Transparent proxy: TP Loader Cloud SDK native integration (#981)

Author: VladislavAtanasov95

cloudplatform/connectivity-destination-service/src/main/java/com/sap/cloud/sdk/cloudplatform/connectivity/NetworkVerifier.java

@@ -0,0 +1,90 @@
+package com.sap.cloud.sdk.cloudplatform.connectivity;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.net.UnknownHostException;
+
+import javax.annotation.Nonnull;
+
+import com.sap.cloud.sdk.cloudplatform.connectivity.exception.DestinationAccessException;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * NetworkVerifier that performs TCP socket-based connectivity verification.
+ *
+ * <p>
+ * This implementation uses standard Java socket connections to verify that a remote host and port combination is
+ * reachable and accepting connections. It establishes a temporary TCP connection to the target endpoint and immediately
+ * closes it upon successful establishment.
+ *
+ * <p>
+ * <strong>Verification Process:</strong>
+ * <ol>
+ * <li>Creates a new TCP socket</li>
+ * <li>Attempts to connect to the specified host and port with a timeout</li>
+ * <li>Immediately closes the connection if successful</li>
+ * <li>Throws appropriate exceptions for failures</li>
+ * </ol>
+ *
+ * <p>
+ * <strong>Timeout Configuration:</strong> The verification uses a fixed timeout of {@value #HOST_REACH_TIMEOUT}
+ * milliseconds to prevent indefinite blocking on unreachable endpoints.
+ *
+ * <p>
+ * <strong>Error Handling:</strong>
+ * <ul>
+ * <li>{@link UnknownHostException} - Host cannot be resolved to an IP address</li>
+ * <li>{@link IOException} - Network connectivity issues or connection refused</li>
+ * </ul>
+ *
+ * @see TransparentProxy
+ * @since 5.24.0
+ */
+@Slf4j
+class NetworkVerifier
+{
+    private static final int HOST_REACH_TIMEOUT = 5000;
+
+    /**
+     * {@inheritDoc}
+     *
+     * <p>
+     * This implementation creates a TCP socket connection to the specified host and port to verify connectivity. The
+     * connection is immediately closed after successful establishment.
+     *
+     * @param host
+     *            {@inheritDoc}
+     * @param port
+     *            {@inheritDoc}
+     * @throws DestinationAccessException
+     *             {@inheritDoc}
+     *             <p>
+     *             Specific error conditions:
+     *             <ul>
+     *             <li>Host resolution failure - when DNS lookup fails</li>
+     *             <li>Connection failure - when host is unreachable or port is closed</li>
+     *             <li>Network timeouts - when connection attempt exceeds timeout</li>
+     *             </ul>
+     */
+    void verifyHostConnectivity( @Nonnull final String host, final int port )
+        throws DestinationAccessException
+    {
+        log.info("Verifying that transparent proxy host is reachable on {}:{}", host, port);
+        try( Socket socket = new Socket() ) {
+            socket.connect(new InetSocketAddress(host, port), HOST_REACH_TIMEOUT);
+            log.info("Successfully verified that transparent proxy host is reachable on {}:{}", host, port);
+        }
+        catch( final UnknownHostException e ) {
+            throw new DestinationAccessException(
+                String.format("Host [%s] could not be resolved. Caused by: %s", host, e.getMessage()),
+                e);
+        }
+        catch( final IOException e ) {
+            throw new DestinationAccessException(
+                String.format("Host [%s] on port [%d] is not reachable. Caused by: %s", host, port, e.getMessage()),
+                e);
+        }
+    }
+}