These are problems 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 since this was written! 56. 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 http://curl.haxx.se/bug/view.cgi?id=2006544 55. 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 http://krbdev.mit.edu/rt/ 53. SFTP busy-loop problem. When doing SFTP uploads, we can see that libcurl occasionally will busy-loop while waiting for certain network conditions. Reported by Pavel Shalagin, explained somewhat by Daniel Stenberg here: http://curl.haxx.se/mail/lib-2008-04/0439.html 52. Gautam Kachroo's issue that identifies a problem with the multi interface where a connection can be re-used without actually being properly SSL-negoatiated: http://curl.haxx.se/mail/lib-2008-01/0277.html 49. 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 http://curl.haxx.se/mail/lib-2008-01/0080.html and Mandriva bug report https://qa.mandriva.com/show_bug.cgi?id=22565 48. If a CONNECT response-headers are larger than BUFSIZE (16KB) when the connection is meant to be kept alive (like for NTLM proxy auth), the function will return prematurely and will confuse the rest of the HTTP protocol code. This should be very rare. 45. libcurl built to support ipv6 uses getaddrinfo() to resolve host names. getaddrinfo() sorts the response list which effectively kills how libcurl deals with round-robin DNS entries. All details: http://curl.haxx.se/mail/lib-2007-07/0168.html initial suggested function to use for randomizing the response: http://curl.haxx.se/mail/lib-2007-07/0178.html 43. There seems to be a problem when connecting to the Microsoft telnet server. http://curl.haxx.se/bug/view.cgi?id=1720605 41. 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: http://curl.haxx.se/bug/view.cgi?id=1693337 39. Steffen Rumler's Race Condition in Curl_proxyCONNECT: http://curl.haxx.se/mail/lib-2007-01/0045.html 38. Kumar Swamy Bhatt's problem in ftp/ssl "LIST" operation: http://curl.haxx.se/mail/lib-2007-01/0103.html 37. Having more than one connection to the same host when doing NTLM authentication (with performs multiple "passes" and authenticates a connection rather than a HTTP request), and particularly when using the multi interface, there's a risk that libcurl will re-use a wrong connection when doing the different passes in the NTLM negotiation and thus fail to negotiate (in seemingly mysterious ways). 35. Both SOCKS5 and SOCKS4 proxy connections are done blocking, which is very bad when used with the multi interface. 34. The SOCKS4 connection codes don't properly acknowledge (connect) timeouts. Also see #12. According to bug #1556528, even the SOCKS5 connect code does not do it right: http://curl.haxx.se/bug/view.cgi?id=1556528, 31. "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. 30. You need to use -g to the command line tool in order to use RFC2732-style IPv6 numerical addresses in URLs. 29. IPv6 URLs with zone ID is not supported. http://www.ietf.org/internet-drafts/draft-fenner-literal-zone-02.txt (expired) specifies the use of a plus sign instead of a percent when specifying zone IDs in URLs to get around the problem of percent signs being special. According to the reporter, Firefox deals with the URL _with_ a percent letter (which seems like a blatant URL spec violation). See http://curl.haxx.se/bug/view.cgi?id=1371118 26. 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 http://curl.haxx.se/bug/view.cgi?id=1281867 23. SOCKS-related problems: A) libcurl doesn't support SOCKS for IPv6. B) libcurl doesn't support FTPS over a SOCKS proxy. E) libcurl doesn't support active FTP over a SOCKS proxy We probably have even more bugs and lack of features when a SOCKS proxy is used. 22. Sending files to a FTP server using curl on VMS, might lead to curl complaining on "unaligned file size" on completion. The problem is related to VMS file structures and the perceived file sizes stat() returns. A possible fix would involve sending a "STRU VMS" command. http://curl.haxx.se/bug/view.cgi?id=1156287 21. 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. 16. FTP URLs passed to curl may contain NUL (0x00) in the RFC 1738 , , and 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 , 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 , anyway (e.g., UNIX pathnames may not contain NUL). 14. Test case 165 might fail on system which has libidn present, but with an old iconv version (2.1.3 is a known bad version), since it doesn't recognize the charset when named ISO8859-1. Changing the name to ISO-8859-1 makes the test pass, but instead makes it fail on Solaris hosts that use its native iconv. 13. curl version 7.12.2 fails on AIX if compiled with --enable-ares. The workaround is to combine --enable-ares with --disable-shared 12. When connecting to a SOCKS proxy, the (connect) timeout is not properly acknowledged after the actual TCP connect (during the SOCKS "negotiate" phase). 10. To get HTTP Negotiate authentication to work fine, 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. http://curl.haxx.se/bug/view.cgi?id=1004841. How? http://curl.haxx.se/mail/lib-2004-08/0182.html 8. Doing resumed upload over HTTP does not work with '-C -', because curl doesn't do a HEAD first to get the initial size. This needs to be done manually for HTTP PUT resume to work, and then '-C [index]'. 7. CURLOPT_USERPWD and CURLOPT_PROXYUSERPWD have no way of providing user names that contain a colon. This can't be fixed easily in a backwards compatible way without adding new options (and then, they should most probably allow setting user name and password separately). 6. 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). 5. libcurl doesn't treat the content-length of compressed data properly, as it seems HTTP servers send the *uncompressed* length in that header and libcurl thinks of it as the *compressed* length. Some explanations are here: http://curl.haxx.se/mail/lib-2003-06/0146.html 2. If a HTTP server responds to a HEAD request and includes a body (thus violating the RFC2616), curl won't wait to read the response but just stop reading and return back. If a second request (let's assume a GET) is then immediately made to the same server again, the connection will be re-used fine of course, and the second request will be sent off but when the response is to get read, the previous response-body is what curl will read and havoc is what happens. More details on this is found in this libcurl mailing list thread: http://curl.haxx.se/mail/lib-2002-08/0000.html