[platform/upstream/curl.git] / docs / TODO

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                Things that could be nice to do in the future

 Things to do in project cURL. Please tell us what you think, contribute and
 send us patches that improve things!

 All bugs documented in the KNOWN_BUGS document are subject for fixing!

 1. libcurl
 1.2 More data sharing
 1.3 struct lifreq
 1.4 signal-based resolver timeouts
 1.5 get rid of PATH_MAX
 1.6 Happy Eyeball dual stack connect
 1.7 Modified buffer size approach

 2. libcurl - multi interface
 2.1 More non-blocking
 2.2 Fix HTTP Pipelining for PUT

 3. Documentation
 3.1  More and better

 4. FTP
 4.1 HOST
 4.2 Alter passive/active on failure and retry
 4.3 Earlier bad letter detection
 4.4 REST for large files
 4.5 FTP proxy support
 4.6 ASCII support

 5. HTTP
 5.1 Better persistency for HTTP 1.0
 5.2 support FF3 sqlite cookie files
 5.3 Rearrange request header order
 5.4 HTTP2/SPDY

 6. TELNET
 6.1 ditch stdin
 6.2 ditch telnet-specific select
 6.3 feature negotiation debug data
 6.4 send data in chunks

 7. SMTP
 7.1 Pipelining
 7.2 Graceful base64 decoding failure
 7.3 Enhanced capability support
 
 8. POP3
 8.1 Pipelining
 8.2 Graceful base64 decoding failure
 8.3 Enhanced capability support
 
 9. IMAP
 9.1 Graceful base64 decoding failure
 9.2 Enhanced capability support
 
 10. LDAP
 10.1 SASL based authentication mechanisms
 
 11. New protocols
 11.1 RSYNC

 12. SSL
 12.1 Disable specific versions
 12.2 Provide mutex locking API
 12.3 Evaluate SSL patches
 12.4 Cache OpenSSL contexts
 12.5 Export session ids
 12.6 Provide callback for cert verification
 12.7 Support other SSL libraries
 12.8 improve configure --with-ssl
 12.9 Support DANE

 13. GnuTLS
 13.1 SSL engine stuff
 13.2 check connection

 14. SASL
 14.1 Other authentication mechanisms
 
 15. Client
 15.1 sync
 15.2 glob posts
 15.3 prevent file overwriting
 15.4 simultaneous parallel transfers
 15.5 provide formpost headers
 15.6 url-specific options
 15.7 warning when setting an option
 15.8 IPv6 addresses with globbing

 16. Build
 16.1 roffit

 17. Test suite
 17.1 SSL tunnel
 17.2 nicer lacking perl message
 17.3 more protocols supported
 17.4 more platforms supported

 18. Next SONAME bump
 18.1 http-style HEAD output for ftp
 18.2 combine error codes
 18.3 extend CURLOPT_SOCKOPTFUNCTION prototype

 19. Next major release
 19.1 cleanup return codes
 19.2 remove obsolete defines
 19.3 size_t
 19.4 remove several functions
 19.5 remove CURLOPT_FAILONERROR
 19.6 remove CURLOPT_DNS_USE_GLOBAL_CACHE
 19.7 remove progress meter from libcurl
 19.8 remove 'curl_httppost' from public
 19.9 have form functions use CURL handle argument
 19.10 Add CURLOPT_MAIL_CLIENT option

==============================================================================

1. libcurl

1.2 More data sharing

 curl_share_* functions already exist and work, and they can be extended to
 share more. For example, enable sharing of the ares channel and the
 connection cache.

1.3 struct lifreq

 Use 'struct lifreq' and SIOCGLIFADDR instead of 'struct ifreq' and
 SIOCGIFADDR on newer Solaris versions as they claim the latter is obsolete.
 To support ipv6 interface addresses for network interfaces properly.

1.4 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 http://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.

1.5 get rid of PATH_MAX

 Having code use and rely on PATH_MAX is not nice:
 http://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html

 Currently the SSH based code uses it a bit, but to remove PATH_MAX from there
 we need libssh2 to properly tell us when we pass in a too small buffer and
 its current API (as of libssh2 1.2.7) doesn't.

1.6 Happy Eyeball dual stack connect

 In order to make alternative technologies not suffer when transitioning, like
 when introducing IPv6 as an alternative to IPv4 and there are more than one
 option existing simultaneously there are reasons to reconsider internal
 choices.

 To make libcurl do blazing fast IPv6 in a dual-stack configuration, this needs
 to be addressed:

    http://tools.ietf.org/html/rfc6555

1.7 Modified buffer size approach

 Current libcurl allocates a fixed 16K size buffer for download and an
 additional 16K for upload. They are always unconditionally part of the easy
 handle. If CRLF translations are requested, an additional 32K "scratch
 buffer" is allocated. A total of 64K transfer buffers in the worst case.

 First, while the handles are not actually in use these buffers could be freed
 so that lingering handles just kept in queues or whatever waste less memory.

 Secondly, SFTP is a protocol that needs to handle many ~30K blocks at once
 since each need to be individually acked and therefore libssh2 must be
 allowed to send (or receive) many separate ones in parallel to achieve high
 transfer speeds. A current libcurl build with a 16K buffer makes that
 impossible, but one with a 512K buffer will reach MUCH faster transfers. But
 allocating 512K unconditionally for all buffers just in case they would like
 to do fast SFTP transfers at some point is not a good solution either.

 Dynamically allocate buffer size depending on protocol in use in combination
 with freeing it after each individual transfer? Other suggestions?


2. libcurl - multi interface

2.1 More non-blocking

 Make sure we don't ever loop because of non-blocking sockets returning
 EWOULDBLOCK or similar. Blocking cases include:

 - Name resolves on non-windows unless c-ares is used
 - NSS SSL connections
 - HTTP proxy CONNECT operations
 - SOCKS proxy handshakes
 - file:// transfers
 - TELNET transfers
 - The "DONE" operation (post transfer protocol-specific actions) for the
   protocols SFTP, SMTP, FTP. Fixing Curl_done() for this is a worthy task.

2.2 Fix HTTP Pipelining for PUT

 HTTP Pipelining can be a way to greatly enhance performance for multiple
 serial requests and currently libcurl only supports that for HEAD and GET
 requests but it should also be possible for PUT.

3. Documentation

3.1  More and better

 Exactly

4. FTP

4.1 HOST

 HOST is a suggested command in the works for a client to tell which host name
 to use, to offer FTP servers named-based virtual hosting:

 http://tools.ietf.org/html/draft-hethmon-mcmurray-ftp-hosts-11

4.2 Alter passive/active on failure and retry

 When trying to connect passively to a server which only supports active
 connections, libcurl returns CURLE_FTP_WEIRD_PASV_REPLY and closes the
 connection. There could be a way to fallback to an active connection (and
 vice versa). http://curl.haxx.se/bug/feature.cgi?id=1754793

4.3 Earlier bad letter detection

 Make the detection of (bad) %0d and %0a codes in FTP url parts earlier in the
 process to avoid doing a resolve and connect in vain.

4.4 REST for large files

 REST fix for servers not behaving well on >2GB requests. This should fail if
 the server doesn't set the pointer to the requested index. The tricky
 (impossible?) part is to figure out if the server did the right thing or not.

4.5 FTP proxy support

 Support the most common FTP proxies, Philip Newton provided a list allegedly
 from ncftp. This is not a subject without debate, and is probably not really
 suitable for libcurl.  http://curl.haxx.se/mail/archive-2003-04/0126.html

4.6 ASCII support

 FTP ASCII transfers do not follow RFC959. They don't convert the data
 accordingly.

5. HTTP

5.1 Better persistency for HTTP 1.0

 "Better" support for persistent connections over HTTP 1.0
 http://curl.haxx.se/bug/feature.cgi?id=1089001

5.2 support FF3 sqlite cookie files

 Firefox 3 is changing from its former format to a a sqlite database instead.
 We should consider how (lib)curl can/should support this.
 http://curl.haxx.se/bug/feature.cgi?id=1871388

5.3 Rearrange request header order

 Server implementors often make an effort to detect browser and to reject
 clients it can detect to not match. One of the last details we cannot yet
 control in libcurl's HTTP requests, which also can be exploited to detect
 that libcurl is in fact used even when it tries to impersonate a browser, is
 the order of the request headers. I propose that we introduce a new option in
 which you give headers a value, and then when the HTTP request is built it
 sorts the headers based on that number. We could then have internally created
 headers use a default value so only headers that need to be moved have to be
 specified.

5.4 HTTP2/SPDY

 The first drafts for HTTP2 have been published
 (http://tools.ietf.org/html/draft-ietf-httpbis-http2-03) and is so far based
 on SPDY (http://www.chromium.org/spdy) designs and experiences. Chances are
 it will end up in that style. Chrome and Firefox already support SPDY and
 lots of web services do.

 It would make sense to implement SPDY support now and later transition into
 or add HTTP2 support as well.

 We should base or HTTP2/SPDY work on a 3rd party library for the protocol
 fiddling. The Spindy library (http://spindly.haxx.se/) was an attempt to make
 such a library with an API suitable for use by libcurl but that effort has
 more or less stalled.  spdylay (https://github.com/tatsuhiro-t/spdylay) may
 be a better option, either used directly or wrapped with a more spindly-like
 API.


6. TELNET

6.1 ditch stdin

Reading input (to send to the remote server) on stdin is a crappy solution for
library purposes. We need to invent a good way for the application to be able
to provide the data to send.

6.2 ditch telnet-specific select

 Move the telnet support's network select() loop go away and merge the code
 into the main transfer loop. Until this is done, the multi interface won't
 work for telnet.

6.3 feature negotiation debug data

  Add telnet feature negotiation data to the debug callback as header data.

6.4 send data in chunks

  Currently, telnet sends data one byte at a time.  This is fine for interactive
  use, but inefficient for any other.  Sent data should be sent in larger
  chunks.

7. SMTP

7.1 Pipelining

 Add support for pipelining emails.

7.2 Graceful base64 decoding failure

 Rather than shutting down the session and returning an error when the
 decoding of a base64 encoded authentication response fails, we should
 gracefully shutdown the authentication process by sending a * response to the
 server as per RFC4954.

7.3 Enhanced capability support

 Add the ability, for an application that uses libcurl, to obtain the list of
 capabilities returned from the EHLO command.

8. POP3

8.1 Pipelining

 Add support for pipelining commands.

8.2 Graceful base64 decoding failure

 Rather than shutting down the session and returning an error when the
 decoding of a base64 encoded authentication response fails, we should
 gracefully shutdown the authentication process by sending a * response to the
 server as per RFC5034.
 
8.3 Enhanced capability support

 Add the ability, for an application that uses libcurl, to obtain the list of
 capabilities returned from the CAPA command.

9. IMAP

9.1 Graceful base64 decoding failure

 Rather than shutting down the session and returning an error when the
 decoding of a base64 encoded authentication response fails, we should
 gracefully shutdown the authentication process by sending a * response to the
 server as per RFC3501.

9.2 Enhanced capability support

 Add the ability, for an application that uses libcurl, to obtain the list of
 capabilities returned from the CAPABILITY command.

10. LDAP

10.1 SASL based authentication mechanisms

 Currently the LDAP module only supports ldap_simple_bind_s() in order to bind
 to an LDAP server. However, this function sends username and password details
 using the simple authentication mechanism (as clear text). However, it should
 be possible to use ldap_bind_s() instead specifing the security context
 information ourselves.

11. New protocols

11.1 RSYNC

 There's no RFC for the protocol or an URI/URL format.  An implementation
 should most probably use an existing rsync library, such as librsync.

12. SSL

12.1 Disable specific versions

 Provide an option that allows for disabling specific SSL versions, such as
 SSLv2 http://curl.haxx.se/bug/feature.cgi?id=1767276

12.2 Provide mutex locking API

 Provide a libcurl API for setting mutex callbacks in the underlying SSL
 library, so that the same application code can use mutex-locking
 independently of OpenSSL or GnutTLS being used.

12.3 Evaluate SSL patches

 Evaluate/apply Gertjan van Wingerde's SSL patches:
 http://curl.haxx.se/mail/lib-2004-03/0087.html

12.4 Cache OpenSSL contexts

 "Look at SSL cafile - quick traces look to me like these are done on every
 request as well, when they should only be necessary once per ssl context (or
 once per handle)". The major improvement we can rather easily do is to make
 sure we don't create and kill a new SSL "context" for every request, but
 instead make one for every connection and re-use that SSL context in the same
 style connections are re-used. It will make us use slightly more memory but
 it will libcurl do less creations and deletions of SSL contexts.

12.5 Export session ids

 Add an interface to libcurl that enables "session IDs" to get
 exported/imported. Cris Bailiff said: "OpenSSL has functions which can
 serialise the current SSL state to a buffer of your choice, and recover/reset
 the state from such a buffer at a later date - this is used by mod_ssl for
 apache to implement and SSL session ID cache".

12.6 Provide callback for cert verification

 OpenSSL supports a callback for customised verification of the peer
 certificate, but this doesn't seem to be exposed in the libcurl APIs. Could
 it be? There's so much that could be done if it were!

12.7 Support other SSL libraries

 Make curl's SSL layer capable of using other free SSL libraries.  Such as
 MatrixSSL (http://www.matrixssl.org/).

12.8 improve configure --with-ssl

 make the configure --with-ssl option first check for OpenSSL, then GnuTLS,
 then NSS...

12.9 Support DANE

 DNS-Based Authentication of Named Entities (DANE) is a way to provide SSL
 keys and certs over DNS using DNSSEC as an alternative to the CA model.
 http://www.rfc-editor.org/rfc/rfc6698.txt

 An initial patch was posted by Suresh Krishnaswamy on March 7th 2013
 (http://curl.haxx.se/mail/lib-2013-03/0075.html) but it was a too simple
 approach. See Daniel's comments:
 http://curl.haxx.se/mail/lib-2013-03/0103.html . libunbound may be the
 correct library to base this development on.

13. GnuTLS

13.1 SSL engine stuff

 Is this even possible?

13.2 check connection

 Add a way to check if the connection seems to be alive, to correspond to the
 SSL_peak() way we use with OpenSSL.

14. SASL

14.1 Other authentication mechanisms

 Add support for GSSAPI to SMTP, POP3 and IMAP.

15. Client

15.1 sync

 "curl --sync http://example.com/feed[1-100].rss" or
 "curl --sync http://example.net/{index,calendar,history}.html"

 Downloads a range or set of URLs using the remote name, but only if the
 remote file is newer than the local file. A Last-Modified HTTP date header
 should also be used to set the mod date on the downloaded file.

15.2 glob posts

 Globbing support for -d and -F, as in 'curl -d "name=foo[0-9]" URL'.
 This is easily scripted though.

15.3 prevent file overwriting

 Add an option that prevents cURL from overwriting existing local files. When
 used, and there already is an existing file with the target file name
 (either -O or -o), a number should be appended (and increased if already
 existing). So that index.html becomes first index.html.1 and then
 index.html.2 etc.

15.4 simultaneous parallel transfers

 The client could be told to use maximum N simultaneous parallel transfers and
 then just make sure that happens. It should of course not make more than one
 connection to the same remote host. This would require the client to use the
 multi interface. http://curl.haxx.se/bug/feature.cgi?id=1558595

15.5 provide formpost headers

 Extending the capabilities of the multipart formposting. How about leaving
 the ';type=foo' syntax as it is and adding an extra tag (headers) which
 works like this: curl -F "coolfiles=@fil1.txt;headers=@fil1.hdr" where
 fil1.hdr contains extra headers like

   Content-Type: text/plain; charset=KOI8-R"
   Content-Transfer-Encoding: base64
   X-User-Comment: Please don't use browser specific HTML code

 which should overwrite the program reasonable defaults (plain/text,
 8bit...)

15.6 url-specific options

 Provide a way to make options bound to a specific URL among several on the
 command line. Possibly by letting ':' separate options between URLs,
 similar to this:

    curl --data foo --url url.com : \
        --url url2.com : \
        --url url3.com --data foo3

 (More details: http://curl.haxx.se/mail/archive-2004-07/0133.html)

 The example would do a POST-GET-POST combination on a single command line.

15.7 warning when setting an option

  Display a warning when libcurl returns an error when setting an option.
  This can be useful to tell when support for a particular feature hasn't been
  compiled into the library.

15.8 IPv6 addresses with globbing

  Currently the command line client needs to get url globbing disabled (with
  -g) for it to support IPv6 numerical addresses. This is a rather silly flaw
  that should be corrected. It probably involves a smarter detection of the
  '[' and ']' letters.

16. Build

16.1 roffit

 Consider extending 'roffit' to produce decent ASCII output, and use that
 instead of (g)nroff when building src/tool_hugehelp.c

17. Test suite

17.1 SSL tunnel

 Make our own version of stunnel for simple port forwarding to enable HTTPS
 and FTP-SSL tests without the stunnel dependency, and it could allow us to
 provide test tools built with either OpenSSL or GnuTLS

17.2 nicer lacking perl message

 If perl wasn't found by the configure script, don't attempt to run the tests
 but explain something nice why it doesn't.

17.3 more protocols supported

 Extend the test suite to include more protocols. The telnet could just do ftp
 or http operations (for which we have test servers).

17.4 more platforms supported

 Make the test suite work on more platforms. OpenBSD and Mac OS. Remove
 fork()s and it should become even more portable.

18. Next SONAME bump

18.1 http-style HEAD output for ftp

 #undef CURL_FTP_HTTPSTYLE_HEAD in lib/ftp.c to remove the HTTP-style headers
 from being output in NOBODY requests over ftp

18.2 combine error codes

 Combine some of the error codes to remove duplicates.  The original
 numbering should not be changed, and the old identifiers would be
 macroed to the new ones in an CURL_NO_OLDIES section to help with
 backward compatibility.

 Candidates for removal and their replacements:

    CURLE_FILE_COULDNT_READ_FILE => CURLE_REMOTE_FILE_NOT_FOUND

    CURLE_FTP_COULDNT_RETR_FILE => CURLE_REMOTE_FILE_NOT_FOUND

    CURLE_FTP_COULDNT_USE_REST => CURLE_RANGE_ERROR

    CURLE_FUNCTION_NOT_FOUND => CURLE_FAILED_INIT

    CURLE_LDAP_INVALID_URL => CURLE_URL_MALFORMAT

    CURLE_TFTP_NOSUCHUSER => CURLE_TFTP_ILLEGAL

    CURLE_TFTP_NOTFOUND => CURLE_REMOTE_FILE_NOT_FOUND

    CURLE_TFTP_PERM => CURLE_REMOTE_ACCESS_DENIED

18.3 extend CURLOPT_SOCKOPTFUNCTION prototype

 The current prototype only provides 'purpose' that tells what the
 connection/socket is for, but not any protocol or similar. It makes it hard
 for applications to differentiate on TCP vs UDP and even HTTP vs FTP and
 similar.

10. Next major release

19.1 cleanup return codes

 curl_easy_cleanup() returns void, but curl_multi_cleanup() returns a
 CURLMcode. These should be changed to be the same.

19.2 remove obsolete defines

 remove obsolete defines from curl/curl.h

19.3 size_t

 make several functions use size_t instead of int in their APIs

19.4 remove several functions

 remove the following functions from the public API:

 curl_getenv

 curl_mprintf (and variations)

 curl_strequal

 curl_strnequal

 They will instead become curlx_ - alternatives. That makes the curl app
 still capable of using them, by building with them from source.

 These functions have no purpose anymore:

 curl_multi_socket

 curl_multi_socket_all

19.5 remove CURLOPT_FAILONERROR

 Remove support for CURLOPT_FAILONERROR, it has gotten too kludgy and weird
 internally. Let the app judge success or not for itself.

19.6 remove CURLOPT_DNS_USE_GLOBAL_CACHE

 Remove support for a global DNS cache. Anything global is silly, and we
 already offer the share interface for the same functionality but done
 "right".

19.7 remove progress meter from libcurl

 The internally provided progress meter output doesn't belong in the library.
 Basically no application wants it (apart from curl) but instead applications
 can and should do their own progress meters using the progress callback.

 The progress callback should then be bumped as well to get proper 64bit
 variable types passed to it instead of doubles so that big files work
 correctly.

19.8 remove 'curl_httppost' from public

 curl_formadd() was made to fill in a public struct, but the fact that the
 struct is public is never really used by application for their own advantage
 but instead often restricts how the form functions can or can't be modified.

 Changing them to return a private handle will benefit the implementation and
 allow us much greater freedoms while still maintining a solid API and ABI.

19.9 have form functions use CURL handle argument

 curl_formadd() and curl_formget() both currently have no CURL handle
 argument, but both can use a callback that is set in the easy handle, and
 thus curl_formget() with callback cannot function without first having
 curl_easy_perform() (or similar) called - which is hard to grasp and a design
 mistake.

19.10 Add CURLOPT_MAIL_CLIENT option

 Rather than use the URL to specify the mail client string to present in the
 HELO and EHLO commands, libcurl should support a new CURLOPT specifically for
 specifing this data as the URL is non-standard and to be honest a bit of a
 hack ;-)

 Please see the following thread for more information:
 http://curl.haxx.se/mail/lib-2012-05/0178.html