improve the logic in DefaultDnsResolver to take into consideration that 'resolvedHost' might not contain '.'

Author: NathanQingyangXu

driver-core/src/main/com/mongodb/internal/dns/DefaultDnsResolver.java

@@ -89,13 +89,12 @@ public List<String> resolveHostFromSrvRecords(final String srvHost, final String
             for (String srvRecord : srvAttributeValues) {
                 String[] split = srvRecord.split(" ");
                 String resolvedHost = split[3].endsWith(".") ? split[3].substring(0, split[3].length() - 1) : split[3];
-                if (srvHostHasLessThanThreeParts && resolvedHost.equals(srvHost)) {
-                    throw new MongoConfigurationException(
-                            format("The SRV host name '%s' has less than three parts and the resolved host '%s' is identical.",
-                                    srvHost, resolvedHost)
-                    );
+                String resolvedHostDomain;
+                if (resolvedHost.contains(".")) {
+                    resolvedHostDomain = resolvedHost.substring(resolvedHost.indexOf('.') + 1);
+                } else {
+                    resolvedHostDomain = "";
                 }
-                String resolvedHostDomain = resolvedHost.substring(resolvedHost.indexOf('.') + 1);
                 if (!sameParentDomain(srvHostDomainParts, resolvedHostDomain)) {
                     throw new MongoConfigurationException(
                             format("The SRV host name '%s' resolved to a host '%s 'that is not in a sub-domain of the SRV host.",

driver-core/src/test/unit/com/mongodb/internal/connection/InitialDnsSeedListDiscoveryProseTest.java

@@ -59,7 +59,7 @@ void tearDown() {
             "mongo.local, driver.mongo.local"
     })
     @DisplayName("1. Allow SRVs with fewer than 3 '.' separated parts")
-    void test1(final String srvHost, final String resolvedHost) {
+    void test_allow_SRVs_with_fewer_than_three_parts(final String srvHost, final String resolvedHost) {
         doTest(srvHost, resolvedHost, false);
     }
 
@@ -70,7 +70,7 @@ void test1(final String srvHost, final String resolvedHost) {
             "blogs.mongodb.com, blogs.evil.com"
     })
     @DisplayName("2. Throw when return address does not end with SRV domain")
-    void test2(final String srvHost, final String resolvedHost) {
+    void test_throw_when_return_address_doesnot_end_with_SRV_domain(final String srvHost, final String resolvedHost) {
         doTest(srvHost, resolvedHost, true);
     }
 
@@ -79,8 +79,8 @@ void test2(final String srvHost, final String resolvedHost) {
             "localhost, localhost",
             "mongo.local, mongo.local"
     })
-    @DisplayName("3. Throw when return address is identical to SRV hostname and return address does not contain '.' separating shared part of domain")
-    void test3(final String srvHost, final String resolvedHost) {
+    @DisplayName("3. Throw when return address is identical to SRV hostname and the SRV hostname has fewer than three `.` separated parts")
+    void test_throw_when_return_address_is_identical_to_SRV_hostname(final String srvHost, final String resolvedHost) {
         doTest(srvHost, resolvedHost, true);
     }
 
@@ -91,7 +91,7 @@ void test3(final String srvHost, final String resolvedHost) {
             "blogs.mongodb.com, cluster.testmongodb.com"
     })
     @DisplayName("4. Throw when return address does not contain '.' separating shared part of domain")
-    void test4(final String srvHost, final String resolvedHost) {
+    void test_throw_when_return_address_doesnot_contain_shared_part_of_domain(final String srvHost, final String resolvedHost) {
         doTest(srvHost, resolvedHost, true);
     }