cURL Docs Known Bugs
This is the document 'docs/KNOWN_BUGS' from the curl release archive.
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! 88. libcurl doesn't support CURLINFO_FILETIME for SFTP transfers and thus curl's -R option also doesn't work then. 87. -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. http://curl.haxx.se/bug/view.cgi?id=1294 86. 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. 85. 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. http://curl.haxx.se/bug/view.cgi?id=1213 84. CURLINFO_SSL_VERIFYRESULT is only implemented for the OpenSSL and NSS backends, so relying on this information in a generic app is flaky. 82. 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. http://curl.haxx.se/bug/view.cgi?id=1222 81. 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! http://curl.haxx.se/bug/view.cgi?id=1169 80. Curl doesn't recognize certificates in DER format in keychain, but it works with PEM. http://curl.haxx.se/bug/view.cgi?id=1065 79. SMTP. 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. http://curl.haxx.se/bug/view.cgi?id=1116 78. curl and libcurl don't always signal the client properly when "sending" zero bytes files - it makes for example the command line client not creating any file at all. Like when using FTP. http://curl.haxx.se/bug/view.cgi?id=1063 76. The SOCKET type in Win64 is 64 bits large (and thus so is curl_socket_t on that platform), and long is only 32 bits. It makes it impossible for curl_easy_getinfo() to return a socket properly with the CURLINFO_LASTSOCKET option as for all other operating systems. 75. 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: http://curl.haxx.se/mail/lib-2009-10/0024.html http://curl.haxx.se/bug/view.cgi?id=896 The WinSSL/schannel version verified to work as mentioned in http://curl.haxx.se/mail/lib-2012-07/0073.html 73. 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: http://curl.haxx.se/bug/view.cgi?id=856 72. "Pausing pipeline problems." http://curl.haxx.se/mail/lib-2009-07/0214.html 70. Problem re-using easy handle after call to curl_multi_remove_handle http://curl.haxx.se/mail/lib-2009-07/0249.html 68. "More questions about ares behavior". http://curl.haxx.se/mail/lib-2009-08/0012.html 67. 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: http://tools.ietf.org/html/draft-reschke-rfc2231-in-http-02 66. When using telnet, the time limitation options don't work. http://curl.haxx.se/bug/view.cgi?id=846 65. 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. 63. When CURLOPT_CONNECT_ONLY is used, the handle cannot reliably be re-used for any further requests or transfers. The work-around is then to close that handle with curl_easy_cleanup() and create a new. Some more details: http://curl.haxx.se/mail/lib-2009-04/0300.html 61. 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:. http://curl.haxx.se/mail/archive-2008-02/0043.html 60. libcurl closes the connection if an HTTP 401 reply is received while it is waiting for the the 100-continue response. http://curl.haxx.se/mail/lib-2008-08/0462.html 58. 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: http://curl.haxx.se/mail/lib-2008-07/0295.html 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=748 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/ 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-negotiated: 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. 43. There seems to be a problem when connecting to the Microsoft telnet server. http://curl.haxx.se/bug/view.cgi?id=649 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=635 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 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=604 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. 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=535 23. SOCKS-related problems: 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. 21. FTP ASCII transfers do not follow RFC959. They don't convert the data accordingly (not for sending nor for receiving). RFC 959 section 188.8.131.52 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 <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). 14. Test case 165 might fail on a 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 (SPNEGO) 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=440 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]'. 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