gscreen design

In order to make screen and gnome-terminal communicate with each other, we first decided to change the screen program’s code to expose a library interface. However since:

1) screen’s code is old fashioned. i.e. it has many global variables which is not desirable for a shared library and

2) screen and g-t are under different licenses.

It is not feasible to make the screen program as a shared library object.

Thus we decided to have a third program as the messenger between g-t and screen. ”Pipes” (or file descriptors) are going to be used to read/write commands from/to screen. 

The flow would be:

When g-t is loaded, it will create an instance of screen with the pipe fd as its parameter. Screen would be modified so that each time a command is written to the pipe, it would react properly.Each terminal would have one instance of the screen fd. Each screen fd can have multiple sub-screens.

To make the pipe bidirectional we actually need two file descriptors:·  

screen –> g-t for:

o        Scroll back buffer contents,

o        Copy,

o        Get current screens,·

g-t –> screen for:

o        Create a new screen,

o        Switch screen,

o        Search,

 o        Paste,

o        Show tab for current screens

Notes: 

Semaphores will be used to prevent deadlock.

A protocol is also needed to make the communication happen.One endpoint of a pipe will write a command to it, the command will be read and interpreted by the other endpoint and proper reaction would be performed.

Protocol initial design:·

:newScreen  options (readonly/writeonly) \r\n· 

:switchTo  screenID \r\n·        

:copy numberOfChars \r\n data data ….data \r\n·

:paste numberOfChars \r\n data data … data \r\n·        

:find searchLiteral \r\n·        

:getScreens \r\n·        

:showTab screen1 options \r\n screen2 options \r\n  …

(To send commands to screen ‘-X’ option can be used.)