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, sourceforge.net hosts project services we take advantage from,
249 like the bug tracker and github hosts the primary git repository. Also
250 again, some companies have sponsored certain parts of the development in the
251 past and I hope some will continue to do so in the future.
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. Over 500 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 cert bundle that used to shipped with curl was very outdated and must
319 be replaced with an up-to-date version by anyone who wants to verify
320 peers. It is no longer provided by curl. The last curl release ever that
321 shipped a ca cert bundle was curl 7.18.0.
323 In the cURL project we've decided not to attempt to keep this file updated
324 (or even present anymore) since deciding what to add to a ca cert bundle is
325 an undertaking we've not been ready to accept, and the one we can get from
326 Mozilla is perfectly fine so there's no need to duplicate that work.
328 Today, with many services performed over HTTPS, every operating system
329 should come with a default ca cert bundle that can be deemed somewhat
330 trustworthy and that collection (if reasonably updated) should be deemed to
331 be a lot better than a private curl version.
333 If you want the most recent collection of ca certs that Mozilla Firefox
334 uses, we recommend that you extract the collection yourself from Mozilla
335 Firefox (by running 'make ca-bundle), or by using our online service setup
336 for this purpose: http://curl.haxx.se/docs/caextract.html
338 1.12 I have a problem who can I chat with?
340 There's a bunch of friendly people hanging out in the #curl channel on the
341 IRC network irc.freenode.net. If you're polite and nice, chances are big
342 that you can get -- or provide -- help instantly.
344 1.13 curl's ECCN number?
346 The US government restricts exports of software that contains or uses
347 cryptography. When doing so, the Export Control Classification Number (ECCN)
348 is used to identify the level of export control etc.
350 ASF gives a good explanation at http://www.apache.org/dev/crypto.html
352 We believe curl's number might be ECCN 5D002, another possibility is
353 5D992. It seems necessary to write them, asking to confirm.
355 Comprehensible explanations of the meaning of such numbers and how to
356 obtain them (resp.) are here
358 http://www.bis.doc.gov/licensing/exportingbasics.htm
359 http://www.bis.doc.gov/licensing/do_i_needaneccn.html
361 An incomprehensible description of the two numbers above is here
362 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
364 1.14 How do I submit my patch?
366 When you have made a patch or a change of whatever sort, and want to submit
367 that to the project, there are a few different ways we prefer:
369 o send a patch to the curl-library mailing list. We're many subscribers
370 there and there are lots of people who can review patches, comment on them
371 and "receive" them properly.
373 o if your patch changes or fixes a bug, you can also opt to submit a bug
374 report in the bug tracker and attach your patch there. There are less
375 people involved there.
377 Lots of more details are found in the CONTRIBUTE and INTERNALS docs.
380 2. Install Related Problems
382 2.1 configure doesn't find OpenSSL even when it is installed
384 This may be because of several reasons.
386 2.1.1 native linker doesn't find openssl
389 Solaris (native cc compiler)
390 HPUX (native cc compiler)
391 SGI IRIX (native cc compiler)
392 SCO UNIX (native cc compiler)
394 When configuring curl, I specify --with-ssl. OpenSSL is installed in
395 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
396 CRYPTO_lock in -lcrypto
398 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
399 -lcrypto, so ld can't find the library. This is due to a bug in the GNU
402 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
403 ./configure places the -L/usr/local/ssl/lib early enough in the command
404 line to make things work
406 2.1.2 only the libssl lib is missing
408 If all include files and the libcrypto lib is present, with only the
409 libssl being missing according to configure, this is mostly likely because
410 a few functions are left out from the libssl.
412 If the function names missing include RSA or RSAREF you can be certain
413 that this is because libssl requires the RSA and RSAREF libs to build.
415 See the INSTALL file section that explains how to add those libs to
416 configure. Make sure that you remove the config.cache file before you
417 rerun configure with the new flags.
419 2.2 Does curl work/build with other SSL libraries?
421 Curl has been written to use a generic SSL function layer internally, and
422 that SSL functionality can then be provided by one out of many different SSL
425 curl can be built to use one of the following SSL alternatives: OpenSSL,
426 GnuTLS, yassl, NSS, PolarSSL, axTLS, Secure Transport (native iOS/OS X),
427 schannel (native Windows) or qssl (native IBM i). They all have their pros
428 and cons, and we try to maintain a comparison of them here:
429 http://curl.haxx.se/docs/ssl-compared.html
431 2.3 Where can I find a copy of LIBEAY32.DLL?
433 That is an OpenSSL binary built for Windows.
435 Curl can be built with OpenSSL to do the SSL stuff. The LIBEAY32.DLL is then
436 what curl needs on a windows machine to do https:// etc. Check out the curl
437 web site to find accurate and up-to-date pointers to recent OpenSSL DLLs and
438 other binary packages.
440 2.4 Does curl support SOCKS (RFC 1928) ?
442 Yes, SOCKS 4 and 5 are supported.
447 3.1 curl: (1) SSL is disabled, https: not supported
449 If you get this output when trying to get anything from a https:// server,
450 it means that the instance of curl/libcurl that you're using was built
451 without support for this protocol.
453 This could've happened if the configure script that was run at build time
454 couldn't find all libs and include files curl requires for SSL to work. If
455 the configure script fails to find them, curl is simply built without SSL
458 To get the https:// support into a curl that was previously built but that
459 reports that https:// is not supported, you should dig through the document
460 and logs and check out why the configure script doesn't find the SSL libs
461 and/or include files.
463 Also, check out the other paragraph in this FAQ labelled "configure doesn't
464 find OpenSSL even when it is installed".
466 3.2 How do I tell curl to resume a transfer?
468 Curl supports resumed transfers both ways on both FTP and HTTP.
471 3.3 Why doesn't my posting using -F work?
473 You can't simply use -F or -d at your choice. The web server that will
474 receive your post expects one of the formats. If the form you're trying to
475 submit uses the type 'multipart/form-data', then and only then you must use
476 the -F type. In all the most common cases, you should use -d which then
477 causes a posting with the type 'application/x-www-form-urlencoded'.
479 This is described in some detail in the MANUAL and TheArtOfHttpScripting
480 documents, and if you don't understand it the first time, read it again
481 before you post questions about this to the mailing list. Also, try reading
482 through the mailing list archives for old postings and questions regarding
485 3.4 How do I tell curl to run custom FTP commands?
487 You can tell curl to perform optional commands both before and/or after a
488 file transfer. Study the -Q/--quote option.
490 Since curl is used for file transfers, you don't normally use curl to
491 perform FTP commands without transferring anything. Therefore you must
492 always specify a URL to transfer to/from even when doing custom FTP
493 commands, or use -I which implies the "no body" option sent to libcurl.
495 3.5 How can I disable the Accept: */* header?
497 You can change all internally generated headers by adding a replacement with
498 the -H/--header option. By adding a header with empty contents you safely
499 disable that one. Use -H "Accept:" to disable that specific header.
501 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
503 To curl, all contents are alike. It doesn't matter how the page was
504 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML
505 files. There's no difference to curl and it doesn't even know what kind of
506 language that generated the page.
508 See also item 3.14 regarding javascript.
510 3.7 Can I use curl to delete/rename a file through FTP?
512 Yes. You specify custom FTP commands with -Q/--quote.
514 One example would be to delete a file after you have downloaded it:
516 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
518 or rename a file after upload:
520 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
522 3.8 How do I tell curl to follow HTTP redirects?
524 Curl does not follow so-called redirects by default. The Location: header
525 that informs the client about this is only interpreted if you're using the
526 -L/--location option. As in:
528 curl -L http://redirector.com
530 Not all redirects are HTTP ones, see 4.14
532 3.9 How do I use curl in my favorite programming language?
534 There exist many language interfaces/bindings for curl that integrates it
535 better with various languages. If you are fluid in a script language, you
536 may very well opt to use such an interface instead of using the command line
539 Find out more about which languages that support curl directly, and how to
540 install and use them, in the libcurl section of the curl web site:
541 http://curl.haxx.se/libcurl/
543 All the various bindings to libcurl are made by other projects and people,
544 outside of the cURL project. The cURL project itself only produces libcurl
545 with its plain C API. If you don't find anywhere else to ask you can ask
546 about bindings on the curl-library list too, but be prepared that people on
547 that list may not know anything about bindings.
549 In October 2009, there were interfaces available for the following
550 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
551 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
552 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
553 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
554 Q, wxwidgets and XBLite. By the time you read this, additional ones may have
557 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
559 Curl adheres to the HTTP spec, which basically means you can play with *any*
560 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
561 XML-RPC are all such ones. You can use -X to set custom requests and -H to
562 set custom headers (or replace internally generated ones).
564 Using libcurl is of course just as fine and you'd just use the proper
565 library options to do the same.
567 3.11 How do I POST with a different Content-Type?
569 You can always replace the internally generated headers with -H/--header.
570 To make a simple HTTP POST with text/xml as content-type, do something like:
572 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
574 3.12 Why do FTP specific features over HTTP proxy fail?
576 Because when you use a HTTP proxy, the protocol spoken on the network will
577 be HTTP, even if you specify a FTP URL. This effectively means that you
578 normally can't use FTP specific features such as FTP upload and FTP quote
581 There is one exception to this rule, and that is if you can "tunnel through"
582 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
583 and is generally not available as proxy admins usually disable tunneling to
584 other ports than 443 (which is used for HTTPS access through proxies).
586 3.13 Why does my single/double quotes fail?
588 To specify a command line option that includes spaces, you might need to
589 put the entire option within quotes. Like in:
591 curl -d " with spaces " url.com
595 curl -d ' with spaces ' url.com
597 Exactly what kind of quotes and how to do this is entirely up to the shell
598 or command line interpreter that you are using. For most unix shells, you
599 can more or less pick either single (') or double (") quotes. For
600 Windows/DOS prompts I believe you're forced to use double (") quotes.
602 Please study the documentation for your particular environment. Examples in
603 the curl docs will use a mix of both these ones as shown above. You must
604 adjust them to work in your environment.
606 Remember that curl works and runs on more operating systems than most single
607 individuals have ever tried.
609 3.14 Does curl support Javascript or PAC (automated proxy config)?
611 Many web pages do magic stuff using embedded Javascript. Curl and libcurl
612 have no built-in support for that, so it will be treated just like any other
615 .pac files are a netscape invention and are sometimes used by organizations
616 to allow them to differentiate which proxies to use. The .pac contents is
617 just a Javascript program that gets invoked by the browser and that returns
618 the name of the proxy to connect to. Since curl doesn't support Javascript,
619 it can't support .pac proxy configuration either.
621 Some workarounds usually suggested to overcome this Javascript dependency:
623 - Depending on the Javascript complexity, write up a script that
624 translates it to another language and execute that.
626 - Read the Javascript code and rewrite the same logic in another language.
628 - Implement a Javascript interpreter, people have successfully used the
629 Mozilla Javascript engine in the past.
631 - Ask your admins to stop this, for a static proxy setup or similar.
633 3.15 Can I do recursive fetches with curl?
635 No. curl itself has no code that performs recursive operations, such as
636 those performed by wget and similar tools.
638 There exist wrapper scripts with that functionality (for example the
639 curlmirror perl script), and you can write programs based on libcurl to do
640 it, but the command line tool curl itself cannot.
642 3.16 What certificates do I need when I use SSL?
644 There are three different kinds of "certificates" to keep track of when we
645 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
647 - Client certificate. The server you communicate may require that you can
648 provide this in order to prove that you actually are who you claim to be.
649 If the server doesn't require this, you don't need a client certificate.
651 A client certificate is always used together with a private key, and the
652 private key has a pass phrase that protects it.
654 - Server certificate. The server you communicate with has a server
655 certificate. You can and should verify this certificate to make sure that
656 you are truly talking to the real server and not a server impersonating
659 - Certificate Authority certificate ("CA cert"). You often have several CA
660 certs in a CA cert bundle that can be used to verify a server certificate
661 that was signed by one of the authorities in the bundle. curl does not
662 come with a CA cert bundle but most curl installs provide one. You can
663 also override the default.
665 The server certificate verification process is made by using a Certificate
666 Authority certificate ("CA cert") that was used to sign the server
667 certificate. Server certificate verification is enabled by default in curl
668 and libcurl and is often the reason for problems as explained in FAQ entry
669 4.12 and the SSLCERTS document
670 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
671 "self-signed" or otherwise signed by a CA that you do not have a CA cert
672 for, cannot be verified. If the verification during a connect fails, you
673 are refused access. You then need to explicitly disable the verification
674 to connect to the server.
676 3.17 How do I list the root dir of an FTP server?
678 There are two ways. The way defined in the RFC is to use an encoded slash
679 in the first path part. List the "/tmp" dir like this:
681 curl ftp://ftp.sunet.se/%2ftmp/
683 or the not-quite-kosher-but-more-readable way, by simply starting the path
684 section of the URL with a slash:
686 curl ftp://ftp.sunet.se//tmp/
688 3.18 Can I use curl to send a POST/PUT and not wait for a response?
692 But you could easily write your own program using libcurl to do such stunts.
694 3.19 How do I get HTTP from a host using a specific IP address?
696 For example, you may be trying out a web site installation that isn't yet in
697 the DNS. Or you have a site using multiple IP addresses for a given host
698 name and you want to address a specific one out of the set.
700 Set a custom Host: header that identifies the server name you want to reach
701 but use the target IP address in the URL:
703 curl --header "Host: www.example.com" http://127.0.0.1/
705 You can also opt to add faked host name entries to curl with the --resolve
706 option. That has the added benefit that things like redirects will also work
707 properly. The above operation would instead be done as:
709 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/
711 3.20 How to SFTP from my user's home directory?
713 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to
714 work with. It means that if you don't specify that you want the user's home
715 directory, you get the actual root directory.
717 To specify a file in your user's home directory, you need to use the correct
718 URL syntax which for sftp might look similar to:
720 curl -O -u user:password sftp://example.com/~/file.txt
722 and for SCP it is just a different protocol prefix:
724 curl -O -u user:password scp://example.com/~/file.txt
726 3.21 Protocol xxx not supported or disabled in libcurl
728 When passing on a URL to curl to use, it may respond that the particular
729 protocol is not supported or disabled. The particular way this error message
730 is phrased is because curl doesn't make a distinction internally of whether
731 a particular protocol is not supported (i.e. never got any code added that
732 knows how to speak that protocol) or if it was explicitly disabled. curl can
733 be built to only support a given set of protocols, and the rest would then
734 be disabled or not supported.
736 Note that this error will also occur if you pass a wrongly spelled protocol
737 part as in "htpt://example.com" or as in the less evident case if you prefix
738 the protocol part with a space as in " http://example.com/".
740 3.22 curl -X gives me HTTP problems
742 In normal circumstances, -X should hardly ever be used.
744 By default you use curl without explicitly saying which request method to
745 use when the URL identifies a HTTP transfer. If you just pass in a URL like
746 "curl http://example.com" it will use GET. If you use -d or -F curl will use
747 POST, -I will cause a HEAD and -T will make it a PUT.
749 If for whatever reason you're not happy with these default choices that curl
750 does for you, you can override those request methods by specifying -X
751 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X
754 It is thus pointless to do "curl -XGET [URL]" as GET would be used
755 anyway. In the same vein it is pointless to do "curl -X POST -d data
756 [URL]"... But you can make a fun and somewhat rare request that sends a
757 request-body in a GET request with something like "curl -X GET -d data
760 Note that -X doesn't change curl's behavior. It only modifies the actual
761 string sent in the request.
763 Accordingly, by using -XPOST on a command line that for example would follow
764 a 303 redirect, you will effectively prevent curl from behaving
770 4.1 Problems connecting to SSL servers.
772 It took a very long time before we could sort out why curl had problems to
773 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
774 error sometimes showed up similar to:
776 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
778 It turned out to be because many older SSL servers don't deal with SSLv3
779 requests properly. To correct this problem, tell curl to select SSLv2 from
780 the command line (-2/--sslv2).
782 There have also been examples where the remote server didn't like the SSLv2
783 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
785 4.2 Why do I get problems when I use & or % in the URL?
787 In general unix shells, the & symbol is treated specially and when used, it
788 runs the specified command in the background. To safely send the & as a part
789 of a URL, you should quote the entire URL by using single (') or double (")
790 quotes around it. Similar problems can also occur on some shells with other
791 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
793 An example that would invoke a remote CGI that uses &-symbols could be:
795 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
797 In Windows, the standard DOS shell treats the %-symbol specially and you
798 need to use TWO %-symbols for each single one you want to use in the URL.
800 Also note that if you want the literal %-symbol to be part of the data you
801 pass in a POST using -d/--data you must encode it as '%25' (which then also
802 needs the %-symbol doubled on Windows machines).
804 4.3 How can I use {, }, [ or ] to specify multiple URLs?
806 Because those letters have a special meaning to the shell, and to be used in
807 a URL specified to curl you must quote them.
809 An example that downloads two URLs (sequentially) would do:
811 curl '{curl,www}.haxx.se'
813 To be able to use those letters as actual parts of the URL (without using
814 them for the curl URL "globbing" system), use the -g/--globoff option:
816 curl -g 'www.site.com/weirdname[].html'
818 4.4 Why do I get downloaded data even though the web page doesn't exist?
820 Curl asks remote servers for the page you specify. If the page doesn't exist
821 at the server, the HTTP protocol defines how the server should respond and
822 that means that headers and a "page" will be returned. That's simply how
825 By using the --fail option you can tell curl explicitly to not get any data
826 if the HTTP return code doesn't say success.
828 4.5 Why do I get return code XXX from a HTTP server?
830 RFC2616 clearly explains the return codes. This is a short transcript. Go
831 read the RFC for exact details:
833 4.5.1 "400 Bad Request"
835 The request could not be understood by the server due to malformed
836 syntax. The client SHOULD NOT repeat the request without modifications.
838 4.5.2 "401 Unauthorized"
840 The request requires user authentication.
842 4.5.3 "403 Forbidden"
844 The server understood the request, but is refusing to fulfil it.
845 Authorization will not help and the request SHOULD NOT be repeated.
847 4.5.4 "404 Not Found"
849 The server has not found anything matching the Request-URI. No indication
850 is given of whether the condition is temporary or permanent.
852 4.5.5 "405 Method Not Allowed"
854 The method specified in the Request-Line is not allowed for the resource
855 identified by the Request-URI. The response MUST include an Allow header
856 containing a list of valid methods for the requested resource.
858 4.5.6 "301 Moved Permanently"
860 If you get this return code and an HTML output similar to this:
862 <H1>Moved Permanently</H1> The document has moved <A
863 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
865 it might be because you request a directory URL but without the trailing
866 slash. Try the same operation again _with_ the trailing URL, or use the
867 -L/--location option to follow the redirection.
869 4.6 Can you tell me what error code 142 means?
871 All curl error codes are described at the end of the man page, in the
872 section called "EXIT CODES".
874 Error codes that are larger than the highest documented error code means
875 that curl has exited due to a crash. This is a serious error, and we
876 appreciate a detailed bug report from you that describes how we could go
877 ahead and repeat this!
879 4.7 How do I keep user names and passwords secret in Curl command lines?
881 This problem has two sides:
883 The first part is to avoid having clear-text passwords in the command line
884 so that they don't appear in 'ps' outputs and similar. That is easily
885 avoided by using the "-K" option to tell curl to read parameters from a file
886 or stdin to which you can pass the secret info. curl itself will also
887 attempt to "hide" the given password by blanking out the option - this
888 doesn't work on all platforms.
890 To keep the passwords in your account secret from the rest of the world is
891 not a task that curl addresses. You could of course encrypt them somehow to
892 at least hide them from being read by human eyes, but that is not what
893 anyone would call security.
895 Also note that regular HTTP (using Basic authentication) and FTP passwords
896 are sent in clear across the network. All it takes for anyone to fetch them
897 is to listen on the network. Eavesdropping is very easy. Use more secure
898 authentication methods (like Digest, Negotiate or even NTLM) or consider the
899 SSL-based alternatives HTTPS and FTPS.
903 It is not a bug if the behavior is documented. Read the docs first.
904 Especially check out the KNOWN_BUGS file, it may be a documented bug!
906 If it is a problem with a binary you've downloaded or a package for your
907 particular platform, try contacting the person who built the package/archive
910 If there is a bug, read the BUGS document first. Then report it as described
913 4.9 Curl can't authenticate to the server that requires NTLM?
915 NTLM support requires OpenSSL, GnuTLS, NSS, Secure Transport, or Microsoft
916 Windows libraries at build-time to provide this functionality.
918 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
919 should not use such ones.
921 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
923 Many web servers allow or demand that the administrator configures the
924 server properly for these requests to work on the web server.
926 Some servers seem to support HEAD only on certain kinds of URLs.
928 To fully grasp this, try the documentation for the particular server
929 software you're trying to interact with. This is not anything curl can do
932 4.11 Why does my HTTP range requests return the full document?
934 Because the range may not be supported by the server, or the server may
935 choose to ignore it and return the full document anyway.
937 4.12 Why do I get "certificate verify failed" ?
939 You invoke curl 7.10 or later to communicate on a https:// URL and get an
940 error back looking something similar to this:
942 curl: (35) SSL: error:14090086:SSL routines:
943 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
945 Then it means that curl couldn't verify that the server's certificate was
946 good. Curl verifies the certificate using the CA cert bundle that comes with
947 the curl installation.
949 To disable the verification (which makes it act like curl did before 7.10),
950 use -k. This does however enable man-in-the-middle attacks.
952 If you get this failure but are having a CA cert bundle installed and used,
953 the server's certificate is not signed by one of the CA's in the bundle. It
954 might for example be self-signed. You then correct this problem by obtaining
955 a valid CA cert for the server. Or again, decrease the security by disabling
958 Details are also in the SSLCERTS file in the release archives, found online
959 here: http://curl.haxx.se/docs/sslcerts.html
961 4.13 Why is curl -R on Windows one hour off?
963 During daylight savings time, when -R is used, curl will set a time that
964 appears one hour off. This happens due to a flaw in how Windows stores and
965 uses file modification times and it is not easily worked around. For details
966 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
968 4.14 Redirects work in browser but not with curl!
970 curl supports HTTP redirects fine (see item 3.8). Browsers generally support
971 at least two other ways to perform directs that curl does not:
973 - Meta tags. You can write a HTML tag that will cause the browser to
974 redirect to another given URL after a certain time.
976 - Javascript. You can write a Javascript program embedded in a HTML page
977 that redirects the browser to another given URL.
979 There is no way to make curl follow these redirects. You must either
980 manually figure out what the page is set to do, or you write a script that
981 parses the results and fetches the new URL.
983 4.15 FTPS doesn't work
985 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
988 When a URL is used that starts with FTPS://, curl assumes implicit SSL on
989 the control connection and will therefore immediately connect and try to
990 speak SSL. FTPS:// connections default to port 990.
992 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
993 of its related flavours). This is the most common method, and the one
994 mandated by RFC4217. This kind of connection then of course uses the
995 standard FTP port 21 by default.
997 4.16 My HTTP POST or PUT requests are slow!
999 libcurl makes all POST and PUT requests (except for POST requests with a
1000 very tiny request body) use the "Expect: 100-continue" header. This header
1001 allows the server to deny the operation early so that libcurl can bail out
1002 already before having to send any data. This is useful in authentication
1005 However, many servers don't implement the Expect: stuff properly and if the
1006 server doesn't respond (positively) within 1 second libcurl will continue
1007 and send off the data anyway.
1009 You can disable libcurl's use of the Expect: header the same way you disable
1010 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
1012 4.17 Non-functional connect timeouts
1014 In most Windows setups having a timeout longer than 21 seconds make no
1015 difference, as it will only send 3 TCP SYN packets and no more. The second
1016 packet sent three seconds after the first and the third six seconds after
1017 the second. No more than three packets are sent, no matter how long the
1020 See option TcpMaxConnectRetransmissions on this page:
1021 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
1023 Also, even on non-Windows systems there may run a firewall or anti-virus
1024 software or similar that accepts the connection but does not actually do
1025 anything else. This will make (lib)curl to consider the connection connected
1026 and thus the connect timeout won't trigger.
1028 4.18 file:// URLs containing drive letters (Windows, NetWare)
1030 When using cURL to try to download a local file, one might use a URL
1035 You'll find that even if D:\blah.txt does exist, cURL returns a 'file
1038 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
1039 file:// URLs must contain a host component, but it is ignored by
1040 most implementations. In the above example, 'D:' is treated as the
1041 host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
1042 If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
1043 and if that doesn't exist you will get the not found error.
1045 To fix this problem, use file:// URLs with *three* leading slashes:
1049 Alternatively, if it makes more sense, specify 'localhost' as the host
1052 file://localhost/D:/blah.txt
1054 In either case, cURL should now be looking for the correct file.
1056 4.19 Why doesn't cURL return an error when the network cable is unplugged?
1058 Unplugging a cable is not an error situation. The TCP/IP protocol stack
1059 was designed to be fault tolerant, so even though there may be a physical
1060 break somewhere the connection shouldn't be affected, just possibly
1061 delayed. Eventually, the physical break will be fixed or the data will be
1062 re-routed around the physical problem through another path.
1064 In such cases, the TCP/IP stack is responsible for detecting when the
1065 network connection is irrevocably lost. Since with some protocols it is
1066 perfectly legal for the client wait indefinitely for data, the stack may
1067 never report a problem, and even when it does, it can take up to 20 minutes
1068 for it to detect an issue. The curl option --keepalive-time enables
1069 keep-alive support in the TCP/IP stack which makes it periodically probe the
1070 connection to make sure it is still available to send data. That should
1071 reliably detect any TCP/IP network failure.
1073 But even that won't detect the network going down before the TCP/IP
1074 connection is established (e.g. during a DNS lookup) or using protocols that
1075 don't use TCP. To handle those situations, curl offers a number of timeouts
1076 on its own. --speed-limit/--speed-time will abort if the data transfer rate
1077 falls too low, and --connect-timeout and --max-time can be used to put an
1078 overall timeout on the connection phase or the entire transfer.
1080 A libcurl-using application running in a known physical environment (e.g.
1081 an embedded device with only a single network connection) may want to act
1082 immediately if its lone network connection goes down. That can be achieved
1083 by having the application monitor the network connection on its own using an
1084 OS-specific mechanism, then signalling libcurl to abort (see also item 5.13).
1089 5.1 Is libcurl thread-safe?
1093 We have written the libcurl code specifically adjusted for multi-threaded
1094 programs. libcurl will use thread-safe functions instead of non-safe ones if
1095 your system has such. Note that you must never share the same handle in
1099 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
1100 need to provide one or two locking functions:
1102 http://www.openssl.org/docs/crypto/threads.html
1104 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
1105 need to provide locking function(s) for libgcrypt (which is used by GnuTLS
1106 for the crypto functions).
1108 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
1110 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
1112 5.2 How can I receive all data into a large memory chunk?
1114 [ See also the examples/getinmemory.c source ]
1116 You are in full control of the callback function that gets called every time
1117 there is data received from the remote server. You can make that callback do
1118 whatever you want. You do not have to write the received data to a file.
1120 One solution to this problem could be to have a pointer to a struct that you
1121 pass to the callback function. You set the pointer using the
1122 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
1123 instead of a FILE * to a file:
1125 /* imaginary struct */
1126 struct MemoryStruct {
1131 /* imaginary callback function */
1133 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
1135 size_t realsize = size * nmemb;
1136 struct MemoryStruct *mem = (struct MemoryStruct *)data;
1138 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
1140 memcpy(&(mem->memory[mem->size]), ptr, realsize);
1141 mem->size += realsize;
1142 mem->memory[mem->size] = 0;
1147 5.3 How do I fetch multiple files with libcurl?
1149 libcurl has excellent support for transferring multiple files. You should
1150 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
1151 with curl_easy_perform(). The handle you get from curl_easy_init() is not
1152 only reusable, but you're even encouraged to reuse it if you can, as that
1153 will enable libcurl to use persistent connections.
1155 5.4 Does libcurl do Winsock initialization on win32 systems?
1157 Yes, if told to in the curl_global_init() call.
1159 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
1161 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
1162 that DLL use the FILE * (as the DLL and the client application cannot access
1163 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
1164 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
1165 file, even if that simply writes the data to the specified FILE *.
1166 Similarly, if you use CURLOPT_READDATA you must also specify
1167 CURLOPT_READFUNCTION.
1169 5.6 What about Keep-Alive or persistent connections?
1171 curl and libcurl have excellent support for persistent connections when
1172 transferring several files from the same server. Curl will attempt to reuse
1173 connections for all URLs specified on the same command line/config file, and
1174 libcurl will reuse connections for all transfers that are made using the
1175 same libcurl handle.
1177 When you use the easy interface, the connection cache is kept within the
1178 easy handle. If you instead use the multi interface, the connection cache
1179 will be kept within the multi handle and will be shared among all the easy
1180 handles that are used within the same multi handle.
1182 5.7 Link errors when building libcurl on Windows!
1184 You need to make sure that your project, and all the libraries (both static
1185 and dynamic) that it links against, are compiled/linked against the same run
1188 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
1189 options to the command line compiler. /MD (linking against MSVCRT dll) seems
1190 to be the most commonly used option.
1192 When building an application that uses the static libcurl library, you must
1193 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
1194 dynamic import symbols. If you're using Visual Studio, you need to instead
1195 add CURL_STATICLIB in the "Preprocessor Definitions" section.
1197 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
1198 have linked against the wrong (static) library. If you want to use the
1199 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
1200 the import libraries below. These are the libraries produced by the various
1201 lib/Makefile.* files:
1203 Target: static lib. import lib for libcurl*.dll.
1204 -----------------------------------------------------------
1205 MingW: libcurl.a libcurldll.a
1206 MSVC (release): libcurl.lib libcurl_imp.lib
1207 MSVC (debug): libcurld.lib libcurld_imp.lib
1208 Borland: libcurl.lib libcurl_imp.lib
1210 5.8 libcurl.so.X: open failed: No such file or directory
1212 This is an error message you might get when you try to run a program linked
1213 with a shared version of libcurl and your run-time linker (ld.so) couldn't
1214 find the shared library named libcurl.so.X. (Where X is the number of the
1215 current libcurl ABI, typically 3 or 4).
1217 You need to make sure that ld.so finds libcurl.so.X. You can do that
1218 multiple ways, and it differs somewhat between different operating systems,
1219 but they are usually:
1221 * Add an option to the linker command line that specify the hard-coded path
1222 the run-time linker should check for the lib (usually -R)
1224 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
1225 should check for libs
1227 * Adjust the system's config to check for libs in the directory where you've
1228 put the dir (like Linux's /etc/ld.so.conf)
1230 'man ld.so' and 'man ld' will tell you more details
1232 5.9 How does libcurl resolve host names?
1234 libcurl supports a large a number of different name resolve functions. One
1235 of them is picked at build-time and will be used unconditionally. Thus, if
1236 you want to change name resolver function you must rebuild libcurl and tell
1237 it to use a different function.
1239 - The non-ipv6 resolver that can use one out of four host name resolve calls
1240 (depending on what your system supports):
1243 B - gethostbyname_r() with 3 arguments
1244 C - gethostbyname_r() with 5 arguments
1245 D - gethostbyname_r() with 6 arguments
1247 - The ipv6-resolver that uses getaddrinfo()
1249 - The c-ares based name resolver that uses the c-ares library for resolves.
1250 Using this offers asynchronous name resolves.
1252 - The threaded resolver (default option on Windows). It uses:
1254 A - gethostbyname() on plain ipv4 hosts
1255 B - getaddrinfo() on ipv6-enabled hosts
1257 Also note that libcurl never resolves or reverse-lookups addresses given as
1258 pure numbers, such as 127.0.0.1 or ::1.
1260 5.10 How do I prevent libcurl from writing the response to stdout?
1262 libcurl provides a default built-in write function that writes received data
1263 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
1264 set CURLOPT_WRITEDATA to a different FILE * handle.
1266 5.11 How do I make libcurl not receive the whole HTTP response?
1268 You make the write callback (or progress callback) return an error and
1269 libcurl will then abort the transfer.
1271 5.12 Can I make libcurl fake or hide my real IP address?
1273 No. libcurl operates on a higher level than so. Besides, faking IP address
1274 would imply sending IP packages with a made-up source address, and then you
1275 normally get a problem with intercepting the packages sent back as they
1276 would then not be routed to you!
1278 If you use a proxy to access remote sites, the sites will not see your local
1279 IP address but instead the address of the proxy.
1281 Also note that on many networks NATs or other IP-munging techniques are used
1282 that makes you see and use a different IP address locally than what the
1283 remote server will see you coming from.
1285 5.13 How do I stop an ongoing transfer?
1287 With the easy interface you make sure to return the correct error code from
1288 one of the callbacks, but none of them are instant. There is no function you
1289 can call from another thread or similar that will stop it immediately.
1290 Instead, you need to make sure that one of the callbacks you use returns an
1291 appropriate value that will stop the transfer. Suitable callbacks that you
1292 can do this with include the progress callback, the read callback and the
1295 If you're using the multi interface, you can also stop a transfer by
1296 removing the particular easy handle from the multi stack at any moment you
1297 think the transfer is done or when you wish to abort the transfer.
1299 5.14 Using C++ non-static functions for callbacks?
1301 libcurl is a C library, it doesn't know anything about C++ member functions.
1303 You can overcome this "limitation" with a relative ease using a static
1304 member function that is passed a pointer to the class:
1306 // f is the pointer to your object.
1307 static YourClass::func(void *buffer, size_t sz, size_t n, void *f)
1309 // Call non-static member function.
1310 static_cast<YourClass*>(f)->nonStaticFunction();
1313 // This is how you pass pointer to the static function:
1314 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func);
1315 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
1317 5.15 How do I get an FTP directory listing?
1319 If you end the FTP URL you request with a slash, libcurl will provide you
1320 with a directory listing of that given directory. You can also set
1321 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
1324 The follow-up question that tend to follow the previous one, is how a
1325 program is supposed to parse the directory listing. How does it know what's
1326 a file and what's a dir and what's a symlink etc. The harsh reality is that
1327 FTP provides no such fine and easy-to-parse output. The output format FTP
1328 servers respond to LIST commands are entirely at the server's own liking and
1329 the NLST output doesn't reveal any types and in many cases don't even
1330 include all the directory entries. Also, both LIST and NLST tend to hide
1331 unix-style hidden files (those that start with a dot) by default so you need
1332 to do "LIST -a" or similar to see them.
1334 The application thus needs to parse the LIST output. One such existing
1335 list parser is available at http://cr.yp.to/ftpparse.html Versions of
1336 libcurl since 7.21.0 also provide the ability to specify a wildcard to
1337 download multiple files from one FTP directory.
1339 5.16 I want a different time-out!
1341 Time and time again users realize that CURLOPT_TIMEOUT and
1342 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all
1343 the various use cases and scenarios applications end up with.
1345 libcurl offers many more ways to time-out operations. A common alternative
1346 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to
1347 specify the lowest possible speed to accept before to consider the transfer
1350 The most flexible way is by writing your own time-out logic and using
1351 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and
1352 use that to figure out exactly when the right condition is met when the
1353 transfer should get stopped.
1355 5.17 Can I write a server with libcurl?
1357 No. libcurl offers no functions or building blocks to build any kind of
1358 internet protocol server. libcurl is only a client-side library. For server
1359 libraries, you need to continue your search elsewhere but there exist many
1360 good open source ones out there for most protocols you could possibly want a
1361 server for. And there are really good stand-alone ones that have been tested
1362 and proven for many years. There's no need for you to reinvent them!
1367 Curl and libcurl are released under a MIT/X derivate license. The license is
1368 very liberal and should not impose a problem for your project. This section
1369 is just a brief summary for the cases we get the most questions. (Parts of
1370 this section was much enhanced by Bjorn Reese.)
1372 We are not lawyers and this is not legal advice. You should probably consult
1373 one if you want true and accurate legal insights without our prejudice. Note
1374 especially that this section concerns the libcurl license only; compiling in
1375 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
1376 the licensing obligations of your application.
1378 6.1 I have a GPL program, can I use the libcurl library?
1382 Since libcurl may be distributed under the MIT/X derivate license, it can be
1383 used together with GPL in any software.
1385 6.2 I have a closed-source program, can I use the libcurl library?
1389 libcurl does not put any restrictions on the program that uses the library.
1391 6.3 I have a BSD licensed program, can I use the libcurl library?
1395 libcurl does not put any restrictions on the program that uses the library.
1397 6.4 I have a program that uses LGPL libraries, can I use libcurl?
1401 The LGPL license doesn't clash with other licenses.
1403 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
1407 The MIT/X derivate license practically allows you to do almost anything with
1408 the sources, on the condition that the copyright texts in the sources are
1411 6.6 Can you please change the curl/libcurl license to XXXX?
1415 We have carefully picked this license after years of development and
1416 discussions and a large amount of people have contributed with source code
1417 knowing that this is the license we use. This license puts the restrictions
1418 we want on curl/libcurl and it does not spread to other programs or
1419 libraries that use it. It should be possible for everyone to use libcurl or
1420 curl in their projects, no matter what license they already have in use.
1422 6.7 What are my obligations when using libcurl in my commercial apps?
1424 Next to none. All you need to adhere to is the MIT-style license (stated in
1425 the COPYING file) which basically says you have to include the copyright
1426 notice in "all copies" and that you may not use the copyright holder's name
1427 when promoting your software.
1429 You do not have to release any of your source code.
1431 You do not have to reveal or make public any changes to the libcurl source
1434 You do not have to broadcast to the world that you are using libcurl within
1437 All we ask is that you disclose "the copyright notice and this permission
1438 notice" somewhere. Most probably like in the documentation or in the section
1439 where other third party dependencies already are mentioned and acknowledged.
1441 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere,
1442 more and more companies are discovering the power of libcurl and take
1443 advantage of it even in commercial environments.
1448 7.1 What is PHP/CURL?
1450 The module for PHP that makes it possible for PHP programs to access curl-
1451 functions from within PHP.
1453 In the cURL project we call this module PHP/CURL to differentiate it from
1454 curl the command line tool and libcurl the library. The PHP team however
1455 does not refer to it like this (for unknown reasons). They call it plain
1456 CURL (often using all caps) or sometimes ext/curl, but both cause much
1457 confusion to users which in turn gives us a higher question load.
1459 7.2 Who wrote PHP/CURL?
1461 PHP/CURL is a module that comes with the regular PHP package. It depends and
1462 uses libcurl, so you need to have libcurl installed properly first before
1463 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
1465 7.3 Can I perform multiple requests using the same handle?
1467 Yes - at least in PHP version 4.3.8 and later (this has been known to not
1468 work in earlier versions, but the exact version when it started to work is
1471 After a transfer, you just set new options in the handle and make another
1472 transfer. This will make libcurl to re-use the same connection if it can.