main: make --api option resolve hostnames via dns (#5249)

Resolves #5249. Calls multiaddr-dns, and picks the first result.
Uses a fixed timeout of 10 seconds. Adds test cases for one, multiple,
and no DNS results.

License: MIT
Signed-off-by: Raúl Kripalani <raul.kripalani@consensys.net>

cmd/ipfs/dnsresolve_test.go

+package main
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"strings"
+	"testing"
+
+	ma "gx/ipfs/QmYmsdtJ3HsodkePE3eU3TsCaP2YvPZJ4LoXnNkDE5Tpt7/go-multiaddr"
+	madns "gx/ipfs/QmfXU2MhWoegxHoeMd3A2ytL2P6CY4FfqGWc23LTNWBwZt/go-multiaddr-dns"
+)
+
+var (
+	ctx         = context.Background()
+	testAddr, _ = ma.NewMultiaddr("/dns4/example.com/tcp/5001")
+)
+
+func makeResolver(n uint8) *madns.Resolver {
+	results := make([]net.IPAddr, n)
+	for i := uint8(0); i < n; i++ {
+		results[i] = net.IPAddr{IP: net.ParseIP(fmt.Sprintf("192.0.2.%d", i))}
+	}
+
+	backend := &madns.MockBackend{
+		IP: map[string][]net.IPAddr{
+			"example.com": results,
+		}}
+
+	return &madns.Resolver{
+		Backend: backend,
+	}
+}
+
+func TestApiEndpointResolveDNSOneResult(t *testing.T) {
+	dnsResolver = makeResolver(1)
+
+	addr, err := resolveAddr(ctx, testAddr)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if ref, _ := ma.NewMultiaddr("/ip4/192.0.2.0/tcp/5001"); !addr.Equal(ref) {
+		t.Errorf("resolved address was different than expected")
+	}
+}
+
+func TestApiEndpointResolveDNSMultipleResults(t *testing.T) {
+	dnsResolver = makeResolver(4)
+
+	addr, err := resolveAddr(ctx, testAddr)
+	if err != nil {
+		t.Error(err)
+	}
+
+	if ref, _ := ma.NewMultiaddr("/ip4/192.0.2.0/tcp/5001"); !addr.Equal(ref) {
+		t.Errorf("resolved address was different than expected")
+	}
+}
+
+func TestApiEndpointResolveDNSNoResults(t *testing.T) {
+	dnsResolver = makeResolver(0)
+
+	addr, err := resolveAddr(ctx, testAddr)
+	if addr != nil || err == nil {
+		t.Error("expected test address not to resolve, and to throw an error")
+	}
+
+	if !strings.HasPrefix(err.Error(), "non-resolvable API endpoint") {
+		t.Errorf("expected error not thrown; actual: %v", err)
+	}
+}

cmd/ipfs/main.go

@@ -34,7 +34,7 @@ import (
 	osh "gx/ipfs/QmXuBJ7DR6k3rmUEKtvVMhwjmXDuJgXXPUt4LQXKBMsU93/go-os-helper"
 	ma "gx/ipfs/QmYmsdtJ3HsodkePE3eU3TsCaP2YvPZJ4LoXnNkDE5Tpt7/go-multiaddr"
 	loggables "gx/ipfs/QmZ4zF1mBrt8C2mSCM4ZYE4aAnv78f7GvrzufJC4G5tecK/go-libp2p-loggables"
-	mdns "gx/ipfs/QmfXU2MhWoegxHoeMd3A2ytL2P6CY4FfqGWc23LTNWBwZt/go-multiaddr-dns"
+	madns "gx/ipfs/QmfXU2MhWoegxHoeMd3A2ytL2P6CY4FfqGWc23LTNWBwZt/go-multiaddr-dns"
 )
 
 // log is the command logger
@@ -42,6 +42,9 @@ var log = logging.Logger("cmd/ipfs")
 
 var errRequestCanceled = errors.New("request canceled")
 
+// declared as a var for testing purposes
+var dnsResolver = madns.DefaultResolver
+
 const (
 	EnvEnableProfiling = "IPFS_PROF"
 	cpuProfile         = "ipfs.cpuprof"
@@ -445,30 +448,31 @@ func getApiClient(ctx context.Context, repoPath, apiAddrStr string) (http.Client
 }
 
 func apiClientForAddr(ctx context.Context, addr ma.Multiaddr) (http.Client, error) {
-	addrs, err := mdns.Resolve(ctx, addr)
+	addr, err := resolveAddr(ctx, addr)
 	if err != nil {
 		return nil, err
 	}
 
-	dialer := &manet.Dialer{}
-	for _, addr := range addrs {
-		ctx, cancelFunc := context.WithTimeout(ctx, 5*time.Second)
-		defer cancelFunc()
+	_, host, err := manet.DialArgs(addr)
+	if err != nil {
+		return nil, err
+	}
 
-		conn, err := dialer.DialContext(ctx, addr)
-		if err != nil {
-			log.Errorf("connection to %s failed, error: %s", addr, err)
-			continue
-		}
-		conn.Close()
+	return http.NewClient(host, http.ClientWithAPIPrefix(corehttp.APIPath)), nil
+}
 
-		_, host, err := manet.DialArgs(addr)
-		if err != nil {
-			continue
-		}
+func resolveAddr(ctx context.Context, addr ma.Multiaddr) (ma.Multiaddr, error) {
+	ctx, cancelFunc := context.WithTimeout(ctx, 10*time.Second)
+	defer cancelFunc()
+
+	addrs, err := dnsResolver.Resolve(ctx, addr)
+	if err != nil {
+		return nil, err
+	}
 
-		return http.NewClient(host, http.ClientWithAPIPrefix(corehttp.APIPath)), nil
+	if len(addrs) == 0 {
+		return nil, errors.New("non-resolvable API endpoint")
 	}
 
-	return nil, errors.New("non-resolvable API endpoint")
+	return addrs[0], nil
 }