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curl/docs/FEATURES.md
Daniel Stenberg 265b14d6b3
metalink: remove 
Warning: this will make existing curl command lines that use metalink to
stop working.

Reasons for removal:

1. We've found several security problems and issues involving the
   metalink support in curl. The issues are not detailed here. When
   working on those, it become apparent to the team that several of the
   problems are due to the system design, metalink library API and what
   the metalink RFC says. They are very hard to fix on the curl side
   only.

2. The metalink usage with curl was only very briefly documented and was
   not following the "normal" curl usage pattern in several ways, making
   it surprising and non-intuitive which could lead to further security
   issues.

3. The metalink library was last updated 6 years ago and wasn't so
   active the years before that either. An unmaintained library means
   there's a security problem waiting to happen. This is probably reason
   enough.

4. Metalink requires an XML parsing library, which is complex code (even
   the smaller alternatives) and to this day often gets security
   updates.

5. Metalink is not a widely used curl feature. In the 2020 curl user
   survey, only 1.4% of the responders said that they'd are using it. In
   2021 that number was 1.2%. Searching the web also show very few
   traces of it being used, even with other tools.

6. The torrent format and associated technology clearly won for
   downloading large files from multiple sources in parallel.

Cloes #7176
2021-06-07 08:14:25 +02:00

5.7 KiB
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Features -- what curl can do

curl tool

  • config file support
  • multiple URLs in a single command line
  • range "globbing" support: [0-13], {one,two,three}
  • multiple file upload on a single command line
  • custom maximum transfer rate
  • redirectable stderr
  • parallel transfers

libcurl

  • full URL syntax with no length limit
  • custom maximum download time
  • custom least download speed acceptable
  • custom output result after completion
  • guesses protocol from host name unless specified
  • uses .netrc
  • progress bar with time statistics while downloading
  • "standard" proxy environment variables support
  • compiles on win32 (reported builds on 70+ operating systems)
  • selectable network interface for outgoing traffic
  • IPv6 support on unix and Windows
  • happy eyeballs dual-stack connects
  • persistent connections
  • SOCKS 4 + 5 support, with or without local name resolving
  • supports user name and password in proxy environment variables
  • operations through HTTP proxy "tunnel" (using CONNECT)
  • replaceable memory functions (malloc, free, realloc, etc)
  • asynchronous name resolving (6)
  • both a push and a pull style interface
  • international domain names (11)

HTTP

  • HTTP/0.9 responses are optionally accepted
  • HTTP/1.0
  • HTTP/1.1
  • HTTP/2, including multiplexing and server push (5)
  • GET
  • PUT
  • HEAD
  • POST
  • multipart formpost (RFC1867-style)
  • authentication: Basic, Digest, NTLM (9) and Negotiate (SPNEGO) (3) to server and proxy
  • resume (both GET and PUT)
  • follow redirects
  • maximum amount of redirects to follow
  • custom HTTP request
  • cookie get/send fully parsed
  • reads/writes the netscape cookie file format
  • custom headers (replace/remove internally generated headers)
  • custom user-agent string
  • custom referrer string
  • range
  • proxy authentication
  • time conditions
  • via HTTP proxy, HTTPS proxy or SOCKS proxy
  • retrieve file modification date
  • Content-Encoding support for deflate and gzip
  • "Transfer-Encoding: chunked" support in uploads
  • automatic data compression (12)

HTTPS (1)

  • (all the HTTP features)
  • HTTP/3 experimental support
  • using client certificates
  • verify server certificate
  • via HTTP proxy, HTTPS proxy or SOCKS proxy
  • select desired encryption
  • select usage of a specific SSL version

FTP

  • download
  • authentication
  • Kerberos 5 (13)
  • active/passive using PORT, EPRT, PASV or EPSV
  • single file size information (compare to HTTP HEAD)
  • 'type=' URL support
  • dir listing
  • dir listing names-only
  • upload
  • upload append
  • upload via http-proxy as HTTP PUT
  • download resume
  • upload resume
  • custom ftp commands (before and/or after the transfer)
  • simple "range" support
  • via HTTP proxy, HTTPS proxy or SOCKS proxy
  • all operations can be tunneled through proxy
  • customizable to retrieve file modification date
  • no dir depth limit

FTPS (1)

  • implicit ftps:// support that use SSL on both connections
  • explicit "AUTH TLS" and "AUTH SSL" usage to "upgrade" plain ftp:// connection to use SSL for both or one of the connections

SCP (8)

  • both password and public key auth

SFTP (7)

  • both password and public key auth
  • with custom commands sent before/after the transfer

TFTP

  • download
  • upload

TELNET

  • connection negotiation
  • custom telnet options
  • stdin/stdout I/O

LDAP (2)

  • full LDAP URL support

DICT

  • extended DICT URL support

FILE

  • URL support
  • upload
  • resume

SMB

  • SMBv1 over TCP and SSL
  • download
  • upload
  • authentication with NTLMv1

SMTP

  • authentication: Plain, Login, CRAM-MD5, Digest-MD5, NTLM (9), Kerberos 5 (4) and External.
  • send e-mails
  • mail from support
  • mail size support
  • mail auth support for trusted server-to-server relaying
  • multiple recipients
  • via http-proxy

SMTPS (1)

  • implicit smtps:// support
  • explicit "STARTTLS" usage to "upgrade" plain smtp:// connections to use SSL
  • via http-proxy

POP3

  • authentication: Clear Text, APOP and SASL
  • SASL based authentication: Plain, Login, CRAM-MD5, Digest-MD5, NTLM (9), Kerberos 5 (4) and External.
  • list e-mails
  • retrieve e-mails
  • enhanced command support for: CAPA, DELE, TOP, STAT, UIDL and NOOP via custom requests
  • via http-proxy

POP3S (1)

  • implicit pop3s:// support
  • explicit "STLS" usage to "upgrade" plain pop3:// connections to use SSL
  • via http-proxy

IMAP

  • authentication: Clear Text and SASL
  • SASL based authentication: Plain, Login, CRAM-MD5, Digest-MD5, NTLM (9), Kerberos 5 (4) and External.
  • list the folders of a mailbox
  • select a mailbox with support for verifying the UIDVALIDITY
  • fetch e-mails with support for specifying the UID and SECTION
  • upload e-mails via the append command
  • enhanced command support for: EXAMINE, CREATE, DELETE, RENAME, STATUS, STORE, COPY and UID via custom requests
  • via http-proxy

IMAPS (1)

  • implicit imaps:// support
  • explicit "STARTTLS" usage to "upgrade" plain imap:// connections to use SSL
  • via http-proxy

MQTT

  • Subscribe to and publish topics using url scheme mqtt://broker/topic

Footnotes

  1. requires a TLS library
  2. requires OpenLDAP or WinLDAP
  3. requires a GSS-API implementation (such as Heimdal or MIT Kerberos) or SSPI (native Windows)
  4. requires a GSS-API implementation, however, only Windows SSPI is currently supported
  5. requires nghttp2
  6. requires c-ares
  7. requires libssh2, libssh or wolfSSH
  8. requires libssh2 or libssh
  9. requires OpenSSL, GnuTLS, mbedTLS, NSS, yassl, Secure Transport or SSPI (native Windows)
  11. requires libidn2 or Windows
  12. requires libz, brotli and/or zstd
  13. requires a GSS-API implementation (such as Heimdal or MIT Kerberos)