weave-scope/probe/resolver.go

package main

import (
	"log"
	"net"
	"strconv"
	"strings"
	"time"

	"github.com/weaveworks/scope/xfer"
)

var (
	tick     = time.Tick
	lookupIP = net.LookupIP
)

type staticResolver struct {
	quit  chan struct{}
	set   func(string, []string)
	peers []peer
}

type peer struct {
	hostname string
	port     string
}

// NewResolver starts a new resolver that periodically
// tries to resolve peers and the calls add() with all the
// resolved IPs.  It explictiy supports hostnames which
// resolve to multiple IPs; it will repeatedly call
// add with the same IP, expecting the target to dedupe.
func newStaticResolver(peers []string, set func(target string, endpoints []string)) staticResolver {
	r := staticResolver{
		quit:  make(chan struct{}),
		set:   set,
		peers: prepareNames(peers),
	}
	go r.loop()
	return r
}

func prepareNames(strs []string) []peer {
	var results []peer
	for _, s := range strs {
		var (
			hostname string
			port     string
		)

		if strings.Contains(s, ":") {
			var err error
			hostname, port, err = net.SplitHostPort(s)
			if err != nil {
				log.Printf("invalid address %s: %v", s, err)
				continue
			}
		} else {
			hostname, port = s, strconv.Itoa(xfer.AppPort)
		}

		results = append(results, peer{hostname, port})
	}
	return results
}

func (r staticResolver) loop() {
	r.resolveHosts()
	t := tick(time.Minute)
	for {
		select {
		case <-t:
			r.resolveHosts()

		case <-r.quit:
			return
		}
	}
}

func (r staticResolver) resolveHosts() {
	for _, peer := range r.peers {
		var addrs []net.IP
		if addr := net.ParseIP(peer.hostname); addr != nil {
			addrs = []net.IP{addr}
		} else {
			var err error
			addrs, err = lookupIP(peer.hostname)
			if err != nil {
				continue
			}
		}

		endpoints := make([]string, 0, len(addrs))
		for _, addr := range addrs {
			// For now, ignore IPv6
			if addr.To4() == nil {
				continue
			}
			endpoints = append(endpoints, net.JoinHostPort(addr.String(), peer.port))
		}
		r.set(peer.hostname, endpoints)
	}
}

func (r staticResolver) Stop() {
	close(r.quit)
}