sdks/java/basys.sdk/src/main/java/org/eclipse/basyx/vab/protocol/http/server/VABHTTPInterface.java

package org.eclipse.basyx.vab.protocol.http.server;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.eclipse.basyx.vab.coder.json.provider.JSONProvider;
import org.eclipse.basyx.vab.exception.provider.MalformedRequestException;
import org.eclipse.basyx.vab.exception.provider.ProviderException;
import org.eclipse.basyx.vab.modelprovider.VABPathTools;
import org.eclipse.basyx.vab.modelprovider.api.IModelProvider;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * VAB provider class that enables access to an IModelProvider via HTTP REST
 * interface<br />
 * <br />
 * REST http interface is as following: <br />
 * - GET /aas/submodels/{subModelId} Retrieves submodel with ID {subModelId}
 * <br />
 * - GET /aas/submodels/{subModelId}/properties/a Retrieve property a of
 * submodel {subModelId}<br />
 * - GET /aas/submodels/{subModelId}/properties/a/b Retrieve property a/b of
 * submodel {subModelId} <br />
 * - POST /aas/submodels/{subModelId}/operations/a Invoke operation a of
 * submodel {subModelId}<br />
 * - POST /aas/submodels/{subModelId}/operations/a/b Invoke operation a/b of
 * submodel {subModelId}
 * 
 * @author kuhn
 *
 */
public class VABHTTPInterface<ModelProvider extends IModelProvider> extends BasysHTTPServlet {
	
	private static Logger logger = LoggerFactory.getLogger(VABHTTPInterface.class);
	
	/**
	 * Version information to identify the version of serialized instances
	 */
	private static final long serialVersionUID = 1L;

	
	/**
	 * Reference to IModelProvider backend
	 */
	protected JSONProvider<ModelProvider> providerBackend = null;

	
	
	/**
	 * Constructor
	 */
	public VABHTTPInterface(ModelProvider provider) {
		// Store provider reference
		providerBackend = new JSONProvider<ModelProvider>(provider);
	}

	
	/**
	 * Access model provider
	 */
	public ModelProvider getModelProvider() {
		return providerBackend.getBackendReference();
	}

	/**
	 * Send JSON encoded response
	 */
	protected void sendJSONResponse(String path, PrintWriter outputStream, Object jsonValue) {
		// Output result
		outputStream.write(jsonValue.toString()); // FIXME throws nullpointer exception if jsonValue is null
		outputStream.flush();
	}

	
	/**
	 * Implement "Get" operation
	 * 
	 * Process HTTP get request - get sub model property value
	 */
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		PrintWriter responseWriter = resp.getWriter();
		
		try {
			String path = extractPath(req);

			// Setup HTML response header
			resp.setContentType("application/json");
			resp.setCharacterEncoding("UTF-8");

			resp.setStatus(200);

			// Process get request
			providerBackend.processBaSysGet(path, responseWriter);
			responseWriter.flush();
		} catch(ProviderException e) {
			int httpCode = ExceptionToHTTPCodeMapper.mapException(e);
			resp.setStatus(httpCode);
			responseWriter.flush();
			logger.error("Exception in HTTP-GET. Response-code: " + httpCode, e);
		}
		
	}

	
	/**
	 * Implement "Set" operation
	 */
	@Override
	protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		PrintWriter responseWriter = resp.getWriter();
		
		try {
			String path = extractPath(req);
			String serValue = extractSerializedValue(req);
			logger.trace("DoPut: {}", serValue);

			resp.setStatus(200);

			providerBackend.processBaSysSet(path, serValue.toString(), responseWriter);
			responseWriter.flush();
		} catch(ProviderException e) {
			int httpCode = ExceptionToHTTPCodeMapper.mapException(e);
			resp.setStatus(httpCode);
			responseWriter.flush();
			logger.error("Exception in HTTP-PUT. Response-code: " + httpCode, e);
		}
	}

	
	/**
	 * <pre>
	 * Handle HTTP POST operation. Creates a new Property, Operation, Event,
	 * Submodel or AAS or invokes an operation.
	 */
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		PrintWriter responseWriter = resp.getWriter();

		try {
			String path = extractPath(req);
			String serValue = extractSerializedValue(req);

			logger.trace("DoPost: {}", serValue);

			// Setup HTML response header
			resp.setStatus(201);
			resp.setContentType("application/json");
			resp.setCharacterEncoding("UTF-8");

			// Check if request is for property creation or operation invoke
			if (VABPathTools.isOperationPath(path)) {
			// Invoke BaSys VAB 'invoke' primitive

				providerBackend.processBaSysInvoke(path, serValue, responseWriter);
				responseWriter.flush();

			} else {
			// Invoke the BaSys 'create' primitive
				providerBackend.processBaSysCreate(path, serValue, responseWriter);
				responseWriter.flush();
			}
		} catch (ProviderException e) {
			int httpCode = ExceptionToHTTPCodeMapper.mapException(e);
			resp.setStatus(httpCode);
			responseWriter.flush();
			logger.error("Exception in HTTP-POST. Response-code: " + httpCode, e);
		}
	}

	
	/**
	 * Handle a HTTP PATCH operation. Updates a map or collection
	 * 
	 */
	@Override
	protected void doPatch(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		PrintWriter responseWriter = resp.getWriter();
		try {
			String path = extractPath(req);
			String serValue = extractSerializedValue(req);
			logger.trace("DoPatch: {}", serValue);

			resp.setStatus(200);

			providerBackend.processBaSysDelete(path, serValue, responseWriter);
			responseWriter.flush();
		} catch(ProviderException e) {
			int httpCode = ExceptionToHTTPCodeMapper.mapException(e);
			resp.setStatus(httpCode);
			responseWriter.flush();
			logger.error("Exception in HTTP-PATCH. Response-code: " + httpCode, e);
		}
	}

	
	/**
	 * Implement "Delete" operation. Deletes any resource under the given path.
	 */
	@Override
	protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		PrintWriter responseWriter = resp.getWriter();

		try {
			String path = extractPath(req);

			// No parameter to read! Provide serialized null
			String nullParam = "";

			resp.setStatus(200);


			providerBackend.processBaSysDelete(path, nullParam, responseWriter);
			responseWriter.flush();
		} catch(ProviderException e) {
			int httpCode = ExceptionToHTTPCodeMapper.mapException(e);
			resp.setStatus(httpCode);
			responseWriter.flush();
			logger.error("Exception in HTTP-DELETE. Response-code: " + httpCode, e);
		}
	}

	
	private String extractPath(HttpServletRequest req) throws UnsupportedEncodingException {
		// Extract path
		String uri = req.getRequestURI();

		// Normalizes URI
		String nUri = "/" + VABPathTools.stripSlashes(uri) + "/";
		String contextPath = req.getContextPath();
		if (nUri.startsWith(contextPath) && nUri.length() > getEnvironmentPathSize(req)) {
			String path = nUri.substring(getEnvironmentPathSize(req) + 1);

			// Decode URL
			path = java.net.URLDecoder.decode(path, "UTF-8");

			return path;
		}
		throw new MalformedRequestException("The passed path " + uri + " is not a possbile path for this server.");
	}

	private int getEnvironmentPathSize(HttpServletRequest req) {
		return req.getContextPath().length() + req.getServletPath().length();
	}


	/**
	 * Read serialized value 
	 * @param req
	 * @return
	 * @throws IOException
	 */
	private String extractSerializedValue(HttpServletRequest req) throws IOException {
		// Read request body
		ServletInputStream is = req.getInputStream();		
		StringBuilder serValue = new StringBuilder();

		// This seems kind of slow...
		while (!is.isFinished()) {
			serValue.append(String.valueOf((char) (byte) is.read()));
		}
		return serValue.toString();
	}
}