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3e33681eaf
curl/docs/KNOWN_BUGS
Daniel Stenberg 3e33681eaf
KNOWN_BUGS: remove five FTP related issues 
- "FTP with CONNECT and slow server"

I believe this is not a problem these days.

- "FTP with NULs in URL parts"

The FTP protocol does not support them properly anyway.

- remove "FTP and empty path parts in the URL"

I don't think this has ever been reported as a real problem but was only
a hypothetical one.

- "Premature transfer end but healthy control channel"

This is not a bug, this is an optimization that *could* be performed but is
not an actual problem.

- "FTP without or slow 220 response"

Instead add to the documentation of the connect timeout that the
connection is considered complete at TCP/TLS/QUIC layer.

Closes #9979
2022-11-26 12:33:58 +01:00

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Known Bugs
These are problems and bugs known to exist at the time of this release. Feel
free to join in and help us correct one or more of these. Also be sure to
check the changelog of the current development status, as one or more of these
problems may have been fixed or changed somewhat since this was written.
1. HTTP
1.3 STARTTRANSFER time is wrong for HTTP POSTs
1.4 multipart formposts file name encoding
1.5 Expect-100 meets 417
1.8 DoH is not used for all name resolves when enabled
1.11 CURLOPT_SEEKFUNCTION not called with CURLFORM_STREAM
2. TLS
2.3 Unable to use PKCS12 certificate with Secure Transport
2.4 Secure Transport will not import PKCS#12 client certificates without a password
2.5 Client cert handling with Issuer DN differs between backends
2.6 CURL_GLOBAL_SSL
2.7 Client cert (MTLS) issues with Schannel
2.8 Schannel disable CURLOPT_SSL_VERIFYPEER and verify hostname
2.9 TLS session cache does not work with TFO
2.10 Store TLS context per transfer instead of per connection
2.11 Schannel TLS 1.2 handshake bug in old Windows versions
2.12 FTPS with Schannel times out file list operation
2.13 CURLOPT_CERTINFO results in CURLE_OUT_OF_MEMORY with Schannel
2.14 Secure Transport disabling hostname validation also disables SNI
2.15 Renegotiate from server may cause hang for OpenSSL backend
3. Email protocols
3.1 IMAP SEARCH ALL truncated response
3.2 No disconnect command
3.3 POP3 expects "CRLF.CRLF" eob for some single-line responses
3.4 AUTH PLAIN for SMTP is not working on all servers
4. Command line
4.1 -J and -O with %-encoded file names
4.2 -J with -C - fails
4.3 --retry and transfer timeouts
5. Build and portability issues
5.1 OS400 port requires deprecated IBM library
5.2 curl-config --libs contains private details
5.3 curl compiled on OSX 10.13 failed to run on OSX 10.10
5.5 cannot handle Unicode arguments in non-Unicode builds on Windows
5.6 make distclean loops forever
5.8 configure finding libs in wrong directory
5.9 Utilize Requires.private directives in libcurl.pc
5.10 curl hangs on SMB upload over stdin
5.11 configure --with-gssapi with Heimdal is ignored on macOS
5.12 flaky Windows CI builds
5.13 long paths are not fully supported on Windows
5.14 Windows Unicode builds use homedir in current locale
6. Authentication
6.1 NTLM authentication and unicode
6.2 MIT Kerberos for Windows build
6.3 NTLM in system context uses wrong name
6.4 Negotiate and Kerberos V5 need a fake user name
6.5 NTLM does not support password with § character
6.6 libcurl can fail to try alternatives with --proxy-any
6.7 Do not clear digest for single realm
6.9 SHA-256 digest not supported in Windows SSPI builds
6.10 curl never completes Negotiate over HTTP
6.11 Negotiate on Windows fails
6.12 cannot use Secure Transport with Crypto Token Kit
6.13 Negotiate against Hadoop HDFS
7. FTP
7.3 FTP with NOBODY and FAILONERROR
7.4 FTP with ACCT
7.5 ASCII FTP
7.9 Passive transfer tries only one IP address
7.10 FTPS needs session reuse
7.11 FTPS upload data loss with TLS 1.3
7.12 FTPS directory listing hangs on Windows with Schannel
8. TELNET
8.2 Microsoft telnet server
9. SFTP and SCP
9.1 SFTP does not do CURLOPT_POSTQUOTE correct
9.2 wolfssh: publickey auth does not work
9.3 Remote recursive folder creation with SFTP
9.4 libssh blocking and infinite loop problem
10. SOCKS
10.3 FTPS over SOCKS
10.4 active FTP over a SOCKS
11. Internals
11.1 Curl leaks .onion hostnames in DNS
11.2 error buffer not set if connection to multiple addresses fails
11.4 HTTP test server 'connection-monitor' problems
11.5 Connection information when using TCP Fast Open
11.7 signal-based resolver timeouts
11.8 DoH leaks memory after followlocation
11.9 DoH does not inherit all transfer options
11.10 Blocking socket operations in non-blocking API
11.11 A shared connection cache is not thread-safe
11.14 Multi perform hangs waiting for threaded resolver
11.15 CURLOPT_OPENSOCKETPAIRFUNCTION is missing
11.16 libcurl uses renames instead of locking for atomic operations
12. LDAP
12.1 OpenLDAP hangs after returning results
12.2 LDAP on Windows does authentication wrong?
12.3 LDAP on Windows does not work
12.4 LDAPS with NSS is slow
13. TCP/IP
13.1 --interface for ipv6 binds to unusable IP address
13.2 Trying local ports fails on Windows
14. DICT
14.1 DICT responses show the underlying protocol
15. CMake
15.1 use correct SONAME
15.2 support build with GnuTLS
15.3 unusable tool_hugehelp.c with MinGW
15.4 build docs/curl.1
15.5 build on Linux links libcurl to libdl
15.6 uses -lpthread instead of Threads::Threads
15.7 generated .pc file contains strange entries
15.8 libcurl.pc uses absolute library paths
15.9 cert paths autodetected when cross-compiling
15.10 libpsl is not supported
15.11 ExternalProject_Add does not set CURL_CA_PATH
15.12 cannot enable LDAPS on Windows
15.13 CMake build with MIT Kerberos does not work
16. Applications
17. HTTP/2
17.1 Excessive HTTP/2 packets with TCP_NODELAY
17.2 HTTP/2 frames while in the connection pool kill reuse
17.3 ENHANCE_YOUR_CALM causes infinite retries
17.4 Connection failures with parallel HTTP/2
17.5 HTTP/2 connections through HTTPS proxy frequently stall
18. HTTP/3
18.1 If the HTTP/3 server closes connection during upload curl hangs
18.2 Transfer closed with n bytes remaining to read
18.4 timeout when reusing an http3 connection
18.9 connection migration does not work
==============================================================================
1. HTTP
1.3 STARTTRANSFER time is wrong for HTTP POSTs
Wrong STARTTRANSFER timer accounting for POST requests Timer works fine with
GET requests, but while using POST the time for CURLINFO_STARTTRANSFER_TIME
is wrong. While using POST CURLINFO_STARTTRANSFER_TIME minus
CURLINFO_PRETRANSFER_TIME is near to zero every time.
https://github.com/curl/curl/issues/218
https://curl.se/bug/view.cgi?id=1213
1.4 multipart formposts file name encoding
When creating multipart formposts. The file name part can be encoded with
something beyond ascii but currently libcurl will only pass in the verbatim
string the app provides. There are several browsers that already do this
encoding. The key seems to be the updated draft to RFC2231:
https://datatracker.ietf.org/doc/html/draft-reschke-rfc2231-in-http-02
1.5 Expect-100 meets 417
If an upload using Expect: 100-continue receives an HTTP 417 response, it
ought to be automatically resent without the Expect:. A workaround is for
the client application to redo the transfer after disabling Expect:.
https://curl.se/mail/archive-2008-02/0043.html
1.8 DoH is not used for all name resolves when enabled
Even if DoH is specified to be used, there are some name resolves that are
done without it. This should be fixed. When the internal function
`Curl_resolver_wait_resolv()` is called, it does not use DoH to complete the
resolve as it otherwise should.
See https://github.com/curl/curl/pull/3857 and
https://github.com/curl/curl/pull/3850
1.11 CURLOPT_SEEKFUNCTION not called with CURLFORM_STREAM
When using libcurl to POST form data using a FILE* with the CURLFORM_STREAM
option of curl_formadd(). I notice that if the connection drops at just the
right time, the POST is reattempted without the data from the file. It seems
like the file stream position is not getting reset to the beginning of the
file. I found the CURLOPT_SEEKFUNCTION option and set that with a function
that performs an fseek() on the FILE*. However, setting that did not seem to
fix the issue or even get called. See https://github.com/curl/curl/issues/768
2. TLS
2.3 Unable to use PKCS12 certificate with Secure Transport
See https://github.com/curl/curl/issues/5403
2.4 Secure Transport will not import PKCS#12 client certificates without a password
libcurl calls SecPKCS12Import with the PKCS#12 client certificate, but that
function rejects certificates that do not have a password.
https://github.com/curl/curl/issues/1308
2.5 Client cert handling with Issuer DN differs between backends
When the specified client certificate does not match any of the
server-specified DNs, the OpenSSL and GnuTLS backends behave differently.
The github discussion may contain a solution.
See https://github.com/curl/curl/issues/1411
2.6 CURL_GLOBAL_SSL
Since libcurl 7.57.0, the flag CURL_GLOBAL_SSL is a no-op. The change was
merged in https://github.com/curl/curl/commit/d661b0afb571a
It was removed since it was
A) never clear for applications on how to deal with init in the light of
different SSL backends (the option was added back in the days when life
was simpler)
B) multissl introduced dynamic switching between SSL backends which
emphasized (A) even more
C) libcurl uses some TLS backend functionality even for non-TLS functions (to
get "good" random) so applications trying to avoid the init for
performance reasons would do wrong anyway
D) not documented carefully so all this mostly just happened to work
for some users
However, in spite of the problems with the feature, there were some users who
apparently depended on this feature and who now claim libcurl is broken for
them. The fix for this situation is not obvious as a downright revert of the
patch is totally ruled out due to those reasons above.
https://github.com/curl/curl/issues/2276
2.7 Client cert (MTLS) issues with Schannel
See https://github.com/curl/curl/issues/3145
2.8 Schannel disable CURLOPT_SSL_VERIFYPEER and verify hostname
This seems to be a limitation in the underlying Schannel API.
https://github.com/curl/curl/issues/3284
2.9 TLS session cache does not work with TFO
See https://github.com/curl/curl/issues/4301
2.10 Store TLS context per transfer instead of per connection
The GnuTLS `backend->cred` and the OpenSSL `backend->ctx` data and their
proxy versions (and possibly other TLS backends), could be better moved to be
stored in the Curl_easy handle instead of in per connection so that a single
transfer that makes multiple connections can reuse the context and reduce
memory consumption.
https://github.com/curl/curl/issues/5102
2.11 Schannel TLS 1.2 handshake bug in old Windows versions
In old versions of Windows such as 7 and 8.1 the Schannel TLS 1.2 handshake
implementation likely has a bug that can rarely cause the key exchange to
fail, resulting in error SEC_E_BUFFER_TOO_SMALL or SEC_E_MESSAGE_ALTERED.
https://github.com/curl/curl/issues/5488
2.12 FTPS with Schannel times out file list operation
"Instead of the command completing, it just sits there until the timeout
expires." - the same command line seems to work with other TLS backends and
other operating systems. See https://github.com/curl/curl/issues/5284.
2.13 CURLOPT_CERTINFO results in CURLE_OUT_OF_MEMORY with Schannel
https://github.com/curl/curl/issues/8741
2.14 Secure Transport disabling hostname validation also disables SNI
SNI is the hostname that is sent by the TLS library to the server as part of
the TLS handshake. Secure Transport does not send SNI when hostname validation
is disabled. Servers that host multiple websites may not know which
certificate to serve without SNI or which backend server to connect to. The
server may serve the certificate of a default server or abort.
If a server aborts a handshake then curl shows error "SSL peer handshake
failed, the server most likely requires a client certificate to connect".
In this case the error may also have been caused by lack of SNI.
https://github.com/curl/curl/issues/6347
2.15 Renegotiate from server may cause hang for OpenSSL backend
A race condition has been observed when, immediately after the initial
handshake, curl has sent an HTTP request to the server and at the same time
the server has sent a TLS hello request (renegotiate) to curl. Both are
waiting for the other to respond. OpenSSL is supposed to send a handshake
response but does not.
https://github.com/curl/curl/issues/6785
https://github.com/openssl/openssl/issues/14722
3. Email protocols
3.1 IMAP SEARCH ALL truncated response
IMAP "SEARCH ALL" truncates output on large boxes. "A quick search of the
code reveals that pingpong.c contains some truncation code, at line 408, when
it deems the server response to be too large truncating it to 40 characters"
https://curl.se/bug/view.cgi?id=1366
3.2 No disconnect command
The disconnect commands (LOGOUT and QUIT) may not be sent by IMAP, POP3 and
SMTP if a failure occurs during the authentication phase of a connection.
3.3 POP3 expects "CRLF.CRLF" eob for some single-line responses
You have to tell libcurl not to expect a body, when dealing with one line
response commands. Please see the POP3 examples and test cases which show
this for the NOOP and DELE commands. https://curl.se/bug/?i=740
3.4 AUTH PLAIN for SMTP is not working on all servers
Specifying "--login-options AUTH=PLAIN" on the command line does not seem to
work correctly.
See https://github.com/curl/curl/issues/4080
4. Command line
4.1 -J and -O with %-encoded file names
-J/--remote-header-name does not decode %-encoded file names. RFC6266 details
how it should be done. The can of worm is basically that we have no charset
handling in curl and ascii >=128 is a challenge for us. Not to mention that
decoding also means that we need to check for nastiness that is attempted,
like "../" sequences and the like. Probably everything to the left of any
embedded slashes should be cut off.
https://curl.se/bug/view.cgi?id=1294
-O also does not decode %-encoded names, and while it has even less
information about the charset involved the process is similar to the -J case.
Note that we will not add decoding to -O without the user asking for it with
some other means as well, since -O has always been documented to use the name
exactly as specified in the URL.
4.2 -J with -C - fails
When using -J (with -O), automatically resumed downloading together with "-C
-" fails. Without -J the same command line works. This happens because the
resume logic is worked out before the target file name (and thus its
pre-transfer size) has been figured out.
https://curl.se/bug/view.cgi?id=1169
4.3 --retry and transfer timeouts
If using --retry and the transfer timeouts (possibly due to using -m or
-y/-Y) the next attempt does not resume the transfer properly from what was
downloaded in the previous attempt but will truncate and restart at the
original position where it was at before the previous failed attempt. See
https://curl.se/mail/lib-2008-01/0080.html and Mandriva bug report
https://qa.mandriva.com/show_bug.cgi?id=22565
5. Build and portability issues
5.1 OS400 port requires deprecated IBM library
curl for OS400 requires QADRT to build, which provides ASCII wrappers for
libc/POSIX functions in the ILE, but IBM no longer supports or even offers
this library to download.
See https://github.com/curl/curl/issues/5176
5.2 curl-config --libs contains private details
"curl-config --libs" will include details set in LDFLAGS when configure is
run that might be needed only for building libcurl. Further, curl-config
--cflags suffers from the same effects with CFLAGS/CPPFLAGS.
5.3 curl compiled on OSX 10.13 failed to run on OSX 10.10
See https://github.com/curl/curl/issues/2905
5.5 cannot handle Unicode arguments in non-Unicode builds on Windows
If a URL or filename cannot be encoded using the user's current codepage then
it can only be encoded properly in the Unicode character set. Windows uses
UTF-16 encoding for Unicode and stores it in wide characters, however curl
and libcurl are not equipped for that at the moment except when built with
_UNICODE and UNICODE defined. And, except for Cygwin, Windows cannot use UTF-8
as a locale.
https://curl.se/bug/?i=345
https://curl.se/bug/?i=731
https://curl.se/bug/?i=3747
5.6 make distclean loops forever
Due to an issue (probably) in automake, "make distclean" can end up in a
never-ending loop.
See https://github.com/curl/curl/issues/7716
5.8 configure finding libs in wrong directory
When the configure script checks for third-party libraries, it adds those
directories to the LDFLAGS variable and then tries linking to see if it
works. When successful, the found directory is kept in the LDFLAGS variable
when the script continues to execute and do more tests and possibly check for
more libraries.
This can make subsequent checks for libraries wrongly detect another
installation in a directory that was previously added to LDFLAGS by another
library check.
A possibly better way to do these checks would be to keep the pristine LDFLAGS
even after successful checks and instead add those verified paths to a
separate variable that only after all library checks have been performed gets
appended to LDFLAGS.
5.9 Utilize Requires.private directives in libcurl.pc
https://github.com/curl/curl/issues/864
5.10 curl hangs on SMB upload over stdin
See https://github.com/curl/curl/issues/7896
5.11 configure --with-gssapi with Heimdal is ignored on macOS
... unless you also pass --with-gssapi-libs
https://github.com/curl/curl/issues/3841
5.12 flaky Windows CI builds
We run many CI builds for each commit and PR on github, and especially a
number of the Windows builds are flaky. This means that we rarely get all CI
builds go green and complete without errors. This is unfortunate as it makes
us sometimes miss actual build problems and it is surprising to newcomers to
the project who (rightfully) do not expect this.
See https://github.com/curl/curl/issues/6972
5.13 long paths are not fully supported on Windows
curl on Windows cannot access long paths (paths longer than 260 characters).
However, as a workaround, the Windows path prefix \\?\ which disables all path
interpretation may work to allow curl to access the path. For example:
\\?\c:\longpath.
See https://github.com/curl/curl/issues/8361
5.14 Windows Unicode builds use homedir in current locale
The Windows Unicode builds of curl use the current locale, but expect Unicode
UTF-8 encoded paths for internal use such as open, access and stat. The user's
home directory is retrieved via curl_getenv in the current locale and not as
UTF-8 encoded Unicode.
See https://github.com/curl/curl/pull/7252 and
https://github.com/curl/curl/pull/7281
6. Authentication
6.1 NTLM authentication and unicode
NTLM authentication involving unicode user name or password only works
properly if built with UNICODE defined together with the Schannel
backend. The original problem was mentioned in:
https://curl.se/mail/lib-2009-10/0024.html
https://curl.se/bug/view.cgi?id=896
The Schannel version verified to work as mentioned in
https://curl.se/mail/lib-2012-07/0073.html
6.2 MIT Kerberos for Windows build
libcurl fails to build with MIT Kerberos for Windows (KfW) due to KfW's
library header files exporting symbols/macros that should be kept private to
the KfW library. See ticket #5601 at https://krbdev.mit.edu/rt/
6.3 NTLM in system context uses wrong name
NTLM authentication using SSPI (on Windows) when (lib)curl is running in
"system context" will make it use wrong(?) user name - at least when compared
to what winhttp does. See https://curl.se/bug/view.cgi?id=535
6.4 Negotiate and Kerberos V5 need a fake user name
In order to get Negotiate (SPNEGO) authentication to work in HTTP or Kerberos
V5 in the email protocols, you need to provide a (fake) user name (this
concerns both curl and the lib) because the code wrongly only considers
authentication if there's a user name provided by setting
conn->bits.user_passwd in url.c https://curl.se/bug/view.cgi?id=440 How?
https://curl.se/mail/lib-2004-08/0182.html A possible solution is to
either modify this variable to be set or introduce a variable such as
new conn->bits.want_authentication which is set when any of the authentication
options are set.
6.5 NTLM does not support password with § character
https://github.com/curl/curl/issues/2120
6.6 libcurl can fail to try alternatives with --proxy-any
When connecting via a proxy using --proxy-any, a failure to establish an
authentication will cause libcurl to abort trying other options if the
failed method has a higher preference than the alternatives. As an example,
--proxy-any against a proxy which advertise Negotiate and NTLM, but which
fails to set up Kerberos authentication will not proceed to try authentication
using NTLM.
https://github.com/curl/curl/issues/876
6.7 Do not clear digest for single realm
https://github.com/curl/curl/issues/3267
6.9 SHA-256 digest not supported in Windows SSPI builds
Windows builds of curl that have SSPI enabled use the native Windows API calls
to create authentication strings. The call to InitializeSecurityContext fails
with SEC_E_QOP_NOT_SUPPORTED which causes curl to fail with CURLE_AUTH_ERROR.
Microsoft does not document supported digest algorithms and that SEC_E error
code is not a documented error for InitializeSecurityContext (digest).
https://github.com/curl/curl/issues/6302
6.10 curl never completes Negotiate over HTTP
Apparently it is not working correctly...?
See https://github.com/curl/curl/issues/5235
6.11 Negotiate on Windows fails
When using --negotiate (or NTLM) with curl on Windows, SSL/TLS handshake
fails despite having a valid kerberos ticket cached. Works without any issue
in Unix/Linux.
https://github.com/curl/curl/issues/5881
6.12 cannot use Secure Transport with Crypto Token Kit
https://github.com/curl/curl/issues/7048
6.13 Negotiate authentication against Hadoop HDFS
https://github.com/curl/curl/issues/8264
7. FTP
7.3 FTP with NOBODY and FAILONERROR
It seems sensible to be able to use CURLOPT_NOBODY and CURLOPT_FAILONERROR
with FTP to detect if a file exists or not, but it is not working:
https://curl.se/mail/lib-2008-07/0295.html
7.4 FTP with ACCT
When doing an operation over FTP that requires the ACCT command (but not when
logging in), the operation will fail since libcurl does not detect this and
thus fails to issue the correct command:
https://curl.se/bug/view.cgi?id=635
7.5 ASCII FTP
FTP ASCII transfers do not follow RFC959. They do not convert the data
accordingly (not for sending nor for receiving). RFC 959 section 3.1.1.1
clearly describes how this should be done:
The sender converts the data from an internal character representation to
the standard 8-bit NVT-ASCII representation (see the Telnet
specification). The receiver will convert the data from the standard
form to his own internal form.
Since 7.15.4 at least line endings are converted.
7.9 Passive transfer tries only one IP address
When doing FTP operations through a proxy at localhost, the reported spotted
that curl only tried to connect once to the proxy, while it had multiple
addresses and a failed connect on one address should make it try the next.
After switching to passive mode (EPSV), curl should try all IP addresses for
"localhost". Currently it tries ::1, but it should also try 127.0.0.1.
See https://github.com/curl/curl/issues/1508
7.10 FTPS needs session reuse
When the control connection is reused for a subsequent transfer, some FTPS
servers complain about "missing session reuse" for the data channel for the
second transfer.
https://github.com/curl/curl/issues/4654
7.11 FTPS upload data loss with TLS 1.3
During FTPS upload curl does not attempt to read TLS handshake messages sent
after the initial handshake. OpenSSL servers running TLS 1.3 may send such a
message. When curl closes the upload connection if unread data has been
received (such as a TLS handshake message) then the TCP protocol sends an
RST to the server, which may cause the server to discard or truncate the
upload if it has not read all sent data yet, and then return an error to curl
on the control channel connection.
Since 7.78.0 this is mostly fixed. curl will do a single read before closing
TLS connections (which causes the TLS library to read handshake messages),
however there is still possibility of an RST if more messages need to be read
or a message arrives after the read but before close (network race condition).
https://github.com/curl/curl/issues/6149
7.12 FTPS directory listing hangs on Windows with Schannel
https://github.com/curl/curl/issues/9161
8. TELNET
8.2 Microsoft telnet server
There seems to be a problem when connecting to the Microsoft telnet server.
https://curl.se/bug/view.cgi?id=649
9. SFTP and SCP
9.1 SFTP does not do CURLOPT_POSTQUOTE correct
When libcurl sends CURLOPT_POSTQUOTE commands when connected to a SFTP server
using the multi interface, the commands are not being sent correctly and
instead the connection is "cancelled" (the operation is considered done)
prematurely. There is a half-baked (busy-looping) patch provided in the bug
report but it cannot be accepted as-is. See
https://curl.se/bug/view.cgi?id=748
9.2 wolfssh: publickey auth does not work
When building curl to use the wolfSSH backend for SFTP, the publickey
authentication does not work. This is simply functionality not written for curl
yet, the necessary API for make this work is provided by wolfSSH.
See https://github.com/curl/curl/issues/4820
9.3 Remote recursive folder creation with SFTP
On this servers, the curl fails to create directories on the remote server
even when the CURLOPT_FTP_CREATE_MISSING_DIRS option is set.
See https://github.com/curl/curl/issues/5204
9.4 libssh blocking and infinite loop problem
In the SSH_SFTP_INIT state for libssh, the ssh session working mode is set to
blocking mode. If the network is suddenly disconnected during sftp
transmission, curl will be stuck, even if curl is configured with a timeout.
https://github.com/curl/curl/issues/8632
10. SOCKS
10.3 FTPS over SOCKS
libcurl does not support FTPS over a SOCKS proxy.
10.4 active FTP over a SOCKS
libcurl does not support active FTP over a SOCKS proxy
11. Internals
11.1 Curl leaks .onion hostnames in DNS
Curl sends DNS requests for hostnames with a .onion TLD. This leaks
information about what the user is attempting to access, and violates this
requirement of RFC7686: https://datatracker.ietf.org/doc/html/rfc7686
Issue: https://github.com/curl/curl/issues/543
11.2 error buffer not set if connection to multiple addresses fails
If you ask libcurl to resolve a hostname like example.com to IPv6 addresses
only. But you only have IPv4 connectivity. libcurl will correctly fail with
CURLE_COULDNT_CONNECT. But the error buffer set by CURLOPT_ERRORBUFFER
remains empty. Issue: https://github.com/curl/curl/issues/544
11.4 HTTP test server 'connection-monitor' problems
The 'connection-monitor' feature of the sws HTTP test server does not work
properly if some tests are run in unexpected order. Like 1509 and then 1525.
See https://github.com/curl/curl/issues/868
11.5 Connection information when using TCP Fast Open
CURLINFO_LOCAL_PORT (and possibly a few other) fails when TCP Fast Open is
enabled.
See https://github.com/curl/curl/issues/1332 and
https://github.com/curl/curl/issues/4296
11.7 signal-based resolver timeouts
libcurl built without an asynchronous resolver library uses alarm() to time
out DNS lookups. When a timeout occurs, this causes libcurl to jump from the
signal handler back into the library with a sigsetjmp, which effectively
causes libcurl to continue running within the signal handler. This is
non-portable and could cause problems on some platforms. A discussion on the
problem is available at https://curl.se/mail/lib-2008-09/0197.html
Also, alarm() provides timeout resolution only to the nearest second. alarm
ought to be replaced by setitimer on systems that support it.
11.8 DoH leaks memory after followlocation
https://github.com/curl/curl/issues/4592
11.9 DoH does not inherit all transfer options
Some options are not inherited because they are not relevant for the DoH SSL
connections, or inheriting the option may result in unexpected behavior. For
example the user's debug function callback is not inherited because it would
be unexpected for internal handles (ie DoH handles) to be passed to that
callback.
If an option is not inherited then it is not possible to set it separately for
DoH without a DoH-specific option. For example: CURLOPT_DOH_SSL_VERIFYHOST,
CURLOPT_DOH_SSL_VERIFYPEER and CURLOPT_DOH_SSL_VERIFYSTATUS.
See https://github.com/curl/curl/issues/6605
11.10 Blocking socket operations in non-blocking API
The list of blocking socket operations is in TODO section "More non-blocking".
11.11 A shared connection cache is not thread-safe
The share interface offers CURL_LOCK_DATA_CONNECT to have multiple easy
handle share a connection cache, but due to how connections are used they are
still not thread-safe when used shared.
See https://github.com/curl/curl/issues/4915 and lib1541.c
11.14 Multi perform hangs waiting for threaded resolver
If a threaded resolver takes a long time to complete, libcurl can be blocked
waiting for it for a longer time than expected - and longer than the set
timeouts.
See https://github.com/curl/curl/issues/2975 and
https://github.com/curl/curl/issues/4852
11.15 CURLOPT_OPENSOCKETPAIRFUNCTION is missing
When libcurl creates sockets with socketpair(), those are not "exposed" in
CURLOPT_OPENSOCKETFUNCTION and therefore might surprise and be unknown to
applications that expect and want all sockets known beforehand. One way to
address this issue is to introduce a CURLOPT_OPENSOCKETPAIRFUNCTION callback.
https://github.com/curl/curl/issues/5747
11.16 libcurl uses renames instead of locking for atomic operations
For saving cookies, alt-svc and hsts files. This is bad when for example the
file is stored in a directory where the application has no write permission
but it has permission for the file.
https://github.com/curl/curl/issues/6882
https://github.com/curl/curl/pull/6884
12. LDAP
12.1 OpenLDAP hangs after returning results
By configuration defaults, OpenLDAP automatically chase referrals on
secondary socket descriptors. The OpenLDAP backend is asynchronous and thus
should monitor all socket descriptors involved. Currently, these secondary
descriptors are not monitored, causing OpenLDAP library to never receive
data from them.
As a temporary workaround, disable referrals chasing by configuration.
The fix is not easy: proper automatic referrals chasing requires a
synchronous bind callback and monitoring an arbitrary number of socket
descriptors for a single easy handle (currently limited to 5).
Generic LDAP is synchronous: OK.
See https://github.com/curl/curl/issues/622 and
https://curl.se/mail/lib-2016-01/0101.html
12.2 LDAP on Windows does authentication wrong?
https://github.com/curl/curl/issues/3116
12.3 LDAP on Windows does not work
A simple curl command line getting "ldap://ldap.forumsys.com" returns an
error that says "no memory" !
https://github.com/curl/curl/issues/4261
12.4 LDAPS with NSS is slow
See https://github.com/curl/curl/issues/5874
13. TCP/IP
13.1 --interface for ipv6 binds to unusable IP address
Since IPv6 provides a lot of addresses with different scope, binding to an
IPv6 address needs to take the proper care so that it does not bind to a
locally scoped address as that is bound to fail.
https://github.com/curl/curl/issues/686
13.2 Trying local ports fails on Windows
This makes '--local-port [range]' to not work since curl can't properly
detect if a port is already in use, so it'll try the first port, use that and
then subsequently fail anyway if that was actually in use.
https://github.com/curl/curl/issues/8112
14. DICT
14.1 DICT responses show the underlying protocol
When getting a DICT response, the protocol parts of DICT are not stripped off
from the output.
https://github.com/curl/curl/issues/1809
15. CMake
15.1 use correct SONAME
The autotools build sets the SONAME properly according to VERSIONINFO in
lib/Makefile.am and so should cmake to make comparable build.
See https://github.com/curl/curl/pull/5935
15.2 support build with GnuTLS
15.3 unusable tool_hugehelp.c with MinGW
see https://github.com/curl/curl/issues/3125
15.4 build docs/curl.1
The cmake build does not create the docs/curl.1 file and therefore must rely on
it being there already. This makes the --manual option not work and test
cases like 1139 cannot function.
15.5 build on Linux links libcurl to libdl
... which it should not need to!
See https://github.com/curl/curl/issues/6165
15.6 uses -lpthread instead of Threads::Threads
See https://github.com/curl/curl/issues/6166
15.7 generated .pc file contains strange entries
The Libs.private field of the generated .pc file contains -lgcc -lgcc_s -lc
-lgcc -lgcc_s
See https://github.com/curl/curl/issues/6167
15.8 libcurl.pc uses absolute library paths
The libcurl.pc file generated by cmake contains things like Libs.private:
/usr/lib64/libssl.so /usr/lib64/libcrypto.so /usr/lib64/libz.so. The
autotools equivalent would say Libs.private: -lssl -lcrypto -lz
See https://github.com/curl/curl/issues/6169
15.9 cert paths autodetected when cross-compiling
The autotools build disables the ca_path/ca_bundle detection when
cross-compiling. The cmake build keeps doing the detection.
See https://github.com/curl/curl/issues/6178
15.10 libpsl is not supported
See https://github.com/curl/curl/issues/6214
15.11 ExternalProject_Add does not set CURL_CA_PATH
CURL_CA_BUNDLE and CURL_CA_PATH are not set properly when cmake's
ExternalProject_Add is used to build curl as a dependency.
See https://github.com/curl/curl/issues/6313
15.12 cannot enable LDAPS on Windows
See https://github.com/curl/curl/issues/6284
15.13 CMake build with MIT Kerberos does not work
Minimum CMake version was bumped in curl 7.71.0 (#5358) Since CMake 3.2
try_compile started respecting the CMAKE_EXE_FLAGS. The code dealing with
MIT Kerberos detection sets few variables to potentially weird mix of space,
and ;-separated flags. It had to blow up at some point. All the CMake checks
that involve compilation are doomed from that point, the configured tree
cannot be built.
https://github.com/curl/curl/issues/6904
16. Applications
17. HTTP/2
17.1 Excessive HTTP/2 packets with TCP_NODELAY
Because of how curl sets TCP_NODELAY by default, HTTP/2 requests are issued
using more separate TCP packets than it would otherwise need to use. This
means spending more bytes than it has to. Just disabling TCP_NODELAY for
HTTP/2 is also not the correct fix because that then makes the outgoing
packets to get delayed.
See https://github.com/curl/curl/issues/6363
17.2 HTTP/2 frames while in the connection pool kill reuse
If the server sends HTTP/2 frames (like for example an HTTP/2 PING frame) to
curl while the connection is held in curl's connection pool, the socket will
be found readable when considered for reuse and that makes curl think it is
dead and then it will be closed and a new connection gets created instead.
This is *best* fixed by adding monitoring to connections while they are kept
in the pool so that pings can be responded to appropriately.
17.3 ENHANCE_YOUR_CALM causes infinite retries
Infinite retries with 2 parallel requests on one connection receiving GOAWAY
with ENHANCE_YOUR_CALM error code.
See https://github.com/curl/curl/issues/5119
17.4 Connection failures with parallel HTTP/2
See https://github.com/curl/curl/issues/5611
17.5 HTTP/2 connections through HTTPS proxy frequently stall
See https://github.com/curl/curl/issues/6936
18. HTTP/3
18.1 If the HTTP/3 server closes connection during upload curl hangs
See https://github.com/curl/curl/issues/6606
18.2 Transfer closed with n bytes remaining to read
HTTP/3 transfers with the Jetty HTTP/3 server seem to not work.
https://github.com/curl/curl/issues/8523
18.4 timeout when reusing an http3 connection
HTTP/3 with quiche seems to not work and always timeout a subsequent transfer
that reuses an already established connection
https://github.com/curl/curl/issues/8764
18.9 connection migration does not work
https://github.com/curl/curl/issues/7695
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