proposal: syscall: add Conn and RawConn interfaces

[mikioh]

Please take a look at the discussion: https://groups.google.com/d/msg/golang-dev/tcl_XFLUfcE/V6JUoZD-DAAJ

The story is like the following:

• As described in x/net/{icmp,ipv4,ipv6}: replumbing in the net and internal/poll packages of go1.9 #19051, Go 1.9 breaks a few packages in golang.org/x/net repository,
• Yikes, I've just remembered that there's inherent fragility due to the runtime reflection hack. Let's fix it at the same time,
• How to repair the breakage? Looks like the required functionality traverses the net, internal/poll and syscall packages. Where is the best place to patch up?
• Do it in the syscall package, plus a bit in the net and internal/poll packages,
• Wait, can we add something new into the locked down package?
• No problem, because it's about exposing new functionality from the standard library for helping itself.

[mikioh]

The detail of the proposed APIs by Mr. Cox is the following:

package syscall

type RawConn interface {
        Control(f func(fd uintptr)) error
        Read(f func(fd uintptr) (done bool)) error
        Write(f func(fd uintptr) (done bool)) error
}

type Conn interface {
        SyscallConn() (syscall.RawConn, error)
}

and then an implementation of a net.Conn may optionally implement syscall.Conn to provide access to its fd as a syscall.RawConn.

[gopherbot]

CL https://golang.org/cl/37039 mentions this issue.

[gopherbot]

CL https://golang.org/cl/37913 mentions this issue.

[gopherbot]

CL https://golang.org/cl/37038 mentions this issue.

[mikioh]

@rsc,

What's the current status of this proposal?

[rsc]

LGTM here and on the CL.

[gopherbot]

Change https://golang.org/cl/71651 mentions this issue: net: make {TCP,UDP}Listener implement syscall.Conn