latency testing node service - just pass in a size param to specify n bytes to reply with. Ex: http://127.0.0.21:7777/?size=5120000 = 5meg response

server.js

//defaut settings
var DEFAULT_SIZE = 1000*1024,
   DEFAULT_CHUNK_SIZE = 250*1024,
   MAX_CHUNK_SIZE = 500*1024;


var http = require('http'),
   url = require('url'),
   buffer;

//build buffer to slice from for responses
buffer = new Buffer(MAX_CHUNK_SIZE);
buffer.fill(97);

//setup and start http server
var server = http.createServer(function(req, resp) {
   var query = url.parse(req.url, true).query,
      size = parseInt(query['size']) || DEFAULT_SIZE,
      chunkSize = query['chunksize'] ? parseInt(query['chunksize']) : undefined,
      bytesWritten = 0,
      slice;
   var headers = {'Content-Type': 'text/plain'};
   if (!chunkSize) { 
      headers['Content-Length'] = size;
      chunkSize = DEFAULT_CHUNK_SIZE;
   }
   resp.writeHead(200, headers);

   while (size - bytesWritten > chunkSize) {
      slice = buffer.slice(0, chunkSize);
      resp.write(slice);
      bytesWritten += slice.length;
   }
   slice = buffer.slice(0, size - bytesWritten);
   resp.end(slice);
});
server.listen(7777);