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I'm trying to implement server push in my Flask project following this tutorial.
I've set it all up with no errors, however when I go to the /stream page, Firefox recognizes it as a file and tries to download it. In Safari it just prints out the data sent. I tried adapting the code to a simpler implementation, where a thread just yields some data each second, however it produced the same results.
My goal is for each time a python script reaches a point in a loop, it will update a progress bar on the web interface.
Any help with this would be great. Thanks.
Edit:
app.py
from flask import Flask, render_template, request, Response
app = Flask(__name__)
def event_stream():
event = "Hello!"
yield 'data: %s\n\n' % event
@app.route('/stream')
def stream():
return Response(event_stream(), mimetype="text/event-stream")
if __name__ == "__main__":
app.debug = True
app.run(threaded=True)
index.html
<!DOCTYPE html>
<html>
<head>
<title></title>
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script type="text/javascript">
var source = new EventSource('/stream');
source.onmessage = function (event) {
alert(event.data);
};
</script>
</head>
<body>
<p>Stream page</p>
</body>
</html>
862
The event stream is a simple stream of text data which must be encoded using UTF-8. Messages in the event stream are separated by a pair of newline characters. A colon as the first character of a line is in essence a comment, and is ignored.
A few examples would be friends' status updates, stock tickers, news feeds, or other automated data push mechanisms (e.g. updating a client-side Web SQL Database or IndexedDB object store). If you'll need to send data to a server, XMLHttpRequest is always a friend. SSEs are sent over traditional HTTP.
Server-Sent Events is designed to use the JavaScript EventSource API in order to subscribe to a stream of data in any popular browser. Through this interface a client requests a particular URL in order to receive an event stream.
EDIT
I've uploaded my sample application to my Github. Check it out here: https://github.com/djdmorrison/flask-progress-example
I've worked it out, but for anyone else who gets the same problem:
The index.html page never actually loads, as it's never called in app.py. The way to do it is by going to a separate route, /page for example, and then returning send_file('index/html'). This will load the index page, create the EventSource linked to /stream, which will then start the stream method in app.py and yield the correct data.
Example which creates a progress bar by increasing x every 0.2 seconds and displaying it on the webpage:
app.py
@app.route('/page')
def get_page():
return send_file('templates/progress.html')
@app.route('/progress')
def progress():
def generate():
x = 0
while x < 100:
print x
x = x + 10
time.sleep(0.2)
yield "data:" + str(x) + "\n\n"
return Response(generate(), mimetype= 'text/event-stream')
progress.html
<!DOCTYPE html>
<html>
<head>
<script src="//ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/js/bootstrap.min.js"></script>
<script>
var source = new EventSource("/progress");
source.onmessage = function(event) {
$('.progress-bar').css('width', event.data+'%').attr('aria-valuenow', event.data);
}
</script>
</head>
<body>
<div class="progress" style="width: 50%; margin: 50px;">
<div class="progress-bar progress-bar-striped active" role="progressbar" aria-valuenow="0" aria-valuemin="0" aria-valuemax="100" style="width: 0%"></div>
</div>
</body>
</html>
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