Source-based routing in Golang

Consider this routing table:

10.11.70.0/23 dev data0 proto kernel scope link src 10.11.70.42
10.11.70.0/23 dev data1 proto kernel scope link src 10.11.71.42
192.168.123.0/24 dev internal0 proto kernel scope link src 192.168.123.42
192.168.123.0/24 dev internal1 proto kernel scope link src 192.168.123.142

Simple net.Dial to either 10.11.70.42 or 10.11.71.42 will match the first subnet and be routed via data0. This problems is usually solved by bonds. But sometimes you need to invent a bicycle.

Usage

import (
    "context"
    "net"
    "net/netip"

    "git.frostfs.info/TrueCloudLab/multinet"
)
import 

d, err := multinet.NewDialer(Config{
    Subnets:  []Subnet{
        {
            Prefix: netip.MustParsePrefix("10.11.70.0/23"),
            SourceIPs: []netip.Addr{
                netip.MustParseAddr("10.11.70.42"),
                netip.MustParseAddr("10.11.71.42"),
            },
        },
        {
            Prefix: netip.MustParsePrefix("192.168.123.0/24"),
            SourceIPs: []netip.Addr{
                netip.MustParseAddr("192.168.123.42"),
                netip.MustParseAddr("192.168.123.142"),
            },
        },
    },
    Balancer: multinet.BalancerTypeRoundRobin,
})
if err != nil {
    // handle error
}

conn, err := d.DialContext(ctx, "tcp", "10.11.70.42")
if err != nil {
    // handle error
}
// do stuff