snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

internal/resolver/dns/fake_net_resolver_test.go

@@ -0,0 +1,126 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package dns_test
+
+import (
+	"context"
+	"net"
+	"sync"
+
+	"google.golang.org/grpc/internal/testutils"
+)
+
+// A fake implementation of the internal.NetResolver interface for use in tests.
+type testNetResolver struct {
+	// A write to this channel is made when this resolver receives a resolution
+	// request. Tests can rely on reading from this channel to be notified about
+	// resolution requests instead of sleeping for a predefined period of time.
+	lookupHostCh *testutils.Channel
+
+	mu              sync.Mutex
+	hostLookupTable map[string][]string   // Name --> list of addresses
+	srvLookupTable  map[string][]*net.SRV // Name --> list of SRV records
+	txtLookupTable  map[string][]string   // Name --> service config for TXT record
+}
+
+func (tr *testNetResolver) LookupHost(ctx context.Context, host string) ([]string, error) {
+	if tr.lookupHostCh != nil {
+		if err := tr.lookupHostCh.SendContext(ctx, nil); err != nil {
+			return nil, err
+		}
+	}
+
+	tr.mu.Lock()
+	defer tr.mu.Unlock()
+
+	if addrs, ok := tr.hostLookupTable[host]; ok {
+		return addrs, nil
+	}
+
+	return nil, &net.DNSError{
+		Err:         "hostLookup error",
+		Name:        host,
+		Server:      "fake",
+		IsTemporary: true,
+	}
+}
+
+func (tr *testNetResolver) UpdateHostLookupTable(table map[string][]string) {
+	tr.mu.Lock()
+	tr.hostLookupTable = table
+	tr.mu.Unlock()
+}
+
+func (tr *testNetResolver) LookupSRV(_ context.Context, service, proto, name string) (string, []*net.SRV, error) {
+	tr.mu.Lock()
+	defer tr.mu.Unlock()
+
+	cname := "_" + service + "._" + proto + "." + name
+	if srvs, ok := tr.srvLookupTable[cname]; ok {
+		return cname, srvs, nil
+	}
+	return "", nil, &net.DNSError{
+		Err:         "srvLookup error",
+		Name:        cname,
+		Server:      "fake",
+		IsTemporary: true,
+	}
+}
+
+func (tr *testNetResolver) LookupTXT(_ context.Context, host string) ([]string, error) {
+	tr.mu.Lock()
+	defer tr.mu.Unlock()
+
+	if sc, ok := tr.txtLookupTable[host]; ok {
+		return sc, nil
+	}
+	return nil, &net.DNSError{
+		Err:         "txtLookup error",
+		Name:        host,
+		Server:      "fake",
+		IsTemporary: true,
+	}
+}
+
+func (tr *testNetResolver) UpdateTXTLookupTable(table map[string][]string) {
+	tr.mu.Lock()
+	tr.txtLookupTable = table
+	tr.mu.Unlock()
+}
+
+// txtRecordServiceConfig generates a slice of strings (aggregately representing
+// a single service config file) for the input config string, that represents
+// the result from a real DNS TXT record lookup.
+func txtRecordServiceConfig(cfg string) []string {
+	// In DNS, service config is encoded in a TXT record via the mechanism
+	// described in RFC-1464 using the attribute name grpc_config.
+	b := append([]byte("grpc_config="), []byte(cfg)...)
+
+	// Split b into multiple strings, each with a max of 255 bytes, which is
+	// the DNS TXT record limit.
+	var r []string
+	for i := 0; i < len(b); i += txtBytesLimit {
+		if i+txtBytesLimit > len(b) {
+			r = append(r, string(b[i:]))
+		} else {
+			r = append(r, string(b[i:i+txtBytesLimit]))
+		}
+	}
+	return r
+}