feat: Automatically configure connections using DNS. Part of #2043. (#2044)

A connection may be configured to using a DNS name instead of an instance name. If the cloudSqlInstance property is
set to be a domain name instead of an instance name, the connector will look up a SRV record for that name and
connect to that instance.

There should be exactly 1 SRV for the database instance. The connector will always use the SRV record with the
highest priority.

Part of #2043

Author: hessjcg

core/src/main/java/com/google/cloud/sql/core/ConnectionConfig.java

@@ -200,6 +200,18 @@ public ConnectionConfig withConnectorConfig(ConnectorConfig config) {
         config);
   }
 
+  /** Creates a new instance of the ConnectionConfig with an updated cloudSqlInstance. */
+  public ConnectionConfig withCloudSqlInstance(String newCloudSqlInstance) {
+    return new ConnectionConfig(
+        newCloudSqlInstance,
+        namedConnector,
+        unixSocketPath,
+        ipTypes,
+        authType,
+        unixSocketPathSuffix,
+        connectorConfig);
+  }
+
   public String getNamedConnector() {
     return namedConnector;
   }

core/src/main/java/com/google/cloud/sql/core/Connector.java

@@ -48,6 +48,8 @@ class Connector {
   private final int serverProxyPort;
   private final ConnectorConfig config;
 
+  private final InstanceConnectionNameResolver instanceNameResolver;
+
   Connector(
       ConnectorConfig config,
       ConnectionInfoRepositoryFactory connectionInfoRepositoryFactory,
@@ -56,7 +58,8 @@ class Connector {
       ListenableFuture<KeyPair> localKeyPair,
       long minRefreshDelayMs,
       long refreshTimeoutMs,
-      int serverProxyPort) {
+      int serverProxyPort,
+      InstanceConnectionNameResolver instanceNameResolver) {
     this.config = config;
 
     this.adminApi =
@@ -66,6 +69,7 @@ class Connector {
     this.localKeyPair = localKeyPair;
     this.minRefreshDelayMs = minRefreshDelayMs;
     this.serverProxyPort = serverProxyPort;
+    this.instanceNameResolver = instanceNameResolver;
   }
 
   public ConnectorConfig getConfig() {
@@ -139,9 +143,20 @@ Socket connect(ConnectionConfig config, long timeoutMs) throws IOException {
     }
   }
 
-  ConnectionInfoCache getConnection(ConnectionConfig config) {
+  ConnectionInfoCache getConnection(final ConnectionConfig config) {
+    CloudSqlInstanceName name = null;
+    try {
+      name = instanceNameResolver.resolve(config.getCloudSqlInstance());
+    } catch (IllegalArgumentException e) {
+      throw new IllegalArgumentException(
+          String.format(
+              "Cloud SQL connection name is invalid: \"%s\"", config.getCloudSqlInstance()),
+          e);
+    }
+    final ConnectionConfig updatedConfig = config.withCloudSqlInstance(name.getConnectionName());
+
     ConnectionInfoCache instance =
-        instances.computeIfAbsent(config, k -> createConnectionInfo(config));
+        instances.computeIfAbsent(updatedConfig, k -> createConnectionInfo(updatedConfig));
 
     // If the client certificate has expired (as when the computer goes to
     // sleep, and the refresh cycle cannot run), force a refresh immediately.

core/src/main/java/com/google/cloud/sql/core/DnsInstanceConnectionNameResolver.java

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * 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 com.google.cloud.sql.core;
+
+import java.util.Collection;
+import java.util.Objects;
+import javax.naming.NameNotFoundException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * An implementation of InstanceConnectionNameResolver that uses DNS SRV records to resolve an
+ * instance name from a domain name.
+ */
+class DnsInstanceConnectionNameResolver implements InstanceConnectionNameResolver {
+  private static final Logger logger =
+      LoggerFactory.getLogger(DnsInstanceConnectionNameResolver.class);
+
+  private final DnsResolver dnsResolver;
+
+  public DnsInstanceConnectionNameResolver(DnsResolver dnsResolver) {
+    this.dnsResolver = dnsResolver;
+  }
+
+  @Override
+  public CloudSqlInstanceName resolve(final String name) {
+    // Attempt to parse the instance name
+    try {
+      return new CloudSqlInstanceName(name);
+    } catch (IllegalArgumentException e) {
+      // Not a well-formed instance name.
+    }
+
+    // Next, attempt to resolve DNS name.
+    Collection<DnsSrvRecord> instanceNames;
+    try {
+      instanceNames = this.dnsResolver.resolveSrv(name);
+    } catch (NameNotFoundException ne) {
+      // No DNS record found. This is not a valid instance name.
+      throw new IllegalArgumentException(
+          String.format("Unable to resolve SRV record for \"%s\".", name));
+    }
+
+    // Use the first valid instance name from the list
+    // or throw an IllegalArgumentException if none of the values can be parsed.
+    return instanceNames.stream()
+        .map(
+            r -> {
+              String target = r.getTarget();
+              // Trim trailing '.' from target field
+              if (target.endsWith(".")) {
+                target = target.substring(0, target.length() - 1);
+              }
+              try {
+                return new CloudSqlInstanceName(target);
+              } catch (IllegalArgumentException e) {
+                logger.info(
+                    "Unable to parse instance name in SRV record for "
+                        + "domain name \"{}\" with target \"{}\"",
+                    name,
+                    target,
+                    e);
+                return null;
+              }
+            })
+        .filter(Objects::nonNull)
+        .findFirst()
+        .orElseThrow(
+            () ->
+                new IllegalArgumentException(
+                    String.format("Unable to parse values of SRV record for \"%s\".", name)));
+  }
+}

core/src/main/java/com/google/cloud/sql/core/DnsResolver.java

@@ -19,6 +19,7 @@
 import java.util.Collection;
 import javax.naming.NameNotFoundException;
 
+/** Wraps the Java DNS API. */
 interface DnsResolver {
-  Collection<DnsSrvRecord> resolveSrv(String domainName) throws NameNotFoundException;
+  Collection<DnsSrvRecord> resolveSrv(String name) throws NameNotFoundException;
 }

core/src/main/java/com/google/cloud/sql/core/InstanceConnectionNameResolver.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * 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 com.google.cloud.sql.core;
+
+/** Resolves the Cloud SQL Instance from the configuration name. */
+interface InstanceConnectionNameResolver {
+
+  /**
+   * Resolves the CloudSqlInstanceName from a configuration string value.
+   *
+   * @param name the configuration string
+   * @return the CloudSqlInstanceName
+   * @throws IllegalArgumentException if the name cannot be resolved.
+   */
+  CloudSqlInstanceName resolve(String name);
+}

core/src/main/java/com/google/cloud/sql/core/InternalConnectorRegistry.java

@@ -332,7 +332,8 @@ private Connector createConnector(ConnectorConfig config) {
         localKeyPair,
         MIN_REFRESH_DELAY_MS,
         connectTimeoutMs,
-        serverProxyPort);
+        serverProxyPort,
+        new DnsInstanceConnectionNameResolver(new JndiDnsResolver()));
   }
 
   /** Register the configuration for a named connector. */

core/src/test/java/com/google/cloud/sql/core/ConnectorTest.java

@@ -34,7 +34,9 @@
 import java.nio.file.Path;
 import java.time.Duration;
 import java.time.Instant;
+import java.util.Collection;
 import java.util.Collections;
+import javax.naming.NameNotFoundException;
 import javax.net.ssl.SSLHandshakeException;
 import org.junit.After;
 import org.junit.Before;
@@ -147,6 +149,57 @@ public void create_successfulPublicConnection() throws IOException, InterruptedE
     assertThat(readLine(socket)).isEqualTo(SERVER_MESSAGE);
   }
 
+  @Test
+  public void create_successfulPublicConnectionWithDomainName()
+      throws IOException, InterruptedException {
+    FakeSslServer sslServer = new FakeSslServer();
+    ConnectionConfig config =
+        new ConnectionConfig.Builder()
+            .withCloudSqlInstance("db.example.com")
+            .withIpTypes("PRIMARY")
+            .build();
+
+    int port = sslServer.start(PUBLIC_IP);
+
+    Connector connector = newConnector(config.getConnectorConfig(), port);
+
+    Socket socket = connector.connect(config, TEST_MAX_REFRESH_MS);
+
+    assertThat(readLine(socket)).isEqualTo(SERVER_MESSAGE);
+  }
+
+  @Test
+  public void create_throwsErrorForUnresolvedDomainName() throws IOException {
+    ConnectionConfig config =
+        new ConnectionConfig.Builder()
+            .withCloudSqlInstance("baddomain.example.com")
+            .withIpTypes("PRIMARY")
+            .build();
+    Connector c = newConnector(config.getConnectorConfig(), DEFAULT_SERVER_PROXY_PORT);
+    RuntimeException ex =
+        assertThrows(RuntimeException.class, () -> c.connect(config, TEST_MAX_REFRESH_MS));
+
+    assertThat(ex)
+        .hasMessageThat()
+        .contains("Cloud SQL connection name is invalid: \"baddomain.example.com\"");
+  }
+
+  @Test
+  public void create_throwsErrorForDomainNameBadTargetValue() throws IOException {
+    ConnectionConfig config =
+        new ConnectionConfig.Builder()
+            .withCloudSqlInstance("badvalue.example.com")
+            .withIpTypes("PRIMARY")
+            .build();
+    Connector c = newConnector(config.getConnectorConfig(), DEFAULT_SERVER_PROXY_PORT);
+    RuntimeException ex =
+        assertThrows(RuntimeException.class, () -> c.connect(config, TEST_MAX_REFRESH_MS));
+
+    assertThat(ex)
+        .hasMessageThat()
+        .contains("Cloud SQL connection name is invalid: \"badvalue.example.com\"");
+  }
+
   private boolean isWindows() {
     String os = System.getProperty("os.name").toLowerCase();
     return os.contains("win");
@@ -210,7 +263,8 @@ public void create_successfulDomainScopedConnection() throws IOException, Interr
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            port);
+            port,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     Socket socket = c.connect(config, TEST_MAX_REFRESH_MS);
 
@@ -271,7 +325,8 @@ public void create_throwsException_adminApiNotEnabled() throws IOException {
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            DEFAULT_SERVER_PROXY_PORT);
+            DEFAULT_SERVER_PROXY_PORT,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     // Use a different project to get Api Not Enabled Error.
     TerminalException ex =
@@ -303,7 +358,8 @@ public void create_throwsException_adminApiReturnsNotAuthorized() throws IOExcep
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            DEFAULT_SERVER_PROXY_PORT);
+            DEFAULT_SERVER_PROXY_PORT,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     // Use a different instance to simulate incorrect permissions.
     TerminalException ex =
@@ -335,7 +391,8 @@ public void create_throwsException_badGateway() throws IOException {
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            DEFAULT_SERVER_PROXY_PORT);
+            DEFAULT_SERVER_PROXY_PORT,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     // If the gateway is down, then this is a temporary error, not a fatal error.
     RuntimeException ex =
@@ -377,7 +434,8 @@ public void create_successfulPublicConnection_withIntermittentBadGatewayErrors()
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            port);
+            port,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     Socket socket = c.connect(config, TEST_MAX_REFRESH_MS);
 
@@ -410,7 +468,8 @@ public void supportsCustomCredentialFactoryWithIAM() throws InterruptedException
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            port);
+            port,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     Socket socket = c.connect(config, TEST_MAX_REFRESH_MS);
 
@@ -442,7 +501,8 @@ public void supportsCustomCredentialFactoryWithNoExpirationTime()
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            port);
+            port,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     Socket socket = c.connect(config, TEST_MAX_REFRESH_MS);
 
@@ -480,7 +540,8 @@ public HttpRequestInitializer create() {
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            DEFAULT_SERVER_PROXY_PORT);
+            DEFAULT_SERVER_PROXY_PORT,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
 
     assertThrows(RuntimeException.class, () -> c.connect(config, TEST_MAX_REFRESH_MS));
   }
@@ -497,7 +558,8 @@ private Connector newConnector(ConnectorConfig config, int port) {
             clientKeyPair,
             10,
             TEST_MAX_REFRESH_MS,
-            port);
+            port,
+            new DnsInstanceConnectionNameResolver(new MockDnsResolver()));
     return connector;
   }
 
@@ -506,4 +568,19 @@ private String readLine(Socket socket) throws IOException {
         new BufferedReader(new InputStreamReader(socket.getInputStream(), UTF_8));
     return bufferedReader.readLine();
   }
+
+  private static class MockDnsResolver implements DnsResolver {
+
+    @Override
+    public Collection<DnsSrvRecord> resolveSrv(String domainName) throws NameNotFoundException {
+      if ("db.example.com".equals(domainName)) {
+        return Collections.singletonList(
+            new DnsSrvRecord("0 10 3307 myProject:myRegion:myInstance."));
+      }
+      if ("badvalue.example.com".equals(domainName)) {
+        return Collections.singletonList(new DnsSrvRecord("0 10 3307 not-an-instance-name."));
+      }
+      throw new NameNotFoundException("Not found: " + domainName);
+    }
+  }
 }

core/src/test/java/com/google/cloud/sql/core/DnsSrvRecordTest.java

@@ -5,7 +5,7 @@
  * 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
+ * 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,