Use flask.jsonify for json responses

This ensures that all json responses have the correct mimetype without needing
the extra boilerplate to set the content-type header.

locust/static/locust.js

@@ -123,8 +123,7 @@ var responseTimeChart = new LocustLineChart($(".charts-container"), "Response Ti
 var usersChart = new LocustLineChart($(".charts-container"), "Number of Users", ["Users"], "users");
 
 function updateStats() {
-    $.get('/stats/requests', function (data) {
-        report = JSON.parse(data);
+    $.get('/stats/requests', function (report) {
         $("#total_rps").html(Math.round(report.total_rps*100)/100);
         //$("#fail_ratio").html(Math.round(report.fail_ratio*10000)/100);
         $("#fail_ratio").html(Math.round(report.fail_ratio*100));

locust/web.py

@@ -9,7 +9,7 @@
 from time import time
 
 import six
-from flask import Flask, make_response, render_template, request
+from flask import Flask, make_response, jsonify, render_template, request
 from gevent import pywsgi
 
 from locust import __version__ as version
@@ -59,16 +59,12 @@ def swarm():
     locust_count = int(request.form["locust_count"])
     hatch_rate = float(request.form["hatch_rate"])
     runners.locust_runner.start_hatching(locust_count, hatch_rate)
-    response = make_response(json.dumps({'success':True, 'message': 'Swarming started'}))
-    response.headers["Content-type"] = "application/json"
-    return response
+    return jsonify({'success': True, 'message': 'Swarming started'})
 
 @app.route('/stop')
 def stop():
     runners.locust_runner.stop()
-    response = make_response(json.dumps({'success':True, 'message': 'Test stopped'}))
-    response.headers["Content-type"] = "application/json"
-    return response
+    return jsonify({'success':True, 'message': 'Test stopped'})
 
 @app.route("/stats/reset")
 def reset_stats():
@@ -135,22 +131,20 @@ def request_stats():
     report["state"] = runners.locust_runner.state
     report["user_count"] = runners.locust_runner.user_count
 
-    return json.dumps(report)
+    return jsonify(report)
 
 @app.route("/exceptions")
 def exceptions():
-    response = make_response(json.dumps({
+    return jsonify({
         'exceptions': [
             {
-                "count": row["count"], 
-                "msg": row["msg"], 
-                "traceback": row["traceback"], 
+                "count": row["count"],
+                "msg": row["msg"],
+                "traceback": row["traceback"],
                 "nodes" : ", ".join(row["nodes"])
             } for row in six.itervalues(runners.locust_runner.exceptions)
         ]
-    }))
-    response.headers["Content-type"] = "application/json"
-    return response
+    })
 
 @app.route("/exceptions/csv")
 def exceptions_csv():