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Code Issues Releases Wiki Activity
0caf1423e5
curl/docs/KNOWN_BUGS
Daniel Stenberg 3ab45a9876
KNOWN_BUGS: TLS session cache doesn't work with TFO 
[skip ci]
Closes #4301
2019-12-16 16:20:16 +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
1.6 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
1.9 HTTP/2 frames while in the connection pool kill reuse
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
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
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 and -O with %-encoded file names
4.2 -J with -C - fails
4.3 --retry and transfer timeouts
4.4 --upload-file . hang if delay in STDIN
4.5 Improve --data-urlencode space encoding
5. Build and portability issues
5.1 USE_UNIX_SOCKETS on Windows
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 Cannot compile against a static build of OpenLDAP
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
5.10 IDN tests failing on Windows / MSYS2
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
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 Stick to same family over SOCKS proxy
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
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
11.5 Connection information when using TCP Fast Open
11.6 slow connect to localhost on Windows
11.7 signal-based resolver timeouts
12. LDAP and OpenLDAP
12.1 OpenLDAP hangs after returning results
12.2 LDAP on Windows does authentication wrong?
12.3 LDAP on Windows doesn't work
13. TCP/IP
13.1 --interface for ipv6 binds to unusable IP address
14 DICT
14.1 DICT responses show the underlying protocol
==============================================================================
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.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
1.7 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
1.9 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.
1.11 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
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
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 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.haxx.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.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
4.4 --upload-file . hangs if delay in STDIN
"(echo start; sleep 1; echo end) | curl --upload-file . http://mywebsite -vv"
... causes a hang when it shouldn't.
See https://github.com/curl/curl/issues/2051
4.5 Improve --data-urlencode space encoding
ASCII space characters in --data-urlencode are currently encoded as %20
rather than +, which RFC 1866 says should be used.
See https://github.com/curl/curl/issues/3229
5. Build and portability issues
5.1 USE_UNIX_SOCKETS on Windows
Due to incorrect CMake checks for the presence of the feature, it will never
be enabled for windows in a cmake build.
See https://github.com/curl/curl/issues/4040
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 Cannot compile against a static build of OpenLDAP
See https://github.com/curl/curl/issues/2367
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
- unusable tool_hugehelp.c with MinGW, see
https://github.com/curl/curl/issues/3125
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 IDN tests failing on Windows / MSYS2
It seems like MSYS2 does some UTF-8-to-something-else conversion for Windows
compatibility.
https://github.com/curl/curl/issues/3747
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.
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
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.
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 Stick to same family over SOCKS proxy
When asked to do FTP over a SOCKS proxy, it might connect to the proxy (and
then subsequently to the remote server) using for example IPv4. When doing
the second connection, curl should make sure that the second connection is
using the same IP protocol version as the first connection did and not try
others, since the remote server will only accept the same.
See https://curl.haxx.se/mail/archive-2018-07/0000.html
8. TELNET
8.1 TELNET and time limitations 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
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.haxx.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.
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
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
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.
https://github.com/curl/curl/issues/1809
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