Default DNS seeding (broken for now, use --seed override).

btc-crawl.go

@@ -1,21 +1,46 @@
 package main
 
 import (
+	"github.com/jessevdk/go-flags"
 	"log"
 )
 
+// Taken from: https://github.com/bitcoin/bitcoin/blob/89d72f3d9b6e7ef051ad1439f266b809f348229b/src/chainparams.cpp#L143
+var defaultDnsSeeds = []string{
+	"seed.bitcoin.sipa.be",
+	"dnsseed.bluematt.me",
+	"dnsseed.bitcoin.dashjr.org",
+	"seed.bitcoinstats.com",
+	"seed.bitnodes.io",
+	"bitseed.xf2.org",
+}
+
+// TODO: Unhardcode these:
+var userAgent string = "/btc-crawl:0.0.1"
+var lastBlock int32 = 0
+
+type Options struct {
+	Verbose []bool   `short:"v" long:"verbose" description:"Show verbose logging."`
+	Seed    []string `short:"s" long:"seed" description:"Override which seeds to use." default-mask:"<bitcoind DNS seeds>"`
+}
+
 func main() {
 	// TODO: Parse args.
-	// TODO: Export to a reasonable format.
-	// TODO: Use proper logger for logging.
-	var seedNodes []string = []string{"85.214.251.25:8333", "62.75.216.13:8333"}
-	client := NewDefaultClient()
-	crawler := NewCrawler(client, seedNodes, 10)
-
-	done, err := crawler.Start()
+	options := Options{}
+	_, err := flags.Parse(&options)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	<-done
+	seedNodes := options.Seed
+
+	// TODO: Export to a reasonable format.
+	// TODO: Use proper logger for logging.
+	if len(seedNodes) == 0 {
+		seedNodes = GetSeedsFromDNS(defaultDnsSeeds)
+	}
+
+	client := NewClient(userAgent, lastBlock)
+	crawler := NewCrawler(client, seedNodes, 10)
+	crawler.Start()
 }

client.go

@@ -4,10 +4,6 @@ import (
 	"github.com/conformal/btcwire"
 )
 
-// TODO: Unhardcode these:
-var userAgent string = "/btc-crawl:0.0.1"
-var lastBlock int32 = 0
-
 type Client struct {
 	btcnet    btcwire.BitcoinNet // Bitcoin Network
 	pver      uint32             // Protocl Version
@@ -15,7 +11,7 @@ type Client struct {
 	lastBlock int32
 }
 
-func NewDefaultClient() *Client {
+func NewClient(userAgent string, lastBlock int32) *Client {
 	return &Client{
 		btcnet:    btcwire.MainNet,
 		pver:      btcwire.ProtocolVersion,

crawler.go

@@ -115,8 +115,7 @@ func (c *Crawler) addAddress(address string) bool {
 	return true
 }
 
-func (c *Crawler) Start() (chan struct{}, error) {
-	done := make(chan struct{}, 1)
+func (c *Crawler) Start() {
 	numWorkers := 0
 	numGood := 0
 
@@ -159,8 +158,7 @@ func (c *Crawler) Start() (chan struct{}, error) {
 
 			if len(c.queue) == 0 && numWorkers == 0 {
 				log.Printf("Done.")
-				done <- struct{}{}
-				return done, nil
+				return
 			}
 
 			<-c.workers

seed.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"github.com/conformal/btcwire"
+	"log"
+	"net"
+	"sync"
+)
+
+func GetSeedsFromDNS(dnsSeeds []string) []string {
+	wait := sync.WaitGroup{}
+	results := make(chan []net.IP)
+
+	for _, address := range dnsSeeds {
+		wait.Add(1)
+		go func() {
+			defer wait.Done()
+			ips, err := net.LookupIP(address)
+			if err != nil {
+				log.Printf("Failed to resolve %s: %v", address, err)
+				return
+			}
+			results <- ips
+		}()
+	}
+
+	go func() {
+		wait.Wait()
+		close(results)
+	}()
+
+	seeds := []string{}
+	for ips := range results {
+		for _, ip := range ips {
+			seeds = append(seeds, net.JoinHostPort(ip.String(), btcwire.MainPort))
+		}
+	}
+
+	log.Printf("Resolved %d seed nodes from %d DNS seeds.", len(seeds), len(dnsSeeds))
+
+	// Note that this will likely include duplicate seeds. The crawler deduplicates them.
+	return seeds
+}