Hi,

So first of all let me list my system specs:

OS: Windows 10, 64 bit

curl version: 7.53.1

Build tool: VS2015 developer command prompt

We're using libcurl in our project and we found slow file download issue
happened randomly inside of curl. We doubt if we used libcurl incorrectly
so I tried to use curl command line tool and download the exact same file.
It turns out the download speed inconsistency happens at cmd tool as well.

So I want to first start from the command tool instead of libcurl. Below is
how I build the command line tool and its configurations.

I grabbed latest curl v7.53.1 from cURL's website. I built the cURL (STATIC
linking) with windows x86 and leave all options as default.

After the build finishes and curl.exe generated, I ran the command
"curl.exe -O http://mydownloadfile.xxx". The download ended with success
but if I ran this cmd couple of times, it shows that there are cases that
the download speed is extremely slow (500K while the regular speed is
~25M). The ratio of reproducing this slowness is 1/10 roughly. I'm sure my
network condition is very stable and fast.

Here is the screenshot from my tests:

[image: Inline image 1]

This issue can also be found at android and iOS. So I think it's not
platform specific. Any idea if that could be a cURL bug or it's already a
known issue? I'm on curl v7.53.1 but I can also see the issue on curl
v7.19.x.

Thanks,

Kai

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