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fix: don't prefer local ports from other addresses when dialing (libp…
…2p#1673) * fix: don't prefer local ports from other addresses when dialing This address may already be in-use (on that other address) somewhere else. Thanks to @schomatis for figuring this out. fixes libp2p#1611 * chore: document reuseport dialer logic
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,114 @@ | ||
| package reuseport | ||
|
|
||
| import ( | ||
| "context" | ||
| "fmt" | ||
| "math/rand" | ||
| "net" | ||
|
|
||
| "github.com/libp2p/go-netroute" | ||
| ) | ||
|
|
||
| type dialer struct { | ||
| // All address that are _not_ loopback or unspecified (0.0.0.0 or ::). | ||
| specific []*net.TCPAddr | ||
| // All loopback addresses (127.*.*.*, ::1). | ||
| loopback []*net.TCPAddr | ||
| // Unspecified addresses (0.0.0.0, ::) | ||
| unspecified []*net.TCPAddr | ||
| } | ||
|
|
||
| func (d *dialer) Dial(network, addr string) (net.Conn, error) { | ||
| return d.DialContext(context.Background(), network, addr) | ||
| } | ||
|
|
||
| func randAddr(addrs []*net.TCPAddr) *net.TCPAddr { | ||
| if len(addrs) > 0 { | ||
| return addrs[rand.Intn(len(addrs))] | ||
| } | ||
| return nil | ||
| } | ||
|
|
||
| // DialContext dials a target addr. | ||
| // | ||
| // In-order: | ||
| // | ||
| // 1. If we're _explicitly_ listening on the prefered source address for the destination address | ||
| // (per the system's routes), we'll use that listener's port as the source port. | ||
| // 2. If we're listening on one or more _unspecified_ addresses (zero address), we'll pick a source | ||
| // port from one of these listener's. | ||
| // 3. Otherwise, we'll let the system pick the source port. | ||
| func (d *dialer) DialContext(ctx context.Context, network, addr string) (net.Conn, error) { | ||
| // We only check this case if the user is listening on a specific address (loopback or | ||
| // otherwise). Generally, users will listen on the "unspecified" address (0.0.0.0 or ::) and | ||
| // we can skip this section. | ||
| // | ||
| // This lets us avoid resolving the address twice, in most cases. | ||
| if len(d.specific) > 0 || len(d.loopback) > 0 { | ||
| tcpAddr, err := net.ResolveTCPAddr(network, addr) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| ip := tcpAddr.IP | ||
| if !ip.IsLoopback() && !ip.IsGlobalUnicast() { | ||
| return nil, fmt.Errorf("undialable IP: %s", ip) | ||
| } | ||
|
|
||
| // If we're listening on some specific address and that specific address happens to | ||
| // be the preferred source address for the target destination address, we try to | ||
| // dial with that address/port. | ||
| // | ||
| // We skip this check if we _aren't_ listening on any specific addresses, because | ||
| // checking routing tables can be expensive and users rarely listen on specific IP | ||
| // addresses. | ||
| if len(d.specific) > 0 { | ||
| if router, err := netroute.New(); err == nil { | ||
| if _, _, preferredSrc, err := router.Route(ip); err == nil { | ||
| for _, optAddr := range d.specific { | ||
| if optAddr.IP.Equal(preferredSrc) { | ||
| return reuseDial(ctx, optAddr, network, addr) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // Otherwise, if we are listening on a loopback address and the destination is also | ||
| // a loopback address, use the port from our loopback listener. | ||
| if len(d.loopback) > 0 && ip.IsLoopback() { | ||
| return reuseDial(ctx, randAddr(d.loopback), network, addr) | ||
| } | ||
| } | ||
|
|
||
| // If we're listening on any uspecified addresses, use a randomly chosen port from one of | ||
| // these listeners. | ||
| if len(d.unspecified) > 0 { | ||
| return reuseDial(ctx, randAddr(d.unspecified), network, addr) | ||
| } | ||
|
|
||
| // Finally, just pick a random port. | ||
| var dialer net.Dialer | ||
| return dialer.DialContext(ctx, network, addr) | ||
| } | ||
|
|
||
| func newDialer(listeners map[*listener]struct{}) *dialer { | ||
| specific := make([]*net.TCPAddr, 0) | ||
| loopback := make([]*net.TCPAddr, 0) | ||
| unspecified := make([]*net.TCPAddr, 0) | ||
|
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||
| for l := range listeners { | ||
| addr := l.Addr().(*net.TCPAddr) | ||
| if addr.IP.IsLoopback() { | ||
| loopback = append(loopback, addr) | ||
| } else if addr.IP.IsUnspecified() { | ||
| unspecified = append(unspecified, addr) | ||
| } else { | ||
| specific = append(specific, addr) | ||
| } | ||
| } | ||
| return &dialer{ | ||
| specific: specific, | ||
| loopback: loopback, | ||
| unspecified: unspecified, | ||
| } | ||
| } |
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