Allow valid SRV hostnames with less than 3 parts

driver-core/src/main/com/mongodb/connection/ClusterSettings.java

@@ -36,7 +36,6 @@
 import static com.mongodb.assertions.Assertions.isTrueArgument;
 import static com.mongodb.assertions.Assertions.notNull;
 import static com.mongodb.internal.connection.ServerAddressHelper.createServerAddress;
-import static java.lang.String.format;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.unmodifiableList;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
@@ -607,11 +606,6 @@ private ClusterSettings(final Builder builder) {
             if (builder.srvHost.contains(":")) {
                 throw new IllegalArgumentException("The srvHost can not contain a host name that specifies a port");
             }
-
-            if (builder.srvHost.split("\\.").length < 3) {
-                throw new IllegalArgumentException(format("An SRV host name '%s' was provided that does not contain at least three parts. "
-                        + "It must contain a hostname, domain name and a top level domain.", builder.srvHost));
-            }
         }
 
         if (builder.hosts.size() > 1 && builder.requiredClusterType == ClusterType.STANDALONE) {

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

@@ -64,13 +64,19 @@ public DefaultDnsResolver(@Nullable final DnsClient dnsClient) {
 
       The priority and weight are ignored, and we just concatenate the host (after removing the ending '.') and port with a
       ':' in between, as expected by ServerAddress.
-
-      It's required that the srvHost has at least three parts (e.g. foo.bar.baz) and that all of the resolved hosts have a parent
-      domain equal to the domain of the srvHost.
     */
     @Override
     public List<String> resolveHostFromSrvRecords(final String srvHost, final String srvServiceName) {
-        String srvHostDomain = srvHost.substring(srvHost.indexOf('.') + 1);
+        List<String> srvHostParts = asList(srvHost.split("\\."));
+
+        String srvHostDomain;
+        boolean srvHasLessThanThreeParts = srvHostParts.size() < 3;
+        if (srvHasLessThanThreeParts) {
+            srvHostDomain = srvHost;
+        } else {
+            srvHostDomain = srvHost.substring(srvHost.indexOf('.') + 1);
+        }
+
         List<String> srvHostDomainParts = asList(srvHostDomain.split("\\."));
         List<String> hosts = new ArrayList<>();
         String resourceName = "_" + srvServiceName + "._tcp." + srvHost;
@@ -84,9 +90,15 @@ public List<String> resolveHostFromSrvRecords(final String srvHost, final String
                 String[] split = srvRecord.split(" ");
                 String resolvedHost = split[3].endsWith(".") ? split[3].substring(0, split[3].length() - 1) : split[3];
                 String resolvedHostDomain = resolvedHost.substring(resolvedHost.indexOf('.') + 1);
-                if (!sameParentDomain(srvHostDomainParts, resolvedHostDomain)) {
+                List<String> resolvedHostDomainParts = asList(resolvedHostDomain.split("\\."));
+                if (!sameDomain(srvHostDomainParts, resolvedHostDomainParts)) {
+                    throw new MongoConfigurationException(
+                            format("The SRV host name '%s' resolved to a host '%s' that does not share domain name",
+                                    srvHost, resolvedHost));
+                }
+                if (srvHasLessThanThreeParts && resolvedHostDomainParts.size() <= srvHostDomainParts.size()) {
                     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.",
+                            format("The SRV host name '%s' resolved to a host '%s' that does not have at least one more domain level",
                                     srvHost, resolvedHost));
                 }
                 hosts.add(resolvedHost + ":" + split[2]);
@@ -98,8 +110,7 @@ public List<String> resolveHostFromSrvRecords(final String srvHost, final String
         return hosts;
     }
 
-    private static boolean sameParentDomain(final List<String> srvHostDomainParts, final String resolvedHostDomain) {
-        List<String> resolvedHostDomainParts = asList(resolvedHostDomain.split("\\."));
+    private static boolean sameDomain(final List<String> srvHostDomainParts, final List<String> resolvedHostDomainParts) {
         if (srvHostDomainParts.size() > resolvedHostDomainParts.size()) {
             return false;
         }

driver-core/src/test/resources/initial-dns-seedlist-discovery/README.md

@@ -0,0 +1,182 @@
+# Initial DNS Seedlist Discovery tests
+
+This directory contains platform-independent tests that drivers can use to prove their conformance to the Initial DNS
+Seedlist Discovery spec.
+
+## Prose Tests
+
+For the following prose tests, it is assumed drivers are be able to stub DNS results to easily test invalid DNS
+resolution results.
+
+### 1. Allow SRVs with fewer than 3 `.` separated parts
+
+When running validation on an SRV string before DNS resolution, do not throw a error due to number of SRV parts.
+
+- `mongodb+srv://localhost`
+- `mongodb+srv://mongo.local`
+
+### 2. Throw when return address does not end with SRV domain
+
+When given a returned address that does NOT end with the original SRV's domain name, throw a runtime error.
+
+For this test, run each of the following cases:
+
+- the SRV `mongodb+srv://localhost` resolving to `localhost.mongodb`
+- the SRV `mongodb+srv://mongo.local` resolving to `test_1.evil.local`
+- the SRV `mongodb+srv://blogs.mongodb.com` resolving to `blogs.evil.com`
+
+Remember, the domain of an SRV with one or two `.` separated parts is the SRVs entire hostname.
+
+### 3. Throw when return address is identical to SRV hostname
+
+When given a returned address that is identical to the SRV hostname and the SRV hostname has fewer than three `.`
+separated parts, throw a runtime error.
+
+For this test, run each of the following cases:
+
+- the SRV `mongodb+srv://localhost` resolving to `localhost`
+- the SRV `mongodb+srv://mongo.local` resolving to `mongo.local`
+
+### 4. Throw when return address does not contain `.` separating shared part of domain
+
+When given a returned address that does NOT share the domain name of the SRV record because it's missing a `.`, throw a
+runtime error.
+
+For this test, run each of the following cases:
+
+- the SRV `mongodb+srv://localhost` resolving to `test_1.cluster_1localhost`
+- the SRV `mongodb+srv://mongo.local` resolving to `test_1.my_hostmongo.local`
+- the SRV `mongodb+srv://blogs.mongodb.com` resolving to `cluster.testmongodb.com`
+
+## Test Setup
+
+The tests in the `replica-set` directory MUST be executed against a three-node replica set on localhost ports 27017,
+27018, and 27019 with replica set name `repl0`.
+
+The tests in the `load-balanced` directory MUST be executed against a load-balanced sharded cluster with the mongos
+servers running on localhost ports 27017 and 27018 and `--loadBalancerPort` 27050 and 27051, respectively (corresponding
+to the script in
+[drivers-evergreen-tools](https://github.com/mongodb-labs/drivers-evergreen-tools/blob/master/.evergreen/run-load-balancer.sh)).
+The load balancers, shard servers, and config servers may run on any open ports.
+
+The tests in the `sharded` directory MUST be executed against a sharded cluster with the mongos servers running on
+localhost ports 27017 and 27018. Shard servers and config servers may run on any open ports.
+
+In all cases, the clusters MUST be started with SSL enabled.
+
+To run the tests that accompany this spec, you need to configure the SRV and TXT records with a real name server. The
+following records are required for these tests:
+
+```
+Record                                    TTL    Class   Address
+localhost.test.build.10gen.cc.            86400  IN A    127.0.0.1
+localhost.sub.test.build.10gen.cc.        86400  IN A    127.0.0.1
+
+Record                                      TTL    Class   Port   Target
+_mongodb._tcp.test1.test.build.10gen.cc.    86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test1.test.build.10gen.cc.    86400  IN SRV  27018  localhost.test.build.10gen.cc.
+_mongodb._tcp.test2.test.build.10gen.cc.    86400  IN SRV  27018  localhost.test.build.10gen.cc.
+_mongodb._tcp.test2.test.build.10gen.cc.    86400  IN SRV  27019  localhost.test.build.10gen.cc.
+_mongodb._tcp.test3.test.build.10gen.cc.    86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test5.test.build.10gen.cc.    86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test6.test.build.10gen.cc.    86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test7.test.build.10gen.cc.    86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test8.test.build.10gen.cc.    86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test10.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test11.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test12.test.build.10gen.cc.   86400  IN SRV  27017  localhost.build.10gen.cc.
+_mongodb._tcp.test13.test.build.10gen.cc.   86400  IN SRV  27017  test.build.10gen.cc.
+_mongodb._tcp.test14.test.build.10gen.cc.   86400  IN SRV  27017  localhost.not-test.build.10gen.cc.
+_mongodb._tcp.test15.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.not-build.10gen.cc.
+_mongodb._tcp.test16.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.not-10gen.cc.
+_mongodb._tcp.test17.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.10gen.not-cc.
+_mongodb._tcp.test18.test.build.10gen.cc.   86400  IN SRV  27017  localhost.sub.test.build.10gen.cc.
+_mongodb._tcp.test19.test.build.10gen.cc.   86400  IN SRV  27017  localhost.evil.build.10gen.cc.
+_mongodb._tcp.test19.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test20.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test21.test.build.10gen.cc.   86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_customname._tcp.test22.test.build.10gen.cc 86400  IN SRV  27017  localhost.test.build.10gen.cc.
+_mongodb._tcp.test23.test.build.10gen.cc.   86400  IN SRV  8000   localhost.test.build.10gen.cc.
+_mongodb._tcp.test24.test.build.10gen.cc.   86400  IN SRV  8000   localhost.test.build.10gen.cc.
+
+Record                                    TTL    Class   Text
+test5.test.build.10gen.cc.                86400  IN TXT  "replicaSet=repl0&authSource=thisDB"
+test6.test.build.10gen.cc.                86400  IN TXT  "replicaSet=repl0"
+test6.test.build.10gen.cc.                86400  IN TXT  "authSource=otherDB"
+test7.test.build.10gen.cc.                86400  IN TXT  "ssl=false"
+test8.test.build.10gen.cc.                86400  IN TXT  "authSource"
+test10.test.build.10gen.cc.               86400  IN TXT  "socketTimeoutMS=500"
+test11.test.build.10gen.cc.               86400  IN TXT  "replicaS" "et=rep" "l0"
+test20.test.build.10gen.cc.               86400  IN TXT  "loadBalanced=true"
+test21.test.build.10gen.cc.               86400  IN TXT  "loadBalanced=false"
+test24.test.build.10gen.cc.               86400  IN TXT  "loadBalanced=true"
+```
+
+Notes:
+
+- `test4` is omitted deliberately to test what happens with no SRV record.
+- `test9` is missing because it was deleted during the development of the tests.
+- The missing `test.` sub-domain in the SRV record target for `test12` is deliberate.
+- `test22` is used to test a custom service name (`customname`).
+- `test23` and `test24` point to port 8000 (HAProxy) and are used for load-balanced tests.
+
+In our tests we have used `localhost.test.build.10gen.cc` as the domain, and then configured
+`localhost.test.build.10gen.cc` to resolve to 127.0.0.1.
+
+You need to adapt the records shown above to replace `test.build.10gen.cc` with your own domain name, and update the
+"uri" field in the YAML or JSON files in this directory with the actual domain.
+
+## Test Format and Use
+
+These YAML and JSON files contain the following fields:
+
+- `uri`: a `mongodb+srv` connection string
+- `seeds`: the expected set of initial seeds discovered from the SRV record
+- `numSeeds`: the expected number of initial seeds discovered from the SRV record. This is mainly used to test
+  `srvMaxHosts`, since randomly selected hosts cannot be deterministically asserted.
+- `hosts`: the discovered topology's list of hosts once SDAM completes a scan
+- `numHosts`: the expected number of hosts discovered once SDAM completes a scan. This is mainly used to test
+  `srvMaxHosts`, since randomly selected hosts cannot be deterministically asserted.
+- `options`: the parsed [URI options](../../uri-options/uri-options.md) as discovered from the
+  [Connection String](../../connection-string/connection-string-spec.md)'s "Connection Options" component and SRV
+  resolution (e.g. TXT records, implicit `tls` default).
+- `parsed_options`: additional, parsed options from other
+  [Connection String](../../connection-string/connection-string-spec.md) components. This is mainly used for asserting
+  `UserInfo` (as `user` and `password`) and `Auth database` (as `auth_database`).
+- `error`: indicates that the parsing of the URI, or the resolving or contents of the SRV or TXT records included
+  errors.
+- `comment`: a comment to indicate why a test would fail.
+- `ping`: if false, the test runner should not run a "ping" operation.
+
+For each YAML file:
+
+- Create a MongoClient initialized with the `mongodb+srv` connection string.
+- Run a "ping" operation unless `ping` is false or `error` is true.
+
+Assertions:
+
+- If `seeds` is specified, drivers SHOULD verify that the set of hosts in the client's initial seedlist matches the list
+  in `seeds`. If `numSeeds` is specified, drivers SHOULD verify that the size of that set matches `numSeeds`.
+
+- If `hosts` is specified, drivers MUST verify that the set of ServerDescriptions in the client's TopologyDescription
+  eventually matches the list in `hosts`. If `numHosts` is specified, drivers MUST verify that the size of that set
+  matches `numHosts`.
+
+- If `options` is specified, drivers MUST verify each of the values under `options` match the MongoClient's parsed value
+  for that option. There may be other options parsed by the MongoClient as well, which a test does not verify.
+
+- If `parsed_options` is specified, drivers MUST verify that each of the values under `parsed_options` match the
+  MongoClient's parsed value for that option. Supported values include, but are not limited to, `user` and `password`
+  (parsed from `UserInfo`) and `auth_database` (parsed from `Auth database`).
+
+- If `error` is specified and `true`, drivers MUST verify that initializing the MongoClient throws an error. If `error`
+  is not specified or is `false`, both initializing the MongoClient and running a ping operation must succeed without
+  throwing any errors.
+
+- If `ping` is not specified or `true`, drivers MUST verify that running a "ping" operation using the initialized
+  MongoClient succeeds. If `ping` is `false`, drivers MUST NOT run a "ping" operation.
+
+  > **Note:** These tests are expected to be run against MongoDB databases with and without authentication enabled. The
+  > "ping" operation does not require authentication so should succeed with URIs that contain no userinfo (i.e. no
+  > username and password). Tests with URIs that contain userinfo always set `ping` to `false` because some drivers will
+  > fail handshake on a connection if userinfo is provided but incorrect.