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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
1.1 CURLFORM_CONTENTLEN in an array
1.2 Disabling HTTP Pipelining
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
1.9 HTTP/2 frames while in the connection pool kill reuse
1.10 Strips trailing dot from host name
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 GnuTLS backend skips really long certificate fields
2.4 DarwinSSL won't import PKCS#12 client certificates without a password
3. Email protocols
3.1 IMAP SEARCH ALL truncated response
3.2 No disconnect command
3.3 SMTP to multiple recipients
3.4 POP3 expects "CRLF.CRLF" eob for some single-line responses
4. Command line
4.1 -J with %-encoded file nameas
4.2 -J with -C - fails
4.3 --retry and transfer timeouts
5. Build and portability issues
5.1 Windows Borland compiler
5.2 curl-config --libs contains private details
5.4 AIX shared build with c-ares fails
5.5 can't handle Unicode arguments in Windows
5.6 cmake support gaps
5.7 Visual Studio project gaps
5.8 configure finding libs in wrong directory
5.9 Utilize Requires.private directives in libcurl.pc
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
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
8. TELNET
8.1 TELNET and time limtiations don't work
8.2 Microsoft telnet server
9. SFTP and SCP
9.1 SFTP doesn't do CURLOPT_POSTQUOTE correct
10. SOCKS
10.1 SOCKS proxy connections are done blocking
10.2 SOCKS don't support timeouts
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 c-ares deviates from stock resolver on http://1346569778
11.4 HTTP test server 'connection-monitor' problems
12. LDAP and OpenLDAP
12.1 OpenLDAP hangs after returning results
13. TCP/IP
13.1 --interface for ipv6 binds to unusable IP address
==============================================================================
1. HTTP
1.1 CURLFORM_CONTENTLEN in an array
It is not possible to pass a 64-bit value using CURLFORM_CONTENTLEN with
CURLFORM_ARRAY, when compiled on 32-bit platforms that support 64-bit
integers. This is because the underlying structure 'curl_forms' uses a dual
purpose char* for storing these values in via casting. For more information
see the now closed related issue:
https://github.com/curl/curl/issues/608
1.2 Disabling HTTP Pipelining
Disabling HTTP Pipelining when there are ongoing transfers can lead to
heap corruption and crash. https://curl.haxx.se/bug/view.cgi?id=1411
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.haxx.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.haxx.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 the 100-continue response.
https://curl.haxx.se/mail/lib-2008-08/0462.html
1.9 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.
1.10 Strips trailing dot from host name
When given a URL with a trailing dot for the host name part:
"https://example.com./", libcurl will strip off the dot and use the name
without a dot internally and send it dot-less in HTTP Host: headers and in
the TLS SNI field.
The HTTP part violates RFC 7230 section 5.4 but the SNI part is accordance
with RFC 6066 section 3.
URLs using these trailing dots are very rare in the wild and we have not seen
or gotten any real-world problems with such URLs reported. The popular
browsers seem to have stayed with not stripping the dot for both uses (thus
they violate RFC 6066 instead of RFC 7230).
Daniel took the discussion to the HTTPbis mailing list in March 2016:
https://lists.w3.org/Archives/Public/ietf-http-wg/2016JanMar/0430.html but
there was not major rush or interest to fix this. The impression I get is
that most HTTP people rather not rock the boat now and instead prioritize web
compatibility rather than to strictly adhere to these RFCs.
Our current approach allows a knowing client to send a custom HTTP header
with the dot added.
It can also be noted that while adding a trailing dot to the host name in
most (all?) cases will make the name resolve to the same set of IP addresses,
many HTTP servers will not happily accept the trailing dot there unless that
has been specifically configured to be a fine virtual host.
If URLs with trailing dots for host names become more popular or even just
used more than for just plain fun experiments, I'm sure we will have reason
to go back and reconsider.
See https://github.com/curl/curl/issues/716 for the discussion.
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 and NSS
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.haxx.se/bug/view.cgi?id=1065
2.3 GnuTLS backend skips really long certificate fields
libcurl calls gnutls_x509_crt_get_dn() with a fixed buffer size and if the
field is too long in the cert, it'll just return an error and the field will
be displayed blank.
2.4 DarwinSSL 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
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.haxx.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 SMTP to multiple recipients
When sending data to multiple recipients, curl will abort and return failure
if one of the recipients indicate failure (on the "RCPT TO"
command). Ordinary mail programs would proceed and still send to the ones
that can receive data. This is subject for change in the future.
https://curl.haxx.se/bug/view.cgi?id=1116
3.4 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.haxx.se/bug/?i=740
4. Command line
4.1 -J with %-encoded file nameas
-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.haxx.se/bug/view.cgi?id=1294
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.haxx.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.haxx.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 Windows Borland compiler
When building with the Windows Borland compiler, it fails because the "tlib"
tool doesn't support hyphens (minus signs) in file names and we have such in
the build. https://curl.haxx.se/bug/view.cgi?id=1222
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.
5.4 AIX shared build with c-ares fails
curl version 7.12.2 fails on AIX if compiled with --enable-ares. The
workaround is to combine --enable-ares with --disable-shared
5.5 can't handle Unicode arguments in 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. And, except for Cygwin,
Windows can't use UTF-8 as a locale.
https://curl.haxx.se/bug/?i=345
https://curl.haxx.se/bug/?i=731
5.6 cmake support gaps
The cmake build setup lacks several features that the autoconf build
offers. This includes:
- use of correct soname for the shared library build
- support for several TLS backends are missing
- the unit tests cause link failures in regular non-static builds
- no nghttp2 check
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
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 WinSSL/schannel
backend. The original problem was mentioned in:
https://curl.haxx.se/mail/lib-2009-10/0024.html
https://curl.haxx.se/bug/view.cgi?id=896
The WinSSL/schannel version verified to work as mentioned in
https://curl.haxx.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.haxx.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.haxx.se/bug/view.cgi?id=440 How?
https://curl.haxx.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.
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.haxx.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.haxx.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.haxx.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.
8. TELNET
8.1 TELNET and time limtiations don't work
When using telnet, the time limitation options don't work.
https://curl.haxx.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.haxx.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.haxx.se/bug/view.cgi?id=748
10. SOCKS
10.1 SOCKS proxy connections are done blocking
Both SOCKS5 and SOCKS4 proxy connections are done blocking, which is very bad
when used with the multi interface.
10.2 SOCKS don't support timeouts
The SOCKS4 connection codes don't properly acknowledge (connect) timeouts.
According to bug #1556528, even the SOCKS5 connect code does not do it right:
https://curl.haxx.se/bug/view.cgi?id=604
When connecting to a SOCK proxy, the (connect) timeout is not properly
acknowledged after the actual TCP connect (during the SOCKS "negotiate"
phase).
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 c-ares deviates from stock resolver on http://1346569778
When using the socket resolvers, that URL becomes:
* Rebuilt URL to: http://1346569778/
* Trying 80.67.6.50...
but with c-ares it instead says "Could not resolve: 1346569778 (Domain name
not found)"
See https://github.com/curl/curl/issues/893
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
12. LDAP and OpenLDAP
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.haxx.se/mail/lib-2016-01/0101.html
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
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