x/net/ipv6: add support for source-specific multicast

This CL introduces methods for the manipulation of source-specifc
group into PacketConn as follows:

JoinSourceSpecificGroup(*net.Interface, net.Addr, net.Addr) error
LeaveSourceSpecificGroup(*net.Interface, net.Addr, net.Addr) error
ExcludeSourceSpecificGroup(*net.Interface, net.Addr, net.Addr) error
IncludeSourceSpecificGroup(*net.Interface, net.Addr, net.Addr) error

Fixes golang/go#8752.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/169510043

ipv6/control.go

@@ -27,6 +27,10 @@ var (
 //	http://tools.ietf.org/html/rfc3493.html
 // RFC 3542  Advanced Sockets Application Program Interface (API) for IPv6
 //	http://tools.ietf.org/html/rfc3542
+// RFC 3678  Socket Interface Extensions for Multicast Source Filters
+//	http://tools.ietf.org/html/rfc3678
+// RFC 4607  Source-Specific Multicast for IP
+//	http://tools.ietf.org/html/rfc4607
 //
 // Note that RFC 3542 obsoletes RFC 2292 but OS X Snow Leopard and the
 // former still support RFC 2292 only.  Please be aware that almost

ipv6/dgramopt_posix.go

@@ -93,7 +93,11 @@ func (c *dgramOpt) SetMulticastLoopback(on bool) error {
 	return setInt(fd, &sockOpts[ssoMulticastLoopback], boolint(on))
 }
 
-// JoinGroup joins the group address group on the interface ifi.
+// JoinGroup joins the group address group on the interface ifi. By
+// default all sources that can cast data to group are accepted. It's
+// possible to mute and unmute data transmission from a specific
+// source by using ExcludeSourceSpecificGroup and
+// IncludeSourceSpecificGroup.
 // It uses the system assigned multicast interface when ifi is nil,
 // although this is not recommended because the assignment depends on
 // platforms and sometimes it might require routing configuration.
@@ -113,6 +117,8 @@ func (c *dgramOpt) JoinGroup(ifi *net.Interface, group net.Addr) error {
 }
 
 // LeaveGroup leaves the group address group on the interface ifi.
+// It's allowed to leave the group which is formed by
+// JoinSourceSpecificGroup for convenience.
 func (c *dgramOpt) LeaveGroup(ifi *net.Interface, group net.Addr) error {
 	if !c.ok() {
 		return syscall.EINVAL
@@ -128,6 +134,94 @@ func (c *dgramOpt) LeaveGroup(ifi *net.Interface, group net.Addr) error {
 	return setGroup(fd, &sockOpts[ssoLeaveGroup], ifi, grp)
 }
 
+// JoinSourceSpecificGroup joins the source-specific group consisting
+// group and source on the interface ifi. It uses the system assigned
+// multicast interface when ifi is nil, although this is not
+// recommended because the assignment depends on platforms and
+// sometimes it might require routing configuration.
+func (c *dgramOpt) JoinSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	if !c.ok() {
+		return syscall.EINVAL
+	}
+	fd, err := c.sysfd()
+	if err != nil {
+		return err
+	}
+	grp := netAddrToIP16(group)
+	if grp == nil {
+		return errMissingAddress
+	}
+	src := netAddrToIP16(source)
+	if src == nil {
+		return errMissingAddress
+	}
+	return setSourceGroup(fd, &sockOpts[ssoJoinSourceGroup], ifi, grp, src)
+}
+
+// LeaveSourceSpecificGroup leaves the source-specific group on the
+// interface ifi.
+func (c *dgramOpt) LeaveSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	if !c.ok() {
+		return syscall.EINVAL
+	}
+	fd, err := c.sysfd()
+	if err != nil {
+		return err
+	}
+	grp := netAddrToIP16(group)
+	if grp == nil {
+		return errMissingAddress
+	}
+	src := netAddrToIP16(source)
+	if src == nil {
+		return errMissingAddress
+	}
+	return setSourceGroup(fd, &sockOpts[ssoLeaveSourceGroup], ifi, grp, src)
+}
+
+// ExcludeSourceSpecificGroup excludes the source-specific group from
+// the already joined groups by either JoinGroup or
+// JoinSourceSpecificGroup on the interface ifi.
+func (c *dgramOpt) ExcludeSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	if !c.ok() {
+		return syscall.EINVAL
+	}
+	fd, err := c.sysfd()
+	if err != nil {
+		return err
+	}
+	grp := netAddrToIP16(group)
+	if grp == nil {
+		return errMissingAddress
+	}
+	src := netAddrToIP16(source)
+	if src == nil {
+		return errMissingAddress
+	}
+	return setSourceGroup(fd, &sockOpts[ssoBlockSourceGroup], ifi, grp, src)
+}
+
+// IncludeSourceSpecificGroup includes the excluded source-specific
+// group by ExcludeSourceSpecificGroup again on the interface ifi.
+func (c *dgramOpt) IncludeSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	if !c.ok() {
+		return syscall.EINVAL
+	}
+	fd, err := c.sysfd()
+	if err != nil {
+		return err
+	}
+	grp := netAddrToIP16(group)
+	if grp == nil {
+		return errMissingAddress
+	}
+	src := netAddrToIP16(source)
+	if src == nil {
+		return errMissingAddress
+	}
+	return setSourceGroup(fd, &sockOpts[ssoUnblockSourceGroup], ifi, grp, src)
+}
+
 // Checksum reports whether the kernel will compute, store or verify a
 // checksum for both incoming and outgoing packets.  If on is true, it
 // returns an offset in bytes into the data of where the checksum

ipv6/dgramopt_stub.go

@@ -44,7 +44,11 @@ func (c *dgramOpt) SetMulticastLoopback(on bool) error {
 	return errOpNoSupport
 }
 
-// JoinGroup joins the group address group on the interface ifi.
+// JoinGroup joins the group address group on the interface ifi. By
+// default all sources that can cast data to group are accepted. It's
+// possible to mute and unmute data transmission from a specific
+// source by using ExcludeSourceSpecificGroup and
+// IncludeSourceSpecificGroup.
 // It uses the system assigned multicast interface when ifi is nil,
 // although this is not recommended because the assignment depends on
 // platforms and sometimes it might require routing configuration.
@@ -53,10 +57,40 @@ func (c *dgramOpt) JoinGroup(ifi *net.Interface, group net.Addr) error {
 }
 
 // LeaveGroup leaves the group address group on the interface ifi.
+// It's allowed to leave the group which is formed by
+// JoinSourceSpecificGroup for convenience.
 func (c *dgramOpt) LeaveGroup(ifi *net.Interface, group net.Addr) error {
 	return errOpNoSupport
 }
 
+// JoinSourceSpecificGroup joins the source-specific group consisting
+// group and source on the interface ifi. It uses the system assigned
+// multicast interface when ifi is nil, although this is not
+// recommended because the assignment depends on platforms and
+// sometimes it might require routing configuration.
+func (c *dgramOpt) JoinSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	return errOpNoSupport
+}
+
+// LeaveSourceSpecificGroup leaves the source-specific group on the
+// interface ifi.
+func (c *dgramOpt) LeaveSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	return errOpNoSupport
+}
+
+// ExcludeSourceSpecificGroup excludes the source-specific group from
+// the already joined groups by either JoinGroup or
+// JoinSourceSpecificGroup on the interface ifi.
+func (c *dgramOpt) ExcludeSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	return errOpNoSupport
+}
+
+// IncludeSourceSpecificGroup includes the excluded source-specific
+// group by ExcludeSourceSpecificGroup again on the interface ifi.
+func (c *dgramOpt) IncludeSourceSpecificGroup(ifi *net.Interface, group, source net.Addr) error {
+	return errOpNoSupport
+}
+
 // Checksum reports whether the kernel will compute, store or verify a
 // checksum for both incoming and outgoing packets.  If on is true, it
 // returns an offset in bytes into the data of where the checksum

ipv6/doc.go

@@ -7,7 +7,8 @@
 //
 // The package provides IP-level socket options that allow
 // manipulation of IPv6 facilities.  The IPv6 and socket options for
-// IPv6 are defined in RFC 2460, RFC 3493 and RFC 3542.
+// IPv6 are defined in RFC 2460, RFC 3493, RFC 3542, RFC 3678 and RFC
+// 4607.
 //
 //
 // Unicasting