Add support for SocketOptions

[spikecurtis]

Signed-off-by: Spike Curtis spike@tigera.io

I'm finding myself needing to set SO_REUSEADDR and SO_REUSEPORT in my application. WDYT of this way of passing them to the library?

[ishidawataru]

How about passing a callback function that will get called before listening/connecting like net pkg?

https://golang.org/pkg/net/#ListenConfig

[spikecurtis]

@ishidawataru is this more what you had in mind?

[ishidawataru]

@spikecurtis Thank you. It's getting close.

Can we use the same function signature as net.ListenConfig for Control() so that we can use the same callback for other transport protocols that could reduce some code duplication?

For example, it'd be better if we can pass this to the Listen API.

Also I'm wondering if we can even reuse net.ListenConfig in this library.

[spikecurtis]

I believe doing that would require me to implement the whole syscall.RawConn interface which is more than I'm really willing to chew off.

[ishidawataru]

https://golang.org/pkg/syscall/#RawConn

How about keeping Read() / Write() empty if you don't have time?
Is it hard to implement Control(f func(fd uintptr)) error ?

[spikecurtis]

Implementing Control only on the RawConn interface isn't too bad, but I need this to work for Dialed sockets. Are you OK with creating a DialConfig to mirror the function of ListenConfig? I'm not up for trying to implement a whole Dialer API.

[ishidawataru]

How about making SocketConfig, put Control(f func(fd uintptr)) error and InitMsg as fields, implement

• (*SocketConfig) Listen(network string, laddr *SCTPAddr)
• (*SocketConfig) Dial(network string, laddr, raddr *SCTPAddr)

which uses Control and InitMsg if needed for listening/dialing?

[spikecurtis]

@ishidawataru Ok, done.

Note that we want SocketConfig to have func(fd uintpr) not func(f func(fd uintptr)) error. The former is useful for setting socket options, latter is implemented by RawConn.

[ishidawataru]

thanks. Can you change like below?

diff --git a/sctp.go b/sctp.go
index 993071c..730b67a 100644
--- a/sctp.go
+++ b/sctp.go
@@ -715,7 +715,7 @@ type SocketConfig struct {
        // If Control is not nil it is called after the socket is created but before
        // it is bound or connected. fd is the file descriptor representing the
        // socket in the OS.
-       Control func(fd uintptr)
+       Control func(network, address string, c syscall.RawConn) error

        // InitMsg is the options to send in the initial SCTP message
        InitMsg InitMsg
diff --git a/sctp_linux.go b/sctp_linux.go
index ce57e0b..47b2263 100644
--- a/sctp_linux.go
+++ b/sctp_linux.go
@@ -172,7 +172,7 @@ func ListenSCTPExt(network string, laddr *SCTPAddr, options InitMsg) (*SCTPListe
 }

 // listenSCTPExtConfig - start listener on specified address/port with given SCTP options and socket configuration
-func listenSCTPExtConfig(network string, laddr *SCTPAddr, options InitMsg, control func(fd uintptr)) (*SCTPListener, error) {
+func listenSCTPExtConfig(network string, laddr *SCTPAddr, options InitMsg, control func(network, address string, c syscall.RawConn) error) (*SCTPListener, error) {
        af, ipv6only := favoriteAddrFamily(network, laddr, nil, "listen")
        sock, err := syscall.Socket(
                af,
@@ -193,7 +193,12 @@ func listenSCTPExtConfig(network string, laddr *SCTPAddr, options InitMsg, contr
                return nil, err
        }
        if control != nil {
-               control(uintptr(sock))
+               c := rawConn{
+                       sockfd: sock,
+               }
+               if err = control(network, laddr.String(), c); err != nil {
+                       return nil, err
+               }
        }
        err = setInitOpts(sock, options)
        if err != nil {
@@ -250,7 +255,7 @@ func DialSCTPExt(network string, laddr, raddr *SCTPAddr, options InitMsg) (*SCTP
 }

 // dialSCTPExtConfig - same as DialSCTP but with given SCTP options and socket configuration
-func dialSCTPExtConfig(network string, laddr, raddr *SCTPAddr, options InitMsg, control func(fd uintptr)) (*SCTPConn, error) {
+func dialSCTPExtConfig(network string, laddr, raddr *SCTPAddr, options InitMsg, control func(network, address string, c syscall.RawConn) error) (*SCTPConn, error) {
        af, ipv6only := favoriteAddrFamily(network, laddr, raddr, "dial")
        sock, err := syscall.Socket(
                af,
@@ -271,7 +276,12 @@ func dialSCTPExtConfig(network string, laddr, raddr *SCTPAddr, options InitMsg,
                return nil, err
        }
        if control != nil {
-               control(uintptr(sock))
+               c := rawConn{
+                       sockfd: sock,
+               }
+               if err = control(network, laddr.String(), c); err != nil {
+                       return nil, err
+               }
        }
        err = setInitOpts(sock, options)
        if err != nil {

Then, we can do like this

// test.go
package main

import (
        "fmt"

        "github.com/ishidawataru/sctp"
        "github.com/libp2p/go-reuseport"
)

func main() {
        c := sctp.SocketConfig{
                Control: reuseport.Control,
        }
        laddr := &sctp.SCTPAddr{}
        ln, err := c.Listen("sctp", laddr)
        fmt.Println(ln, err)
}

$ go build test.go
$ strace ./test 2>&1 | grep SOL_SOCKET
setsockopt(3, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0
setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(3, SOL_SOCKET, SO_REUSEPORT, [1], 4) = 0

[spikecurtis]

Nice! I've made those changes

[ishidawataru]

Thanks. LGTM. Please squash into one commit.

[spikecurtis]

Squashed

[ishidawataru]

Thanks! merged.

[shanehooker]

Is there an example or UT of this new usage? Can we modify, extend the ListenSCTPExt() and DialSCTPExt() to include all of the socket options described in RFC6458?
https://tools.ietf.org/html/rfc6458

For an application using SCTP, many of these parameters need to be configurable and I need an API to be able to modify them.