Overview
Desktop Pass Through (or DTPT) is a protocol used for sharing the host's internet connection with the device, ie. a proprietary proxy protocol (yes, another one). The host listens on TCP port 5721 and the device connects to it with one or more clients. The MessageType of the first request initializes the connection to either a NSPSession or a ConnectionSession. A NSPSession is used to perform DNS lookups, whilst a ConnectionSession is used to connect to a given host (a new session is created for every external host that the device wishes to have a session with).
DTPT will be enabled when sync-engine is running. Note that DTPT requires an existing partnership.
NSPSession
All requests and responses have a fixed size of 20 bytes.
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Message type identifier. |
Padding |
2 |
Padding. |
QValue |
8 |
A QWORD. |
DValue1 |
4 |
A DWORD. |
DValue2 |
4 |
A DWORD. |
LookupBeginRequest
RPC version of WSALookupServiceBegin, where the payload is WSAQUERYSET serialized (see below).
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 9. |
Padding |
2 |
Padding. |
QValue |
8 |
Unused. |
dwControlFlags |
4 |
Flags as documented for WSALookupServiceBegin. |
PayloadSize |
4 |
Number of bytes of payload following, containing the serialized WSAQUERYSET (documented below). |
LookupBeginResponse
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 10. |
Padding |
2 |
Padding. |
Handle |
8 |
The handle returned by WSALookupServiceBegin. |
LastError |
4 |
Last error, set to a non-zero value in case of failure. |
DValue2 |
4 |
Unused. |
LookupNextRequest
RPC version of WSALookupServiceNext.
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 11. |
Padding |
2 |
Padding. |
Handle |
8 |
The handle returned in the LookupBeginResponse. |
DValue1 |
4 |
Unused. |
BufferSize |
4 |
Number of bytes of buffer space allocated for the response. The response' LastError will be set to WSAEFAULT (0x271e) and DataSize will be set to the minimum size required. |
LookupNextResponse
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 12. |
Padding |
2 |
Padding. |
QValue |
8 |
Unused. |
LastError |
4 |
Last error, set to a non-zero value in case of failure. |
DataSize |
4 |
Contains the number of bytes of payload if LastError is 0, elsewise it contains the minimum buffer space required if LastError is set to WSAEFAULT. On success, the payload contains a serialized WSAQUERYSET (documented below). |
LookupEndRequest
RPC version of WSALookupServiceEnd.
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 13. |
Padding |
2 |
Padding. |
Handle |
8 |
The handle returned in the LookupBeginResponse. |
DValue1 |
4 |
Unused. |
DValue2 |
4 |
Unused. |
ConnectionSession
ConnectRequest
This request has a fixed size of 36 bytes.
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 1. |
Address |
30 |
sockaddr_in or sockaddr_in6, serialized (see below). |
LastError |
4 |
Last error, set to 0 in this case. |
ConnectResponse
This response has a fixed size of 36 bytes.
Name |
Size |
Description |
Version |
1 |
Set to 1. |
MessageType |
1 |
Set to 0x5A on success, 0x5B on failure. |
Address |
30 |
The address of the local socket, as returned from getsockname, sockaddr_in or sockaddr_in6, serialized (see below). |
LastError |
4 |
Last error, set to a non-zero value in case of failure. |
Encodings
Packed fields
Each packed field contains a little-endian DWORD specifying the number of bytes following, followed by that many bytes of data. All fields have to end on 4 byte boundary, so trailing padding is added to ensure this.
WSAQUERYSET serialized
It has mostly packed fields (denoted PF in the Type column) following one another:
Name |
Size |
Description |
WSAQUERYSET |
PF, Raw |
Contains a flat representation of the WSAQUERYSET, and will thus be 60 bytes big (sizeof(WSAQUERYSET)). |
WSAQUERYSET.lpszServiceInstanceName |
PF, Unicode C-string |
The lpszServiceInstanceName of the WSAQUERYSET. |
WSAQUERYSET.lpServiceClassId |
PF, Raw GUID (16 bytes) |
The lpServiceClassId of the WSAQUERYSET. |
WSAQUERYSET.lpszComment |
PF, Unicode C-string |
The lpszComment of the WSAQUERYSET. |
WSAQUERYSET.lpNSProviderId |
PF, Raw GUID (16 bytes) |
The lpNSProviderId of the WSAQUERYSET. |
WSAQUERYSET.lpszContext |
PF, Unicode C-string |
The lpszContext of the WSAQUERYSET. |
WSAQUERYSET.dwNumberOfProtocols |
UINT32LE |
A UINT32 (little-endian) containing the number of AFPROTOCOL structures following in the next packet field. |
WSAQUERYSET.lpafpProtocols |
PF, AFPROTOCOL |
AFPROTOCOL structures following each other. |
WSAQUERYSET.lpszQueryString |
PF, Unicode C-string |
The lpszQueryString of the WSAQUERYSET. |
WSAQUERYSET.dwNumberOfCsAddrs |
UINT32LE |
A UINT32 (little-endian) containing the number of CSADDR_INFO structures following in the next packet field. |
WSAQUERYSET.lpcsaBuffer |
PF, CSADDR_INFO |
CSADDR_INFO structures following each other. The next fields contain the LocalAddr and RemoteAddr for SOCKET_ADDRESS structure 0 to n. |
WSAQUERYSET.lpcsaBuffer[n].LocalAddr |
PF, SOCKET_ADDRESS |
SOCKET_ADDRESS structure for CSADDR_INFO n. |
WSAQUERYSET.lpcsaBuffer[n].RemoteAddr |
PF, SOCKET_ADDRESS |
SOCKET_ADDRESS structure for CSADDR_INFO n. |
WSAQUERYSET.lpBlob |
PF, BLOB (8 bytes) |
The BLOB structure. |
WSAQUERYSET.lpBlob->pBlobData |
PF, byte[] (WSAQUERYSET.lpBlob->cbSize bytes long) |
The pBlobData member of the BLOB. |
sockaddr_in serialized
Name |
Size |
Description |
sin_family |
4 |
Family in little-endian -- AF_INET (2) in this case. |
Padding |
4 |
Padding bytes. |
sin_port |
2 |
Port in big-endian. |
sin_addr |
4 |
Address in big-endian. |
Reserved |
16 |
|
sockaddr_in6 serialized
Name |
Size |
Description |
sin6_family |
4 |
Family in little-endian -- AF_INET6 (23) in this case. |
Padding |
4 |
Padding bytes. |
sin6_port |
2 |
Port in big-endian. |
sin6_addr |
16 |
Address in big-endian. |
sin6_scope_id |
4 |
Scope id in big-endian. |