Curl Post of a given size timeouts after curl ends up in an infinite loop

[alexissavin]

I did this

Create a file of the proper size (in my case the size that trigger the issue is 261680, it likely varies depending on the environment):
truncate -s 261680 test.tgz
Upload it to some http endpoint over SSL (nginx):
curl -v -X POST -Ffile=@test.tgz --url "https://domain.test/upload" --connect-timeout 30 --max-time 30;
The transfert timeout, using more verbose output ('-vvv'), we observe the following:

...
ff80: ................................................................
ffc0: ...........
ffcd: --------------------------eecMwy2lW5vukdsCCq1CPO--.
09:00:58.594998 [0-0] == Info: [SSL] ossl_bio_cf_in_read(len=5) -> -1, err=81
09:00:58.596477 [0-0] == Info: [SSL] cf_recv(len=102400) -> -1, 81
09:00:58.597919 [0-0] == Info: [READ] cr_mime_read(len=1), too small, return
09:00:58.599120 [0-0] == Info: [READ] cr_mime_read(len=1, total=261892, read=261891) -> 0, 0, 0
09:00:58.602436 [0-0] == Info: [READ] client_read(len=65536) -> 0, nread=0, eos=0
09:00:58.604165 [0-0] == Info: [SSL] ossl_bio_cf_in_read(len=5) -> -1, err=81
09:00:58.605379 [0-0] == Info: [SSL] cf_recv(len=102400) -> -1, 81
09:00:58.606428 [0-0] == Info: [READ] cr_mime_read(len=1), too small, return
09:00:58.607558 [0-0] == Info: [READ] cr_mime_read(len=1, total=261892, read=261891) -> 0, 0, 0
09:00:58.609084 [0-0] == Info: [READ] client_read(len=65536) -> 0, nread=0, eos=0
09:00:58.610537 [0-0] == Info: [SSL] ossl_bio_cf_in_read(len=5) -> -1, err=81
....

I highly suspect a relation with some code from commit c90a3f1:

Curl_mime_read() may go into an infinite loop when called with buffer lengths <= 4. Some encoders, like base64, are not prepared for that.

I expected the following

Transfert should complete normally (as it did in the past using curl 8.6.0 or 8.8.0).
Issue seems occurring in curl >= 8.10.0.

curl/libcurl version

# curl --version
curl 8.10.1 (amd64-portbld-freebsd14.1) libcurl/8.10.1 OpenSSL/3.0.15 zlib/1.3.1 libpsl/0.21.5 libssh/0.11.1/openssl/zlib nghttp2/1.64.0
Release-Date: 2024-09-18
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns pop3 pop3s rtsp scp sftp smtp smtps telnet tftp
Features: alt-svc AsynchDNS HSTS HTTP2 HTTPS-proxy IPv6 Largefile libz NTLM PSL SSL threadsafe TLS-SRP UnixSockets

operating system

FreeBSD 14.2-STABLE

[alexissavin]

@icing since you authored #c90a3f1 maybe you will see clearer into this ?

[icing]

Thanks for your precise report. I was able to reproduce the problem in a test case and made a fix in #15691. Hope this works for you as well.

[alexissavin]

Thanks for the prompt feedback and fix.
Any idea when this could be officially released ?

[icing]

It will be part of curl 8.11.1 on December 11th.

[alexissavin]

Excellent, many thanks