--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mupdf-source/thirdparty/curl/docs/TODO	Mon Sep 15 11:43:07 2025 +0200
@@ -0,0 +1,1127 @@
+                                  _   _ ____  _
+                              ___| | | |  _ \| |
+                             / __| | | | |_) | |
+                            | (__| |_| |  _ <| |___
+                             \___|\___/|_| \_\_____|
+
+                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!
+
+ Be aware that these are things that we could do, or have once been considered
+ things we could do. If you want to work on any of these areas, please
+ consider bringing it up for discussions first on the mailing list so that we
+ all agree it is still a good idea for the project!
+
+ All bugs documented in the KNOWN_BUGS document are subject for fixing!
+
+ 1. libcurl
+ 1.1 TFO support on Windows
+ 1.3 struct lifreq
+ 1.5 get rid of PATH_MAX
+ 1.7 Support HTTP/2 for HTTP(S) proxies
+ 1.8 CURLOPT_RESOLVE for any port number
+ 1.9 Cache negative name resolves
+ 1.10 auto-detect proxy
+ 1.11 minimize dependencies with dynamically loaded modules
+ 1.12 updated DNS server while running
+ 1.13 c-ares and CURLOPT_OPENSOCKETFUNCTION
+ 1.14 Typesafe curl_easy_setopt()
+ 1.15 Monitor connections in the connection pool
+ 1.16 Try to URL encode given URL
+ 1.17 Add support for IRIs
+ 1.18 try next proxy if one doesn't work
+ 1.20 SRV and URI DNS records
+ 1.22 CURLINFO_PAUSE_STATE
+ 1.23 Offer API to flush the connection pool
+ 1.24 TCP Fast Open for windows
+ 1.25 Expose tried IP addresses that failed
+ 1.27 hardcode the "localhost" addresses
+ 1.28 FD_CLOEXEC
+ 1.29 Upgrade to websockets
+ 1.30 config file parsing
+
+ 2. libcurl - multi interface
+ 2.1 More non-blocking
+ 2.2 Better support for same name resolves
+ 2.3 Non-blocking curl_multi_remove_handle()
+ 2.4 Split connect and authentication process
+ 2.5 Edge-triggered sockets should work
+ 2.6 multi upkeep
+
+ 3. Documentation
+ 3.2 Provide cmake config-file
+
+ 4. FTP
+ 4.1 HOST
+ 4.2 Alter passive/active on failure and retry
+ 4.3 Earlier bad letter detection
+ 4.5 ASCII support
+ 4.6 GSSAPI via Windows SSPI
+ 4.7 STAT for LIST without data connection
+ 4.8 Option to ignore private IP addresses in PASV response
+
+ 5. HTTP
+ 5.1 Better persistency for HTTP 1.0
+ 5.3 Rearrange request header order
+ 5.4 Allow SAN names in HTTP/2 server push
+ 5.5 auth= in URLs
+
+ 6. TELNET
+ 6.1 ditch stdin
+ 6.2 ditch telnet-specific select
+ 6.3 feature negotiation debug data
+
+ 7. SMTP
+ 7.2 Enhanced capability support
+ 7.3 Add CURLOPT_MAIL_CLIENT option
+
+ 8. POP3
+ 8.2 Enhanced capability support
+
+ 9. IMAP
+ 9.1 Enhanced capability support
+
+ 10. LDAP
+ 10.1 SASL based authentication mechanisms
+
+ 11. SMB
+ 11.1 File listing support
+ 11.2 Honor file timestamps
+ 11.3 Use NTLMv2
+ 11.4 Create remote directories
+
+ 12. New protocols
+
+ 13. SSL
+ 13.2 Provide mutex locking API
+ 13.3 Support in-memory certs/ca certs/keys
+ 13.4 Cache/share OpenSSL contexts
+ 13.5 Export session ids
+ 13.6 Provide callback for cert verification
+ 13.7 improve configure --with-ssl
+ 13.8 Support DANE
+ 13.10 Support Authority Information Access certificate extension (AIA)
+ 13.11 Support intermediate & root pinning for PINNEDPUBLICKEY
+ 13.12 Support HSTS
+ 13.14 Support the clienthello extension
+
+ 14. GnuTLS
+ 14.2 check connection
+
+ 15. WinSSL/SChannel
+ 15.1 Add support for client certificate authentication
+ 15.3 Add support for the --ciphers option
+ 15.4 Add option to disable client certificate auto-send
+
+ 16. SASL
+ 16.1 Other authentication mechanisms
+ 16.2 Add QOP support to GSSAPI authentication
+ 16.3 Support binary messages (i.e.: non-base64)
+
+ 17. SSH protocols
+ 17.1 Multiplexing
+ 17.3 Support better than MD5 hostkey hash
+ 17.4 Support CURLOPT_PREQUOTE
+
+ 18. Command line tool
+ 18.1 sync
+ 18.2 glob posts
+ 18.3 prevent file overwriting
+ 18.5 UTF-8 filenames in Content-Disposition
+ 18.7 at least N milliseconds between requests
+ 18.9 Choose the name of file in braces for complex URLs
+ 18.10 improve how curl works in a windows console window
+ 18.11 Windows: set attribute 'archive' for completed downloads
+ 18.12 keep running, read instructions from pipe/socket
+ 18.15 --retry should resume
+ 18.16 send only part of --data
+ 18.17 consider file name from the redirected URL with -O ?
+ 18.18 retry on network is unreachable
+ 18.19 expand ~/ in config files
+ 18.20 host name sections in config files
+
+ 19. Build
+ 19.1 roffit
+ 19.2 Enable PIE and RELRO by default
+ 19.3 cmake test suite improvements
+
+ 20. Test suite
+ 20.1 SSL tunnel
+ 20.2 nicer lacking perl message
+ 20.3 more protocols supported
+ 20.4 more platforms supported
+ 20.5 Add support for concurrent connections
+ 20.6 Use the RFC6265 test suite
+ 20.7 Support LD_PRELOAD on macOS
+
+ 21. Next SONAME bump
+ 21.1 http-style HEAD output for FTP
+ 21.2 combine error codes
+ 21.3 extend CURLOPT_SOCKOPTFUNCTION prototype
+
+ 22. Next major release
+ 22.1 cleanup return codes
+ 22.2 remove obsolete defines
+ 22.3 size_t
+ 22.4 remove several functions
+ 22.5 remove CURLOPT_FAILONERROR
+ 22.7 remove progress meter from libcurl
+ 22.8 remove 'curl_httppost' from public
+
+==============================================================================
+
+1. libcurl
+
+1.1 TFO support on Windows
+
+ TCP Fast Open is supported on several platforms but not on Windows. Work on
+ this was once started but never finished.
+
+ See https://github.com/curl/curl/pull/3378
+
+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.
+
+1.5 get rid of PATH_MAX
+
+ Having code use and rely on PATH_MAX is not nice:
+ https://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html
+
+ Currently the libssh2 SSH based code uses it, 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.
+
+1.7 Support HTTP/2 for HTTP(S) proxies
+
+ Support for doing HTTP/2 to HTTP and HTTPS proxies is still missing.
+
+ See https://github.com/curl/curl/issues/3570
+
+1.8 CURLOPT_RESOLVE for any port number
+
+ This option allows applications to set a replacement IP address for a given
+ host + port pair. Consider making support for providing a replacement address
+ for the host name on all port numbers.
+
+ See https://github.com/curl/curl/issues/1264
+
+1.9 Cache negative name resolves
+
+ A name resolve that has failed is likely to fail when made again within a
+ short period of time. Currently we only cache positive responses.
+
+1.10 auto-detect proxy
+
+ libcurl could be made to detect the system proxy setup automatically and use
+ that. On Windows, macOS and Linux desktops for example.
+
+ The pull-request to use libproxy for this was deferred due to doubts on the
+ reliability of the dependency and how to use it:
+ https://github.com/curl/curl/pull/977
+
+ libdetectproxy is a (C++) library for detecting the proxy on Windows
+ https://github.com/paulharris/libdetectproxy
+
+1.11 minimize dependencies with dynamically loaded modules
+
+ We can create a system with loadable modules/plug-ins, where these modules
+ would be the ones that link to 3rd party libs. That would allow us to avoid
+ having to load ALL dependencies since only the necessary ones for this
+ app/invoke/used protocols would be necessary to load.  See
+ https://github.com/curl/curl/issues/349
+
+1.12 updated DNS server while running
+
+ If /etc/resolv.conf gets updated while a program using libcurl is running, it
+ is may cause name resolves to fail unless res_init() is called. We should
+ consider calling res_init() + retry once unconditionally on all name resolve
+ failures to mitigate against this. Firefox works like that. Note that Windows
+ doesn't have res_init() or an alternative.
+
+ https://github.com/curl/curl/issues/2251
+
+1.13 c-ares and CURLOPT_OPENSOCKETFUNCTION
+
+ curl will create most sockets via the CURLOPT_OPENSOCKETFUNCTION callback and
+ close them with the CURLOPT_CLOSESOCKETFUNCTION callback. However, c-ares
+ does not use those functions and instead opens and closes the sockets
+ itself. This means that when curl passes the c-ares socket to the
+ CURLMOPT_SOCKETFUNCTION it isn't owned by the application like other sockets.
+
+ See https://github.com/curl/curl/issues/2734
+
+1.14 Typesafe curl_easy_setopt()
+
+ One of the most common problems in libcurl using applications is the lack of
+ type checks for curl_easy_setopt() which happens because it accepts varargs
+ and thus can take any type.
+
+ One possible solution to this is to introduce a few different versions of the
+ setopt version for the different kinds of data you can set.
+
+  curl_easy_set_num() - sets a long value
+
+  curl_easy_set_large() - sets a curl_off_t value
+
+  curl_easy_set_ptr() - sets a pointer
+
+  curl_easy_set_cb() - sets a callback PLUS its callback data
+
+1.15 Monitor connections in the connection pool
+
+ libcurl's connection cache or pool holds a number of open connections for the
+ purpose of possible subsequent connection reuse. It may contain a few up to a
+ significant amount of connections. Currently, libcurl leaves all connections
+ as they are and first when a connection is iterated over for matching or
+ reuse purpose it is verified that it is still alive.
+
+ Those connections may get closed by the server side for idleness or they may
+ get a HTTP/2 ping from the peer to verify that they're still alive. By adding
+ monitoring of the connections while in the pool, libcurl can detect dead
+ connections (and close them) better and earlier, and it can handle HTTP/2
+ pings to keep such ones alive even when not actively doing transfers on them.
+
+1.16 Try to URL encode given URL
+
+ Given a URL that for example contains spaces, libcurl could have an option
+ that would try somewhat harder than it does now and convert spaces to %20 and
+ perhaps URL encoded byte values over 128 etc (basically do what the redirect
+ following code already does).
+
+ https://github.com/curl/curl/issues/514
+
+1.17 Add support for IRIs
+
+ IRIs (RFC 3987) allow localized, non-ascii, names in the URL. To properly
+ support this, curl/libcurl would need to translate/encode the given input
+ from the input string encoding into percent encoded output "over the wire".
+
+ To make that work smoothly for curl users even on Windows, curl would
+ probably need to be able to convert from several input encodings.
+
+1.18 try next proxy if one doesn't work
+
+ Allow an application to specify a list of proxies to try, and failing to
+ connect to the first go on and try the next instead until the list is
+ exhausted. Browsers support this feature at least when they specify proxies
+ using PACs.
+
+ https://github.com/curl/curl/issues/896
+
+1.20 SRV and URI DNS records
+
+ Offer support for resolving SRV and URI DNS records for libcurl to know which
+ server to connect to for various protocols (including HTTP!).
+
+1.22 CURLINFO_PAUSE_STATE
+
+ Return information about the transfer's current pause state, in both
+ directions. https://github.com/curl/curl/issues/2588
+
+1.23 Offer API to flush the connection pool
+
+ Sometimes applications want to flush all the existing connections kept alive.
+ An API could allow a forced flush or just a forced loop that would properly
+ close all connections that have been closed by the server already.
+
+1.24 TCP Fast Open for windows
+
+ libcurl supports the CURLOPT_TCP_FASTOPEN option since 7.49.0 for Linux and
+ Mac OS. Windows supports TCP Fast Open starting with Windows 10, version 1607
+ and we should add support for it.
+
+1.25 Expose tried IP addresses that failed
+
+ When libcurl fails to connect to a host, it should be able to offer the
+ application the list of IP addresses that were used in the attempt.
+
+ https://github.com/curl/curl/issues/2126
+
+1.27 hardcode the "localhost" addresses
+
+ There's this new spec getting adopted that says "localhost" should always and
+ unconditionally be a local address and not get resolved by a DNS server. A
+ fine way for curl to fix this would be to simply hard-code the response to
+ 127.0.0.1 and/or ::1 (depending on what IP versions that are requested). This
+ is what the browsers probably will do with this hostname.
+
+ https://bugzilla.mozilla.org/show_bug.cgi?id=1220810
+
+ https://tools.ietf.org/html/draft-ietf-dnsop-let-localhost-be-localhost-02
+
+1.28 FD_CLOEXEC
+
+ It sets the close-on-exec flag for the file descriptor, which causes the file
+ descriptor to be automatically (and atomically) closed when any of the
+ exec-family functions succeed. Should probably be set by default?
+
+ https://github.com/curl/curl/issues/2252
+
+1.29 Upgrade to websockets
+
+ libcurl could offer a smoother path to get to a websocket connection.
+ See https://github.com/curl/curl/issues/3523
+
+ Michael Kaufmann suggestion here:
+ https://curl.haxx.se/video/curlup-2017/2017-03-19_05_Michael_Kaufmann_Websocket_support_for_curl.mp4
+
+1.30 config file parsing
+
+ Consider providing an API, possibly in a separate companion library, for
+ parsing a config file like curl's -K/--config option to allow applications to
+ get the same ability to read curl options from files.
+
+ See https://github.com/curl/curl/issues/3698
+
+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 or the threaded resolver is used
+ - 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 Better support for same name resolves
+
+ If a name resolve has been initiated for name NN and a second easy handle
+ wants to resolve that name as well, make it wait for the first resolve to end
+ up in the cache instead of doing a second separate resolve. This is
+ especially needed when adding many simultaneous handles using the same host
+ name when the DNS resolver can get flooded.
+
+2.3 Non-blocking curl_multi_remove_handle()
+
+ The multi interface has a few API calls that assume a blocking behavior, like
+ add_handle() and remove_handle() which limits what we can do internally. The
+ multi API need to be moved even more into a single function that "drives"
+ everything in a non-blocking manner and signals when something is done. A
+ remove or add would then only ask for the action to get started and then
+ multi_perform() etc still be called until the add/remove is completed.
+
+2.4 Split connect and authentication process
+
+ The multi interface treats the authentication process as part of the connect
+ phase. As such any failures during authentication won't trigger the relevant
+ QUIT or LOGOFF for protocols such as IMAP, POP3 and SMTP.
+
+2.5 Edge-triggered sockets should work
+
+ The multi_socket API should work with edge-triggered socket events. One of
+ the internal actions that need to be improved for this to work perfectly is
+ the 'maxloops' handling in transfer.c:readwrite_data().
+
+2.6 multi upkeep
+
+ In libcurl 7.62.0 we introduced curl_easy_upkeep. It unfortunately only works
+ on easy handles. We should introduces a version of that for the multi handle,
+ and also consider doing "upkeep" automatically on connections in the
+ connection pool when the multi handle is in used.
+
+ See https://github.com/curl/curl/issues/3199
+
+3. Documentation
+
+3.2 Provide cmake config-file
+
+ A config-file package is a set of files provided by us to allow applications
+ to write cmake scripts to find and use libcurl easier. See
+ https://github.com/curl/curl/issues/885
+
+4. FTP
+
+4.1 HOST
+
+ HOST is a command for a client to tell which host name to use, to offer FTP
+ servers named-based virtual hosting:
+
+ https://tools.ietf.org/html/rfc7151
+
+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). https://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.
+
+4.5 ASCII support
+
+ FTP ASCII transfers do not follow RFC959. They don't convert the data
+ accordingly.
+
+4.6 GSSAPI via Windows SSPI
+
+ In addition to currently supporting the SASL GSSAPI mechanism (Kerberos V5)
+ via third-party GSS-API libraries, such as Heimdal or MIT Kerberos, also add
+ support for GSSAPI authentication via Windows SSPI.
+
+4.7 STAT for LIST without data connection
+
+ Some FTP servers allow STAT for listing directories instead of using LIST,
+ and the response is then sent over the control connection instead of as the
+ otherwise usedw data connection: https://www.nsftools.com/tips/RawFTP.htm#STAT
+
+ This is not detailed in any FTP specification.
+
+4.8 Option to ignore private IP addresses in PASV response
+
+ Some servers respond with and some other FTP client implementations can
+ ignore private (RFC 1918 style) IP addresses when received in PASV responses.
+ To consider for libcurl as well. See https://github.com/curl/curl/issues/1455
+
+5. HTTP
+
+5.1 Better persistency for HTTP 1.0
+
+ "Better" support for persistent connections over HTTP 1.0
+ https://curl.haxx.se/bug/feature.cgi?id=1089001
+
+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 Allow SAN names in HTTP/2 server push
+
+ curl only allows HTTP/2 push promise if the provided :authority header value
+ exactly matches the host name given in the URL. It could be extended to allow
+ any name that would match the Subject Alternative Names in the server's TLS
+ certificate.
+
+ See https://github.com/curl/curl/pull/3581
+
+5.5 auth= in URLs
+
+ Add the ability to specify the preferred authentication mechanism to use by
+ using ;auth=<mech> in the login part of the URL.
+
+ For example:
+
+ http://test:pass;auth=NTLM@example.com would be equivalent to specifying
+ --user test:pass;auth=NTLM or --user test:pass --ntlm from the command line.
+
+ Additionally this should be implemented for proxy base URLs as well.
+
+
+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.
+
+
+7. SMTP
+
+7.2 Enhanced capability support
+
+ Add the ability, for an application that uses libcurl, to obtain the list of
+ capabilities returned from the EHLO command.
+
+7.3 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
+ specifying 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:
+ https://curl.haxx.se/mail/lib-2012-05/0178.html
+
+
+8. POP3
+
+8.2 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 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 specifying the security context
+ information ourselves.
+
+11. SMB
+
+11.1 File listing support
+
+Add support for listing the contents of a SMB share. The output should probably
+be the same as/similar to FTP.
+
+11.2 Honor file timestamps
+
+The timestamp of the transferred file should reflect that of the original file.
+
+11.3 Use NTLMv2
+
+Currently the SMB authentication uses NTLMv1.
+
+11.4 Create remote directories
+
+Support for creating remote directories when uploading a file to a directory
+that doesn't exist on the server, just like --ftp-create-dirs.
+
+12. New protocols
+
+13. SSL
+
+13.2 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.
+
+13.3 Support in-memory certs/ca certs/keys
+
+ You can specify the private and public keys for SSH/SSL as file paths. Some
+ programs want to avoid using files and instead just pass them as in-memory
+ data blobs. There's probably a challenge to make this work across the
+ plethory of different TLS and SSH backends that curl supports.
+ https://github.com/curl/curl/issues/2310
+
+13.4 Cache/share 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.
+
+ Technically, the "caching" is probably best implemented by getting added to
+ the share interface so that easy handles who want to and can reuse the
+ context specify that by sharing with the right properties set.
+
+ https://github.com/curl/curl/issues/1110
+
+13.5 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".
+
+13.6 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!
+
+13.7 improve configure --with-ssl
+
+ make the configure --with-ssl option first check for OpenSSL, then GnuTLS,
+ then NSS...
+
+13.8 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.
+ https://www.rfc-editor.org/rfc/rfc6698.txt
+
+ An initial patch was posted by Suresh Krishnaswamy on March 7th 2013
+ (https://curl.haxx.se/mail/lib-2013-03/0075.html) but it was a too simple
+ approach. See Daniel's comments:
+ https://curl.haxx.se/mail/lib-2013-03/0103.html . libunbound may be the
+ correct library to base this development on.
+
+ Björn Stenberg wrote a separate initial take on DANE that was never
+ completed.
+
+13.10 Support Authority Information Access certificate extension (AIA)
+
+ AIA can provide various things like CRLs but more importantly information
+ about intermediate CA certificates that can allow validation path to be
+ fulfilled when the HTTPS server doesn't itself provide them.
+
+ Since AIA is about downloading certs on demand to complete a TLS handshake,
+ it is probably a bit tricky to get done right.
+
+ See https://github.com/curl/curl/issues/2793
+
+13.11 Support intermediate & root pinning for PINNEDPUBLICKEY
+
+ CURLOPT_PINNEDPUBLICKEY does not consider the hashes of intermediate & root
+ certificates when comparing the pinned keys. Therefore it is not compatible
+ with "HTTP Public Key Pinning" as there also intermediate and root certificates
+ can be pinned. This is very useful as it prevents webadmins from "locking
+ themself out of their servers".
+
+ Adding this feature would make curls pinning 100% compatible to HPKP and allow
+ more flexible pinning.
+
+13.12 Support HSTS
+
+ "HTTP Strict Transport Security" is TOFU (trust on first use), time-based
+ features indicated by a HTTP header send by the webserver. It is widely used
+ in browsers and it's purpose is to prevent insecure HTTP connections after
+ a previous HTTPS connection. It protects against SSLStripping attacks.
+
+ Doc: https://developer.mozilla.org/en-US/docs/Web/Security/HTTP_strict_transport_security
+ RFC 6797: https://tools.ietf.org/html/rfc6797
+
+13.14 Support the clienthello extension
+
+ Certain stupid networks and middle boxes have a problem with SSL handshake
+ pakets that are within a certain size range because how that sets some bits
+ that previously (in older TLS version) were not set. The clienthello
+ extension adds padding to avoid that size range.
+
+ https://tools.ietf.org/html/rfc7685
+ https://github.com/curl/curl/issues/2299
+
+14. GnuTLS
+
+14.2 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.
+
+15. WinSSL/SChannel
+
+15.1 Add support for client certificate authentication
+
+ WinSSL/SChannel currently makes use of the OS-level system and user
+ certificate and private key stores. This does not allow the application
+ or the user to supply a custom client certificate using curl or libcurl.
+
+ Therefore support for the existing -E/--cert and --key options should be
+ implemented by supplying a custom certificate to the SChannel APIs, see:
+ - Getting a Certificate for Schannel
+   https://msdn.microsoft.com/en-us/library/windows/desktop/aa375447.aspx
+
+15.3 Add support for the --ciphers option
+
+ The cipher suites used by WinSSL/SChannel are configured on an OS-level
+ instead of an application-level. This does not allow the application or
+ the user to customize the configured cipher suites using curl or libcurl.
+
+ Therefore support for the existing --ciphers option should be implemented
+ by mapping the OpenSSL/GnuTLS cipher suites to the SChannel APIs, see
+ - Specifying Schannel Ciphers and Cipher Strengths
+   https://msdn.microsoft.com/en-us/library/windows/desktop/aa380161.aspx
+
+15.4 Add option to disable client certificate auto-send
+
+ Microsoft says "By default, Schannel will, with no notification to the client,
+ attempt to locate a client certificate and send it to the server." That could
+ be considered a privacy violation and unexpected.
+
+ Some Windows users have come to expect that default behavior and to change the
+ default to make it consistent with other SSL backends would be a breaking
+ change. An option should be added that can be used to disable the default
+ Schannel auto-send behavior.
+
+ https://github.com/curl/curl/issues/2262
+
+16. SASL
+
+16.1 Other authentication mechanisms
+
+ Add support for other authentication mechanisms such as OLP,
+ GSS-SPNEGO and others.
+
+16.2 Add QOP support to GSSAPI authentication
+
+ Currently the GSSAPI authentication only supports the default QOP of auth
+ (Authentication), whilst Kerberos V5 supports both auth-int (Authentication
+ with integrity protection) and auth-conf (Authentication with integrity and
+ privacy protection).
+
+16.3 Support binary messages (i.e.: non-base64)
+
+  Mandatory to support LDAP SASL authentication.
+
+
+17. SSH protocols
+
+17.1 Multiplexing
+
+ SSH is a perfectly fine multiplexed protocols which would allow libcurl to do
+ multiple parallel transfers from the same host using the same connection,
+ much in the same spirit as HTTP/2 does. libcurl however does not take
+ advantage of that ability but will instead always create a new connection for
+ new transfers even if an existing connection already exists to the host.
+
+ To fix this, libcurl would have to detect an existing connection and "attach"
+ the new transfer to the existing one.
+
+17.3 Support better than MD5 hostkey hash
+
+ libcurl offers the CURLOPT_SSH_HOST_PUBLIC_KEY_MD5 option for verifying the
+ server's key. MD5 is generally being deprecated so we should implement
+ support for stronger hashing algorithms. libssh2 itself is what provides this
+ underlying functionality and it supports at least SHA-1 as an alternative.
+ SHA-1 is also being deprecated these days so we should consider working with
+ libssh2 to instead offer support for SHA-256 or similar.
+
+17.4 Support CURLOPT_PREQUOTE
+
+ The two other QUOTE options are supported for SFTP, but this was left out for
+ unknown reasons!
+
+18. Command line tool
+
+18.1 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.
+
+18.2 glob posts
+
+ Globbing support for -d and -F, as in 'curl -d "name=foo[0-9]" URL'.
+ This is easily scripted though.
+
+18.3 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.
+
+18.5 UTF-8 filenames in Content-Disposition
+
+ RFC 6266 documents how UTF-8 names can be passed to a client in the
+ Content-Disposition header, and curl does not support this.
+
+ https://github.com/curl/curl/issues/1888
+
+18.7 at least N milliseconds between requests
+
+ Allow curl command lines issue a lot of request against services that limit
+ users to no more than N requests/second or similar. Could be implemented with
+ an option asking that at least a certain time has elapsed since the previous
+ request before the next one will be performed. Example:
+
+    $ curl "https://example.com/api?input=[1-1000]" -d yadayada --after 500
+
+ See https://github.com/curl/curl/issues/3920
+
+18.9 Choose the name of file in braces for complex URLs
+
+ When using braces to download a list of URLs and you use complicated names
+ in the list of alternatives, it could be handy to allow curl to use other
+ names when saving.
+
+ Consider a way to offer that. Possibly like
+ {partURL1:name1,partURL2:name2,partURL3:name3} where the name following the
+ colon is the output name.
+
+ See https://github.com/curl/curl/issues/221
+
+18.10 improve how curl works in a windows console window
+
+ If you pull the scrollbar when transferring with curl in a Windows console
+ window, the transfer is interrupted and can get disconnected. This can
+ probably be improved. See https://github.com/curl/curl/issues/322
+
+18.11 Windows: set attribute 'archive' for completed downloads
+
+ The archive bit (FILE_ATTRIBUTE_ARCHIVE, 0x20) separates files that shall be
+ backed up from those that are either not ready or have not changed.
+
+ Downloads in progress are neither ready to be backed up, nor should they be
+ opened by a different process. Only after a download has been completed it's
+ sensible to include it in any integer snapshot or backup of the system.
+
+ See https://github.com/curl/curl/issues/3354
+
+18.12 keep running, read instructions from pipe/socket
+
+ Provide an option that makes curl not exit after the last URL (or even work
+ without a given URL), and then make it read instructions passed on a pipe or
+ over a socket to make further instructions so that a second subsequent curl
+ invoke can talk to the still running instance and ask for transfers to get
+ done, and thus maintain its connection pool, DNS cache and more.
+
+18.15 --retry should resume
+
+ When --retry is used and curl actually retries transfer, it should use the
+ already transferred data and do a resumed transfer for the rest (when
+ possible) so that it doesn't have to transfer the same data again that was
+ already transferred before the retry.
+
+ See https://github.com/curl/curl/issues/1084
+
+18.16 send only part of --data
+
+ When the user only wants to send a small piece of the data provided with
+ --data or --data-binary, like when that data is a huge file, consider a way
+ to specify that curl should only send a piece of that. One suggested syntax
+ would be: "--data-binary @largefile.zip!1073741823-2147483647".
+
+ See https://github.com/curl/curl/issues/1200
+
+18.17 consider file name from the redirected URL with -O ?
+
+ When a user gives a URL and uses -O, and curl follows a redirect to a new
+ URL, the file name is not extracted and used from the newly redirected-to URL
+ even if the new URL may have a much more sensible file name.
+
+ This is clearly documented and helps for security since there's no surprise
+ to users which file name that might get overwritten. But maybe a new option
+ could allow for this or maybe -J should imply such a treatment as well as -J
+ already allows for the server to decide what file name to use so it already
+ provides the "may overwrite any file" risk.
+
+ This is extra tricky if the original URL has no file name part at all since
+ then the current code path will error out with an error message, and we can't
+ *know* already at that point if curl will be redirected to a URL that has a
+ file name...
+
+ See https://github.com/curl/curl/issues/1241
+
+18.18 retry on network is unreachable
+
+ The --retry option retries transfers on "transient failures". We later added
+ --retry-connrefused to also retry for "connection refused" errors.
+
+ Suggestions have been brought to also allow retry on "network is unreachable"
+ errors and while totally reasonable, maybe we should consider a way to make
+ this more configurable than to add a new option for every new error people
+ want to retry for?
+
+ https://github.com/curl/curl/issues/1603
+
+18.19 expand ~/ in config files
+
+ For example .curlrc could benefit from being able to do this.
+
+ See https://github.com/curl/curl/issues/2317
+
+18.20 host name sections in config files
+
+ config files would be more powerful if they could set different
+ configurations depending on used URLs, host name or possibly origin. Then a
+ default .curlrc could a specific user-agent only when doing requests against
+ a certain site.
+
+
+19. Build
+
+19.1 roffit
+
+ Consider extending 'roffit' to produce decent ASCII output, and use that
+ instead of (g)nroff when building src/tool_hugehelp.c
+
+19.2 Enable PIE and RELRO by default
+
+ Especially when having programs that execute curl via the command line, PIE
+ renders the exploitation of memory corruption vulnerabilities a lot more
+ difficult. This can be attributed to the additional information leaks being
+ required to conduct a successful attack. RELRO, on the other hand, masks
+ different binary sections like the GOT as read-only and thus kills a handful
+ of techniques that come in handy when attackers are able to arbitrarily
+ overwrite memory. A few tests showed that enabling these features had close
+ to no impact, neither on the performance nor on the general functionality of
+ curl.
+
+19.3 cmake test suite improvements
+
+ The cmake build doesn't support 'make show' so it doesn't know which tests
+ are in the makefile or not (making appveyor builds do many false warnings
+ about it) nor does it support running the test suite if building out-of-tree.
+
+ See https://github.com/curl/curl/issues/3109
+
+20. Test suite
+
+20.1 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
+
+20.2 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.
+
+20.3 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).
+
+20.4 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.
+
+20.5 Add support for concurrent connections
+
+ Tests 836, 882 and 938 were designed to verify that separate connections
+ aren't used when using different login credentials in protocols that
+ shouldn't re-use a connection under such circumstances.
+
+ Unfortunately, ftpserver.pl doesn't appear to support multiple concurrent
+ connections. The read while() loop seems to loop until it receives a
+ disconnect from the client, where it then enters the waiting for connections
+ loop. When the client opens a second connection to the server, the first
+ connection hasn't been dropped (unless it has been forced - which we
+ shouldn't do in these tests) and thus the wait for connections loop is never
+ entered to receive the second connection.
+
+20.6 Use the RFC6265 test suite
+
+ A test suite made for HTTP cookies (RFC 6265) by Adam Barth is available at
+ https://github.com/abarth/http-state/tree/master/tests
+
+ It'd be really awesome if someone would write a script/setup that would run
+ curl with that test suite and detect deviances. Ideally, that would even be
+ incorporated into our regular test suite.
+
+20.7 Support LD_PRELOAD on macOS
+
+ LD_RELOAD doesn't work on macOS, but there are tests which require it to run
+ properly. Look into making the preload support in runtests.pl portable such
+ that it uses DYLD_INSERT_LIBRARIES on macOS.
+
+21. Next SONAME bump
+
+21.1 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
+
+21.2 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
+
+21.3 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.
+
+22. Next major release
+
+22.1 cleanup return codes
+
+ curl_easy_cleanup() returns void, but curl_multi_cleanup() returns a
+ CURLMcode. These should be changed to be the same.
+
+22.2 remove obsolete defines
+
+ remove obsolete defines from curl/curl.h
+
+22.3 size_t
+
+ make several functions use size_t instead of int in their APIs
+
+22.4 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
+
+22.5 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.
+
+22.7 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.
+
+22.8 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 maintaining a solid API and ABI.