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Fiddler and Server-sent Events

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Windows

This is a migrated thread and some comments may be shown as answers.

Connor asked on 13 Nov 2017, 05:45 PM

I'm having trouble with Fiddler on pages using server-sent events. The eventsource just stays in a pending status if Fiddler captures the request. I don't need to inspect the events in Fiddler, but I would like to be able to inspect the other requests in Fiddler without breaking the page.

While Fiddler is capturing sessions:

Run a server side event server such as https://github.com/hemanth/sse-now
Open a page that connects to the server (below)

Result: Events are not received

Following the same steps while Fiddler is not capturing sessions, everything works as expected. Enabling streaming does not solve the issue.

Is this a bug in Fiddler or is there some way I configure Fiddler to handle this?

Example testSSE.html

<!DOCTYPE html>

<html>

<head>

<meta charset="utf-8">

<meta name="viewport" content="width=device-width">

<title>SSE demo</title>

</head>

<body>

</body>

<script>

var source = new EventSource('http://localhost:8000');

source.onmessage = function(e) {

document.body.innerHTML += e.data + '<br>';

};

</script>

</html>

3 Answers, 1 is accepted

answered on 29 Mar 2018, 02:40 PM

I have a similar problem as Connor. The response header shows as HTTP/1.1 200 OK.

Request Count: 1

Bytes Sent: 485(headers:485; body:0)
Bytes Received: 12,207(headers:260; body:11,947)

It shows it received the data back but within the Transformer it says "No Response body."

GET http://emojitrack-gostreamer.herokuapp.com/subscribe/eps HTTP/1.1
Host: emojitrack-gostreamer.herokuapp.com
Connection: keep-alive
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.181 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9

HTTP/1.1 200 OK
Connection: keep-alive
Access-Control-Allow-Origin: *
Cache-Control: no-cache
Content-Type: text/event-stream; charset=utf-8
Server: emojitrack-gostreamer
Date: Thu, 29 Mar 2018 14:37:54 GMT
Transfer-Encoding: chunked
Via: 1.1 vegur

answered on 10 Apr 2018, 01:09 PM

Hello Vishal,

Sorry, for the late reply. Fiddler needs to read the whole response before the Transformer is able to apply a different compression. The Server-sent events is a stream technology which means that the server's response never ends.

However, you could use the COMETPeek command on the Web Session's context menu to take a "snapshot" of the in-progress response, allowing you to inspect the partial response data read from the server.

Regards,
Simeon
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