swarm: add CLI --ens-endpoint flag (#14386)

Implement a CLI flag that can be repeated to allow multiple ENS
resolvers for different TLDs.

swarm/api/api.go

@@ -17,6 +17,7 @@
 package api
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -40,6 +41,69 @@ type Resolver interface {
 	Resolve(string) (common.Hash, error)
 }
 
+// errNoResolver is returned by MultiResolver.Resolve if no resolver
+// can be found for the address.
+var errNoResolver = errors.New("no resolver")
+
+// MultiResolver is used to resolve URL addresses based on their TLDs.
+// Each TLD can have multiple resolvers, and the resoluton from the
+// first one in the sequence will be returned.
+type MultiResolver struct {
+	resolvers map[string][]Resolver
+}
+
+// MultiResolverOption sets options for MultiResolver and is used as
+// arguments for its constructor.
+type MultiResolverOption func(*MultiResolver)
+
+// MultiResolverOptionWithResolver adds a Resolver to a list of resolvers
+// for a specific TLD. If TLD is an empty string, the resolver will be added
+// to the list of default resolver, the ones that will be used for resolution
+// of addresses which do not have their TLD resolver specified.
+func MultiResolverOptionWithResolver(r Resolver, tld string) MultiResolverOption {
+	return func(m *MultiResolver) {
+		if _, ok := m.resolvers[tld]; !ok {
+			m.resolvers[tld] = []Resolver{}
+		}
+		m.resolvers[tld] = append(m.resolvers[tld], r)
+	}
+}
+
+// NewMultiResolver creates a new instance of MultiResolver.
+func NewMultiResolver(opts ...MultiResolverOption) (m *MultiResolver) {
+	m = &MultiResolver{
+		resolvers: map[string][]Resolver{},
+	}
+	for _, o := range opts {
+		o(m)
+	}
+	return m
+}
+
+// Resolve resolves address by choosing a Resolver by TLD.
+// If there are more default Resolvers, or for a specific TLD,
+// the Hash from the the first one which does not return error
+// will be returned.
+func (m MultiResolver) Resolve(addr string) (h common.Hash, err error) {
+	rs, _ := m.resolvers[""]
+	if i := strings.LastIndex(addr, "."); i >= 0 {
+		rstld, ok := m.resolvers[addr[i+1:]]
+		if ok {
+			rs = rstld
+		}
+	}
+	if rs == nil {
+		return h, errNoResolver
+	}
+	for _, r := range rs {
+		h, err = r.Resolve(addr)
+		if err == nil {
+			return
+		}
+	}
+	return
+}
+
 /*
 Api implements webserver/file system related content storage and retrieval
 on top of the dpa

swarm/api/api_test.go

@@ -237,3 +237,120 @@ func TestAPIResolve(t *testing.T) {
 		})
 	}
 }
+
+func TestMultiResolver(t *testing.T) {
+	doesntResolve := newTestResolver("")
+
+	ethAddr := "swarm.eth"
+	ethHash := "0x2222222222222222222222222222222222222222222222222222222222222222"
+	ethResolve := newTestResolver(ethHash)
+
+	testAddr := "swarm.test"
+	testHash := "0x1111111111111111111111111111111111111111111111111111111111111111"
+	testResolve := newTestResolver(testHash)
+
+	tests := []struct {
+		desc   string
+		r      Resolver
+		addr   string
+		result string
+		err    error
+	}{
+		{
+			desc: "No resolvers, returns error",
+			r:    NewMultiResolver(),
+			err:  errNoResolver,
+		},
+		{
+			desc:   "One default resolver, returns resolved address",
+			r:      NewMultiResolver(MultiResolverOptionWithResolver(ethResolve, "")),
+			addr:   ethAddr,
+			result: ethHash,
+		},
+		{
+			desc: "Two default resolvers, returns resolved address",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(ethResolve, ""),
+				MultiResolverOptionWithResolver(ethResolve, ""),
+			),
+			addr:   ethAddr,
+			result: ethHash,
+		},
+		{
+			desc: "Two default resolvers, first doesn't resolve, returns resolved address",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(doesntResolve, ""),
+				MultiResolverOptionWithResolver(ethResolve, ""),
+			),
+			addr:   ethAddr,
+			result: ethHash,
+		},
+		{
+			desc: "Default resolver doesn't resolve, tld resolver resolve, returns resolved address",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(doesntResolve, ""),
+				MultiResolverOptionWithResolver(ethResolve, "eth"),
+			),
+			addr:   ethAddr,
+			result: ethHash,
+		},
+		{
+			desc: "Three TLD resolvers, third resolves, returns resolved address",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(doesntResolve, "eth"),
+				MultiResolverOptionWithResolver(doesntResolve, "eth"),
+				MultiResolverOptionWithResolver(ethResolve, "eth"),
+			),
+			addr:   ethAddr,
+			result: ethHash,
+		},
+		{
+			desc: "One TLD resolver doesn't resolve, returns error",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(doesntResolve, ""),
+				MultiResolverOptionWithResolver(ethResolve, "eth"),
+			),
+			addr:   ethAddr,
+			result: ethHash,
+		},
+		{
+			desc: "One defautl and one TLD resolver, all doesn't resolve, returns error",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(doesntResolve, ""),
+				MultiResolverOptionWithResolver(doesntResolve, "eth"),
+			),
+			addr:   ethAddr,
+			result: ethHash,
+			err:    errors.New(`DNS name not found: "swarm.eth"`),
+		},
+		{
+			desc: "Two TLD resolvers, both resolve, returns resolved address",
+			r: NewMultiResolver(
+				MultiResolverOptionWithResolver(ethResolve, "eth"),
+				MultiResolverOptionWithResolver(testResolve, "test"),
+			),
+			addr:   testAddr,
+			result: testHash,
+		},
+	}
+	for _, x := range tests {
+		t.Run(x.desc, func(t *testing.T) {
+			res, err := x.r.Resolve(x.addr)
+			if err == nil {
+				if x.err != nil {
+					t.Fatalf("expected error %q, got result %q", x.err, res.Hex())
+				}
+				if res.Hex() != x.result {
+					t.Fatalf("expected result %q, got %q", x.result, res.Hex())
+				}
+			} else {
+				if x.err == nil {
+					t.Fatalf("expected no error, got %q", err)
+				}
+				if err.Error() != x.err.Error() {
+					t.Fatalf("expected error %q, got %q", x.err, err)
+				}
+			}
+		})
+	}
+}