dnsseed: implement scaffold for a coredns plugin

dnsseed/dnsseed.go

@@ -0,0 +1,30 @@
+package dnsseed
+
+import (
+	"context"
+
+	"github.com/coredns/coredns/plugin"
+	"github.com/miekg/dns"
+	"github.com/zcashfoundation/dnsseeder/zcash"
+)
+
+// ZcashSeeder discovers IP addresses by asking Zcash peers for them.
+type ZcashSeeder struct {
+	Next plugin.Handler
+
+	seeder *zcash.Seeder
+}
+
+// Name satisfies the Handler interface.
+func (zs ZcashSeeder) Name() string { return "dnsseed" }
+
+// Ready implements the ready.Readiness interface, once this flips to true CoreDNS
+// assumes this plugin is ready for queries; it is not checked again.
+func (zs ZcashSeeder) Ready() bool {
+	// setup() has attempted an initial connection to the backing peer already.
+	return zs.seeder.Ready()
+}
+
+func (zs ZcashSeeder) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+	return plugin.NextOrFailure(zs.Name(), zs.Next, ctx, w, r)
+}

dnsseed/dnsseed_test.go

@@ -0,0 +1,3 @@
+package dnsseed
+
+// TODO: intialize mock peers and test serving their addr inventories as A records

dnsseed/setup.go

@@ -0,0 +1,67 @@
+package dnsseed
+
+import (
+	"net"
+
+	"github.com/caddyserver/caddy"
+	"github.com/coredns/coredns/core/dnsserver"
+	"github.com/coredns/coredns/plugin"
+	clog "github.com/coredns/coredns/plugin/pkg/log"
+
+	"github.com/zcashfoundation/dnsseeder/zcash"
+	"github.com/zcashfoundation/dnsseeder/zcash/network"
+)
+
+var log = clog.NewWithPlugin("dnsseed")
+
+func init() { plugin.Register("dnsseed", setup) }
+
+// setup is the function that gets called when the config parser see the token "dnsseed". Setup is responsible
+// for parsing any extra options the example plugin may have. The first token this function sees is "dnsseed".
+func setup(c *caddy.Controller) error {
+	var networkArg, hostArg string
+
+	c.Next() // Ignore "dnsseed" and give us the next token.
+
+	if !c.Args(&networkArg, &hostArg) {
+		return plugin.Error("dnsseed", c.ArgErr())
+	}
+
+	var magic network.Network
+	switch networkArg {
+	case "mainnet":
+		magic = network.Mainnet
+	case "testnet":
+		magic = network.Testnet
+	default:
+		return plugin.Error("dnsseed", c.Errf("Config error: expected {mainnet, testnet}, got %s", networkArg))
+	}
+
+	address, port, err := net.SplitHostPort(hostArg)
+	if err != nil {
+		return plugin.Error("dnsseed", c.Errf("Config error: expected 'host:port', got %s", hostArg))
+	}
+
+	// XXX: If we wanted to register Prometheus metrics, this would be the place.
+
+	seeder, err := zcash.NewSeeder(magic)
+	if err != nil {
+		return plugin.Error("dnsseed", err)
+	}
+
+	err = seeder.Connect(address, port)
+	if err != nil {
+		return plugin.Error("dnsseed", err)
+	}
+
+	// TODO: make initial addr request
+	// TODO: begin update timer
+
+	// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
+	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
+		return ZcashSeeder{Next: next, seeder: seeder}
+	})
+
+	// All OK, return a nil error.
+	return nil
+}

dnsseed/setup_test.go

@@ -0,0 +1,26 @@
+package dnsseed
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/caddyserver/caddy"
+)
+
+// TestSetup tests the various things that should be parsed by setup.
+func TestSetup(t *testing.T) {
+	c := caddy.NewTestController("dns", "dnsseed mainnet 127.0.0.1:8233")
+	if err := setup(c); err != nil {
+		if strings.Contains(err.Error(), "connection refused") {
+			// No local peer running
+			// TODO: mock a local peer, which will be easier with an API rework in the zcash package
+			t.Skip()
+		}
+		t.Fatalf("Expected no errors, but got: %v", err)
+	}
+
+	c = caddy.NewTestController("dns", "dnsseed boop snoot")
+	if err := setup(c); err == nil {
+		t.Fatalf("Expected errors, but got: %v", err)
+	}
+}

zcash/client.go

@@ -271,3 +271,9 @@ func (s *Seeder) WaitForAddresses(n int, timeout time.Duration) error {
 		return ErrAddressTimeout
 	}
 }
+
+// Ready reports if the seeder is ready to provide addresses.
+func (s *Seeder) Ready() bool {
+	// TODO report ready when we have some addresses
+	return false
+}