swarm/api: fix error reporting in api.Resolve (#14464)

Previously, resolve errors were being swallowed and the returned error
was a generic "not a content hash" which isn't helpful.

This updates the Resolve function to fail fast rather than only
returning an error at the end, and also adds test coverage.

swarm/api/api_test.go

@@ -17,6 +17,7 @@
 package api
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -117,3 +118,122 @@ func TestApiPut(t *testing.T) {
 		checkResponse(t, resp, exp)
 	})
 }
+
+// testResolver implements the Resolver interface and either returns the given
+// hash if it is set, or returns a "name not found" error
+type testResolver struct {
+	hash *common.Hash
+}
+
+func newTestResolver(addr string) *testResolver {
+	r := &testResolver{}
+	if addr != "" {
+		hash := common.HexToHash(addr)
+		r.hash = &hash
+	}
+	return r
+}
+
+func (t *testResolver) Resolve(addr string) (common.Hash, error) {
+	if t.hash == nil {
+		return common.Hash{}, fmt.Errorf("DNS name not found: %q", addr)
+	}
+	return *t.hash, nil
+}
+
+// TestAPIResolve tests resolving URIs which can either contain content hashes
+// or ENS names
+func TestAPIResolve(t *testing.T) {
+	ensAddr := "swarm.eth"
+	hashAddr := "1111111111111111111111111111111111111111111111111111111111111111"
+	resolvedAddr := "2222222222222222222222222222222222222222222222222222222222222222"
+	doesResolve := newTestResolver(resolvedAddr)
+	doesntResolve := newTestResolver("")
+
+	type test struct {
+		desc      string
+		dns       Resolver
+		addr      string
+		immutable bool
+		result    string
+		expectErr error
+	}
+
+	tests := []*test{
+		{
+			desc:   "DNS not configured, hash address, returns hash address",
+			dns:    nil,
+			addr:   hashAddr,
+			result: hashAddr,
+		},
+		{
+			desc:      "DNS not configured, ENS address, returns error",
+			dns:       nil,
+			addr:      ensAddr,
+			expectErr: errors.New(`no DNS to resolve name: "swarm.eth"`),
+		},
+		{
+			desc:   "DNS configured, hash address, hash resolves, returns resolved address",
+			dns:    doesResolve,
+			addr:   hashAddr,
+			result: resolvedAddr,
+		},
+		{
+			desc:      "DNS configured, immutable hash address, hash resolves, returns hash address",
+			dns:       doesResolve,
+			addr:      hashAddr,
+			immutable: true,
+			result:    hashAddr,
+		},
+		{
+			desc:   "DNS configured, hash address, hash doesn't resolve, returns hash address",
+			dns:    doesntResolve,
+			addr:   hashAddr,
+			result: hashAddr,
+		},
+		{
+			desc:   "DNS configured, ENS address, name resolves, returns resolved address",
+			dns:    doesResolve,
+			addr:   ensAddr,
+			result: resolvedAddr,
+		},
+		{
+			desc:      "DNS configured, immutable ENS address, name resolves, returns error",
+			dns:       doesResolve,
+			addr:      ensAddr,
+			immutable: true,
+			expectErr: errors.New(`immutable address not a content hash: "swarm.eth"`),
+		},
+		{
+			desc:      "DNS configured, ENS address, name doesn't resolve, returns error",
+			dns:       doesntResolve,
+			addr:      ensAddr,
+			expectErr: errors.New(`DNS name not found: "swarm.eth"`),
+		},
+	}
+	for _, x := range tests {
+		t.Run(x.desc, func(t *testing.T) {
+			api := &Api{dns: x.dns}
+			uri := &URI{Addr: x.addr, Scheme: "bzz"}
+			if x.immutable {
+				uri.Scheme = "bzzi"
+			}
+			res, err := api.Resolve(uri)
+			if err == nil {
+				if x.expectErr != nil {
+					t.Fatalf("expected error %q, got result %q", x.expectErr, res)
+				}
+				if res.String() != x.result {
+					t.Fatalf("expected result %q, got %q", x.result, res)
+				}
+			} else {
+				if x.expectErr == nil {
+					t.Fatalf("expected no error, got %q", err)
+				}
+				if err.Error() != x.expectErr.Error() {
+					t.Fatalf("expected error %q, got %q", x.expectErr, err)
+				}
+			}
+		})
+	}
+}