Hello, I maintain a Windows application (written in VC 2017) that basically uploads thousands of email messages into Microsoft Exchange/Ofice 365, via their EWS protocol. I have been successfully using libcurl 7.64 for a while.
Recently we did have some problem with logging in to some servers, and I determined that the issue could be fixed by updating to libcurl 7.71 (not sure why). However I ran into some other problem with this version, where for some reason after several thousand messages, libcurl seemed to be returning null data in response to a GET. However I am *not* asking about that problem in this message. The above problem went away when I switched to libcurl 7.73. However, this version has its own problem, a serious performance issue, where large chunks of data seem to be taking 1 second to upload, vs a fraction of a second seen with the previous version. Take a look at the attached two log files, slow_upload.txt and fast_upload.txt. These are logs of the debug function after I do a POST. In the slow version, each 64k chunk of data is taking approximately 1 second. In the fast version, each chunk is a fraction of a second or not even measurable. These results are consistent when doing multiple tests at different times of the day. I don't think it is related to EWS server variability. Keep in mind that the exact same main program binary executable code is running in each test, only the libcurl.dll has been changed. Any idea what could be causing this? I've also included some of my code that performs the POST operation (cleaned up of a lot of extraneous stuff). Hopefully there is some curl option that I can set or change that fixes this. Thanks for your help.
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