Intermittent bug with asyncio and MS Edge

[Frank Millman]

On 2020-03-21 8:04 PM, Barry Scott wrote:
> 
> 
>> On 21 Mar 2020, at 13:43, Frank Millman <frank at chagford.com> wrote:
>>
>> Hi all
>>
>> I have a strange intermittent bug.
>>
>> The role-players -
>>     asyncio on Python 3.8 running on Windows 10
>>     Microsoft Edge running as a browser on the same machine
>>
>> The bug does not occur with Python 3.7.
>> It does not occur with Chrome or Firefox.
>> It does not occur when MS Edge connects to another host on the network, running the same Python program (Python 3.8 on Fedora 31).
>>
>> The symptoms -
>>     On receiving a connection, I send an HTML page to the browser,
>>         which has 20 lines like this -
>>
>>     <script type="text/javascript" src="src/main.js"></script>
>>     <script type="text/javascript" src="src/on_load.js"></script>
>>     ...
>>
>> Intermittently, one or other of the script files is not received by MS Edge.
>>
[...]
>> >> I don't know whether the problem lies with Python or MS Edge, but as 
it does not happen with Python 3.7, I am suspecting that something 
changed in 3.8 which does not match MS Edge's expectations.
> 
> I'd look at the network traffic with wireshark to see if there is anything different between edge and the other browsers.
> 

You are leading me into deep waters here :-)  I have never used 
Wireshark before. I have now downloaded it and am running it - it 
generates a *lot* of data, most of which I do not understand yet!

One thing immediately stands out. When I run it with MS Edge and 
Python3.8, it shows a lot of lines highlighted in red, with the symbols 
[RST,ACK]. They do not appear when running Chrome, and they do not 
appear when running Python3.7.

I have another data point. I tried putting an asyncio.sleep() after 
sending each file. A value of 0.01 made no difference, but a value of 
0.1 makes the problem go away.

I will keep digging, but I thought I would post this information now in 
case it helps with diagnosis.

Frank