[docs] add middleware examples (first draft)

examples/bodyDecoder-middleware.js

+
+var Store = require('./lib/store')
+  , http = require('http')
+
+http.createServer(new Store().handler()).listen(7531, function () {
+//try these commands:
+// get index:
+// curl localhost:7531
+// []
+//
+// get a doc:
+// curl localhost:7531/foo
+// {"error":"not_found"}
+//
+// post an doc:
+// curl -X POST localhost:7531/foo -d '{"content": "hello", "type": "greeting"}'
+// {"ok":true}
+//
+// get index (now, not empty)
+// curl localhost:7531
+// ["/foo"]
+//
+// get doc 
+// curl localhost:7531/foo
+// {"content": "hello", "type": "greeting"}
+
+//
+// now, suppose we wanted to direct all objects where type == "greeting" to a different store 
+// than where type == "insult"
+//
+// we can use connect connect-bodyDecoder and some custom logic to send insults to another Store.
+
+//insult server:
+
+  http.createServer(new Store().handler()).listen(2600, function () {
+
+  //greetings -> 7531, insults-> 2600 
+
+  // now, start a proxy server.
+
+    var bodyParser = require('connect/lib/middleware/bodyParser')
+    //don't worry about incoming contont type
+    //bodyParser.parse[''] = JSON.parse
+
+    require('http-proxy').createServer(
+      //refactor the body parser and re-streamer into a separate package
+      bodyParser(),
+      //body parser absorbs the data and end events before passing control to the next
+      // middleware. if we want to proxy it, we'll need to re-emit these events after 
+      //passing control to the middleware.
+      function (req, res, next) {
+        //remove bodyParser's listeners
+        req.removeAllListeners('data')
+        req.removeAllListeners('end')
+        next()
+        process.nextTick(function () {
+          if(req.body)
+            req.emit('data', JSON.stringify(req.body))
+          req.emit('end')
+        })
+      },
+      function (req, res, proxy) {
+        //if your posting an obect which contains type: "insult"
+        //it will get redirected to port 2600.
+        //normal get requests will go to 7531 nad will not return insults.
+        var port = (req.body && req.body.type === 'insult' ? 2600 : 7531)
+        proxy.proxyRequest(req, res, {host: 'localhost', port: port})
+      }
+    ).listen(1337, function () {
+      var request = require('request')
+      //bodyParser needs content-type set to application/json
+      //if we use request, it will set automatically if we use the 'json:' field.
+      function post (greeting, type) {
+        request.post({
+          url: 'http://localhost:1337/' + greeting,
+          json: {content: greeting, type: type || "greeting"}
+        })
+      }
+      post("hello")
+      post("g'day")
+      post("kiora")
+      post("houdy")
+      post("java", "insult")
+
+      //now, the insult should have been proxied to 2600
+      
+      //curl localhost:2600
+      //["/java"]
+
+      //but the greetings will be sent to 7531
+
+      //curl localhost:7531
+      //["/hello","/g%27day","/kiora","/houdy"]
+
+    })
+  })
+})

examples/jsonp-middleware.js

+var Store = require('./lib/store')
+  , http = require('http')
+
+//
+// jsonp is a handy technique for getting around the limitations of the same-origin policy. 
+// (http://en.wikipedia.org/wiki/Same_origin_policy) 
+// 
+// normally, to dynamically update a page you use an XmlHttpRequest. this has flakey support 
+// is some browsers and is restricted by the same origin policy. you cannot perform XHR requests to
+// someone else's server. one way around this would be to proxy requests to all the servers you want
+// to xhr to, and your core server - so that everything has the same port and host.
+// 
+// another way, is to turn json into javascript. (which is exempt from the same origin policy) 
+// this is done by wrapping the json object in a function call, and then including a script tag.
+//
+// here we're proxing our own JSON returning server, but we could proxy any server on the internet,
+// and our client side app would be slurping down JSONP from anywhere.
+// 
+// curl localhost:1337/whatever?callback=alert
+// alert([]) //which is valid javascript!
+//
+// also see http://en.wikipedia.org/wiki/JSONP#JSONP
+//
+
+http.createServer(new Store().handler()).listen(7531)
+
+require('http-proxy').createServer(
+  require('connect-jsonp')(true),
+  'localhost', 7531
+).listen(1337)

examples/url-middleware2.js

+var util = require('util'),
+    colors = require('colors'),
+    http = require('http'),
+    httpProxy = require('http-proxy'),
+    Store = require('./lib/store') 
+//
+// This is an example of a url-routing middleware.
+// This is not intended for production use, but rather as
+// an example of how to write a middleware.
+//
+
+function matcher (url, dest) {
+  // First, turn the URL into a regex.  
+  // NOTE: Turning user input directly into a Regular Expression is NOT SAFE.
+  var r = new RegExp(url.replace(/\//, '\\/'));
+  // This next block of code may look a little confusing. 
+  // It returns a closure (anonymous function) for each URL to be matched,
+  // storing them in an array - on each request, if the URL matches one that has
+  // a function stored for it, the function will be called.
+  return function (url) {
+    var m = r(url)
+    if (!m) {
+      return;
+    }
+    var path = url.slice(m[0].length);
+    console.log('proxy:', url, '->', dest);
+    return {url: path, dest: dest};
+  }
+}
+
+exports.urls = function (urls) {
+  // This is the entry point for our middleware.
+  // 'matchers' is the array of URL matchers, as mentioned above.
+  var matchers = [];
+  for (var url in urls) {
+    // Call the 'matcher' function above, and store the resulting closure.
+    matchers.push(matcher(url, urls[url]));
+  }
+
+  // This closure is returned as the request handler.
+  return function (req, res, next) {
+    //
+    // in node-http-proxy middlewares, `proxy` is the prototype of `next`
+    // (this means node-http-proxy middlewares support both the connect API (req, res, next)
+    // and the node-http-proxy API (req, res, proxy)
+    //
+    var proxy = next;
+    for (var k in matchers) {
+      // for each URL matcher, try the request's URL.
+      var m = matchers[k](req.url);
+      // If it's a match:
+      if (m) {
+        // Replace the local URL with the destination URL.
+        req.url = m.url;
+        // If routing to a server on another domain, the hostname in the request must be changed.
+        req.headers.host = m.host;
+        // Once any changes are taken care of, this line makes the magic happen.
+        proxy.proxyRequest(req, res, m.dest);
+      }
+    }
+  }
+}
+
+http.createServer(new Store().handler()).listen(7531)
+
+// Now we set up our proxy.
+httpProxy.createServer(
+  // This is where our middlewares go, with any options desired - in this case,
+  // the list of routes/URLs and their destinations.
+  exports.urls({
+    '/store': { port: 7531, host: 'localhost' },
+    '/': { port: 9000, host: 'localhost' }
+  })
+).listen(8000);
+
+//
+// Target Http Server (to listen for requests on 'localhost')
+//
+http.createServer(
+  function (req, res) {
+    res.writeHead(200, { 'Content-Type': 'text/plain' });
+    res.write('request successfully proxied to: ' + req.url + '\n' + JSON.stringify(req.headers, true, 2));
+    res.end();
+  }).listen(9000);
+
+// And finally, some colored startup output.
+util.puts('http proxy server'.blue + ' started '.green.bold + 'on port '.blue + '8000'.yellow);
+util.puts('http server '.blue + 'started '.green.bold + 'on port '.blue + '9000 '.yellow);
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