Transparent proxy: TP Loader Cloud SDK native integration

Author: VladislavAtanasov95

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

@@ -0,0 +1,223 @@
+package com.sap.cloud.sdk.cloudplatform.connectivity;
+
+import java.io.IOException;
+import java.net.*;
+
+import javax.annotation.Nonnull;
+
+import com.sap.cloud.sdk.cloudplatform.connectivity.exception.DestinationAccessException;
+
+import io.vavr.control.Try;
+
+/**
+ * A transparent proxy loader that enables routing traffic through a single registered gateway host.
+ *
+ * <p>
+ * This class provides a mechanism to register a proxy gateway that will handle all destination requests transparently.
+ * Once registered, all destination lookups will be routed through the configured gateway host and port.
+ *
+ * <p>
+ * <strong>Key Features:</strong>
+ * <ul>
+ * <li>Single gateway registration - only one proxy can be registered at a time</li>
+ * <li>Host validation - ensures hosts don't contain paths and are reachable</li>
+ * <li>Automatic scheme normalization - defaults to HTTP if no scheme provided</li>
+ * <li>Network connectivity validation before registration</li>
+ * </ul>
+ *
+ * <p>
+ * <strong>Usage Example:</strong>
+ *
+ * <pre>{@code
+ * // Register with default port 80
+ * TransparentProxy.register("gateway.svc.cluster.local");
+ *
+ * // Register with custom port
+ * TransparentProxy.register("http://gateway.svc.cluster.local", 8080);
+ * }</pre>
+ *
+ * <p>
+ * <strong>Thread Safety:</strong> This class uses static state and is not thread-safe. Registration should be performed
+ * during application initialization.
+ *
+ * @since 5.24.0
+ */
+public class TransparentProxy implements DestinationLoader
+{
+    private static final Integer DEFAULT_PORT = 80;
+    private static final String SCHEME_SEPARATOR = "://";
+    private static final String HTTP_SCHEME = org.apache.http.HttpHost.DEFAULT_SCHEME_NAME + SCHEME_SEPARATOR;
+    private static final String PATH_SEPARATOR = "/";
+    private static final String PORT_SEPARATOR = ":";
+    private static final String HOST_CONTAINS_PATH_ERROR_MESSAGE_TEMPLATE =
+        "Host '%s' contains a path '%s'. Paths are not allowed in host registration.";
+    static String uri;
+    static NetworkValidator networkValidator = new DefaultNetworkValidator();
+
+    /**
+     * Registers a transparent proxy gateway using the default port 80.
+     *
+     * <p>
+     * This method registers the specified host as a transparent proxy gateway that will handle all subsequent
+     * destination requests. The host will be validated for reachability and must not contain any path components.
+     *
+     * <p>
+     * If no scheme is provided, HTTP will be used by default. The final URI will be constructed as:
+     * {@code <normalized-host>:80}
+     *
+     * @param host
+     *            the gateway host to register (e.g., "gateway.svc.cluster.local") Must not contain paths or be null
+     * @throws DestinationAccessException
+     *             if the proxy is already registered, the host contains a path, or the host is not reachable on port 80
+     * @throws IllegalArgumentException
+     *             if host is null
+     * @see #register(String, Integer)
+     */
+    public static void register( @Nonnull final String host )
+    {
+        registerLoader(host, DEFAULT_PORT);
+    }
+
+    /**
+     * Registers a transparent proxy gateway with a specified port.
+     *
+     * <p>
+     * This method registers the specified host and port as a transparent proxy gateway that will handle all subsequent
+     * destination requests. The host will be validated for reachability on the specified port and must not contain any
+     * path components.
+     *
+     * <p>
+     * If no scheme is provided, HTTP will be used by default. The final URI will be constructed as:
+     * {@code <normalized-host>:<port>}
+     *
+     * @param host
+     *            the gateway host to register (e.g., "gateway" or "http://gateway") Must not contain paths or be null
+     * @param port
+     *            the port number to use for the gateway connection. Must not be null and should be a valid port number
+     *            (1-65535)
+     * @throws DestinationAccessException
+     *             if the proxy is already registered, the host contains a path, or the host is not reachable on the
+     *             specified port
+     * @throws IllegalArgumentException
+     *             if host or port is null
+     * @see #register(String)
+     */
+    public static void register( @Nonnull final String host, @Nonnull final Integer port )
+    {
+        registerLoader(host, port);
+    }
+
+    private static void registerLoader( @Nonnull final String host, final Integer port )
+    {
+        if( uri != null ) {
+            throw new DestinationAccessException(
+                "TransparentProxy is already registered. Only one registration is allowed.");
+        }
+
+        validateHostHasNoPath(host);
+
+        final String normalizedHost = normalizeHostWithScheme(host);
+        final String hostForValidation = extractHostForValidation(normalizedHost);
+
+        validateHostConnectivity(hostForValidation, port);
+
+        TransparentProxy.uri = String.format("%s%s%d", normalizedHost, PORT_SEPARATOR, port);
+        DestinationAccessor.prependDestinationLoader(new TransparentProxy());
+    }
+
+    @Nonnull
+    private static String normalizeHostWithScheme( @Nonnull final String host )
+    {
+        if( host.contains(SCHEME_SEPARATOR) ) {
+            return host;
+        }
+        return HTTP_SCHEME + host;
+    }
+
+    private static String extractHostForValidation( @Nonnull final String normalizedHost )
+    {
+        try {
+            final URI uri = new URI(normalizedHost);
+            return uri.getHost();
+        }
+        catch( final URISyntaxException e ) {
+            String host = normalizedHost;
+            if( host.contains(SCHEME_SEPARATOR) ) {
+                host = host.substring(host.indexOf(SCHEME_SEPARATOR) + 3);
+            }
+            if( host.contains(PORT_SEPARATOR) ) {
+                host = host.substring(0, host.indexOf(PORT_SEPARATOR));
+            }
+            return host;
+        }
+    }
+
+    private static void validateHostConnectivity( @Nonnull final String host, final int port )
+    {
+        networkValidator.validateHostConnectivity(host, port);
+    }
+
+    private static void validateHostHasNoPath( @Nonnull final String host )
+    {
+        try {
+            final URI uri = new URI(host.contains(SCHEME_SEPARATOR) ? host : HTTP_SCHEME + host);
+            final String path = uri.getPath();
+            if( path != null && !path.isEmpty() ) {
+                throw new DestinationAccessException(
+                    String.format(HOST_CONTAINS_PATH_ERROR_MESSAGE_TEMPLATE, host, path));
+            }
+        }
+        catch( final URISyntaxException e ) {
+            final String hostToCheck =
+                host.contains(SCHEME_SEPARATOR) ? host.substring(host.indexOf(SCHEME_SEPARATOR) + 3) : host;
+            if( hostToCheck.contains(PATH_SEPARATOR) ) {
+                final String pathPart = hostToCheck.substring(hostToCheck.indexOf(PATH_SEPARATOR));
+                throw new DestinationAccessException(
+                    String.format(HOST_CONTAINS_PATH_ERROR_MESSAGE_TEMPLATE, host, pathPart));
+            }
+        }
+    }
+
+    @Nonnull
+    @Override
+    public Try<Destination> tryGetDestination( @Nonnull String destinationName )
+    {
+        return Try.success(TransparentProxyDestination.gateway(destinationName, uri).build());
+    }
+
+    @Nonnull
+    @Override
+    public Try<Destination> tryGetDestination( @Nonnull String destinationName, @Nonnull DestinationOptions options )
+    {
+        return Try.success(TransparentProxyDestination.gateway(destinationName, uri).build());
+    }
+
+    interface NetworkValidator
+    {
+        void validateHostConnectivity( @Nonnull String host, int port )
+            throws DestinationAccessException;
+    }
+
+    static class DefaultNetworkValidator implements NetworkValidator
+    {
+        private static final int HOST_REACH_TIMEOUT = 5000;
+
+        @Override
+        public void validateHostConnectivity( @Nonnull final String host, final int port )
+            throws DestinationAccessException
+        {
+            try( Socket socket = new Socket() ) {
+                socket.connect(new InetSocketAddress(host, port), HOST_REACH_TIMEOUT);
+            }
+            catch( final UnknownHostException e ) {
+                throw new DestinationAccessException(String.format("Host [%s] could not be resolved", host), e);
+            }
+            catch( final IOException e ) {
+                throw new DestinationAccessException(
+                    String.format("Host [%s] on port [%d] is not reachable", host, port),
+                    e);
+            }
+        }
+    }
+
+}