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KNOWN_BUGS
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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
1.2 Multiple methods in a single WWW-Authenticate: header
1.3 STARTTRANSFER time is wrong for HTTP POSTs
1.4 multipart formposts file name encoding
1.5 Expect-100 meets 417
1.6 Unnecessary close when 401 received waiting for 100
1.7 Deflate error after all content was received
1.8 DoH isn't used for all name resolves when enabled
1.11 CURLOPT_SEEKFUNCTION not called with CURLFORM_STREAM
2. TLS
2.1 CURLINFO_SSL_VERIFYRESULT has limited support
2.2 DER in keychain
2.3 Unable to use PKCS12 certificate with Secure Transport
2.4 Secure Transport won't 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 doesn't 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
2.14 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
5.4 Build with statically built dependency
5.5 can't handle Unicode arguments in non-Unicode builds on Windows
5.7 Visual Studio project gaps
5.8 configure finding libs in wrong directory
5.9 Utilize Requires.private directives in libcurl.pc
5.10 SMB tests fail with Python 2
5.11 configure --with-gssapi with Heimdal is ignored on macOS
5.12 flaky Windows CI builds
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 doesn't support password with § character
6.6 libcurl can fail to try alternatives with --proxy-any
6.7 Don't clear digest for single realm
6.8 RTSP authentication breaks without redirect support
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 Can't use Secure Transport with Crypto Token Kit
7. FTP
7.1 FTP without or slow 220 response
7.2 FTP with CONNECT and slow server
7.3 FTP with NOBODY and FAILONERROR
7.4 FTP with ACCT
7.5 ASCII FTP
7.6 FTP with NULs in URL parts
7.7 FTP and empty path parts in the URL
7.8 Premature transfer end but healthy control channel
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
8. TELNET
8.1 TELNET and time limitations don't work
8.2 Microsoft telnet server
9. SFTP and SCP
9.1 SFTP doesn't do CURLOPT_POSTQUOTE correct
9.2 wolfssh: publickey auth doesn't work
9.3 Remote recursive folder creation with SFTP
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
11.3 Disconnects don't do verbose
11.4 HTTP test server 'connection-monitor' problems
11.5 Connection information when using TCP Fast Open
11.6 slow connect to localhost on Windows
11.7 signal-based resolver timeouts
11.8 DoH leaks memory after followlocation
11.9 DoH doesn't inherit all transfer options
11.10 Blocking socket operations in non-blocking API
11.11 A shared connection cache is not thread-safe
11.12 'no_proxy' string-matches IPv6 numerical addresses
11.13 wakeup socket disconnect causes havoc
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 doesn't work
12.4 LDAPS with NSS is slow
13. TCP/IP
13.1 --interface for ipv6 binds to unusable IP address
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 libspsl 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
16.1 pulseUI VPN client
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
18. HTTP/3
18.1 If the HTTP/3 server closes connection during upload curl hangs
18.2 Uploading HTTP/3 files gets interrupted at certain file sizes
18.3 HTTP/3 download is 5x times slower than HTTP/2
18.4 Downloading with HTTP/3 produces broken files
18.5 HTTP/3 download with quiche halts after a while
18.6 HTTP/3 multipart POST with quiche fails
18.7 HTTP/3 quiche upload large file fails
18.8 HTTP/3 doesn't support client certs
18.9 connection migration doesn't work
==============================================================================
1. HTTP
1.2 Multiple methods in a single WWW-Authenticate: header
The HTTP responses headers WWW-Authenticate: can provide information about
multiple authentication methods as multiple headers or as several methods
within a single header. The latter way, several methods in the same physical
line, is not supported by libcurl's parser. (For no good reason.)
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://tools.ietf.org/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
1.6 Unnecessary close when 401 received waiting for 100
libcurl closes the connection if an HTTP 401 reply is received while it is
waiting for the 100-continue response.
https://curl.se/mail/lib-2008-08/0462.html
1.7 Deflate error after all content was received
There's a situation where we can get an error in a HTTP response that is
compressed, when that error is detected after all the actual body contents
have been received and delivered to the application. This is tricky, but is
ultimately a broken server.
See https://github.com/curl/curl/issues/2719
1.8 DoH isn't 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 doesn't 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
I'm using libcurl to POST form data using a FILE* with the CURLFORM_STREAM
option of curl_formadd(). I've noticed 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 isn't 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 didn't
seem to fix the issue or even get called. See
https://github.com/curl/curl/issues/768
2. TLS
2.1 CURLINFO_SSL_VERIFYRESULT has limited support
CURLINFO_SSL_VERIFYRESULT is only implemented for the OpenSSL, NSS and
GnuTLS backends, so relying on this information in a generic app is flaky.
2.2 DER in keychain
Curl doesn't recognize certificates in DER format in keychain, but it works
with PEM. https://curl.se/bug/view.cgi?id=1065
2.3 Unable to use PKCS12 certificate with Secure Transport
See https://github.com/curl/curl/issues/5403
2.4 Secure Transport won't 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 doesn't 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) never very carefully documented 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 doesn't 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.
2.14 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 doesn't.
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 doesn't 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 doesn't 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 doesn't 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 won't 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 doesn't 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
5.4 Build with statically built dependency
The build scripts in curl (autotools, cmake and others) are primarily done to
work with shared/dynamic third party dependencies. When linking with shared
libraries, the dependency "chain" is handled automatically by the library
loader - on all modern systems.
If you instead link with a static library, we need to provide all the
dependency libraries already at the link command line.
Figuring out all the dependency libraries for a given library is hard, as it
might also involve figuring out the dependencies of the dependencies and they
may vary between platforms and even change between versions.
When using static dependencies, the build scripts will mostly assume that
you, the user, will provide all the necessary additional dependency libraries
as additional arguments in the build. With configure, by setting LIBS/LDFLAGS
on the command line.
We welcome help to improve curl's ability to link with static libraries, but
it is likely a task that we can never fully support.
5.5 can't handle Unicode arguments in non-Unicode builds on Windows
If a URL or filename can't 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 can't use UTF-8
as a locale.
https://curl.se/bug/?i=345
https://curl.se/bug/?i=731
https://curl.se/bug/?i=3747
5.7 Visual Studio project gaps
The Visual Studio projects lack some features that the autoconf and nmake
builds offer, such as the following:
- support for zlib and nghttp2
- use of static runtime libraries
- add the test suite components
In addition to this the following could be implemented:
- support for other development IDEs
- add PATH environment variables for third-party DLLs
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 SMB tests fail with Python 2
The error message says "TreeConnectAndX not found".
See https://github.com/curl/curl/issues/5983
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 very flaky. This means that we rarely get
all CI builds go green and complete without errors. This is very unfortunate
as it makes us sometimes miss actual build problems and it is surprising to
newcomers to the project who (rightfully) don't expect this.
See https://github.com/curl/curl/issues/6972
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 e-mail 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 doesn't 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 won't proceed to try authentication
using NTLM.
https://github.com/curl/curl/issues/876
6.7 Don't clear digest for single realm
https://github.com/curl/curl/issues/3267
6.8 RTSP authentication breaks without redirect support
RTSP authentication broke in 7.66.0. A work-around is to enable RTSP in
CURLOPT_REDIR_PROTOCOLS. Authentication should however not be considered an
actual redirect so a "proper" fix needs to be different and not require users
to allow redirects to RTSP to work.
See https://github.com/curl/curl/pull/4750
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 isn't 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/TSL 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 Can't use Secure Transport with Crypto Token Kit
https://github.com/curl/curl/issues/7048
7. FTP
7.1 FTP without or slow 220 response
If a connection is made to a FTP server but the server then just never sends
the 220 response or otherwise is dead slow, libcurl will not acknowledge the
connection timeout during that phase but only the "real" timeout - which may
surprise users as it is probably considered to be the connect phase to most
people. Brought up (and is being misunderstood) in:
https://curl.se/bug/view.cgi?id=856
7.2 FTP with CONNECT and slow server
When doing FTP over a socks proxy or CONNECT through HTTP proxy and the multi
interface is used, libcurl will fail if the (passive) TCP connection for the
data transfer isn't more or less instant as the code does not properly wait
for the connect to be confirmed. See test case 564 for a first shot at a test
case.
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 doesn't 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 don't 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.
7.6 FTP with NULs in URL parts
FTP URLs passed to curl may contain NUL (0x00) in the RFC 1738 <user>,
<password>, and <fpath> components, encoded as "%00". The problem is that
curl_unescape does not detect this, but instead returns a shortened C string.
From a strict FTP protocol standpoint, NUL is a valid character within RFC
959 <string>, so the way to handle this correctly in curl would be to use a
data structure other than a plain C string, one that can handle embedded NUL
characters. From a practical standpoint, most FTP servers would not
meaningfully support NUL characters within RFC 959 <string>, anyway (e.g.,
Unix pathnames may not contain NUL).
7.7 FTP and empty path parts in the URL
libcurl ignores empty path parts in FTP URLs, whereas RFC1738 states that
such parts should be sent to the server as 'CWD ' (without an argument). The
only exception to this rule, is that we knowingly break this if the empty
part is first in the path, as then we use the double slashes to indicate that
the user wants to reach the root dir (this exception SHALL remain even when
this bug is fixed).
7.8 Premature transfer end but healthy control channel
When 'multi_done' is called before the transfer has been completed the normal
way, it is considered a "premature" transfer end. In this situation, libcurl
closes the connection assuming it doesn't know the state of the connection so
it can't be reused for subsequent requests.
With FTP however, this isn't necessarily true but there are a bunch of
situations (listed in the ftp_done code) where it *could* keep the connection
alive even in this situation - but the current code doesn't. Fixing this would
allow libcurl to reuse FTP connections better.
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 hasn't 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
8. TELNET
8.1 TELNET and time limitations don't work
When using telnet, the time limitation options don't work.
https://curl.se/bug/view.cgi?id=846
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 doesn't 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 doesn't work
When building curl to use the wolfSSH backend for SFTP, the publickey
authentication doesn't 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 CURLOPT_FTP_CREATE_MISSING_DIRS option is set.
See https://github.com/curl/curl/issues/5204
10. SOCKS
10.3 FTPS over SOCKS
libcurl doesn't support FTPS over a SOCKS proxy.
10.4 active FTP over a SOCKS
libcurl doesn't 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://tools.ietf.org/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
11.3 Disconnects don't do verbose
Due to how libcurl keeps connections alive in the "connection pool" after use
to potentially transcend the life-time of the initial easy handle that was
used to drive the transfer over that connection, it uses a *separate* and
internal easy handle when it shuts down the connection. That separate
connection might not have the exact same settings as the original easy
handle, and in particular it is often note-worthy that it doesn't have the
same VERBOSE and debug callbacks setup so that an application will not get
the protocol data for the disconnect phase of a transfer the same way it got
all the other data.
This is because the original easy handle might have already been freed at that
point and the application might not at all be prepared that the callback
would get called again long after the handle was freed.
See for example https://github.com/curl/curl/issues/6995
11.4 HTTP test server 'connection-monitor' problems
The 'connection-monitor' feature of the sws HTTP test server doesn't 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
11.6 slow connect to localhost on Windows
When connecting to "localhost" on Windows, curl will resolve the name for
both ipv4 and ipv6 and try to connect to both happy eyeballs-style. Something
in there does however make it take 200 milliseconds to succeed - which is the
HAPPY_EYEBALLS_TIMEOUT define exactly. Lowering that define speeds up the
connection, suggesting a problem in the HE handling.
If we can *know* that we're talking to a local host, we should lower the
happy eyeballs delay timeout for IPv6 (related: hardcode the "localhost"
addresses, mentioned in TODO). Possibly we should reduce that delay for all.
https://github.com/curl/curl/issues/2281
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 doesn't 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
11.12 'no_proxy' string-matches IPv6 numerical addresses
This has the downside that "::1" for example doesn't match "::0:1" even
though they are in fact the same address.
See https://github.com/curl/curl/issues/5745
11.13 wakeup socket disconnect causes havoc
waking an iPad breaks the wakeup socket pair, triggering a POLLIN event and
resulting in SOCKERRNO being set to ENOTCONN.
This condition, and other possible error conditions on the wakeup socket, are
not handled, so the condition remains on the FD and curl_multi_poll will
never block again.
See https://github.com/curl/curl/issues/6132 and
https://github.com/curl/curl/pull/6133
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 expects and wants 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 doesn't 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 doesn't bind to a
locally scoped address as that is bound to fail.
https://github.com/curl/curl/issues/686
14. DICT
14.1 DICT responses show the underlying protocol
When getting a DICT response, the protocol parts of DICT aren't stripped off
from the output.