QWSSocket Porting Notes (UNIX Domain Socket only)

QWSSocket Notes

Background

• Qt Embedded uses QWSSocket and QWSServerSocket as the communication mechanism between QWSServer and QWSClient.

• Both QWSSocket/QWSServerSocket are #define-d to be either QUnixSocket/QUnixSocketServer or QTcpSocket/QTcpServer depending on the value of "QT_NO_SXE".

QWSSocket Inheritance Tree

• QWSSocket inherits from QWS_SOCK_BASE

  • QWS_SOCK_BASE is either QUnixSocket or QTcpSocket

• QWSServerSocket inherits from QWS_SOCK_SERVER_BASE

  • QWS_SOCK_SERVER_BASE is either QUnixSocketServer or QTcpServer

Qt and Unix Domain Socket

• Localhost-only socket using file descriptor (using file path instead of addresses as in network sockets). QWSServer/QWSClient calls qws_qtePipeFileName() to get this path.

  • TODO: Find out this naming convention and provide similar ability for our channels port.

• Can send data and ancillary messages (file descriptors and credentials). "man 7 unix" for more info on ancillary messages.

  • TODO: Find out if Qt uses any ancillary messages besides data. Without ancillary messages, our QWSSocket port using channels will be easier.

• Qt uses the regular socket functions to set up Unix domain sockets. This includes calls to socket(), setsockopt(), bind(), listen(), accept(), connect(), close(), select(), sendmsg(), recvmsg().

  • Note that Qt calls select() for checking for data to read within a specified amount of time. In our case, we can simply do polling (not poll() call) and use some sleeping mechanism to achieve this effect, though we'll waste CPU cycles.
  • TODO: Provide these similar interface on top of our channels. We can use "channel" prefix to distinguish the two version and mass-replace them with sed or something.

Porting Approach

• We should make new files to replace qunixsocket* and qunixsocketserver while keeping the same interface.

• On calls that we don't support, e.g. ancillary messages, we can simply print out an error message.

• Right now there are two big tasks:

  • TODO 1. Implement the socket calls above on top of our channels
  • TODO 2. Re-implement QUnixSocket and QUnixSocketServer on top of our wrappers of socket calls from part 1.

Relevant Files

• qwsutils_qws.h
• qwssocket_qws.*
• qunixsocket*
• qunixsocketserver*
• qwindow_system_qws.*

References

• Qt Embedded source (src/gui/)
• Man pages