How to mock a complex REST call from the server side?

Question

While working with javascript that uses REST services extensively -- including using vocabs like GET, PUT, POST, DELETES, etc; I have found it hard to mock the server side so front end development can go on independently (of back end).

It is also useful to sometimes capture multi-step data, so we can help reproduce the entire chain of REST even (or bugs related to the front end that are triggered from these chains)

What tools can I use to mock REST calls, esp stateful ones? (i.e. if I do a PUT on some resource, I expect the next GET on it to change somehow)

I tried SOAPUI 4.0.1 and it's REST mocking is disappointing. Plus, my need is beyond single state mocking (which anyone can do with a static .json file). I need to do state transition type of mocks; working with Content-Range headers would be best.

Anyone?

Answer 1

I actually ended up creating my own Java REST Mock Engine that can basically mock any response. As long as you can handcraft or cut-paste a text file that simulates the entire http response, you can use my solution to mock the service.

Here's the servlet:

package com.mockrest.debug;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.Arrays;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import javax.servlet.GenericServlet;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class MockGridData
 */
public class MockRest extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public MockRest() {
        super();
        // TODO Auto-generated constructor stub
    }

    @Override
    public void service(ServletRequest req, ServletResponse res)
            throws ServletException, IOException {
        sub:{
            HttpServletRequest request = (HttpServletRequest)req;
            HttpServletResponse response = (HttpServletResponse)res;
            String setdata = request.getParameter("__setdata");
            if (setdata!=null && setdata.length()>0){
                System.err.println("Setting Data...");
                HttpSession sess = request.getSession(true);
                String data = "/"+request.getParameter("__setdata");
                sess.setAttribute("data", data);
                try{
                    InputStream is = getServletContext().getResourceAsStream(data);
                    if (is!=null){
                        is.close();
                        response.getWriter().write("Successfully pointed next REST call to:"+data);
                    }
                    else{
                        response.sendError(500, "Cannot find resource:"+data);
                    }
                }
                catch (IOException ioe){
                    response.sendError(500, Arrays.deepToString(ioe.getStackTrace()));
                }

            }
            else{
                System.err.println("Fetching Data...");
                HttpSession sess = request.getSession(false);
                if (sess==null || sess.getAttribute("data")==null){
                    response.sendError(500,"Session invalid or no Previous Data Set!");
                }
                String rsrc = (String)sess.getAttribute("data");
                System.err.println("Resource Being used:"+rsrc);
                InputStream is = getServletContext().getResourceAsStream(rsrc);
                if (is!=null){
                    String statusline = readLine(is);
                    Pattern statusPat = Pattern.compile("^HTTP/1.1 ([0-9]+) (.*)$");
                    Matcher m = statusPat.matcher(statusline);
                    if (m!=null && m.matches()){
                        int status = Integer.valueOf(m.group(1));
                        response.setStatus(status, m.group(2));
                    }
                    else{
                        throw new ServletException("Bad input file: status line parsing failed, got this as status line:"+statusline);
                    }
                    String line;
                    Pattern httpHeaderPat = Pattern.compile("^([^:]+): (.*)$");
                    while ((line=readLine(is))!=null){
                        if (line.length()==0){
                            // end of headers
                            break;
                        }
                        Matcher m2 = httpHeaderPat.matcher(line);
                        if (m2!=null && m2.matches()){
                            response.setHeader(m2.group(1), m2.group(2));
                        }
                    }
                    OutputStream os = response.getOutputStream();
                    byte[] buf = new byte[1024];
                    int size;
                    while ((size=is.read(buf))>0){
                        os.write(buf, 0, size);
                    }
                    os.flush();
                }
            }
        }
    }

    private String readLine(InputStream is) throws IOException {
        StringBuffer sb = new StringBuffer();
        char c;
        while ((c=(char)is.read())!='\n'){
            sb.append(c);
        }
        if (sb.charAt(sb.length()-1) == '\r'){
            sb.deleteCharAt(sb.length()-1);
        }
        return sb.toString();
    }

}

To configure it, place prebuilt response files inside your WebContent folder. I usually end these files with .http extensions.

An example init.http file is below. Pretend we placed this file inside a folder called data inside WebContent:

HTTP/1.1 200 OK
Date: Wed, 26 Oct 2011 18:31:45 GMT
Server: Microsoft-IIS/6.0
X-Powered-By: ASP.NET
X-AspNet-Version: 4.0.30319
Content-Range: items 0-1/2
Content-Length: 385
Cache-Control: private
Content-Type: application/json

[
  {
    "id": "249F0",
    "field1": " Global",
    "displaystartdate": "2007-10-20",
    "displayenddate": "2012-10-20",
    "status": "Major Delay",
    "children": true
  },
  {
    "id": "962581",
    "field2": "Europe",
    "displaystartdate": "2007-10-20",
    "displayenddate": "2012-10-20",
    "status": "Major Delay",
    "children": true
  }
]

Headers must separate with body by an empty line (no spaces, nada). People familiar with http will notice it's a pure http response. This is on purpose.

You can use this tool to simulate any of the http headers you want the response to have; even going so far to respond with different server header(in my example, I simulated the response pretending to be IIS 6.0); or a different HTTP status code, etc.

To invoke it from your browser/javascript; first prime it with:

http://yourserver/yourweb/MockGridData?__setdata=data/init.http

Then in your javascript or REST AJAX call, if it goes to

http://yourserver/yourweb/MockGridData

with any method or parameter; it will get the http response you previously crafted with; even down to the Content-Range; Cache headers; etc. If you then need the subsequent AJAX call to return something else, simply call with __setdata again. I suggest you setup a few buttons to do the explicit state transition in your web app.

Assuming everything is setup, for a simulated REST chain, a developer may do:

1. invoke

   http://yourserver/yourweb/MockGridData?__setdata=data/init.http
   

2. run a javascript module that will result in calling (say, with GET)

   http://yourserver/yourweb/MockGridData
   

3. click a button that then does:

   http://yourserver/yourweb/MockGridData?__setdata=data/step1.http
   

4. run another javascript step that will result in calling (say, with PUT)

   http://yourserver/yourweb/MockGridData
   

5. click another button that then does:

   http://yourserver/yourweb/MockGridData?__setdata=data/step2.http
   

6. run another javascript step that will result in calling (say, with GET)

   http://yourserver/yourweb/MockGridData
   

   but this time expecting different result than #4.

This should even work with binary and gzipped responses, but I haven't tested that.

Answer 2

Here is another homegrown rest-mocking tool: https://github.com/mkotsur/restito.