TODO -- nice to have features
libcurl
1.1 TFO support on Windows
1.2 Consult %APPDATA% also for .netrc
1.3 struct lifreq
1.4 alt-svc sharing
1.5 get rid of PATH_MAX
1.6 thread-safe sharing
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 connect to multiple IPs in parallel
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 does not work
1.19 provide timing info for each redirect
1.20 SRV and URI DNS records
1.21 netrc caching and sharing
1.22 CURLINFO_PAUSE_STATE
1.23 Offer API to flush the connection pool
1.25 Expose tried IP addresses that failed
1.28 FD_CLOEXEC
1.29 WebSocket read callback
1.30 config file parsing
1.31 erase secrets from heap/stack after use
1.32 add asynch getaddrinfo support
1.33 make DoH inherit more transfer properties
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
2.7 Virtual external sockets
2.8 dynamically decide to use socketpair
Documentation
3.1 Improve documentation about fork safety
FTP
4.1 HOST
4.4 Support CURLOPT_PREQUOTE for directories listings
4.6 GSSAPI via Windows SSPI
4.7 STAT for LIST without data connection
4.8 Passive transfer could try other IP addresses
HTTP
5.1 Provide the error body from a CONNECT response
5.2 Obey Retry-After in redirects
5.3 Rearrange request header order
5.4 Allow SAN names in HTTP/2 server push
5.5 auth= in URLs
5.6 alt-svc should fallback if alt-svc does not work
5.7 Require HTTP version X or higher
TELNET
6.1 ditch stdin
6.2 ditch telnet-specific select
6.3 feature negotiation debug data
6.4 exit immediately upon connection if stdin is /dev/null
SMTP
7.1 Passing NOTIFY option to CURLOPT_MAIL_RCPT
7.2 Enhanced capability support
7.3 Add CURLOPT_MAIL_CLIENT option
POP3
8.2 Enhanced capability support
IMAP
9.1 Enhanced capability support
9.2 upload unread
LDAP
10.1 SASL based authentication mechanisms
10.2 CURLOPT_SSL_CTX_FUNCTION for LDAPS
10.3 Paged searches on LDAP server
10.4 Certificate-Based Authentication
SMB
11.1 File listing support
11.2 Honor file timestamps
11.3 Use NTLMv2
11.4 Create remote directories
FILE
12.1 Directory listing on non-POSIX
TLS
13.1 TLS-PSK with OpenSSL
13.2 TLS channel binding
13.3 Defeat TLS fingerprinting
13.4 Consider OCSP stapling by default
13.5 Export session ids
13.6 Provide callback for cert verification
13.7 Less memory massaging with Schannel
13.8 Support DANE
13.9 TLS record padding
13.10 Support Authority Information Access certificate extension (AIA)
13.11 Some TLS options are not offered for HTTPS proxies
13.13 Make sure we forbid TLS 1.3 post-handshake authentication
13.14 Support the clienthello extension
13.15 Select signature algorithms
13.16 Share the CA cache
13.17 Add missing features to TLS backends
Schannel
15.1 Extend support for client certificate authentication
15.2 Extend support for the --ciphers option
15.4 Add option to allow abrupt server closure
SASL
16.1 Other authentication mechanisms
16.2 Add QOP support to GSSAPI authentication
SSH protocols
17.1 Multiplexing
17.2 Handle growing SFTP files
17.3 Read keys from ~/.ssh/id_ecdsa, id_ed25519
17.4 Support CURLOPT_PREQUOTE
17.5 SSH over HTTPS proxy with more backends
17.6 SFTP with SCP://
Command line tool
18.1 sync
18.2 glob posts
18.4 --proxycommand
18.5 UTF-8 filenames in Content-Disposition
18.6 Option to make -Z merge lined based outputs on stdout
18.7 specify which response codes that make -f/--fail return error
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
18.13 Acknowledge Ratelimit headers
18.14 --dry-run
18.15 --retry should resume
18.17 consider filename from the redirected URL with -O ?
18.18 retry on network is unreachable
18.19 expand ~/ in config files
18.20 hostname sections in config files
18.21 retry on the redirected-to URL
18.23 Set the modification date on an uploaded file
18.24 Use multiple parallel transfers for a single download
18.25 Prevent terminal injection when writing to terminal
18.26 Custom progress meter update interval
18.27 -J and -O with %-encoded filenames
18.28 -J with -C -
18.29 --retry and transfer timeouts
Build
19.2 Enable PIE and RELRO by default
19.3 Do not use GNU libtool on OpenBSD
19.4 Package curl for Windows in a signed installer
19.5 make configure use --cache-file more and better
Test suite
20.1 SSL tunnel
20.2 nicer lacking perl message
20.3 more protocols supported
20.4 more platforms supported
20.6 Use the RFC 6265 test suite
20.8 Run web-platform-tests URL tests
MQTT
21.1 Support rate-limiting
21.2 Support MQTTS
21.3 Handle network blocks
TFTP
22.1 TFTP does not convert LF to CRLF for mode=netascii
Gopher
23.1 Handle network blocks
1. libcurl
1.1 TFO support on Windows
libcurl supports the CURLOPT_TCP_FASTOPEN option since 7.49.0 for Linux and macOS. Windows supports TCP Fast Open starting with Windows 10, version 1607 and we should add support for it.
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
1.2 Consult %APPDATA% also for .netrc
%APPDATA%\.netrc is not considered when running on Windows. should not it?
See https://github.com/curl/curl/issues/4016
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 alt-svc sharing
The share interface could benefit from allowing the alt-svc cache to be possible to share between easy handles.
See https://github.com/curl/curl/issues/4476
The share interface offers CURL_LOCK_DATA_CONNECT to have multiple easy handle share a connection cache, but due to how connections are used they are still not thread-safe when used shared.
See https://github.com/curl/curl/issues/4915 and lib1541.c
The share interface offers CURL_LOCK_DATA_HSTS to have multiple easy handle share a HSTS cache, but this is not thread-safe.
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) does not.
1.6 thread-safe sharing
Using the share interface users can share some data between easy handles but several of the sharing options are documented as not safe and supported to share between multiple concurrent threads. Fixing this would enable more users to share data in more powerful ways.
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 hostname 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 does not have res_init() or an alternative.
https://github.com/curl/curl/issues/2251
1.13 c-ares and CURLOPT_OPENSOCKETFUNCTION
curl creates 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 is not owned by the application like other sockets.
See https://github.com/curl/curl/issues/2734
1.14 connect to multiple IPs in parallel
curl currently implements the happy eyeball algorithm for connecting to the IPv4 and IPv6 alternatives for a host in parallel, sticking with the connection that "wins". We could implement a similar algorithm per individual IP family as well when there are multiple available addresses: start with the first address, then start a second attempt N milliseconds after and then a third another N milliseconds later. That way there would be less waiting when the first IP has problems. It also improves the connection timeout value handling for multiple address situations.
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 an HTTP/2 ping from the peer to verify that they are 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 does not 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
1.19 provide timing info for each redirect
curl and libcurl provide timing information via a set of different time-stamps (CURLINFO_*_TIME). When curl is following redirects, those returned time value are the accumulated sums. An improvement could be to offer separate timings for each redirect.
https://github.com/curl/curl/issues/6743
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).
1.21 netrc caching and sharing
The netrc file is read and parsed each time a connection is setup, which means that if a transfer needs multiple connections for authentication or redirects, the file might be reread (and parsed) multiple times. This makes it impossible to provide the file as a pipe.
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.
1.25 Expose tried IP addresses that failed
When libcurl fails to connect to a host, it could offer the application the addresses that were used in the attempt. Source + dest IP, source + dest port and protocol (UDP or TCP) for each failure. Possibly as a callback. Perhaps also provide "reason".
https://github.com/curl/curl/issues/2126
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 WebSocket read callback
Call the read callback once the connection is established to allow sending the first message in the connection.
https://github.com/curl/curl/issues/11402
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
1.31 erase secrets from heap/stack after use
Introducing a concept and system to erase secrets from memory after use, it could help mitigate and lessen the impact of (future) security problems etc. However: most secrets are passed to libcurl as clear text from the application and then clearing them within the library adds nothing...
https://github.com/curl/curl/issues/7268
1.32 add asynch getaddrinfo support
Use getaddrinfo_a() to provide an asynch name resolver backend to libcurl that does not use threads and does not depend on c-ares. The getaddrinfo_a function is (probably?) glibc specific but that is a widely used libc among our users.
https://github.com/curl/curl/pull/6746
1.33 make DoH inherit more transfer properties
Some options are not inherited because they are not relevant for the DoH SSL connections, or inheriting the option may result in unexpected behavior. For example the user's debug function callback is not inherited because it would be unexpected for internal handles (ie DoH handles) to be passed to that callback.
If an option is not inherited then it is not possible to set it separately for DoH without a DoH-specific option. For example: CURLOPT_DOH_SSL_VERIFYHOST, CURLOPT_DOH_SSL_VERIFYPEER and CURLOPT_DOH_SSL_VERIFYSTATUS.
See https://github.com/curl/curl/issues/6605
2. libcurl - multi interface
2.1 More non-blocking
Make sure we do not 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.
- The threaded resolver may block on cleanup: https://github.com/curl/curl/issues/4852
- file:// transfers
- TELNET transfers
- GSSAPI authentication for FTP transfers
- The "DONE" operation (post transfer protocol-specific actions) for the protocols SFTP, SMTP, FTP. Fixing multi_done() for this is a worthy task.
- curl_multi_remove_handle for any of the above. See section 2.3.
- Calling curl_ws_send() from a callback
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 does not 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
2.7 Virtual external sockets
libcurl performs operations on the given file descriptor that presumes it is a socket and an application cannot replace them at the moment. Allowing an application to fully replace those would allow a larger degree of freedom and flexibility.
See https://github.com/curl/curl/issues/5835
2.8 dynamically decide to use socketpair
For users who do not use curl_multi_wait() or do not care for curl_multi_wakeup(), we could introduce a way to make libcurl NOT create a socketpair in the multi handle.
See https://github.com/curl/curl/issues/4829
3. Documentation
3.1 Improve documentation about fork safety
See https://github.com/curl/curl/issues/6968
4. FTP
4.1 HOST
HOST is a command for a client to tell which hostname to use, to offer FTP servers named-based virtual hosting:
https://datatracker.ietf.org/doc/html/rfc7151
4.4 Support CURLOPT_PREQUOTE for directions listings
The lack of support is mostly an oversight and requires the FTP state machine to get updated to get fixed.
https://github.com/curl/curl/issues/8602
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 Passive transfer could try other IP addresses
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 could 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
5. HTTP
5.1 Provide the error body from a CONNECT response
When curl receives a body response from a CONNECT request to a proxy, it always just reads and ignores it. It would make some users happy if curl instead optionally would be able to make that responsible available. Via a new callback? Through some other means?
See https://github.com/curl/curl/issues/9513
5.2 Obey Retry-After in redirects
The Retry-After is said to dicate "the minimum time that the user agent is asked to wait before issuing the redirected request" and libcurl does not obey this.
See https://github.com/curl/curl/issues/11447
5.3 Rearrange request header order
Server implementers 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 hostname 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.
5.6 alt-svc should fallback if alt-svc does not work
The alt-svc: header provides a set of alternative services for curl to use instead of the original. If the first attempted one fails, it should try the next etc and if all alternatives fail go back to the original.
See https://github.com/curl/curl/issues/4908
5.7 Require HTTP version X or higher
curl and libcurl provide options for trying higher HTTP versions (for example HTTP/2) but then still allows the server to pick version 1.1. We could consider adding a way to require a minimum version.
See https://github.com/curl/curl/issues/7980
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 does not work for telnet.
6.3 feature negotiation debug data
Add telnet feature negotiation data to the debug callback as header data.
6.4 exit immediately upon connection if stdin is /dev/null
If it did, curl could be used to probe if there is an server there listening on a specific port. That is, the following command would exit immediately after the connection is established with exit code 0:
curl -s --connect-timeout 2 telnet://example.com:80 </dev/null
7. SMTP
7.1 Passing NOTIFY option to CURLOPT_MAIL_RCPT
Is there a way to pass the NOTIFY option to the CURLOPT_MAIL_RCPT option ? I set a string that already contains a bracket. For instance something like that: curl_slist_append( recipients, "<foo@bar> NOTIFY=SUCCESS,FAILURE" );
https://github.com/curl/curl/issues/8232
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.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.
9.2 upload unread
Uploads over IMAP currently always set the email as "read" (or "seen"). It would be good to offer a way for users to select for uploads to remain unread.
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.
10.2 CURLOPT_SSL_CTX_FUNCTION for LDAPS
CURLOPT_SSL_CTX_FUNCTION works perfectly for HTTPS and email protocols, but it has no effect for LDAPS connections.
https://github.com/curl/curl/issues/4108
10.3 Paged searches on LDAP server
https://github.com/curl/curl/issues/4452
10.4 Certificate-Based Authentication
LDAPS not possible with macOS and Windows with Certificate-Based Authentication
https://github.com/curl/curl/issues/9641
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 does not exist on the server, just like --ftp-create-dirs.
12. FILE
12.1 Directory listing on non-POSIX
Listing the contents of a directory accessed with FILE only works on platforms with opendir. Support could be added for more systems, like Windows.
13. TLS
13.1 TLS-PSK with OpenSSL
Transport Layer Security pre-shared key ciphersuites (TLS-PSK) is a set of cryptographic protocols that provide secure communication based on pre-shared keys (PSKs). These pre-shared keys are symmetric keys shared in advance among the communicating parties.
https://github.com/curl/curl/issues/5081
13.2 TLS channel binding
TLS 1.2 and 1.3 provide the ability to extract some secret data from the TLS connection and use it in the client request (usually in some sort of authentication) to ensure that the data sent is bound to the specific TLS connection and cannot be successfully intercepted by a proxy. This functionality can be used in a standard authentication mechanism such as GSS-API or SCRAM, or in custom approaches like custom HTTP Authentication headers.
For TLS 1.2, the binding type is usually tls-unique, and for TLS 1.3 it is tls-exporter.
https://datatracker.ietf.org/doc/html/rfc5929 https://datatracker.ietf.org/doc/html/rfc9266 https://github.com/curl/curl/issues/9226
13.3 Defeat TLS fingerprinting
By changing the order of TLS extensions provided in the TLS handshake, it is sometimes possible to circumvent TLS fingerprinting by servers. The TLS extension order is of course not the only way to fingerprint a client.
13.4 Consider OCSP stapling by default
Treat a negative response a reason for aborting the connection. Since OCSP stapling is presumed to get used much less in the future when Let's Encrypt drops the OCSP support, the benefit of this might however be limited.
https://github.com/curl/curl/issues/15483
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 does not seem to be exposed in the libcurl APIs. Could it be? There is so much that could be done if it were.
13.7 Less memory massaging with Schannel
The Schannel backend does a lot of custom memory management we would rather avoid: the repeated alloc + free in sends and the custom memory + realloc system for encrypted and decrypted data. That should be avoided and reduced for 1) efficiency and 2) safety.
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.se/mail/lib-2013-03/0075.html) but it was a too simple approach. See Daniel's comments: https://curl.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.
13.9 TLS record padding
TLS (1.3) offers optional record padding and OpenSSL provides an API for it. I could make sense for libcurl to offer this ability to applications to make traffic patterns harder to figure out by network traffic observers.
See https://github.com/curl/curl/issues/5398
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 does not 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 Some TLS options are not offered for HTTPS proxies
Some TLS related options to the command line tool and libcurl are only provided for the server and not for HTTPS proxies. --proxy-tls-max, --proxy-tlsv1.3, --proxy-curves and a few more. For more Documentation on this see: https://curl.se/libcurl/c/tls-options.html
https://github.com/curl/curl/issues/12286
13.13 Make sure we forbid TLS 1.3 post-handshake authentication
RFC 8740 explains how using HTTP/2 must forbid the use of TLS 1.3 post-handshake authentication. We should make sure to live up to that.
See https://github.com/curl/curl/issues/5396
13.14 Support the clienthello extension
Certain stupid networks and middle boxes have a problem with SSL handshake packets 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://datatracker.ietf.org/doc/html/rfc7685 https://github.com/curl/curl/issues/2299
13.15 Select signature algorithms
Consider adding an option or a way for users to select TLS signature algorithm. The signature algorithms set by a client are used directly in the supported signature algorithm in the client hello message.
https://github.com/curl/curl/issues/12982
13.16 Share the CA cache
For TLS backends that supports CA caching, it makes sense to allow the share object to be used to store the CA cache as well via the share API. Would allow multiple easy handles to reuse the CA cache and save themselves from a lot of extra processing overhead.
13.17 Add missing features to TLS backends
The feature matrix at https://curl.se/libcurl/c/tls-options.html shows which features are supported by which TLS backends, and thus also where there are feature gaps.
15. Schannel
15.1 Extend support for client certificate authentication
The existing support for the -E/--cert and --key options could be extended by supplying a custom certificate and key in PEM format, see: - Getting a Certificate for Schannel
https://msdn.microsoft.com/en-us/library/windows/desktop/aa375447.aspx
15.2 Extend support for the --ciphers option
The existing support for the --ciphers option could be extended 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 allow abrupt server closure
libcurl with Schannel errors without a known termination point from the server (such as length of transfer, or SSL "close notify" alert) to prevent against a truncation attack. Really old servers may neglect to send any termination point. An option could be added to ignore such abrupt closures.
https://github.com/curl/curl/issues/4427
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).
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 does 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.
17.2 Handle growing SFTP files
The SFTP code in libcurl checks the file size *before* a transfer starts and then proceeds to transfer exactly that amount of data. If the remote file grows while the transfer is in progress libcurl does not notice and does not adapt. The OpenSSH SFTP command line tool does and libcurl could also just attempt to download more to see if there is more to get...
https://github.com/curl/curl/issues/4344
17.3 Read keys from ~/.ssh/id_ecdsa, id_ed25519
The libssh2 backend in curl is limited to only reading keys from id_rsa and id_dsa, which makes it fail connecting to servers that use more modern key types.
https://github.com/curl/curl/issues/8586
17.4 Support CURLOPT_PREQUOTE
The two other QUOTE options are supported for SFTP, but this was left out for unknown reasons.
17.5 SSH over HTTPS proxy with more backends
The SSH based protocols SFTP and SCP did not work over HTTPS proxy at all until PR https://github.com/curl/curl/pull/6021 brought the functionality with the libssh2 backend. Presumably, this support can/could be added for the other backends as well.
17.6 SFTP with SCP://
OpenSSH 9 switched their 'scp' tool to speak SFTP under the hood. Going forward it might be worth having curl or libcurl attempt SFTP if SCP fails to follow suite.
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.
18.4 --proxycommand
Allow the user to make curl run a command and use its stdio to make requests and not do any network connection by itself. Example:
curl --proxycommand 'ssh pi@raspberrypi.local -W 10.1.1.75 80'
http://some/otherwise/unavailable/service.php
See https://github.com/curl/curl/issues/4941
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
18.6 Option to make -Z merge lined based outputs on stdout
When a user requests multiple lined based files using -Z and sends them to stdout, curl does not "merge" and send complete lines fine but may send partial lines from several sources.
https://github.com/curl/curl/issues/5175
18.7 specify which response codes that make -f/--fail return error
Allows a user to better specify exactly which error code(s) that are fine and which are errors for their specific uses cases
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 is 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.
18.13 Acknowledge Ratelimit headers
Consider a command line option that can make curl do multiple serial requests while acknowledging server specified rate limits: https://datatracker.ietf.org/doc/draft-ietf-httpapi-ratelimit-headers/
See https://github.com/curl/curl/issues/5406
18.14 --dry-run
A command line option that makes curl show exactly what it would do and send if it would run for real.
See https://github.com/curl/curl/issues/5426
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 does not have to transfer the same data again that was already transferred before the retry.
See https://github.com/curl/curl/issues/1084
18.17 consider filename 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 filename is not extracted and used from the newly redirected-to URL even if the new URL may have a much more sensible filename.
This is clearly documented and helps for security since there is no surprise to users which filename 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 filename to use so it already provides the "may overwrite any file" risk.
This is extra tricky if the original URL has no filename part at all since then the current code path does error out with an error message, and we cannot *know* already at that point if curl is redirected to a URL that has a filename...
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 hostname sections in config files
config files would be more powerful if they could set different configurations depending on used URLs, hostname or possibly origin. Then a default .curlrc could a specific user-agent only when doing requests against a certain site.
18.21 retry on the redirected-to URL
When curl is told to --retry a failed transfer and follows redirects, it might get an HTTP 429 response from the redirected-to URL and not the original one, which then could make curl decide to rather retry the transfer on that URL only instead of the original operation to the original URL.
Perhaps extra emphasized if the original transfer is a large POST that redirects to a separate GET, and that GET is what gets the 529
See https://github.com/curl/curl/issues/5462
18.23 Set the modification date on an uploaded file
For SFTP and possibly FTP, curl could offer an option to set the modification time for the uploaded file.
See https://github.com/curl/curl/issues/5768
18.24 Use multiple parallel transfers for a single download
To enhance transfer speed, downloading a single URL can be split up into multiple separate range downloads that get combined into a single final result.
An ideal implementation would not use a specified number of parallel transfers, but curl could: - First start getting the full file as transfer A - If after N seconds have passed and the transfer is expected to continue for
M seconds or more, add a new transfer (B) that asks for the second half of A's content (and stop A at the middle).
- If splitting up the work improves the transfer rate, it could then be done
again. Then again, etc up to a limit.
This way, if transfer B fails (because Range: is not supported) it lets transfer A remain the single one. N and M could be set to some sensible defaults.
See https://github.com/curl/curl/issues/5774
18.25 Prevent terminal injection when writing to terminal
curl could offer an option to make escape sequence either non-functional or avoid cursor moves or similar to reduce the risk of a user getting tricked by clever tricks.
See https://github.com/curl/curl/issues/6150
18.26 Custom progress meter update interval
Users who are for example doing large downloads in CI or remote setups might want the occasional progress meter update to see that the transfer is progressing and has not stuck, but they may not appreciate the many-times-a-second frequency curl can end up doing it with now.
18.27 -J and -O with %-encoded filenames
-J/--remote-header-name does not decode %-encoded filenames. RFC 6266 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.se/bug/view.cgi?id=1294
-O also does not 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 do not decode -O without the user asking for it with some other means, since -O has always been documented to use the name exactly as specified in the URL.
18.28 -J with -C -
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 filename (and thus its pre-transfer size) has been figured out. This can be improved.
https://curl.se/bug/view.cgi?id=1169
18.29 --retry and transfer timeouts
If using --retry and the transfer timeouts (possibly due to using -m or -y/-Y) the next attempt does not resume the transfer properly from what was downloaded in the previous attempt but truncates and restarts at the original position where it was at before the previous failed attempt. See https://curl.se/mail/lib-2008-01/0080.html and Mandriva bug report https://qa.mandriva.com/show_bug.cgi?id=22565
19. Build
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 Do not use GNU libtool on OpenBSD
When compiling curl on OpenBSD with "--enable-debug" it gives linking errors when you use GNU libtool. This can be fixed by using the libtool provided by OpenBSD itself. However for this the user always needs to invoke make with "LIBTOOL=/usr/bin/libtool". It would be nice if the script could have some magic to detect if this system is an OpenBSD host and then use the OpenBSD libtool instead.
See https://github.com/curl/curl/issues/5862
19.4 Package curl for Windows in a signed installer
See https://github.com/curl/curl/issues/5424
19.5 make configure use --cache-file more and better
The configure script can be improved to cache more values so that repeated invokes run much faster.
See https://github.com/curl/curl/issues/7753
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 was not found by the configure script, do not attempt to run the tests but explain something nice why it does not.
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 macOS. Remove fork()s and it should become even more portable.
20.6 Use the RFC 6265 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 would be good 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.
20.8 Run web-platform-tests URL tests
Run web-platform-tests URL tests and compare results with browsers on wpt.fyi
It would help us find issues to fix and help us document where our parser differs from the WHATWG URL spec parsers.
See https://github.com/curl/curl/issues/4477
21. MQTT
21.1 Support rate-limiting
The rate-limiting logic is done in the PERFORMING state in multi.c but MQTT is not (yet) implemented to use that.
21.2 Support MQTTS
21.3 Handle network blocks
Running test suite with `CURL_DBG_SOCK_WBLOCK=90 ./runtests.pl -a mqtt` makes several MQTT test cases fail where they should not.
22. TFTP
22.1 TFTP does not convert LF to CRLF for mode=netascii
RFC 3617 defines that an TFTP transfer can be done using "netascii" mode. curl does not support extracting that mode from the URL nor does it treat such transfers specifically. It should probably do LF to CRLF translations for them.
See https://github.com/curl/curl/issues/12655
23. Gopher
23.1 Handle network blocks
Running test suite with `CURL_DBG_SOCK_WBLOCK=90 ./runtests.pl -a 1200 to 1300` makes several Gopher test cases fail where they should not.