5 \___|\___/|_| \_\_____|
13 1.4 When will you make curl do XXXX ?
15 1.6 What do you get for making curl?
16 1.7 What about CURL from curl.com?
17 1.8 I have a problem who do I mail?
18 1.9 Where do I buy commercial support for curl?
19 1.10 How many are using curl?
20 1.11 Why don't you update ca-bundle.crt
21 1.12 I have a problem who can I chat with?
22 1.13 curl's ECCN number?
23 1.14 How do I submit my patch?
25 2. Install Related Problems
26 2.1 configure doesn't find OpenSSL even when it is installed
27 2.1.1 native linker doesn't find OpenSSL
28 2.1.2 only the libssl lib is missing
29 2.2 Does curl work/build with other SSL libraries?
30 2.3 Where can I find a copy of LIBEAY32.DLL?
31 2.4 Does curl support SOCKS (RFC 1928) ?
34 3.1 curl: (1) SSL is disabled, https: not supported
35 3.2 How do I tell curl to resume a transfer?
36 3.3 Why doesn't my posting using -F work?
37 3.4 How do I tell curl to run custom FTP commands?
38 3.5 How can I disable the Accept: */* header?
39 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
40 3.7 Can I use curl to delete/rename a file through FTP?
41 3.8 How do I tell curl to follow HTTP redirects?
42 3.9 How do I use curl in my favorite programming language?
43 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
44 3.11 How do I POST with a different Content-Type?
45 3.12 Why do FTP specific features over HTTP proxy fail?
46 3.13 Why does my single/double quotes fail?
47 3.14 Does curl support Javascript or PAC (automated proxy config)?
48 3.15 Can I do recursive fetches with curl?
49 3.16 What certificates do I need when I use SSL?
50 3.17 How do I list the root dir of an FTP server?
51 3.18 Can I use curl to send a POST/PUT and not wait for a response?
52 3.19 How do I get HTTP from a host using a specific IP address?
53 3.20 How to SFTP from my user's home directory?
54 3.21 Protocol xxx not supported or disabled in libcurl
55 3.22 curl -X gives me HTTP problems
58 4.1 Problems connecting to SSL servers.
59 4.2 Why do I get problems when I use & or % in the URL?
60 4.3 How can I use {, }, [ or ] to specify multiple URLs?
61 4.4 Why do I get downloaded data even though the web page doesn't exist?
62 4.5 Why do I get return code XXX from a HTTP server?
63 4.5.1 "400 Bad Request"
64 4.5.2 "401 Unauthorized"
67 4.5.5 "405 Method Not Allowed"
68 4.5.6 "301 Moved Permanently"
69 4.6 Can you tell me what error code 142 means?
70 4.7 How do I keep user names and passwords secret in Curl command lines?
72 4.9 Curl can't authenticate to the server that requires NTLM?
73 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
74 4.11 Why does my HTTP range requests return the full document?
75 4.12 Why do I get "certificate verify failed" ?
76 4.13 Why is curl -R on Windows one hour off?
77 4.14 Redirects work in browser but not with curl!
78 4.15 FTPS doesn't work
79 4.16 My HTTP POST or PUT requests are slow!
80 4.17 Non-functional connect timeouts on Windows
81 4.18 file:// URLs containing drive letters (Windows, NetWare)
82 4.19 Why doesn't cURL return an error when the network cable is unplugged?
85 5.1 Is libcurl thread-safe?
86 5.2 How can I receive all data into a large memory chunk?
87 5.3 How do I fetch multiple files with libcurl?
88 5.4 Does libcurl do Winsock initing on win32 systems?
89 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
90 5.6 What about Keep-Alive or persistent connections?
91 5.7 Link errors when building libcurl on Windows!
92 5.8 libcurl.so.X: open failed: No such file or directory
93 5.9 How does libcurl resolve host names?
94 5.10 How do I prevent libcurl from writing the response to stdout?
95 5.11 How do I make libcurl not receive the whole HTTP response?
96 5.12 Can I make libcurl fake or hide my real IP address?
97 5.13 How do I stop an ongoing transfer?
98 5.14 Using C++ non-static functions for callbacks?
99 5.15 How do I get an FTP directory listing?
100 5.16 I want a different time-out!
101 5.17 Can I write a server with libcurl?
104 6.1 I have a GPL program, can I use the libcurl library?
105 6.2 I have a closed-source program, can I use the libcurl library?
106 6.3 I have a BSD licensed program, can I use the libcurl library?
107 6.4 I have a program that uses LGPL libraries, can I use libcurl?
108 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
109 6.6 Can you please change the curl/libcurl license to XXXX?
110 6.7 What are my obligations when using libcurl in my commercial apps?
113 7.1 What is PHP/CURL?
114 7.2 Who wrote PHP/CURL?
115 7.3 Can I perform multiple requests using the same handle?
117 ==============================================================================
123 cURL is the name of the project. The name is a play on 'Client for URLs',
124 originally with URL spelled in uppercase to make it obvious it deals with
125 URLs. The fact it can also be pronounced 'see URL' also helped, it works as
126 an abbreviation for "Client URL Request Library" or why not the recursive
127 version: "Curl URL Request Library".
129 The cURL project produces two products:
133 A free and easy-to-use client-side URL transfer library, supporting DICT,
134 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3,
135 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP.
137 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
138 kerberos, HTTP form based upload, proxies, cookies, user+password
139 authentication, file transfer resume, http proxy tunneling and more!
141 libcurl is highly portable, it builds and works identically on numerous
142 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
143 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac
144 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF,
145 Android, Minix, IBM TPF and more...
147 libcurl is free, thread-safe, IPv6 compatible, feature rich, well
152 A command line tool for getting or sending files using URL syntax.
154 Since curl uses libcurl, curl supports the same wide range of common
155 Internet protocols that libcurl does.
157 We pronounce curl and cURL with an initial k sound: [kurl].
159 There are numerous sub-projects and related projects that also use the word
160 curl in the project names in various combinations, but you should take
161 notice that this FAQ is directed at the command-line tool named curl (and
162 libcurl the library), and may therefore not be valid for other curl-related
163 projects. (There is however a small section for the PHP/CURL in this FAQ.)
167 libcurl is a reliable and portable library which provides you with an easy
168 interface to a range of common Internet protocols.
170 You can use libcurl for free in your application, be it open source,
171 commercial or closed-source.
173 libcurl is most probably the most portable, most powerful and most often
174 used C-based multi-platform file transfer library on this planet - be it
175 open source or commercial.
177 1.3 What is curl not?
179 Curl is not a wget clone. That is a common misconception. Never, during
180 curl's development, have we intended curl to replace wget or compete on its
181 market. Curl is targeted at single-shot file transfers.
183 Curl is not a web site mirroring program. If you want to use curl to mirror
184 something: fine, go ahead and write a script that wraps around curl to make
185 it reality (like curlmirror.pl does).
187 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
188 but if you want systematic and sequential behavior you should write a
189 script (or write a new program that interfaces libcurl) and do it.
191 Curl is not a PHP tool, even though it works perfectly well when used from
192 or with PHP (when using the PHP/CURL module).
194 Curl is not a program for a single operating system. Curl exists, compiles,
195 builds and runs under a wide range of operating systems, including all
196 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
199 1.4 When will you make curl do XXXX ?
201 We love suggestions of what to change in order to make curl and libcurl
202 better. We do however believe in a few rules when it comes to the future of
205 * Curl -- the command line tool -- is to remain a non-graphical command line
206 tool. If you want GUIs or fancy scripting capabilities, you should look
207 for another tool that uses libcurl.
209 * We do not add things to curl that other small and available tools already
210 do very fine at the side. Curl's output is fine to pipe into another
211 program or redirect to another file for the next program to interpret.
213 * We focus on protocol related issues and improvements. If you wanna do more
214 magic with the supported protocols than curl currently does, chances are
215 big we will agree. If you wanna add more protocols, we may very well
218 * If you want someone else to make all the work while you wait for us to
219 implement it for you, that is not a very friendly attitude. We spend a
220 considerable time already on maintaining and developing curl. In order to
221 get more out of us, you should consider trading in some of your time and
224 * If you write the code, chances are bigger that it will get into curl
229 curl and libcurl are not made by any single individual. Daniel Stenberg is
230 project leader and main developer, but other persons' submissions are
231 important and crucial. Anyone can contribute and post their changes and
232 improvements and have them inserted in the main sources (of course on the
233 condition that developers agree on that the fixes are good).
235 The full list of all contributors is found in the docs/THANKS file.
237 curl is developed by a community, with Daniel at the wheel.
239 1.6 What do you get for making curl?
241 Project cURL is entirely free and open. No person gets paid for developing
242 (lib)curl on full or even part time. We do this voluntarily on our spare
243 time. Occasionally companies pay individual developers to work on curl, but
244 that's up to each company and developer. It is not controlled by nor
245 supervised in any way by the project.
247 We still get help from companies. Haxx provides web site, bandwidth, mailing
248 lists etc and sourceforge.net hosts project services we take advantage from,
249 like the bug tracker. Also again, some companies have sponsored certain
250 parts of the development in the past and I hope some will continue to do so
253 If you want to support our project, consider a donation or a banner-program
254 or even better: by helping us coding, documenting, testing etc.
256 1.7 What about CURL from curl.com?
258 During the summer 2001, curl.com was busy advertising their client-side
259 programming language for the web, named CURL.
261 We are in no way associated with curl.com or their CURL programming
264 Our project name curl has been in effective use since 1998. We were not the
265 first computer related project to use the name "curl" and do not claim any
266 first-hand rights to the name.
268 We recognize that we will be living in parallel with curl.com and wish them
271 1.8 I have a problem who do I mail?
273 Please do not mail any single individual unless you really need to. Keep
274 curl-related questions on a suitable mailing list. All available mailing
275 lists are listed in the MANUAL document and online at
276 http://curl.haxx.se/mail/
278 Keeping curl-related questions and discussions on mailing lists allows
279 others to join in and help, to share their ideas, contribute their
280 suggestions and spread their wisdom. Keeping discussions on public mailing
281 lists also allows for others to learn from this (both current and future
282 users thanks to the web based archives of the mailing lists), thus saving us
283 from having to repeat ourselves even more. Thanks for respecting this.
285 If you have found or simply suspect a security problem in curl or libcurl,
286 mail curl-security at haxx.se (closed list of receivers, mails are not
287 disclosed) and tell. Then we can produce a fix in a timely manner before the
288 flaw is announced to the world, thus lessen the impact the problem will have
291 1.9 Where do I buy commercial support for curl?
293 curl is fully open source. It means you can hire any skilled engineer to fix
294 your curl-related problems.
296 We list available alternatives on the curl web site:
297 http://curl.haxx.se/support.html
299 1.10 How many are using curl?
301 It is impossible to tell.
303 We don't know how many users that knowingly have installed and use curl.
305 We don't know how many users that use curl without knowing that they are in
308 We don't know how many users that downloaded or installed curl and then
311 In May 2012 Daniel did a counting game and came up with a number that may
312 be completely wrong or somewhat accurate. 300 million!
314 See http://daniel.haxx.se/blog/2012/05/16/300m-users/
316 1.11 Why don't you update ca-bundle.crt
318 The ca-bundle.crt file that used to be bundled with curl was very outdated
319 (it being last modified year 2000 should tell) and must be replaced with a
320 much more modern and up-to-date version by anyone who wants to verify peers
321 anyway. It is no longer provided, the last curl release that shipped it was
324 In the cURL project we've decided not to attempt to keep this file updated
325 (or even present anymore) since deciding what to add to a ca cert bundle is
326 an undertaking we've not been ready to accept, and the one we can get from
327 Mozilla is perfectly fine so there's no need to duplicate that work.
329 Today, with many services performed over HTTPS, every operating system
330 should come with a default ca cert bundle that can be deemed somewhat
331 trustworthy and that collection (if reasonably updated) should be deemed to
332 be a lot better than a private curl version.
334 If you want the most recent collection of ca certs that Mozilla Firefox
335 uses, we recommend that you extract the collection yourself from Mozilla
336 Firefox (by running 'make ca-bundle), or by using our online service setup
337 for this purpose: http://curl.haxx.se/docs/caextract.html
339 1.12 I have a problem who can I chat with?
341 There's a bunch of friendly people hanging out in the #curl channel on the
342 IRC network irc.freenode.net. If you're polite and nice, chances are big
343 that you can get -- or provide -- help instantly.
345 1.13 curl's ECCN number?
347 The US government restricts exports of software that contains or uses
348 cryptography. When doing so, the Export Control Classification Number (ECCN)
349 is used to identify the level of export control etc.
351 ASF gives a good explanation at http://www.apache.org/dev/crypto.html
353 We believe curl's number might be ECCN 5D002, another possibility is
354 5D992. It seems necessary to write them, asking to confirm.
356 Comprehensible explanations of the meaning of such numbers and how to
357 obtain them (resp.) are here
359 http://www.bis.doc.gov/licensing/exportingbasics.htm
360 http://www.bis.doc.gov/licensing/do_i_needaneccn.html
362 An incomprehensible description of the two numbers above is here
363 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
365 1.14 How do I submit my patch?
367 When you have made a patch or a change of whatever sort, and want to submit
368 that to the project, there are a few different ways we prefer:
370 o send a patch to the curl-library mailing list. We're many subscribers
371 there and there are lots of people who can review patches, comment on them
372 and "receive" them properly.
374 o if your patch changes or fixes a bug, you can also opt to submit a bug
375 report in the bug tracker and attach your patch there. There are less
376 people involved there.
378 Lots of more details are found in the CONTRIBUTE and INTERNALS docs.
381 2. Install Related Problems
383 2.1 configure doesn't find OpenSSL even when it is installed
385 This may be because of several reasons.
387 2.1.1 native linker doesn't find openssl
390 Solaris (native cc compiler)
391 HPUX (native cc compiler)
392 SGI IRIX (native cc compiler)
393 SCO UNIX (native cc compiler)
395 When configuring curl, I specify --with-ssl. OpenSSL is installed in
396 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
397 CRYPTO_lock in -lcrypto
399 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
400 -lcrypto, so ld can't find the library. This is due to a bug in the GNU
403 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
404 ./configure places the -L/usr/local/ssl/lib early enough in the command
405 line to make things work
407 2.1.2 only the libssl lib is missing
409 If all include files and the libcrypto lib is present, with only the
410 libssl being missing according to configure, this is mostly likely because
411 a few functions are left out from the libssl.
413 If the function names missing include RSA or RSAREF you can be certain
414 that this is because libssl requires the RSA and RSAREF libs to build.
416 See the INSTALL file section that explains how to add those libs to
417 configure. Make sure that you remove the config.cache file before you
418 rerun configure with the new flags.
420 2.2 Does curl work/build with other SSL libraries?
422 Curl has been written to use a generic SSL function layer internally, and
423 that SSL functionality can then be provided by one out of many different SSL
426 curl can be built to use one of the following SSL alternatives: OpenSSL,
427 GnuTLS, yassl, NSS, PolarSSL, axTLS, Secure Transport (native iOS/OS X),
428 schannel (native Windows) or qssl (native IBM i). They all have their pros
429 and cons, and we try to maintain a comparison of them here:
430 http://curl.haxx.se/docs/ssl-compared.html
432 2.3 Where can I find a copy of LIBEAY32.DLL?
434 That is an OpenSSL binary built for Windows.
436 Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
437 on a windows machine to do https://. Check out the curl web site to find
438 accurate and up-to-date pointers to recent OpenSSL DLLs and other binary
441 2.4 Does curl support SOCKS (RFC 1928) ?
443 Yes, SOCKS 4 and 5 are supported.
448 3.1 curl: (1) SSL is disabled, https: not supported
450 If you get this output when trying to get anything from a https:// server,
451 it means that the instance of curl/libcurl that you're using was built
452 without support for this protocol.
454 This could've happened if the configure script that was run at build time
455 couldn't find all libs and include files curl requires for SSL to work. If
456 the configure script fails to find them, curl is simply built without SSL
459 To get the https:// support into a curl that was previously built but that
460 reports that https:// is not supported, you should dig through the document
461 and logs and check out why the configure script doesn't find the SSL libs
462 and/or include files.
464 Also, check out the other paragraph in this FAQ labelled "configure doesn't
465 find OpenSSL even when it is installed".
467 3.2 How do I tell curl to resume a transfer?
469 Curl supports resumed transfers both ways on both FTP and HTTP.
472 3.3 Why doesn't my posting using -F work?
474 You can't simply use -F or -d at your choice. The web server that will
475 receive your post assumes one of the formats. If the form you're trying to
476 "fake" sets the type to 'multipart/form-data', then and only then you must
477 use the -F type. In all the most common cases, you should use -d which then
478 causes a posting with the type 'application/x-www-form-urlencoded'.
480 This is described in some detail in the MANUAL and TheArtOfHttpScripting
481 documents, and if you don't understand it the first time, read it again
482 before you post questions about this to the mailing list. Also, try reading
483 through the mailing list archives for old postings and questions regarding
486 3.4 How do I tell curl to run custom FTP commands?
488 You can tell curl to perform optional commands both before and/or after a
489 file transfer. Study the -Q/--quote option.
491 Since curl is used for file transfers, you don't normally use curl to
492 perform FTP commands without transferring anything. Therefore you must
493 always specify a URL to transfer to/from even when doing custom FTP
494 commands, or use -I which implies the "no body" option sent to libcurl.
496 3.5 How can I disable the Accept: */* header?
498 You can change all internally generated headers by adding a replacement with
499 the -H/--header option. By adding a header with empty contents you safely
500 disable that one. Use -H "Accept:" to disable that specific header.
502 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
504 To curl, all contents are alike. It doesn't matter how the page was
505 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain
506 HTML-files. There's no difference to curl and it doesn't even know what kind
507 of language that generated the page.
509 See also item 3.14 regarding javascript.
511 3.7 Can I use curl to delete/rename a file through FTP?
513 Yes. You specify custom FTP commands with -Q/--quote.
515 One example would be to delete a file after you have downloaded it:
517 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
519 or rename a file after upload:
521 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
523 3.8 How do I tell curl to follow HTTP redirects?
525 Curl does not follow so-called redirects by default. The Location: header
526 that informs the client about this is only interpreted if you're using the
527 -L/--location option. As in:
529 curl -L http://redirector.com
531 Not all redirects are HTTP ones, see 4.14
533 3.9 How do I use curl in my favorite programming language?
535 There exist many language interfaces/bindings for curl that integrates it
536 better with various languages. If you are fluid in a script language, you
537 may very well opt to use such an interface instead of using the command line
540 Find out more about which languages that support curl directly, and how to
541 install and use them, in the libcurl section of the curl web site:
542 http://curl.haxx.se/libcurl/
544 All the various bindings to libcurl are made by other projects and people,
545 outside of the cURL project. The cURL project itself only produces libcurl
546 with its plain C API. If you don't find anywhere else to ask you can ask
547 about bindings on the curl-library list too, but be prepared that people on
548 that list may not know anything about bindings.
550 In October 2009, there were interfaces available for the following
551 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
552 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
553 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
554 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
555 Q, wxwidgets and XBLite. By the time you read this, additional ones may have
558 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
560 Curl adheres to the HTTP spec, which basically means you can play with *any*
561 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
562 XML-RPC are all such ones. You can use -X to set custom requests and -H to
563 set custom headers (or replace internally generated ones).
565 Using libcurl is of course just as fine and you'd just use the proper
566 library options to do the same.
568 3.11 How do I POST with a different Content-Type?
570 You can always replace the internally generated headers with -H/--header.
571 To make a simple HTTP POST with text/xml as content-type, do something like:
573 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
575 3.12 Why do FTP specific features over HTTP proxy fail?
577 Because when you use a HTTP proxy, the protocol spoken on the network will
578 be HTTP, even if you specify a FTP URL. This effectively means that you
579 normally can't use FTP specific features such as FTP upload and FTP quote
582 There is one exception to this rule, and that is if you can "tunnel through"
583 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
584 and is generally not available as proxy admins usually disable tunneling to
585 other ports than 443 (which is used for HTTPS access through proxies).
587 3.13 Why does my single/double quotes fail?
589 To specify a command line option that includes spaces, you might need to
590 put the entire option within quotes. Like in:
592 curl -d " with spaces " url.com
596 curl -d ' with spaces ' url.com
598 Exactly what kind of quotes and how to do this is entirely up to the shell
599 or command line interpreter that you are using. For most unix shells, you
600 can more or less pick either single (') or double (") quotes. For
601 Windows/DOS prompts I believe you're forced to use double (") quotes.
603 Please study the documentation for your particular environment. Examples in
604 the curl docs will use a mix of both these ones as shown above. You must
605 adjust them to work in your environment.
607 Remember that curl works and runs on more operating systems than most single
608 individuals have ever tried.
610 3.14 Does curl support Javascript or PAC (automated proxy config)?
612 Many web pages do magic stuff using embedded Javascript. Curl and libcurl
613 have no built-in support for that, so it will be treated just like any other
616 .pac files are a netscape invention and are sometimes used by organizations
617 to allow them to differentiate which proxies to use. The .pac contents is
618 just a Javascript program that gets invoked by the browser and that returns
619 the name of the proxy to connect to. Since curl doesn't support Javascript,
620 it can't support .pac proxy configuration either.
622 Some workarounds usually suggested to overcome this Javascript dependency:
624 - Depending on the Javascript complexity, write up a script that
625 translates it to another language and execute that.
627 - Read the Javascript code and rewrite the same logic in another language.
629 - Implement a Javascript interpreter, people have successfully used the
630 Mozilla Javascript engine in the past.
632 - Ask your admins to stop this, for a static proxy setup or similar.
634 3.15 Can I do recursive fetches with curl?
636 No. curl itself has no code that performs recursive operations, such as
637 those performed by wget and similar tools.
639 There exist wrapper scripts with that functionality (for example the
640 curlmirror perl script), and you can write programs based on libcurl to do
641 it, but the command line tool curl itself cannot.
643 3.16 What certificates do I need when I use SSL?
645 There are three different kinds of "certificates" to keep track of when we
646 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
648 - Client certificate. The server you communicate may require that you can
649 provide this in order to prove that you actually are who you claim to be.
650 If the server doesn't require this, you don't need a client certificate.
652 A client certificate is always used together with a private key, and the
653 private key has a pass phrase that protects it.
655 - Server certificate. The server you communicate with has a server
656 certificate. You can and should verify this certificate to make sure that
657 you are truly talking to the real server and not a server impersonating
660 - Certificate Authority certificate ("CA cert"). You often have several CA
661 certs in a CA cert bundle that can be used to verify a server certificate
662 that was signed by one of the authorities in the bundle. curl does not
663 come with a CA cert bundle but most curl installs provide one. You can
664 also override the default.
666 The server certificate verification process is made by using a Certificate
667 Authority certificate ("CA cert") that was used to sign the server
668 certificate. Server certificate verification is enabled by default in curl
669 and libcurl and is often the reason for problems as explained in FAQ entry
670 4.12 and the SSLCERTS document
671 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
672 "self-signed" or otherwise signed by a CA that you do not have a CA cert
673 for, cannot be verified. If the verification during a connect fails, you
674 are refused access. You then need to explicitly disable the verification
675 to connect to the server.
677 3.17 How do I list the root dir of an FTP server?
679 There are two ways. The way defined in the RFC is to use an encoded slash
680 in the first path part. List the "/tmp" dir like this:
682 curl ftp://ftp.sunet.se/%2ftmp/
684 or the not-quite-kosher-but-more-readable way, by simply starting the path
685 section of the URL with a slash:
687 curl ftp://ftp.sunet.se//tmp/
689 3.18 Can I use curl to send a POST/PUT and not wait for a response?
693 But you could easily write your own program using libcurl to do such stunts.
695 3.19 How do I get HTTP from a host using a specific IP address?
697 For example, you may be trying out a web site installation that isn't yet in
698 the DNS. Or you have a site using multiple IP addresses for a given host
699 name and you want to address a specific one out of the set.
701 Set a custom Host: header that identifies the server name you want to reach
702 but use the target IP address in the URL:
704 curl --header "Host: www.example.com" http://127.0.0.1/
706 You can also opt to add faked host name entries to curl with the --resolve
707 option. That has the added benefit that things like redirects will also work
708 properly. The above operation would instead be done as:
710 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/
712 3.20 How to SFTP from my user's home directory?
714 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to
715 work with. It means that if you don't specify that you want the user's home
716 directory, you get the actual root directory.
718 To specify a file in your user's home directory, you need to use the correct
719 URL syntax which for sftp might look similar to:
721 curl -O -u user:password sftp://example.com/~/file.txt
723 and for SCP it is just a different protocol prefix:
725 curl -O -u user:password scp://example.com/~/file.txt
727 3.21 Protocol xxx not supported or disabled in libcurl
729 When passing on a URL to curl to use, it may respond that the particular
730 protocol is not supported or disabled. The particular way this error message
731 is phrased is because curl doesn't make a distinction internally of whether
732 a particular protocol is not supported (ie never got any code added that
733 knows how to speak that protocol) or if it was explicitly disabled. curl can
734 be built to only support a given set of protocols, and the rest would then
735 be disabled or not supported.
737 Note that this error will also occur if you pass a wrongly spelled protocol
738 part as in "htpt://example.com" or as in the less evident case if you prefix
739 the protocol part with a space as in " http://example.com/".
741 3.22 curl -X gives me HTTP problems
743 In normal circumstances, -X should hardly ever be used.
745 By default you use curl without explicitly saying which request method to
746 use when the URL identifies a HTTP transfer. If you just pass in a URL like
747 "curl http://example.com" it will use GET. If you use -d or -F curl will use
748 POST, -I will cause a HEAD and -T will make it a PUT.
750 If for whatever reason you're not happy with these default choices that curl
751 does for you, you can override those request methods by specifying -X
752 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X
755 It is thus pointless to do "curl -XGET [URL]" as GET would be used
756 anyway. In the same vein it is pointless to do "curl -X POST -d data
757 [URL]"... But you can make a fun and somewhat rare request that sends a
758 request-body in a GET request with something like "curl -X GET -d data
761 Note that -X doesn't change curl's behavior. It only modifies the actual
762 string sent in the request.
764 Accordingly, by using -XPOST on a command line that for example would follow
765 a 303 redirect, you will effectively prevent curl from behaving
771 4.1 Problems connecting to SSL servers.
773 It took a very long time before we could sort out why curl had problems to
774 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
775 error sometimes showed up similar to:
777 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
779 It turned out to be because many older SSL servers don't deal with SSLv3
780 requests properly. To correct this problem, tell curl to select SSLv2 from
781 the command line (-2/--sslv2).
783 There have also been examples where the remote server didn't like the SSLv2
784 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
786 4.2 Why do I get problems when I use & or % in the URL?
788 In general unix shells, the & symbol is treated specially and when used, it
789 runs the specified command in the background. To safely send the & as a part
790 of a URL, you should quote the entire URL by using single (') or double (")
791 quotes around it. Similar problems can also occur on some shells with other
792 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
794 An example that would invoke a remote CGI that uses &-symbols could be:
796 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
798 In Windows, the standard DOS shell treats the %-symbol specially and you
799 need to use TWO %-symbols for each single one you want to use in the URL.
801 Also note that if you want the literal %-symbol to be part of the data you
802 pass in a POST using -d/--data you must encode it as '%25' (which then also
803 needs the %-symbol doubled on Windows machines).
805 4.3 How can I use {, }, [ or ] to specify multiple URLs?
807 Because those letters have a special meaning to the shell, and to be used in
808 a URL specified to curl you must quote them.
810 An example that downloads two URLs (sequentially) would do:
812 curl '{curl,www}.haxx.se'
814 To be able to use those letters as actual parts of the URL (without using
815 them for the curl URL "globbing" system), use the -g/--globoff option:
817 curl -g 'www.site.com/weirdname[].html'
819 4.4 Why do I get downloaded data even though the web page doesn't exist?
821 Curl asks remote servers for the page you specify. If the page doesn't exist
822 at the server, the HTTP protocol defines how the server should respond and
823 that means that headers and a "page" will be returned. That's simply how
826 By using the --fail option you can tell curl explicitly to not get any data
827 if the HTTP return code doesn't say success.
829 4.5 Why do I get return code XXX from a HTTP server?
831 RFC2616 clearly explains the return codes. This is a short transcript. Go
832 read the RFC for exact details:
834 4.5.1 "400 Bad Request"
836 The request could not be understood by the server due to malformed
837 syntax. The client SHOULD NOT repeat the request without modifications.
839 4.5.2 "401 Unauthorized"
841 The request requires user authentication.
843 4.5.3 "403 Forbidden"
845 The server understood the request, but is refusing to fulfil it.
846 Authorization will not help and the request SHOULD NOT be repeated.
848 4.5.4 "404 Not Found"
850 The server has not found anything matching the Request-URI. No indication
851 is given of whether the condition is temporary or permanent.
853 4.5.5 "405 Method Not Allowed"
855 The method specified in the Request-Line is not allowed for the resource
856 identified by the Request-URI. The response MUST include an Allow header
857 containing a list of valid methods for the requested resource.
859 4.5.6 "301 Moved Permanently"
861 If you get this return code and an HTML output similar to this:
863 <H1>Moved Permanently</H1> The document has moved <A
864 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
866 it might be because you request a directory URL but without the trailing
867 slash. Try the same operation again _with_ the trailing URL, or use the
868 -L/--location option to follow the redirection.
870 4.6 Can you tell me what error code 142 means?
872 All curl error codes are described at the end of the man page, in the
873 section called "EXIT CODES".
875 Error codes that are larger than the highest documented error code means
876 that curl has exited due to a crash. This is a serious error, and we
877 appreciate a detailed bug report from you that describes how we could go
878 ahead and repeat this!
880 4.7 How do I keep user names and passwords secret in Curl command lines?
882 This problem has two sides:
884 The first part is to avoid having clear-text passwords in the command line
885 so that they don't appear in 'ps' outputs and similar. That is easily
886 avoided by using the "-K" option to tell curl to read parameters from a file
887 or stdin to which you can pass the secret info. curl itself will also
888 attempt to "hide" the given password by blanking out the option - this
889 doesn't work on all platforms.
891 To keep the passwords in your account secret from the rest of the world is
892 not a task that curl addresses. You could of course encrypt them somehow to
893 at least hide them from being read by human eyes, but that is not what
894 anyone would call security.
896 Also note that regular HTTP (using Basic authentication) and FTP passwords
897 are sent in clear across the network. All it takes for anyone to fetch them
898 is to listen on the network. Eavesdropping is very easy. Use more secure
899 authentication methods (like Digest, Negotiate or even NTLM) or consider the
900 SSL-based alternatives HTTPS and FTPS.
904 It is not a bug if the behavior is documented. Read the docs first.
905 Especially check out the KNOWN_BUGS file, it may be a documented bug!
907 If it is a problem with a binary you've downloaded or a package for your
908 particular platform, try contacting the person who built the package/archive
911 If there is a bug, read the BUGS document first. Then report it as described
914 4.9 Curl can't authenticate to the server that requires NTLM?
916 NTLM support requires OpenSSL, GnuTLS, NSS, Secure Transport, or Microsoft
917 Windows libraries at build-time to provide this functionality.
919 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
920 should not use such ones.
922 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
924 Many web servers allow or demand that the administrator configures the
925 server properly for these requests to work on the web server.
927 Some servers seem to support HEAD only on certain kinds of URLs.
929 To fully grasp this, try the documentation for the particular server
930 software you're trying to interact with. This is not anything curl can do
933 4.11 Why does my HTTP range requests return the full document?
935 Because the range may not be supported by the server, or the server may
936 choose to ignore it and return the full document anyway.
938 4.12 Why do I get "certificate verify failed" ?
940 You invoke curl 7.10 or later to communicate on a https:// URL and get an
941 error back looking something similar to this:
943 curl: (35) SSL: error:14090086:SSL routines:
944 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
946 Then it means that curl couldn't verify that the server's certificate was
947 good. Curl verifies the certificate using the CA cert bundle that comes with
948 the curl installation.
950 To disable the verification (which makes it act like curl did before 7.10),
951 use -k. This does however enable man-in-the-middle attacks.
953 If you get this failure but are having a CA cert bundle installed and used,
954 the server's certificate is not signed by one of the CA's in the bundle. It
955 might for example be self-signed. You then correct this problem by obtaining
956 a valid CA cert for the server. Or again, decrease the security by disabling
959 Details are also in the SSLCERTS file in the release archives, found online
960 here: http://curl.haxx.se/docs/sslcerts.html
962 4.13 Why is curl -R on Windows one hour off?
964 During daylight savings time, when -R is used, curl will set a time that
965 appears one hour off. This happens due to a flaw in how Windows stores and
966 uses file modification times and it is not easily worked around. For details
967 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
969 4.14 Redirects work in browser but not with curl!
971 curl supports HTTP redirects fine (see item 3.8). Browsers generally support
972 at least two other ways to perform directs that curl does not:
974 - Meta tags. You can write a HTML tag that will cause the browser to
975 redirect to another given URL after a certain time.
977 - Javascript. You can write a Javascript program embedded in a HTML page
978 that redirects the browser to another given URL.
980 There is no way to make curl follow these redirects. You must either
981 manually figure out what the page is set to do, or you write a script that
982 parses the results and fetches the new URL.
984 4.15 FTPS doesn't work
986 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
989 When a URL is used that starts with FTPS://, curl assumes implicit SSL on
990 the control connection and will therefore immediately connect and try to
991 speak SSL. FTPS:// connections default to port 990.
993 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
994 of its related flavours). This is the most common method, and the one
995 mandated by RFC4217. This kind of connection then of course uses the
996 standard FTP port 21 by default.
998 4.16 My HTTP POST or PUT requests are slow!
1000 libcurl makes all POST and PUT requests (except for POST requests with a
1001 very tiny request body) use the "Expect: 100-continue" header. This header
1002 allows the server to deny the operation early so that libcurl can bail out
1003 already before having to send any data. This is useful in authentication
1006 However, many servers don't implement the Expect: stuff properly and if the
1007 server doesn't respond (positively) within 1 second libcurl will continue
1008 and send off the data anyway.
1010 You can disable libcurl's use of the Expect: header the same way you disable
1011 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
1013 4.17 Non-functional connect timeouts
1015 In most Windows setups having a timeout longer than 21 seconds make no
1016 difference, as it will only send 3 TCP SYN packets and no more. The second
1017 packet sent three seconds after the first and the third six seconds after
1018 the second. No more than three packets are sent, no matter how long the
1021 See option TcpMaxConnectRetransmissions on this page:
1022 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
1024 Also, even on non-Windows systems there may run a firewall or anti-virus
1025 software or similar that accepts the connection but does not actually do
1026 anything else. This will make (lib)curl to consider the connection connected
1027 and thus the connect timeout won't trigger.
1029 4.18 file:// URLs containing drive letters (Windows, NetWare)
1031 When using cURL to try to download a local file, one might use a URL
1036 You'll find that even if D:\blah.txt does exist, cURL returns a 'file
1039 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
1040 file:// URLs must contain a host component, but it is ignored by
1041 most implementations. In the above example, 'D:' is treated as the
1042 host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
1043 If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
1044 and if that doesn't exist you will get the not found error.
1046 To fix this problem, use file:// URLs with *three* leading slashes:
1050 Alternatively, if it makes more sense, specify 'localhost' as the host
1053 file://localhost/D:/blah.txt
1055 In either case, cURL should now be looking for the correct file.
1057 4.19 Why doesn't cURL return an error when the network cable is unplugged?
1059 Unplugging the cable is not an error situation. The TCP/IP protocol stack
1060 was designed to be fault tolerant, so even though there may be a physical
1061 break somewhere the connection shouldn't be affected, just possibly
1062 delayed. Eventually, the physical break will be fixed or the data will be
1063 re-routed around the physical problem.
1065 In such cases, the TCP/IP stack is responsible for detecting when the
1066 network connection is irrevocably lost. Since with some protocols it is
1067 perfectly legal for the client wait indefinitely for data, the stack may
1068 never report a problem, and even when it does, it can take up to 20 minutes
1069 for it to detect an issue. The curl option --keepalive-time enables
1070 keep-alive support in the TCP/IP stack which makes it periodically probe the
1071 connection to make sure it is still available to send data. That should
1072 reliably detect any TCP/IP network failure.
1074 But even that won't detect the network going down before the TCP/IP
1075 connection is established (e.g. during a DNS lookup) or using protocols that
1076 don't use TCP. To handle those situations, curl offers a number of timeouts
1077 on its own. --speed-limit/--speed-time will abort if the data transfer rate
1078 falls too low, and --connect-timeout and --max-time can be used to put an
1079 overall timeout on the connection phase or the entire transfer.
1084 5.1 Is libcurl thread-safe?
1088 We have written the libcurl code specifically adjusted for multi-threaded
1089 programs. libcurl will use thread-safe functions instead of non-safe ones if
1090 your system has such.
1092 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
1093 need to provide one or two locking functions:
1095 http://www.openssl.org/docs/crypto/threads.html
1097 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
1098 need to provide locking function(s) for libgcrypt (which is used by GnuTLS
1099 for the crypto functions).
1101 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
1103 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
1105 5.2 How can I receive all data into a large memory chunk?
1107 [ See also the examples/getinmemory.c source ]
1109 You are in full control of the callback function that gets called every time
1110 there is data received from the remote server. You can make that callback do
1111 whatever you want. You do not have to write the received data to a file.
1113 One solution to this problem could be to have a pointer to a struct that you
1114 pass to the callback function. You set the pointer using the
1115 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
1116 instead of a FILE * to a file:
1118 /* imaginary struct */
1119 struct MemoryStruct {
1124 /* imaginary callback function */
1126 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
1128 size_t realsize = size * nmemb;
1129 struct MemoryStruct *mem = (struct MemoryStruct *)data;
1131 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
1133 memcpy(&(mem->memory[mem->size]), ptr, realsize);
1134 mem->size += realsize;
1135 mem->memory[mem->size] = 0;
1140 5.3 How do I fetch multiple files with libcurl?
1142 libcurl has excellent support for transferring multiple files. You should
1143 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
1144 with curl_easy_perform(). The handle you get from curl_easy_init() is not
1145 only reusable, but you're even encouraged to reuse it if you can, as that
1146 will enable libcurl to use persistent connections.
1148 5.4 Does libcurl do Winsock initialization on win32 systems?
1150 Yes, if told to in the curl_global_init() call.
1152 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
1154 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
1155 that DLL use the FILE * (as the DLL and the client application cannot access
1156 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
1157 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
1158 file, even if that simply writes the data to the specified FILE *.
1159 Similarly, if you use CURLOPT_READDATA you must also specify
1160 CURLOPT_READFUNCTION.
1162 5.6 What about Keep-Alive or persistent connections?
1164 curl and libcurl have excellent support for persistent connections when
1165 transferring several files from the same server. Curl will attempt to reuse
1166 connections for all URLs specified on the same command line/config file, and
1167 libcurl will reuse connections for all transfers that are made using the
1168 same libcurl handle.
1170 When you use the easy interface, the connection cache is kept within the
1171 easy handle. If you instead use the multi interface, the connection cache
1172 will be kept within the multi handle and will be shared among all the easy
1173 handles that are used within the same multi handle.
1175 5.7 Link errors when building libcurl on Windows!
1177 You need to make sure that your project, and all the libraries (both static
1178 and dynamic) that it links against, are compiled/linked against the same run
1181 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
1182 options to the command line compiler. /MD (linking against MSVCRT dll) seems
1183 to be the most commonly used option.
1185 When building an application that uses the static libcurl library, you must
1186 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
1187 dynamic import symbols. If you're using Visual Studio, you need to instead
1188 add CURL_STATICLIB in the "Preprocessor Definitions" section.
1190 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
1191 have linked against the wrong (static) library. If you want to use the
1192 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
1193 the import libraries below. These are the libraries produced by the various
1194 lib/Makefile.* files:
1196 Target: static lib. import lib for libcurl*.dll.
1197 -----------------------------------------------------------
1198 MingW: libcurl.a libcurldll.a
1199 MSVC (release): libcurl.lib libcurl_imp.lib
1200 MSVC (debug): libcurld.lib libcurld_imp.lib
1201 Borland: libcurl.lib libcurl_imp.lib
1203 5.8 libcurl.so.X: open failed: No such file or directory
1205 This is an error message you might get when you try to run a program linked
1206 with a shared version of libcurl and your run-time linker (ld.so) couldn't
1207 find the shared library named libcurl.so.X. (Where X is the number of the
1208 current libcurl ABI, typically 3 or 4).
1210 You need to make sure that ld.so finds libcurl.so.X. You can do that
1211 multiple ways, and it differs somewhat between different operating systems,
1212 but they are usually:
1214 * Add an option to the linker command line that specify the hard-coded path
1215 the run-time linker should check for the lib (usually -R)
1217 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
1218 should check for libs
1220 * Adjust the system's config to check for libs in the directory where you've
1221 put the dir (like Linux's /etc/ld.so.conf)
1223 'man ld.so' and 'man ld' will tell you more details
1225 5.9 How does libcurl resolve host names?
1227 libcurl supports a large a number of different name resolve functions. One
1228 of them is picked at build-time and will be used unconditionally. Thus, if
1229 you want to change name resolver function you must rebuild libcurl and tell
1230 it to use a different function.
1232 - The non-ipv6 resolver that can use one out of four host name resolve calls
1233 (depending on what your system supports):
1236 B - gethostbyname_r() with 3 arguments
1237 C - gethostbyname_r() with 5 arguments
1238 D - gethostbyname_r() with 6 arguments
1240 - The ipv6-resolver that uses getaddrinfo()
1242 - The c-ares based name resolver that uses the c-ares library for resolves.
1243 Using this offers asynchronous name resolves.
1245 - The threaded resolver (default option on Windows). It uses:
1247 A - gethostbyname() on plain ipv4 hosts
1248 B - getaddrinfo() on ipv6-enabled hosts
1250 Also note that libcurl never resolves or reverse-lookups addresses given as
1251 pure numbers, such as 127.0.0.1 or ::1.
1253 5.10 How do I prevent libcurl from writing the response to stdout?
1255 libcurl provides a default built-in write function that writes received data
1256 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
1257 set CURLOPT_WRITEDATA to a different FILE * handle.
1259 5.11 How do I make libcurl not receive the whole HTTP response?
1261 You make the write callback (or progress callback) return an error and
1262 libcurl will then abort the transfer.
1264 5.12 Can I make libcurl fake or hide my real IP address?
1266 No. libcurl operates on a higher level than so. Besides, faking IP address
1267 would imply sending IP packages with a made-up source address, and then you
1268 normally get a problem with intercepting the packages sent back as they
1269 would then not be routed to you!
1271 If you use a proxy to access remote sites, the sites will not see your local
1272 IP address but instead the address of the proxy.
1274 Also note that on many networks NATs or other IP-munging techniques are used
1275 that makes you see and use a different IP address locally than what the
1276 remote server will see you coming from.
1278 5.13 How do I stop an ongoing transfer?
1280 With the easy interface you make sure to return the correct error code from
1281 one of the callbacks, but none of them are instant. There is no function you
1282 can call from another thread or similar that will stop it immediately.
1283 Instead, you need to make sure that one of the callbacks you use returns an
1284 appropriate value that will stop the transfer. Suitable callbacks that you
1285 can do this with include the progress callback, the read callback and the
1288 If you're using the multi interface, you can also stop a transfer by
1289 removing the particular easy handle from the multi stack at any moment you
1290 think the transfer is done.
1292 5.14 Using C++ non-static functions for callbacks?
1294 libcurl is a C library, it doesn't know anything about C++ member functions.
1296 You can overcome this "limitation" with a relative ease using a static
1297 member function that is passed a pointer to the class:
1299 // f is the pointer to your object.
1300 static YourClass::func(void *buffer, size_t sz, size_t n, void *f)
1302 // Call non-static member function.
1303 static_cast<YourClass*>(f)->nonStaticFunction();
1306 // This is how you pass pointer to the static function:
1307 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func);
1308 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
1310 5.15 How do I get an FTP directory listing?
1312 If you end the FTP URL you request with a slash, libcurl will provide you
1313 with a directory listing of that given directory. You can also set
1314 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
1317 The follow-up question that tend to follow the previous one, is how a
1318 program is supposed to parse the directory listing. How does it know what's
1319 a file and what's a dir and what's a symlink etc. The harsh reality is that
1320 FTP provides no such fine and easy-to-parse output. The output format FTP
1321 servers respond to LIST commands are entirely at the server's own liking and
1322 the NLST output doesn't reveal any types and in many cases don't even
1323 include all the directory entries. Also, both LIST and NLST tend to hide
1324 unix-style hidden files (those that start with a dot) by default so you need
1325 to do "LIST -a" or similar to see them.
1327 The application thus needs to parse the LIST output. One such existing
1328 list parser is available at http://cr.yp.to/ftpparse.html Versions of
1329 libcurl since 7.21.0 also provide the ability to specify a wildcard to
1330 download multiple files from one FTP directory.
1332 5.16 I want a different time-out!
1334 Time and time again users realize that CURLOPT_TIMEOUT and
1335 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all
1336 the various use cases and scenarios applications end up with.
1338 libcurl offers many more ways to time-out operations. A common alternative
1339 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to
1340 specify the lowest possible speed to accept before to consider the transfer
1343 The most flexible way is by writing your own time-out logic and using
1344 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and
1345 use that to figure out exactly when the right condition is met when the
1346 transfer should get stopped.
1348 5.17 Can I write a server with libcurl?
1350 No. libcurl offers no functions or building blocks to build any kind of
1351 internet protocol server. libcurl is only a client-side library. For server
1352 libraries, you need to continue your search elsewhere but there exist many
1353 good open source ones out there for most protocols you could possibly want a
1354 server for. And there are really good stand-alone ones that have been tested
1355 and proven for many years. There's no need for you to reinvent them!
1360 Curl and libcurl are released under a MIT/X derivate license. The license is
1361 very liberal and should not impose a problem for your project. This section
1362 is just a brief summary for the cases we get the most questions. (Parts of
1363 this section was much enhanced by Bjorn Reese.)
1365 We are not lawyers and this is not legal advice. You should probably consult
1366 one if you want true and accurate legal insights without our prejudice. Note
1367 especially that this section concerns the libcurl license only; compiling in
1368 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
1369 the licensing obligations of your application.
1371 6.1 I have a GPL program, can I use the libcurl library?
1375 Since libcurl may be distributed under the MIT/X derivate license, it can be
1376 used together with GPL in any software.
1378 6.2 I have a closed-source program, can I use the libcurl library?
1382 libcurl does not put any restrictions on the program that uses the library.
1384 6.3 I have a BSD licensed program, can I use the libcurl library?
1388 libcurl does not put any restrictions on the program that uses the library.
1390 6.4 I have a program that uses LGPL libraries, can I use libcurl?
1394 The LGPL license doesn't clash with other licenses.
1396 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
1400 The MIT/X derivate license practically allows you to do almost anything with
1401 the sources, on the condition that the copyright texts in the sources are
1404 6.6 Can you please change the curl/libcurl license to XXXX?
1408 We have carefully picked this license after years of development and
1409 discussions and a large amount of people have contributed with source code
1410 knowing that this is the license we use. This license puts the restrictions
1411 we want on curl/libcurl and it does not spread to other programs or
1412 libraries that use it. It should be possible for everyone to use libcurl or
1413 curl in their projects, no matter what license they already have in use.
1415 6.7 What are my obligations when using libcurl in my commercial apps?
1417 Next to none. All you need to adhere to is the MIT-style license (stated in
1418 the COPYING file) which basically says you have to include the copyright
1419 notice in "all copies" and that you may not use the copyright holder's name
1420 when promoting your software.
1422 You do not have to release any of your source code.
1424 You do not have to reveal or make public any changes to the libcurl source
1427 You do not have to broadcast to the world that you are using libcurl within
1430 All we ask is that you disclose "the copyright notice and this permission
1431 notice" somewhere. Most probably like in the documentation or in the section
1432 where other third party dependencies already are mentioned and acknowledged.
1434 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere,
1435 more and more companies are discovering the power of libcurl and take
1436 advantage of it even in commercial environments.
1441 7.1 What is PHP/CURL?
1443 The module for PHP that makes it possible for PHP programs to access curl-
1444 functions from within PHP.
1446 In the cURL project we call this module PHP/CURL to differentiate it from
1447 curl the command line tool and libcurl the library. The PHP team however
1448 does not refer to it like this (for unknown reasons). They call it plain
1449 CURL (often using all caps) or sometimes ext/curl, but both cause much
1450 confusion to users which in turn gives us a higher question load.
1452 7.2 Who wrote PHP/CURL?
1454 PHP/CURL is a module that comes with the regular PHP package. It depends and
1455 uses libcurl, so you need to have libcurl installed properly first before
1456 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
1458 7.3 Can I perform multiple requests using the same handle?
1460 Yes - at least in PHP version 4.3.8 and later (this has been known to not
1461 work in earlier versions, but the exact version when it started to work is
1464 After a transfer, you just set new options in the handle and make another
1465 transfer. This will make libcurl to re-use the same connection if it can.