GODRIVER-3284 Allow valid SRV hostnames with less than 3 parts.

x/mongo/driver/connstring/initial_dns_seedlist_discovery_prose_test.go

@@ -0,0 +1,122 @@
+// Copyright (C) MongoDB, Inc. 2024-present.
+//
+// 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
+
+package connstring
+
+import (
+	"fmt"
+	"net"
+	"testing"
+
+	"go.mongodb.org/mongo-driver/v2/internal/assert"
+	"go.mongodb.org/mongo-driver/v2/x/mongo/driver/dns"
+)
+
+func TestInitialDNSSeedlistDiscoveryProse(t *testing.T) {
+	newTestParser := func(record string) *parser {
+		return &parser{&dns.Resolver{
+			LookupSRV: func(_, _, _ string) (string, []*net.SRV, error) {
+				return "", []*net.SRV{
+					{
+						Target: record,
+						Port:   27017,
+					},
+				}, nil
+			},
+			LookupTXT: func(string) ([]string, error) {
+				return nil, nil
+			},
+		}}
+	}
+
+	t.Run("1. Allow SRVs with fewer than 3 . separated parts", func(t *testing.T) {
+		t.Parallel()
+
+		cases := []struct {
+			record string
+			uri    string
+		}{
+			{"test_1.localhost", "mongodb+srv://localhost"},
+			{"test_1.mongo.local", "mongodb+srv://mongo.local"},
+		}
+		for _, c := range cases {
+			c := c
+			t.Run(c.uri, func(t *testing.T) {
+				t.Parallel()
+
+				_, err := newTestParser(c.record).parse(c.uri)
+				assert.NoError(t, err, "expected no URI parsing error, got %v", err)
+			})
+		}
+	})
+	t.Run("2. Throw when return address does not end with SRV domain", func(t *testing.T) {
+		t.Parallel()
+
+		cases := []struct {
+			record string
+			uri    string
+		}{
+			{"localhost.mongodb", "mongodb+srv://localhost"},
+			{"test_1.evil.local", "mongodb+srv://mongo.local"},
+			{"blogs.evil.com", "mongodb+srv://blogs.mongodb.com"},
+		}
+		for _, c := range cases {
+			c := c
+			t.Run(c.uri, func(t *testing.T) {
+				t.Parallel()
+
+				_, err := newTestParser(c.record).parse(c.uri)
+				assert.ErrorContains(t, err, "Domain suffix from SRV record not matched input domain")
+			})
+		}
+	})
+	t.Run("3. Throw when return address is identical to SRV hostname", func(t *testing.T) {
+		t.Parallel()
+
+		cases := []struct {
+			record string
+			uri    string
+			labels int
+		}{
+			{"localhost", "mongodb+srv://localhost", 1},
+			{"mongo.local", "mongodb+srv://mongo.local", 2},
+		}
+		for _, c := range cases {
+			c := c
+			t.Run(c.uri, func(t *testing.T) {
+				t.Parallel()
+
+				_, err := newTestParser(c.record).parse(c.uri)
+				expected := fmt.Sprintf(
+					"Server record (%d levels) should have more domain levels than parent URI (%d levels)",
+					c.labels, c.labels,
+				)
+				assert.ErrorContains(t, err, expected)
+			})
+		}
+	})
+	t.Run("4. Throw when return address does not contain . separating shared part of domain", func(t *testing.T) {
+		t.Parallel()
+
+		cases := []struct {
+			record string
+			uri    string
+		}{
+			{"test_1.cluster_1localhost", "mongodb+srv://localhost"},
+			{"test_1.my_hostmongo.local", "mongodb+srv://mongo.local"},
+			{"cluster.testmongodb.com", "mongodb+srv://blogs.mongodb.com"},
+		}
+		for _, c := range cases {
+			c := c
+			t.Run(c.uri, func(t *testing.T) {
+				t.Parallel()
+
+				_, err := newTestParser(c.record).parse(c.uri)
+				assert.ErrorContains(t, err, "Domain suffix from SRV record not matched input domain")
+			})
+		}
+	})
+}

x/mongo/driver/dns/dns.go

@@ -113,15 +113,18 @@ func (r *Resolver) fetchSeedlistFromSRV(host string, srvName string, stopOnErr b
 func validateSRVResult(recordFromSRV, inputHostName string) error {
 	separatedInputDomain := strings.Split(strings.ToLower(inputHostName), ".")
 	separatedRecord := strings.Split(strings.ToLower(recordFromSRV), ".")
-	if len(separatedRecord) < 2 {
-		return errors.New("DNS name must contain at least 2 labels")
+	if l := len(separatedInputDomain); l < 3 && len(separatedRecord) <= l {
+		return fmt.Errorf("Server record (%d levels) should have more domain levels than parent URI (%d levels)", l, len(separatedRecord))
 	}
 	if len(separatedRecord) < len(separatedInputDomain) {
 		return errors.New("Domain suffix from SRV record not matched input domain")
 	}
 
-	inputDomainSuffix := separatedInputDomain[1:]
-	domainSuffixOffset := len(separatedRecord) - (len(separatedInputDomain) - 1)
+	inputDomainSuffix := separatedInputDomain
+	if len(inputDomainSuffix) > 2 {
+		inputDomainSuffix = inputDomainSuffix[1:]
+	}
+	domainSuffixOffset := len(separatedRecord) - len(inputDomainSuffix)
 
 	recordDomainSuffix := separatedRecord[domainSuffixOffset:]
 	for ix, label := range inputDomainSuffix {