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

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:
invoke
http://yourserver/yourweb/MockGridData?__setdata=data/init.http
run a javascript module that will result in calling (say, with GET)
http://yourserver/yourweb/MockGridData
click a button that then does:
http://yourserver/yourweb/MockGridData?__setdata=data/step1.http
run another javascript step that will result in calling (say, with PUT)
http://yourserver/yourweb/MockGridData
click another button that then does:
http://yourserver/yourweb/MockGridData?__setdata=data/step2.http
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.