conn: Wishlist for Redo

[miri64]

After a few month of working with conn we found some short-comings to it that need to be fixed in later iterations. This issue tries to collect these.

• connection-less support for connection-less protocols (goal: easy integration of simple lightweight stacks)
• connection-bound support for connection-less protocols if stack requires connections (goal: easy integration of full-featured stacks (e.g. lwIP))
• thread-shared connections (see POSIX sockets: open socket is bound to a specific thread #4388)
• asynchronous send/receive (select)
• non-blocking read/write
• options

... Feel free to add to this

[DipSwitch]

Non-blocking read/write would be nice aswell :) although this could also be solved with select.

I think however that epoll would be simpler to implement than select, and could also be faster. Aswell as in the kernel / stack implementation as in application implementation.

[miri64]

epoll sounds indeed nice (and could be implemented as well), but the problem is that most libraries still use select(). So purely from a porting perspective we need to implement it at some point anyway.

[miri64]

The discussion regarding epoll was also held in #4222.

[kaspar030]

• remove redundant address family / address length parameters (former implies the latter)
• UDP needs a way to specify source / target interface for link-local and multicast

[miri64]

• remove redundant address family / address length parameters (former implies the latter)

Only valid for IP-only protocols AFAWK, but true.

• UDP needs a way to specify source / target interface for link-local and multicast

That might be do-able with options for a conn object (setsockopts style). Another feature we might need.

[haukepetersen]

postponed.

[kYc0o]

Postponed again...

[miri64]

Realized in #5758.