5 \___|\___/|_| \_\_____|
7 Things that could be nice to do in the future
9 Things to do in project cURL. Please tell us what you think, contribute and
10 send us patches that improve things!
12 Be aware that these are things that we could do, or have once been considered
13 things we could do. If you want to work on any of these areas, please
14 consider bringing it up for discussions first on the mailing list so that we
15 all agree it is still a good idea for the project!
17 All bugs documented in the KNOWN_BUGS document are subject for fixing!
22 1.4 signal-based resolver timeouts
23 1.5 get rid of PATH_MAX
24 1.6 Modified buffer size approach
25 1.7 Detect when called from within callbacks
26 1.8 Allow SSL (HTTPS) to proxy
27 1.9 Cache negative name resolves
29 1.11 minimize dependencies with dynamicly loaded modules
31 2. libcurl - multi interface
33 2.2 Fix HTTP Pipelining for PUT
34 2.3 Better support for same name resolves
37 3.1 Update date and version in man pages
41 4.2 Alter passive/active on failure and retry
42 4.3 Earlier bad letter detection
43 4.4 REST for large files
45 4.6 GSSAPI via Windows SSPI
46 4.7 STAT for LIST without data connection
49 5.1 Better persistency for HTTP 1.0
50 5.2 support FF3 sqlite cookie files
51 5.3 Rearrange request header order
54 5.6 Refuse "downgrade" redirects
58 6.2 ditch telnet-specific select
59 6.3 feature negotiation debug data
60 6.4 send data in chunks
64 7.2 Enhanced capability support
68 8.2 Enhanced capability support
71 9.1 Enhanced capability support
74 10.1 SASL based authentication mechanisms
77 11.1 File listing support
78 11.2 Honor file timestamps
85 13.1 Disable specific versions
86 13.2 Provide mutex locking API
87 13.3 Evaluate SSL patches
88 13.4 Cache OpenSSL contexts
89 13.5 Export session ids
90 13.6 Provide callback for cert verification
91 13.7 improve configure --with-ssl
99 15.1 Add support for client certificate authentication
100 15.2 Add support for custom server certificate validation
101 15.3 Add support for the --ciphers option
104 16.1 Other authentication mechanisms
105 16.2 Add QOP support to GSSAPI authentication
110 17.3 prevent file overwriting
111 17.4 simultaneous parallel transfers
112 17.5 provide formpost headers
113 17.6 warning when setting an option
114 17.7 warning when sending binary output to terminal
115 17.8 offer color-coded HTTP header output
116 17.9 Choose the name of file in braces for complex URLs
117 17.10 improve how curl works in a windows console window
124 19.2 nicer lacking perl message
125 19.3 more protocols supported
126 19.4 more platforms supported
127 19.5 Add support for concurrent connections
130 20.1 http-style HEAD output for FTP
131 20.2 combine error codes
132 20.3 extend CURLOPT_SOCKOPTFUNCTION prototype
134 21. Next major release
135 21.1 cleanup return codes
136 21.2 remove obsolete defines
138 21.4 remove several functions
139 21.5 remove CURLOPT_FAILONERROR
140 21.6 remove CURLOPT_DNS_USE_GLOBAL_CACHE
141 21.7 remove progress meter from libcurl
142 21.8 remove 'curl_httppost' from public
143 21.9 have form functions use CURL handle argument
144 21.10 Add CURLOPT_MAIL_CLIENT option
146 ==============================================================================
150 1.2 More data sharing
152 curl_share_* functions already exist and work, and they can be extended to
153 share more. For example, enable sharing of the ares channel and the
158 Use 'struct lifreq' and SIOCGLIFADDR instead of 'struct ifreq' and
159 SIOCGIFADDR on newer Solaris versions as they claim the latter is obsolete.
160 To support IPv6 interface addresses for network interfaces properly.
162 1.4 signal-based resolver timeouts
164 libcurl built without an asynchronous resolver library uses alarm() to time
165 out DNS lookups. When a timeout occurs, this causes libcurl to jump from the
166 signal handler back into the library with a sigsetjmp, which effectively
167 causes libcurl to continue running within the signal handler. This is
168 non-portable and could cause problems on some platforms. A discussion on the
169 problem is available at http://curl.haxx.se/mail/lib-2008-09/0197.html
171 Also, alarm() provides timeout resolution only to the nearest second. alarm
172 ought to be replaced by setitimer on systems that support it.
174 1.5 get rid of PATH_MAX
176 Having code use and rely on PATH_MAX is not nice:
177 http://insanecoding.blogspot.com/2007/11/pathmax-simply-isnt.html
179 Currently the SSH based code uses it a bit, but to remove PATH_MAX from there
180 we need libssh2 to properly tell us when we pass in a too small buffer and
181 its current API (as of libssh2 1.2.7) doesn't.
183 1.6 Modified buffer size approach
185 Current libcurl allocates a fixed 16K size buffer for download and an
186 additional 16K for upload. They are always unconditionally part of the easy
187 handle. If CRLF translations are requested, an additional 32K "scratch
188 buffer" is allocated. A total of 64K transfer buffers in the worst case.
190 First, while the handles are not actually in use these buffers could be freed
191 so that lingering handles just kept in queues or whatever waste less memory.
193 Secondly, SFTP is a protocol that needs to handle many ~30K blocks at once
194 since each need to be individually acked and therefore libssh2 must be
195 allowed to send (or receive) many separate ones in parallel to achieve high
196 transfer speeds. A current libcurl build with a 16K buffer makes that
197 impossible, but one with a 512K buffer will reach MUCH faster transfers. But
198 allocating 512K unconditionally for all buffers just in case they would like
199 to do fast SFTP transfers at some point is not a good solution either.
201 Dynamically allocate buffer size depending on protocol in use in combination
202 with freeing it after each individual transfer? Other suggestions?
204 1.7 Detect when called from within callbacks
206 We should set a state variable before calling callbacks, so that we
207 subsequently can add code within libcurl that returns error if called within
208 callbacks for when that's not supported.
210 1.8 Allow SSL (HTTPS) to proxy
212 To prevent local users from snooping on your traffic to the proxy. Supported
214 https://www.chromium.org/developers/design-documents/secure-web-proxy
216 ...and by Firefox soon:
217 https://bugzilla.mozilla.org/show_bug.cgi?id=378637
219 1.9 Cache negative name resolves
221 A name resolve that has failed is likely to fail when made again within a
222 short period of time. Currently we only cache positive responses.
224 1.10 Support IDNA2008
226 International Domain Names are supported in libcurl since years back, powered
227 by libidn. libidn implements IDNA2003 which has been superseded by IDNA2008.
228 libidn2 is an existing library offering support for IDNA2008.
230 1.11 minimize dependencies with dynamicly loaded modules
232 We can create a system with loadable modules/plug-ins, where these modules
233 would be the ones that link to 3rd party libs. That would allow us to avoid
234 having to load ALL dependencies since only the necessary ones for this
235 app/invoke/used protocols would be necessary to load. See
236 https://github.com/bagder/curl/issues/349
238 2. libcurl - multi interface
240 2.1 More non-blocking
242 Make sure we don't ever loop because of non-blocking sockets returning
243 EWOULDBLOCK or similar. Blocking cases include:
245 - Name resolves on non-windows unless c-ares is used
246 - NSS SSL connections
247 - HTTP proxy CONNECT operations
248 - SOCKS proxy handshakes
251 - The "DONE" operation (post transfer protocol-specific actions) for the
252 protocols SFTP, SMTP, FTP. Fixing Curl_done() for this is a worthy task.
254 2.2 Fix HTTP Pipelining for PUT
256 HTTP Pipelining can be a way to greatly enhance performance for multiple
257 serial requests and currently libcurl only supports that for HEAD and GET
258 requests but it should also be possible for PUT.
260 2.3 Better support for same name resolves
262 If a name resolve has been initiated for name NN and a second easy handle
263 wants to resolve that name as well, make it wait for the first resolve to end
264 up in the cache instead of doing a second separate resolve. This is
265 especially needed when adding many simultaneous handles using the same host
266 name when the DNS resolver can get flooded.
271 3.1 Update date and version in man pages
273 'maketgz' or another suitable script could update the .TH sections of the man
274 pages at release time to use the current date and curl/libcurl version
281 HOST is a command for a client to tell which host name to use, to offer FTP
282 servers named-based virtual hosting:
284 https://tools.ietf.org/html/rfc7151
286 4.2 Alter passive/active on failure and retry
288 When trying to connect passively to a server which only supports active
289 connections, libcurl returns CURLE_FTP_WEIRD_PASV_REPLY and closes the
290 connection. There could be a way to fallback to an active connection (and
291 vice versa). http://curl.haxx.se/bug/feature.cgi?id=1754793
293 4.3 Earlier bad letter detection
295 Make the detection of (bad) %0d and %0a codes in FTP URL parts earlier in the
296 process to avoid doing a resolve and connect in vain.
298 4.4 REST for large files
300 REST fix for servers not behaving well on >2GB requests. This should fail if
301 the server doesn't set the pointer to the requested index. The tricky
302 (impossible?) part is to figure out if the server did the right thing or not.
306 FTP ASCII transfers do not follow RFC959. They don't convert the data
309 4.6 GSSAPI via Windows SSPI
311 In addition to currently supporting the SASL GSSAPI mechanism (Kerberos V5)
312 via third-party GSS-API libraries, such as Heimdal or MIT Kerberos, also add
313 support for GSSAPI authentication via Windows SSPI.
315 4.7 STAT for LIST without data connection
317 Some FTP servers allow STAT for listing directories instead of using LIST, and
318 the response is then sent over the control connection instead of as the
319 otherwise usedw data connection: http://www.nsftools.com/tips/RawFTP.htm#STAT
321 This is not detailed in any FTP specification.
325 5.1 Better persistency for HTTP 1.0
327 "Better" support for persistent connections over HTTP 1.0
328 http://curl.haxx.se/bug/feature.cgi?id=1089001
330 5.2 support FF3 sqlite cookie files
332 Firefox 3 is changing from its former format to a a sqlite database instead.
333 We should consider how (lib)curl can/should support this.
334 http://curl.haxx.se/bug/feature.cgi?id=1871388
336 5.3 Rearrange request header order
338 Server implementors often make an effort to detect browser and to reject
339 clients it can detect to not match. One of the last details we cannot yet
340 control in libcurl's HTTP requests, which also can be exploited to detect
341 that libcurl is in fact used even when it tries to impersonate a browser, is
342 the order of the request headers. I propose that we introduce a new option in
343 which you give headers a value, and then when the HTTP request is built it
344 sorts the headers based on that number. We could then have internally created
345 headers use a default value so only headers that need to be moved have to be
350 Chrome and Firefox already support SPDY and lots of web services do. There's
351 a library for us to use for this (spdylay) that has a similar API and the
352 same author as nghttp2.
354 spdylay: https://github.com/tatsuhiro-t/spdylay
358 Add the ability to specify the preferred authentication mechanism to use by
359 using ;auth=<mech> in the login part of the URL.
363 http://test:pass;auth=NTLM@example.com would be equivalent to specifying --user
364 test:pass;auth=NTLM or --user test:pass --ntlm from the command line.
366 Additionally this should be implemented for proxy base URLs as well.
368 5.6 Refuse "downgrade" redirects
370 See https://github.com/bagder/curl/issues/226
372 Consider a way to tell curl to refuse to "downgrade" protocol with a redirect
373 and/or possibly a bit that refuses redirect to change protocol completely.
380 Reading input (to send to the remote server) on stdin is a crappy solution for
381 library purposes. We need to invent a good way for the application to be able
382 to provide the data to send.
384 6.2 ditch telnet-specific select
386 Move the telnet support's network select() loop go away and merge the code
387 into the main transfer loop. Until this is done, the multi interface won't
390 6.3 feature negotiation debug data
392 Add telnet feature negotiation data to the debug callback as header data.
394 6.4 send data in chunks
396 Currently, telnet sends data one byte at a time. This is fine for interactive
397 use, but inefficient for any other. Sent data should be sent in larger
404 Add support for pipelining emails.
406 7.2 Enhanced capability support
408 Add the ability, for an application that uses libcurl, to obtain the list of
409 capabilities returned from the EHLO command.
415 Add support for pipelining commands.
417 8.2 Enhanced capability support
419 Add the ability, for an application that uses libcurl, to obtain the list of
420 capabilities returned from the CAPA command.
424 9.1 Enhanced capability support
426 Add the ability, for an application that uses libcurl, to obtain the list of
427 capabilities returned from the CAPABILITY command.
431 10.1 SASL based authentication mechanisms
433 Currently the LDAP module only supports ldap_simple_bind_s() in order to bind
434 to an LDAP server. However, this function sends username and password details
435 using the simple authentication mechanism (as clear text). However, it should
436 be possible to use ldap_bind_s() instead specifying the security context
437 information ourselves.
441 11.1 File listing support
443 Add support for listing the contents of a SMB share. The output should probably
444 be the same as/similar to FTP.
446 11.2 Honor file timestamps
448 The timestamp of the transferred file should reflect that of the original file.
452 Currently the SMB authentication uses NTLMv1.
458 There's no RFC for the protocol or an URI/URL format. An implementation
459 should most probably use an existing rsync library, such as librsync.
463 13.1 Disable specific versions
465 Provide an option that allows for disabling specific SSL versions, such as
466 SSLv2 http://curl.haxx.se/bug/feature.cgi?id=1767276
468 13.2 Provide mutex locking API
470 Provide a libcurl API for setting mutex callbacks in the underlying SSL
471 library, so that the same application code can use mutex-locking
472 independently of OpenSSL or GnutTLS being used.
474 13.3 Evaluate SSL patches
476 Evaluate/apply Gertjan van Wingerde's SSL patches:
477 http://curl.haxx.se/mail/lib-2004-03/0087.html
479 13.4 Cache OpenSSL contexts
481 "Look at SSL cafile - quick traces look to me like these are done on every
482 request as well, when they should only be necessary once per SSL context (or
483 once per handle)". The major improvement we can rather easily do is to make
484 sure we don't create and kill a new SSL "context" for every request, but
485 instead make one for every connection and re-use that SSL context in the same
486 style connections are re-used. It will make us use slightly more memory but
487 it will libcurl do less creations and deletions of SSL contexts.
489 13.5 Export session ids
491 Add an interface to libcurl that enables "session IDs" to get
492 exported/imported. Cris Bailiff said: "OpenSSL has functions which can
493 serialise the current SSL state to a buffer of your choice, and recover/reset
494 the state from such a buffer at a later date - this is used by mod_ssl for
495 apache to implement and SSL session ID cache".
497 13.6 Provide callback for cert verification
499 OpenSSL supports a callback for customised verification of the peer
500 certificate, but this doesn't seem to be exposed in the libcurl APIs. Could
501 it be? There's so much that could be done if it were!
503 13.7 improve configure --with-ssl
505 make the configure --with-ssl option first check for OpenSSL, then GnuTLS,
510 DNS-Based Authentication of Named Entities (DANE) is a way to provide SSL
511 keys and certs over DNS using DNSSEC as an alternative to the CA model.
512 https://www.rfc-editor.org/rfc/rfc6698.txt
514 An initial patch was posted by Suresh Krishnaswamy on March 7th 2013
515 (http://curl.haxx.se/mail/lib-2013-03/0075.html) but it was a too simple
516 approach. See Daniel's comments:
517 http://curl.haxx.se/mail/lib-2013-03/0103.html . libunbound may be the
518 correct library to base this development on.
522 14.1 SSL engine stuff
524 Is this even possible?
526 14.2 check connection
528 Add a way to check if the connection seems to be alive, to correspond to the
529 SSL_peak() way we use with OpenSSL.
533 15.1 Add support for client certificate authentication
535 WinSSL/SChannel currently makes use of the OS-level system and user
536 certificate and private key stores. This does not allow the application
537 or the user to supply a custom client certificate using curl or libcurl.
539 Therefore support for the existing -E/--cert and --key options should be
540 implemented by supplying a custom certificate to the SChannel APIs, see:
541 - Getting a Certificate for Schannel
542 https://msdn.microsoft.com/en-us/library/windows/desktop/aa375447.aspx
544 15.2 Add support for custom server certificate validation
546 WinSSL/SChannel currently makes use of the OS-level system and user
547 certificate trust store. This does not allow the application or user to
548 customize the server certificate validation process using curl or libcurl.
550 Therefore support for the existing --cacert or --capath options should be
551 implemented by supplying a custom certificate to the SChannel APIs, see:
552 - Getting a Certificate for Schannel
553 https://msdn.microsoft.com/en-us/library/windows/desktop/aa375447.aspx
555 15.3 Add support for the --ciphers option
557 The cipher suites used by WinSSL/SChannel are configured on an OS-level
558 instead of an application-level. This does not allow the application or
559 the user to customize the configured cipher suites using curl or libcurl.
561 Therefore support for the existing --ciphers option should be implemented
562 by mapping the OpenSSL/GnuTLS cipher suites to the SChannel APIs, see
563 - Specifying Schannel Ciphers and Cipher Strengths
564 https://msdn.microsoft.com/en-us/library/windows/desktop/aa380161.aspx
568 16.1 Other authentication mechanisms
570 Add support for other authentication mechanisms such as OLP,
571 GSS-SPNEGO and others.
573 16.2 Add QOP support to GSSAPI authentication
575 Currently the GSSAPI authentication only supports the default QOP of auth
576 (Authentication), whilst Kerberos V5 supports both auth-int (Authentication
577 with integrity protection) and auth-conf (Authentication with integrity and
584 "curl --sync http://example.com/feed[1-100].rss" or
585 "curl --sync http://example.net/{index,calendar,history}.html"
587 Downloads a range or set of URLs using the remote name, but only if the
588 remote file is newer than the local file. A Last-Modified HTTP date header
589 should also be used to set the mod date on the downloaded file.
593 Globbing support for -d and -F, as in 'curl -d "name=foo[0-9]" URL'.
594 This is easily scripted though.
596 17.3 prevent file overwriting
598 Add an option that prevents cURL from overwriting existing local files. When
599 used, and there already is an existing file with the target file name
600 (either -O or -o), a number should be appended (and increased if already
601 existing). So that index.html becomes first index.html.1 and then
604 17.4 simultaneous parallel transfers
606 The client could be told to use maximum N simultaneous parallel transfers and
607 then just make sure that happens. It should of course not make more than one
608 connection to the same remote host. This would require the client to use the
609 multi interface. http://curl.haxx.se/bug/feature.cgi?id=1558595
611 17.5 provide formpost headers
613 Extending the capabilities of the multipart formposting. How about leaving
614 the ';type=foo' syntax as it is and adding an extra tag (headers) which
615 works like this: curl -F "coolfiles=@fil1.txt;headers=@fil1.hdr" where
616 fil1.hdr contains extra headers like
618 Content-Type: text/plain; charset=KOI8-R"
619 Content-Transfer-Encoding: base64
620 X-User-Comment: Please don't use browser specific HTML code
622 which should overwrite the program reasonable defaults (plain/text,
625 17.6 warning when setting an option
627 Display a warning when libcurl returns an error when setting an option.
628 This can be useful to tell when support for a particular feature hasn't been
629 compiled into the library.
631 17.7 warning when sending binary output to terminal
633 Provide a way that prompts the user for confirmation before binary data is
634 sent to the terminal, much in the style 'less' does it.
636 17.8 offer color-coded HTTP header output
638 By offering different color output on the header name and the header
639 contents, they could be made more readable and thus help users working on
642 17.9 Choose the name of file in braces for complex URLs
644 When using braces to download a list of URLs and you use complicated names
645 in the list of alternatives, it could be handy to allow curl to use other
648 Consider a way to offer that. Possibly like
649 {partURL1:name1,partURL2:name2,partURL3:name3} where the name following the
650 colon is the output name.
652 See https://github.com/bagder/curl/issues/221
654 17.10 improve how curl works in a windows console window
656 If you pull the scrollbar when transferring with curl in a Windows console
657 window, the transfer is interrupted and can get disconnected. This can
658 probably be improved. See https://github.com/bagder/curl/issues/322
665 Consider extending 'roffit' to produce decent ASCII output, and use that
666 instead of (g)nroff when building src/tool_hugehelp.c
672 Make our own version of stunnel for simple port forwarding to enable HTTPS
673 and FTP-SSL tests without the stunnel dependency, and it could allow us to
674 provide test tools built with either OpenSSL or GnuTLS
676 19.2 nicer lacking perl message
678 If perl wasn't found by the configure script, don't attempt to run the tests
679 but explain something nice why it doesn't.
681 19.3 more protocols supported
683 Extend the test suite to include more protocols. The telnet could just do FTP
684 or http operations (for which we have test servers).
686 19.4 more platforms supported
688 Make the test suite work on more platforms. OpenBSD and Mac OS. Remove
689 fork()s and it should become even more portable.
691 19.5 Add support for concurrent connections
693 Tests 836, 882 and 938 were designed to verify that separate connections aren't
694 used when using different login credentials in protocols that shouldn't re-use
695 a connection under such circumstances.
697 Unfortunately, ftpserver.pl doesn't appear to support multiple concurrent
698 connections. The read while() loop seems to loop until it receives a disconnect
699 from the client, where it then enters the waiting for connections loop. When
700 the client opens a second connection to the server, the first connection hasn't
701 been dropped (unless it has been forced - which we shouldn't do in these tests)
702 and thus the wait for connections loop is never entered to receive the second
707 20.1 http-style HEAD output for FTP
709 #undef CURL_FTP_HTTPSTYLE_HEAD in lib/ftp.c to remove the HTTP-style headers
710 from being output in NOBODY requests over FTP
712 20.2 combine error codes
714 Combine some of the error codes to remove duplicates. The original
715 numbering should not be changed, and the old identifiers would be
716 macroed to the new ones in an CURL_NO_OLDIES section to help with
717 backward compatibility.
719 Candidates for removal and their replacements:
721 CURLE_FILE_COULDNT_READ_FILE => CURLE_REMOTE_FILE_NOT_FOUND
723 CURLE_FTP_COULDNT_RETR_FILE => CURLE_REMOTE_FILE_NOT_FOUND
725 CURLE_FTP_COULDNT_USE_REST => CURLE_RANGE_ERROR
727 CURLE_FUNCTION_NOT_FOUND => CURLE_FAILED_INIT
729 CURLE_LDAP_INVALID_URL => CURLE_URL_MALFORMAT
731 CURLE_TFTP_NOSUCHUSER => CURLE_TFTP_ILLEGAL
733 CURLE_TFTP_NOTFOUND => CURLE_REMOTE_FILE_NOT_FOUND
735 CURLE_TFTP_PERM => CURLE_REMOTE_ACCESS_DENIED
737 20.3 extend CURLOPT_SOCKOPTFUNCTION prototype
739 The current prototype only provides 'purpose' that tells what the
740 connection/socket is for, but not any protocol or similar. It makes it hard
741 for applications to differentiate on TCP vs UDP and even HTTP vs FTP and
744 21. Next major release
746 21.1 cleanup return codes
748 curl_easy_cleanup() returns void, but curl_multi_cleanup() returns a
749 CURLMcode. These should be changed to be the same.
751 21.2 remove obsolete defines
753 remove obsolete defines from curl/curl.h
757 make several functions use size_t instead of int in their APIs
759 21.4 remove several functions
761 remove the following functions from the public API:
765 curl_mprintf (and variations)
771 They will instead become curlx_ - alternatives. That makes the curl app
772 still capable of using them, by building with them from source.
774 These functions have no purpose anymore:
778 curl_multi_socket_all
780 21.5 remove CURLOPT_FAILONERROR
782 Remove support for CURLOPT_FAILONERROR, it has gotten too kludgy and weird
783 internally. Let the app judge success or not for itself.
785 21.6 remove CURLOPT_DNS_USE_GLOBAL_CACHE
787 Remove support for a global DNS cache. Anything global is silly, and we
788 already offer the share interface for the same functionality but done
791 21.7 remove progress meter from libcurl
793 The internally provided progress meter output doesn't belong in the library.
794 Basically no application wants it (apart from curl) but instead applications
795 can and should do their own progress meters using the progress callback.
797 The progress callback should then be bumped as well to get proper 64bit
798 variable types passed to it instead of doubles so that big files work
801 21.8 remove 'curl_httppost' from public
803 curl_formadd() was made to fill in a public struct, but the fact that the
804 struct is public is never really used by application for their own advantage
805 but instead often restricts how the form functions can or can't be modified.
807 Changing them to return a private handle will benefit the implementation and
808 allow us much greater freedoms while still maintaining a solid API and ABI.
810 21.9 have form functions use CURL handle argument
812 curl_formadd() and curl_formget() both currently have no CURL handle
813 argument, but both can use a callback that is set in the easy handle, and
814 thus curl_formget() with callback cannot function without first having
815 curl_easy_perform() (or similar) called - which is hard to grasp and a design
818 21.10 Add CURLOPT_MAIL_CLIENT option
820 Rather than use the URL to specify the mail client string to present in the
821 HELO and EHLO commands, libcurl should support a new CURLOPT specifically for
822 specifying this data as the URL is non-standard and to be honest a bit of a
825 Please see the following thread for more information:
826 http://curl.haxx.se/mail/lib-2012-05/0178.html