Intermittent bug with asyncio and MS Edge

[Frank Millman]

On 2020-03-22 10:45 AM, Chris Angelico wrote:
> On Sun, Mar 22, 2020 at 6:58 PM Frank Millman <frank at chagford.com> wrote:
>>> 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.
> 
> Interesting. RST means "Reset" and is sent when the connection is
> closed. Which direction were these packets sent (Edge to Python or
> Python to Edge)? You can tell by the source and destination ports -
> one of them is going to be the port Python is listening on (eg 80 or
> 443), so if the destination port is 80, it's being sent *to* Python,
> and if the source port is 80, it's being sent *from* Python.
> 

They are all being sent *from* Python *to* Edge.

>> 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.
> 
> Interesting also.
> 
> Can you recreate the problem without Edge? It sounds like something's
> going on with concurrent transfers, so it'd be awesome if you can
> replace Edge with another Python program, and then post both programs.
> 

Do you mean write a program that emulates a browser - make a connection, 
receive the HTML page, send a GET request for each file, and receive the 
results?

I will give it a go!

> Also of interest: Does the problem go away if you change "Connection:
> Keep-Alive" to "Connection: Close" in your headers?
> 

Yes, the problem does go away.

Frank