Large number of XOFFs sent while downloading file over SOCKS

Just wanted to document this before I forget.

When downloading a file over tor's SOCKS port, I see a lot of XOFFs being sent. I don't think that it's expected that we'd see so many XOFF messages given that we're downloading with curl and writing to /dev/null.

tor -Log "[edge]debug notice file /tmp/tor.log" -LogTimeGranularity 1

curl -x socks5h://localhost:9050 https://ash-speed.hetzner.com/100MB.bin > /dev/null

$ grep XOFF /tmp/tor.log
Sep 22 17:17:03.914 [info] flow_control_decide_xoff(): Sending XOFF: 249020 249000
Sep 22 17:17:04.262 [info] flow_control_decide_xoff(): Sending XOFF: 249020 249000
Sep 22 17:17:04.713 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:05.062 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:05.154 [info] flow_control_decide_xoff(): Sending XOFF: 249478 249000
Sep 22 17:17:05.205 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:05.228 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:05.435 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:05.513 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:06.370 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:06.527 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:10.977 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:12.725 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:14.697 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:15.332 [info] flow_control_decide_xoff(): Sending XOFF: 249498 249000
Sep 22 17:17:21.131 [info] flow_control_decide_xoff(): Sending XOFF: 249316 249000
Sep 22 17:17:27.099 [info] flow_control_decide_xoff(): Sending XOFF: 249286 249000
Sep 22 17:17:37.498 [info] flow_control_decide_xoff(): Sending XOFF: 249056 249000
Sep 22 17:17:39.231 [info] flow_control_decide_xoff(): Sending XOFF: 249148 249000
Sep 22 17:17:39.888 [info] flow_control_decide_xoff(): Sending XOFF: 249132 249000
Sep 22 17:17:41.979 [info] flow_control_decide_xoff(): Sending XOFF: 249118 249000
Sep 22 17:17:42.124 [info] flow_control_decide_xoff(): Sending XOFF: 249118 249000
Sep 22 17:17:46.279 [info] flow_control_decide_xoff(): Sending XOFF: 249148 249000
Sep 22 17:17:47.672 [info] flow_control_decide_xoff(): Sending XOFF: 249370 249000
Sep 22 17:17:52.737 [info] flow_control_decide_xoff(): Sending XOFF: 249416 249000
Sep 22 17:18:02.352 [info] flow_control_decide_xoff(): Sending XOFF: 249010 249000
Sep 22 17:18:04.989 [info] flow_control_decide_xoff(): Sending XOFF: 249056 249000

$ tor --version
Tor version 0.4.8.17.
This build of Tor is covered by the GNU General Public License (https://www.gnu.org/licenses/gpl-3.0.en.html)
Tor is running on Linux with Libevent 2.1.12-stable, OpenSSL 3.2.4, Zlib 1.3.1.zlib-ng, Liblzma 5.8.1, Libzstd 1.5.7 and Glibc 2.41 as libc.
Tor compiled with GCC version 15.1.1