 2

MSNC

Introduction • P2P • Object Descriptor • Display Pictures • File Transfer

Scenarios

Microsoft Messenger for Mac

MSNP on WebTV (MSNTV)

Binary headers

P2P messages consist of a 48-byte binary header, zero or more bytes of content, and at the end a 4-byte binary footer.

The 48-byte binary header consists of 6 DWORDs and 3 QWORDS, which are all in little endian (little end first) order, where a DWORD is a 32-bit (4 byte) unsigned integer and QWORD is 64 bits (8 bytes).

Fields in the table are index, byte offset, data type, name used for the field in this documentation, and description.

1	0	DWORD	SessionID	The SessionID, which is zero when the Clients are negotiating about the session.
2	4	DWORD	Identifier	The first message you receive from the other client is the BaseIndentifier, the other messages contains a number near the BaseIdentifier.
3	8	QWORD	Data offset	Explained under Splitting big messages. Most often the messages are not split, and this value is 0.
4	16	QWORD	Total data size	Case 1: The byte size of all data sent between the header and footer of all of the message parts. This is the same independent of how many pieces the message is split in. Case 2: If this is an acknowledgement, this field is a copy of the same field in the message acknowledged. Sending acknowledgements
5	24	DWORD	Message length	The byte size of the data between the header and footer of this particular message.
6	28	DWORD	Flag	Identifies the message type. See the flags section
7	32	DWORD	Acknowledged identifier	If the SessionID field is zero and the data doesn't contain the SessionID then this field contains the Identifier of the previous received message. If the data contains the SessionID or if the SessionID field is non-zero then this field is just some random generated number.
8	36	DWORD	Acknowledged unique ID	In case the message is an acknowledgement, this is a copy of the previous field of the acknowledged message. Else this is 0.
9	40	QWORD	Acknowledged data size	In case the message is an acknowledgement, this is a copy of the Total data size field of the acknowledged message. Else this is 0.

Flags

The flags field in binary header can take the following values:

• 0x0: no flags specified
• 0x1: chunk out-of-order
• 0x2: acknowledgement
• 0x4: there is a pending invite
• 0x8: error on the binary level
• 0x20: display picture/custom emoticon data
• 0x01000030: file transfer data

Splitting big messages

When the content of the message between the binary header and footer is larger then 1202 characters (or 1352 in case of a Direct Connection), the data must be sent in separate messages, each a complete P2P message with a Content-Type, P2P-dest, binary header and binary footer. The message is acknowledged from the receiving client only when all parts have been received, with the total size of the content as acknowledged data size. Here is the binary header you should use when splitting messages:

• SessionID: The same Session ID as you've used when handshaking
• Identifier: It must be the identifier used in the "data preparation" message + 1. It will stay the same for all parts.
• Data Offset: Amount of data (in bytes) that has been sent up to this part.
• Total data size: Amount of data (in bytes) that will be sent.
• Message length: Amount of data (in bytes) in this part.
• Message type: Type of message, see the upper paragraph.
• Acknowledged identifier: Random number.
• Identifier: 0
• Acknowledged data size: 0

Sending acknowledgements

When a client sends you a P2P-message, you should always reply with a sort of Acknowledgement Message (otherwise the official MSN Client will probably refuse your datum). Let's suppose that you've received and decoded a certain binary header. The acknowledgement message you can send has the following binary header:

• SessionID: Session ID of the received binary header
• Identifier: You can simply invert the identifier in the received binary header (~identifier in C++)
• Data Offset: 0
• Total data size: Same as the "total data size" field of the received binary header
• Message length: 0
• Message type: 2
• Acknowledged identifier: You can simply add one to the identifier in the received binary header
• Identifier: Identifier of the received binary header
• Acknowledged data size: Same as the "total data size" field of the received binary header

The footer is 4-bytes long and only contains 0s.

Note that when messages are split, you should only send one acknowledgement when the last part of the split message is received.

Footer

The 4-byte binary footer consists of 1 DWORD which is in big endian (big end first) order and that field represents the ApplicationIdentifier (AppID). If this field is zero, then the clients are negotiating about the session. The ApplicationIdentifier is 0x1 for display picture and emoticon transfer, 0x2 for file transfers, and for games it's specified by the start nenu code.

P2Pv2 Binary Headers -- WLM 2009

When the client Alice logs in using MSNP18, and starts a session to another WLM 2009 client Bob (I believe Alice knows the client type of Bob by the GUID that is attached to the email in Bob's JOI command) then the file transfer binary header is substantially changed.

All data is Big Endian. The binary header size is dynamic - It can be 8(0x08) and 24(0x18) The new P2P protocol allways(?) has header and message part.

For all of them - (WORD is 2 bytes long)

1	BYTE	HL	Length of header.
2	BYTE	OP	Operation code. 0: None, 2: Ack, 3: Init session.
3	WORD	ML	Message length without header length. (but included the header's message length)
4	DWORD	BaseID	Initially random (?) To get the next one add the payload length.
TLVs	BYTE[HL-8]	TLV Data	TLV list consists of TLV-encoded pairs (type, length, value). A whole TLV list is padded with zeros to fit 4-byte boundary. If header length(HL) greater then 8 TLVs = ReadBytes(HeaderLength - 8) ; else process data packet (D). TLVs: T=0x1(1) L=0xc(12): IPv6 address of sender/receiver. T=0x2(2) L=0x4(4): ACK identifier.
DH	DHL	Data Header	BYTE DHL: Data header length BYTE TFCombination: 0x1=First, 0x4=Msn object (display picture, emoticon etc), 0x6=File transfer WORD PackageNumber: Package number DWORD SessionID: Session Identifier BYTE[DHL-8] Data packets TLVs: if (DHL>8) then read bytes(DHL - 8). T=0x1(1) L=0x8(8): Data remaining.
D	ML-DHL	Data Packet	SLP messsage or data packet
F	DWORD	Footer	The footer.

First P2P message

H: 18 03 05 4e 13 63 d5 a0 01 0c 00 02 00 00 00 0e 76 2d 0f 01 00 00 00 00 DH: 08 01 00 00 00 00 00 00 D: SLPMessage

All type of header has the follow fields:

1	0x18	Length of header	24
2	0x03	Operation code	The first p2p message. Initialize session.
3	0x05 0x4e	Size of message	1358 = 1350+8(0x08)
4	0x13 0x63 0xd5 0xa0	Base ID	The next Base ID += Size of message
TLVs	01 0c 00020000 000e762d 0f010000 (00 00)	TLV data	T=01,L=12,V=00020000 000e762d 0f010000. (00 00 = Padded with zeros to fit 4-byte boundary.)
DH	08 01 00 00 00 00 00 00	Data Header	08=DataHeaderLength, 01=TFCombination, 00 00=PackageNumber, 00 00 00 00 = Session ID, No TLV because DataHeaderLength=8, not greater then 8. So process data (SLP)
D	SLP	SLP	SLP Message

An acknowledgement

H: 08 02 00 00 93 e7 20 56 DH: (no data) D: (no data) F: 00 00 00 00

1	0x08	Length of header	8
2	0x02	Operation code	Acknowledgement
3	0x00 0x00	Size of message	0
4	0x93 0xe7 0x20 0x56	Base ID	AckIdentifier = Base ID + Size of Message
TLVs	(No tlv data)	TLVs	Length of header <= 8, so no TLVs in this sample package.
DH	(no data)	Data Header	Size of message is 0.
D	(no data)	Data	Size of message is 0.
F	0x00 0x00 0x00 0x00	Footer	Footer is 0 (always).

File Transfer

H: 08 00 05 70 13 63 da ee DH: 14 07 00 00 d1 c5 26 da 01 08 00 00 00 00 00 02 04 1c 00 00 D: ...

1	0x08	Length of header	8
2	0x00	Operation code	None
3	0x05 0x70	Size of message	1392 = 1372+20(0x14)
4	0x13 0x63 0xda 0xee	Base ID	The next Base ID += Size of message
TLVs	(No tlv data)	TLVs	Length of header <= 8, so no TLVs in this sample package.
DH	14 07 0000 d1c526da 01 08 00000000 0002041c 0000	Data Header	0x14(20)=DataHeaderLength, 0x7=TFCombination(The first file transfer message. 0x06 is all other file transfer message), 0000=PackageNumber, d1 c5 26 da = Session ID from SLP, T(01) L(08) V(00 00 00 00 00 02 04 1c - data remaining) Padding(00 00)
D	Data	Data	File data

Display Picture

H: 08 00 05 70 03 a3 da ee DH: 14 05 00 00 d1 c5 26 dc 01 08 00 00 00 00 00 00 34 f5 00 00 D: ...

1	0x08	Length of header	8
2	0x00	Operation code	None
3	0x05 0x70	Size of message	1392 = 1372+20(0x14)
4	0x03 0xa3 0xda 0xee	Base ID	The next Base ID += Size of message
TLVs	(No tlv data)	TLVs	Length of header <= 8, so no TLVs in this sample package.
DH	14 05 0000 d1c526da 01 08 00000000 0002041c 0000	Data Header	0x14(20)=DataHeaderLength, 0x5=TFCombination(The first display picture message. 0x04 is all other display picture message), 0000=PackageNumber, d1 c5 26 da = Session ID from SLP, T(01) L(08) V(00 00 00 00 00 00 34 f5 - data remaining) Padding(00 00)
D	Data	Data	Picture data

Before the start of the file transfer, bytes 10-13 contain the BaseIdentifier of the MSG we are replying to.

When transferring file data, the header size is 28 bytes. Unless it's the last chunk - then its 16 bytes, because the Remaining size field isn't in header's message.

For more information

P2Pv1 and P2Pv2 Header Definitions

Binary header research on MSNC10 (The new P2P protocol used in WLM 2009 and MSNP18)