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?
102 5.18 Does libcurl use threads?
105 6.1 I have a GPL program, can I use the libcurl library?
106 6.2 I have a closed-source program, can I use the libcurl library?
107 6.3 I have a BSD licensed program, can I use the libcurl library?
108 6.4 I have a program that uses LGPL libraries, can I use libcurl?
109 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
110 6.6 Can you please change the curl/libcurl license to XXXX?
111 6.7 What are my obligations when using libcurl in my commercial apps?
114 7.1 What is PHP/CURL?
115 7.2 Who wrote PHP/CURL?
116 7.3 Can I perform multiple requests using the same handle?
118 ==============================================================================
124 cURL is the name of the project. The name is a play on 'Client for URLs',
125 originally with URL spelled in uppercase to make it obvious it deals with
126 URLs. The fact it can also be pronounced 'see URL' also helped, it works as
127 an abbreviation for "Client URL Request Library" or why not the recursive
128 version: "Curl URL Request Library".
130 The cURL project produces two products:
134 A free and easy-to-use client-side URL transfer library, supporting DICT,
135 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3,
136 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP.
138 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
139 kerberos, HTTP form based upload, proxies, cookies, user+password
140 authentication, file transfer resume, http proxy tunneling and more!
142 libcurl is highly portable, it builds and works identically on numerous
143 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
144 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac
145 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF,
146 Android, Minix, IBM TPF and more...
148 libcurl is free, thread-safe, IPv6 compatible, feature rich, well
153 A command line tool for getting or sending files using URL syntax.
155 Since curl uses libcurl, curl supports the same wide range of common
156 Internet protocols that libcurl does.
158 We pronounce curl and cURL with an initial k sound: [kurl].
160 There are numerous sub-projects and related projects that also use the word
161 curl in the project names in various combinations, but you should take
162 notice that this FAQ is directed at the command-line tool named curl (and
163 libcurl the library), and may therefore not be valid for other curl-related
164 projects. (There is however a small section for the PHP/CURL in this FAQ.)
168 libcurl is a reliable and portable library which provides you with an easy
169 interface to a range of common Internet protocols.
171 You can use libcurl for free in your application, be it open source,
172 commercial or closed-source.
174 libcurl is most probably the most portable, most powerful and most often
175 used C-based multi-platform file transfer library on this planet - be it
176 open source or commercial.
178 1.3 What is curl not?
180 Curl is not a wget clone. That is a common misconception. Never, during
181 curl's development, have we intended curl to replace wget or compete on its
182 market. Curl is targeted at single-shot file transfers.
184 Curl is not a web site mirroring program. If you want to use curl to mirror
185 something: fine, go ahead and write a script that wraps around curl to make
186 it reality (like curlmirror.pl does).
188 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
189 but if you want systematic and sequential behavior you should write a
190 script (or write a new program that interfaces libcurl) and do it.
192 Curl is not a PHP tool, even though it works perfectly well when used from
193 or with PHP (when using the PHP/CURL module).
195 Curl is not a program for a single operating system. Curl exists, compiles,
196 builds and runs under a wide range of operating systems, including all
197 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
200 1.4 When will you make curl do XXXX ?
202 We love suggestions of what to change in order to make curl and libcurl
203 better. We do however believe in a few rules when it comes to the future of
206 Curl -- the command line tool -- is to remain a non-graphical command line
207 tool. If you want GUIs or fancy scripting capabilities, you should look for
208 another tool that uses libcurl.
210 We do not add things to curl that other small and available tools already do
211 very fine at the side. Curl's output is fine to pipe into another program or
212 redirect to another file for the next program to interpret.
214 We focus on protocol related issues and improvements. If you wanna do more
215 magic with the supported protocols than curl currently does, chances are big
216 we will agree. If you wanna add more protocols, we may very well agree.
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 faster.
228 curl and libcurl are not made by any single individual. Daniel Stenberg is
229 project leader and main developer, but other persons' submissions are
230 important and crucial. Anyone can contribute and post their changes and
231 improvements and have them inserted in the main sources (of course on the
232 condition that developers agree on that the fixes are good).
234 The full list of all contributors is found in the docs/THANKS file.
236 curl is developed by a community, with Daniel at the wheel.
238 1.6 What do you get for making curl?
240 Project cURL is entirely free and open. No person gets paid for developing
241 (lib)curl on full or even part time. We do this voluntarily on our spare
242 time. Occasionally companies pay individual developers to work on curl, but
243 that's up to each company and developer. It is not controlled by nor
244 supervised in any way by the project.
246 We still get help from companies. Haxx provides web site, bandwidth, mailing
247 lists etc, sourceforge.net hosts project services we take advantage from,
248 like the bug tracker and github hosts the primary git repository. Also
249 again, some companies have sponsored certain parts of the development in the
250 past and I hope some will continue to do so in the future.
252 If you want to support our project, consider a donation or a banner-program
253 or even better: by helping us coding, documenting, testing etc.
255 1.7 What about CURL from curl.com?
257 During the summer 2001, curl.com was busy advertising their client-side
258 programming language for the web, named CURL.
260 We are in no way associated with curl.com or their CURL programming
263 Our project name curl has been in effective use since 1998. We were not the
264 first computer related project to use the name "curl" and do not claim any
267 We recognize that we will be living in parallel with curl.com and wish them
270 1.8 I have a problem who do I mail?
272 Please do not mail any single individual unless you really need to. Keep
273 curl-related questions on a suitable mailing list. All available mailing
274 lists are listed in the MANUAL document and online at
275 http://curl.haxx.se/mail/
277 Keeping curl-related questions and discussions on mailing lists allows
278 others to join in and help, to share their ideas, contribute their
279 suggestions and spread their wisdom. Keeping discussions on public mailing
280 lists also allows for others to learn from this (both current and future
281 users thanks to the web based archives of the mailing lists), thus saving us
282 from having to repeat ourselves even more. Thanks for respecting this.
284 If you have found or simply suspect a security problem in curl or libcurl,
285 mail curl-security at haxx.se (closed list of receivers, mails are not
286 disclosed) and tell. Then we can produce a fix in a timely manner before the
287 flaw is announced to the world, thus lessen the impact the problem will have
290 1.9 Where do I buy commercial support for curl?
292 curl is fully open source. It means you can hire any skilled engineer to fix
293 your curl-related problems.
295 We list available alternatives on the curl web site:
296 http://curl.haxx.se/support.html
298 1.10 How many are using curl?
300 It is impossible to tell.
302 We don't know how many users that knowingly have installed and use curl.
304 We don't know how many users that use curl without knowing that they are in
307 We don't know how many users that downloaded or installed curl and then
310 In May 2012 Daniel did a counting game and came up with a number that may
311 be completely wrong or somewhat accurate. Over 500 million!
313 See http://daniel.haxx.se/blog/2012/05/16/300m-users/
315 1.11 Why don't you update ca-bundle.crt
317 The ca cert bundle that used to shipped with curl was very outdated and must
318 be replaced with an up-to-date version by anyone who wants to verify
319 peers. It is no longer provided by curl. The last curl release ever that
320 shipped a ca cert bundle was curl 7.18.0.
322 In the cURL project we've decided not to attempt to keep this file updated
323 (or even present anymore) since deciding what to add to a ca cert bundle is
324 an undertaking we've not been ready to accept, and the one we can get from
325 Mozilla is perfectly fine so there's no need to duplicate that work.
327 Today, with many services performed over HTTPS, every operating system
328 should come with a default ca cert bundle that can be deemed somewhat
329 trustworthy and that collection (if reasonably updated) should be deemed to
330 be a lot better than a private curl version.
332 If you want the most recent collection of ca certs that Mozilla Firefox
333 uses, we recommend that you extract the collection yourself from Mozilla
334 Firefox (by running 'make ca-bundle), or by using our online service setup
335 for this purpose: http://curl.haxx.se/docs/caextract.html
337 1.12 I have a problem who can I chat with?
339 There's a bunch of friendly people hanging out in the #curl channel on the
340 IRC network irc.freenode.net. If you're polite and nice, chances are big
341 that you can get -- or provide -- help instantly.
343 1.13 curl's ECCN number?
345 The US government restricts exports of software that contains or uses
346 cryptography. When doing so, the Export Control Classification Number (ECCN)
347 is used to identify the level of export control etc.
349 ASF gives a good explanation at http://www.apache.org/dev/crypto.html
351 We believe curl's number might be ECCN 5D002, another possibility is
352 5D992. It seems necessary to write them, asking to confirm.
354 Comprehensible explanations of the meaning of such numbers and how to
355 obtain them (resp.) are here
357 http://www.bis.doc.gov/licensing/exportingbasics.htm
358 http://www.bis.doc.gov/licensing/do_i_needaneccn.html
360 An incomprehensible description of the two numbers above is here
361 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
363 1.14 How do I submit my patch?
365 When you have made a patch or a change of whatever sort, and want to submit
366 that to the project, there are a few different ways we prefer:
368 o send a patch to the curl-library mailing list. We're many subscribers
369 there and there are lots of people who can review patches, comment on them
370 and "receive" them properly.
372 o if your patch changes or fixes a bug, you can also opt to submit a bug
373 report in the bug tracker and attach your patch there. There are less
374 people involved there.
376 Lots of more details are found in the CONTRIBUTE and INTERNALS docs.
379 2. Install Related Problems
381 2.1 configure doesn't find OpenSSL even when it is installed
383 This may be because of several reasons.
385 2.1.1 native linker doesn't find openssl
388 Solaris (native cc compiler)
389 HPUX (native cc compiler)
390 SGI IRIX (native cc compiler)
391 SCO UNIX (native cc compiler)
393 When configuring curl, I specify --with-ssl. OpenSSL is installed in
394 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
395 CRYPTO_lock in -lcrypto
397 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
398 -lcrypto, so ld can't find the library. This is due to a bug in the GNU
401 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
402 ./configure places the -L/usr/local/ssl/lib early enough in the command
403 line to make things work
405 2.1.2 only the libssl lib is missing
407 If all include files and the libcrypto lib is present, with only the
408 libssl being missing according to configure, this is mostly likely because
409 a few functions are left out from the libssl.
411 If the function names missing include RSA or RSAREF you can be certain
412 that this is because libssl requires the RSA and RSAREF libs to build.
414 See the INSTALL file section that explains how to add those libs to
415 configure. Make sure that you remove the config.cache file before you
416 rerun configure with the new flags.
418 2.2 Does curl work/build with other SSL libraries?
420 Curl has been written to use a generic SSL function layer internally, and
421 that SSL functionality can then be provided by one out of many different SSL
424 curl can be built to use one of the following SSL alternatives: OpenSSL,
425 GnuTLS, yassl, NSS, PolarSSL, axTLS, Secure Transport (native iOS/OS X),
426 WinSSL (native Windows) or qssl (native IBM i). They all have their pros
427 and cons, and we try to maintain a comparison of them here:
428 http://curl.haxx.se/docs/ssl-compared.html
430 2.3 Where can I find a copy of LIBEAY32.DLL?
432 That is an OpenSSL binary built for Windows.
434 Curl can be built with OpenSSL to do the SSL stuff. The LIBEAY32.DLL is then
435 what curl needs on a windows machine to do https:// etc. Check out the curl
436 web site to find accurate and up-to-date pointers to recent OpenSSL DLLs and
437 other binary packages.
439 2.4 Does curl support SOCKS (RFC 1928) ?
441 Yes, SOCKS 4 and 5 are supported.
446 3.1 curl: (1) SSL is disabled, https: not supported
448 If you get this output when trying to get anything from a https:// server,
449 it means that the instance of curl/libcurl that you're using was built
450 without support for this protocol.
452 This could've happened if the configure script that was run at build time
453 couldn't find all libs and include files curl requires for SSL to work. If
454 the configure script fails to find them, curl is simply built without SSL
457 To get the https:// support into a curl that was previously built but that
458 reports that https:// is not supported, you should dig through the document
459 and logs and check out why the configure script doesn't find the SSL libs
460 and/or include files.
462 Also, check out the other paragraph in this FAQ labelled "configure doesn't
463 find OpenSSL even when it is installed".
465 3.2 How do I tell curl to resume a transfer?
467 Curl supports resumed transfers both ways on both FTP and HTTP.
470 3.3 Why doesn't my posting using -F work?
472 You can't simply use -F or -d at your choice. The web server that will
473 receive your post expects one of the formats. If the form you're trying to
474 submit uses the type 'multipart/form-data', then and only then you must use
475 the -F type. In all the most common cases, you should use -d which then
476 causes a posting with the type 'application/x-www-form-urlencoded'.
478 This is described in some detail in the MANUAL and TheArtOfHttpScripting
479 documents, and if you don't understand it the first time, read it again
480 before you post questions about this to the mailing list. Also, try reading
481 through the mailing list archives for old postings and questions regarding
484 3.4 How do I tell curl to run custom FTP commands?
486 You can tell curl to perform optional commands both before and/or after a
487 file transfer. Study the -Q/--quote option.
489 Since curl is used for file transfers, you don't normally use curl to
490 perform FTP commands without transferring anything. Therefore you must
491 always specify a URL to transfer to/from even when doing custom FTP
492 commands, or use -I which implies the "no body" option sent to libcurl.
494 3.5 How can I disable the Accept: */* header?
496 You can change all internally generated headers by adding a replacement with
497 the -H/--header option. By adding a header with empty contents you safely
498 disable that one. Use -H "Accept:" to disable that specific header.
500 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
502 To curl, all contents are alike. It doesn't matter how the page was
503 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML
504 files. There's no difference to curl and it doesn't even know what kind of
505 language that generated the page.
507 See also item 3.14 regarding javascript.
509 3.7 Can I use curl to delete/rename a file through FTP?
511 Yes. You specify custom FTP commands with -Q/--quote.
513 One example would be to delete a file after you have downloaded it:
515 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
517 or rename a file after upload:
519 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
521 3.8 How do I tell curl to follow HTTP redirects?
523 Curl does not follow so-called redirects by default. The Location: header
524 that informs the client about this is only interpreted if you're using the
525 -L/--location option. As in:
527 curl -L http://redirector.com
529 Not all redirects are HTTP ones, see 4.14
531 3.9 How do I use curl in my favorite programming language?
533 There exist many language interfaces/bindings for curl that integrates it
534 better with various languages. If you are fluid in a script language, you
535 may very well opt to use such an interface instead of using the command line
538 Find out more about which languages that support curl directly, and how to
539 install and use them, in the libcurl section of the curl web site:
540 http://curl.haxx.se/libcurl/
542 All the various bindings to libcurl are made by other projects and people,
543 outside of the cURL project. The cURL project itself only produces libcurl
544 with its plain C API. If you don't find anywhere else to ask you can ask
545 about bindings on the curl-library list too, but be prepared that people on
546 that list may not know anything about bindings.
548 In October 2009, there were interfaces available for the following
549 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
550 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
551 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
552 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
553 Q, wxwidgets and XBLite. By the time you read this, additional ones may have
556 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
558 Curl adheres to the HTTP spec, which basically means you can play with *any*
559 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
560 XML-RPC are all such ones. You can use -X to set custom requests and -H to
561 set custom headers (or replace internally generated ones).
563 Using libcurl is of course just as fine and you'd just use the proper
564 library options to do the same.
566 3.11 How do I POST with a different Content-Type?
568 You can always replace the internally generated headers with -H/--header.
569 To make a simple HTTP POST with text/xml as content-type, do something like:
571 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
573 3.12 Why do FTP specific features over HTTP proxy fail?
575 Because when you use a HTTP proxy, the protocol spoken on the network will
576 be HTTP, even if you specify a FTP URL. This effectively means that you
577 normally can't use FTP specific features such as FTP upload and FTP quote
580 There is one exception to this rule, and that is if you can "tunnel through"
581 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
582 and is generally not available as proxy admins usually disable tunneling to
583 other ports than 443 (which is used for HTTPS access through proxies).
585 3.13 Why does my single/double quotes fail?
587 To specify a command line option that includes spaces, you might need to
588 put the entire option within quotes. Like in:
590 curl -d " with spaces " url.com
594 curl -d ' with spaces ' url.com
596 Exactly what kind of quotes and how to do this is entirely up to the shell
597 or command line interpreter that you are using. For most unix shells, you
598 can more or less pick either single (') or double (") quotes. For
599 Windows/DOS prompts I believe you're forced to use double (") quotes.
601 Please study the documentation for your particular environment. Examples in
602 the curl docs will use a mix of both these ones as shown above. You must
603 adjust them to work in your environment.
605 Remember that curl works and runs on more operating systems than most single
606 individuals have ever tried.
608 3.14 Does curl support Javascript or PAC (automated proxy config)?
610 Many web pages do magic stuff using embedded Javascript. Curl and libcurl
611 have no built-in support for that, so it will be treated just like any other
614 .pac files are a netscape invention and are sometimes used by organizations
615 to allow them to differentiate which proxies to use. The .pac contents is
616 just a Javascript program that gets invoked by the browser and that returns
617 the name of the proxy to connect to. Since curl doesn't support Javascript,
618 it can't support .pac proxy configuration either.
620 Some workarounds usually suggested to overcome this Javascript dependency:
622 Depending on the Javascript complexity, write up a script that translates it
623 to another language and execute that.
625 Read the Javascript code and rewrite the same logic in another language.
627 Implement a Javascript interpreter, people have successfully used the
628 Mozilla Javascript engine in the past.
630 Ask your admins to stop this, for a static proxy setup or similar.
632 3.15 Can I do recursive fetches with curl?
634 No. curl itself has no code that performs recursive operations, such as
635 those performed by wget and similar tools.
637 There exist wrapper scripts with that functionality (for example the
638 curlmirror perl script), and you can write programs based on libcurl to do
639 it, but the command line tool curl itself cannot.
641 3.16 What certificates do I need when I use SSL?
643 There are three different kinds of "certificates" to keep track of when we
644 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
648 The server you communicate may require that you can provide this in order to
649 prove that you actually are who you claim to be. If the server doesn't
650 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.
657 The server you communicate with has a server certificate. You can and should
658 verify this certificate to make sure that you are truly talking to the real
659 server and not a server impersonating it.
661 CERTIFICATE AUTHORITY CERTIFICATE ("CA cert")
663 You often have several CA certs in a CA cert bundle that can be used to
664 verify a server certificate that was signed by one of the authorities in the
665 bundle. curl does not come with a CA cert bundle but most curl installs
666 provide one. You can also override the default.
668 The server certificate verification process is made by using a Certificate
669 Authority certificate ("CA cert") that was used to sign the server
670 certificate. Server certificate verification is enabled by default in curl
671 and libcurl and is often the reason for problems as explained in FAQ entry
672 4.12 and the SSLCERTS document
673 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
674 "self-signed" or otherwise signed by a CA that you do not have a CA cert
675 for, cannot be verified. If the verification during a connect fails, you are
676 refused access. You then need to explicitly disable the verification to
677 connect to the server.
679 3.17 How do I list the root dir of an FTP server?
681 There are two ways. The way defined in the RFC is to use an encoded slash
682 in the first path part. List the "/tmp" dir like this:
684 curl ftp://ftp.sunet.se/%2ftmp/
686 or the not-quite-kosher-but-more-readable way, by simply starting the path
687 section of the URL with a slash:
689 curl ftp://ftp.sunet.se//tmp/
691 3.18 Can I use curl to send a POST/PUT and not wait for a response?
695 But you could easily write your own program using libcurl to do such stunts.
697 3.19 How do I get HTTP from a host using a specific IP address?
699 For example, you may be trying out a web site installation that isn't yet in
700 the DNS. Or you have a site using multiple IP addresses for a given host
701 name and you want to address a specific one out of the set.
703 Set a custom Host: header that identifies the server name you want to reach
704 but use the target IP address in the URL:
706 curl --header "Host: www.example.com" http://127.0.0.1/
708 You can also opt to add faked host name entries to curl with the --resolve
709 option. That has the added benefit that things like redirects will also work
710 properly. The above operation would instead be done as:
712 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/
714 3.20 How to SFTP from my user's home directory?
716 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to
717 work with. It means that if you don't specify that you want the user's home
718 directory, you get the actual root directory.
720 To specify a file in your user's home directory, you need to use the correct
721 URL syntax which for sftp might look similar to:
723 curl -O -u user:password sftp://example.com/~/file.txt
725 and for SCP it is just a different protocol prefix:
727 curl -O -u user:password scp://example.com/~/file.txt
729 3.21 Protocol xxx not supported or disabled in libcurl
731 When passing on a URL to curl to use, it may respond that the particular
732 protocol is not supported or disabled. The particular way this error message
733 is phrased is because curl doesn't make a distinction internally of whether
734 a particular protocol is not supported (i.e. never got any code added that
735 knows how to speak that protocol) or if it was explicitly disabled. curl can
736 be built to only support a given set of protocols, and the rest would then
737 be disabled or not supported.
739 Note that this error will also occur if you pass a wrongly spelled protocol
740 part as in "htpt://example.com" or as in the less evident case if you prefix
741 the protocol part with a space as in " http://example.com/".
743 3.22 curl -X gives me HTTP problems
745 In normal circumstances, -X should hardly ever be used.
747 By default you use curl without explicitly saying which request method to
748 use when the URL identifies a HTTP transfer. If you just pass in a URL like
749 "curl http://example.com" it will use GET. If you use -d or -F curl will use
750 POST, -I will cause a HEAD and -T will make it a PUT.
752 If for whatever reason you're not happy with these default choices that curl
753 does for you, you can override those request methods by specifying -X
754 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X
757 It is thus pointless to do "curl -XGET [URL]" as GET would be used
758 anyway. In the same vein it is pointless to do "curl -X POST -d data
759 [URL]"... But you can make a fun and somewhat rare request that sends a
760 request-body in a GET request with something like "curl -X GET -d data
763 Note that -X doesn't change curl's behavior. It only modifies the actual
764 string sent in the request.
766 Accordingly, by using -XPOST on a command line that for example would follow
767 a 303 redirect, you will effectively prevent curl from behaving
773 4.1 Problems connecting to SSL servers.
775 It took a very long time before we could sort out why curl had problems to
776 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
777 error sometimes showed up similar to:
779 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
781 It turned out to be because many older SSL servers don't deal with SSLv3
782 requests properly. To correct this problem, tell curl to select SSLv2 from
783 the command line (-2/--sslv2).
785 There have also been examples where the remote server didn't like the SSLv2
786 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
788 4.2 Why do I get problems when I use & or % in the URL?
790 In general unix shells, the & symbol is treated specially and when used, it
791 runs the specified command in the background. To safely send the & as a part
792 of a URL, you should quote the entire URL by using single (') or double (")
793 quotes around it. Similar problems can also occur on some shells with other
794 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
796 An example that would invoke a remote CGI that uses &-symbols could be:
798 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
800 In Windows, the standard DOS shell treats the percent sign specially and you
801 need to use TWO percent signs for each single one you want to use in the
804 If you want a literal percent sign to be part of the data you pass in a POST
805 using -d/--data you must encode it as '%25' (which then also needs the
806 percent sign doubled on Windows machines).
808 4.3 How can I use {, }, [ or ] to specify multiple URLs?
810 Because those letters have a special meaning to the shell, and to be used in
811 a URL specified to curl you must quote them.
813 An example that downloads two URLs (sequentially) would do:
815 curl '{curl,www}.haxx.se'
817 To be able to use those letters as actual parts of the URL (without using
818 them for the curl URL "globbing" system), use the -g/--globoff option:
820 curl -g 'www.site.com/weirdname[].html'
822 4.4 Why do I get downloaded data even though the web page doesn't exist?
824 Curl asks remote servers for the page you specify. If the page doesn't exist
825 at the server, the HTTP protocol defines how the server should respond and
826 that means that headers and a "page" will be returned. That's simply how
829 By using the --fail option you can tell curl explicitly to not get any data
830 if the HTTP return code doesn't say success.
832 4.5 Why do I get return code XXX from a HTTP server?
834 RFC2616 clearly explains the return codes. This is a short transcript. Go
835 read the RFC for exact details:
837 4.5.1 "400 Bad Request"
839 The request could not be understood by the server due to malformed
840 syntax. The client SHOULD NOT repeat the request without modifications.
842 4.5.2 "401 Unauthorized"
844 The request requires user authentication.
846 4.5.3 "403 Forbidden"
848 The server understood the request, but is refusing to fulfil it.
849 Authorization will not help and the request SHOULD NOT be repeated.
851 4.5.4 "404 Not Found"
853 The server has not found anything matching the Request-URI. No indication
854 is given of whether the condition is temporary or permanent.
856 4.5.5 "405 Method Not Allowed"
858 The method specified in the Request-Line is not allowed for the resource
859 identified by the Request-URI. The response MUST include an Allow header
860 containing a list of valid methods for the requested resource.
862 4.5.6 "301 Moved Permanently"
864 If you get this return code and an HTML output similar to this:
866 <H1>Moved Permanently</H1> The document has moved <A
867 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
869 it might be because you request a directory URL but without the trailing
870 slash. Try the same operation again _with_ the trailing URL, or use the
871 -L/--location option to follow the redirection.
873 4.6 Can you tell me what error code 142 means?
875 All curl error codes are described at the end of the man page, in the
876 section called "EXIT CODES".
878 Error codes that are larger than the highest documented error code means
879 that curl has exited due to a crash. This is a serious error, and we
880 appreciate a detailed bug report from you that describes how we could go
881 ahead and repeat this!
883 4.7 How do I keep user names and passwords secret in Curl command lines?
885 This problem has two sides:
887 The first part is to avoid having clear-text passwords in the command line
888 so that they don't appear in 'ps' outputs and similar. That is easily
889 avoided by using the "-K" option to tell curl to read parameters from a file
890 or stdin to which you can pass the secret info. curl itself will also
891 attempt to "hide" the given password by blanking out the option - this
892 doesn't work on all platforms.
894 To keep the passwords in your account secret from the rest of the world is
895 not a task that curl addresses. You could of course encrypt them somehow to
896 at least hide them from being read by human eyes, but that is not what
897 anyone would call security.
899 Also note that regular HTTP (using Basic authentication) and FTP passwords
900 are sent in clear across the network. All it takes for anyone to fetch them
901 is to listen on the network. Eavesdropping is very easy. Use more secure
902 authentication methods (like Digest, Negotiate or even NTLM) or consider the
903 SSL-based alternatives HTTPS and FTPS.
907 It is not a bug if the behavior is documented. Read the docs first.
908 Especially check out the KNOWN_BUGS file, it may be a documented bug!
910 If it is a problem with a binary you've downloaded or a package for your
911 particular platform, try contacting the person who built the package/archive
914 If there is a bug, read the BUGS document first. Then report it as described
917 4.9 Curl can't authenticate to the server that requires NTLM?
919 NTLM support requires OpenSSL, GnuTLS, NSS, Secure Transport, or Microsoft
920 Windows libraries at build-time to provide this functionality.
922 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
923 should not use such ones.
925 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
927 Many web servers allow or demand that the administrator configures the
928 server properly for these requests to work on the web server.
930 Some servers seem to support HEAD only on certain kinds of URLs.
932 To fully grasp this, try the documentation for the particular server
933 software you're trying to interact with. This is not anything curl can do
936 4.11 Why does my HTTP range requests return the full document?
938 Because the range may not be supported by the server, or the server may
939 choose to ignore it and return the full document anyway.
941 4.12 Why do I get "certificate verify failed" ?
943 You invoke curl 7.10 or later to communicate on a https:// URL and get an
944 error back looking something similar to this:
946 curl: (35) SSL: error:14090086:SSL routines:
947 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
949 Then it means that curl couldn't verify that the server's certificate was
950 good. Curl verifies the certificate using the CA cert bundle that comes with
951 the curl installation.
953 To disable the verification (which makes it act like curl did before 7.10),
954 use -k. This does however enable man-in-the-middle attacks.
956 If you get this failure but are having a CA cert bundle installed and used,
957 the server's certificate is not signed by one of the CA's in the bundle. It
958 might for example be self-signed. You then correct this problem by obtaining
959 a valid CA cert for the server. Or again, decrease the security by disabling
962 Details are also in the SSLCERTS file in the release archives, found online
963 here: http://curl.haxx.se/docs/sslcerts.html
965 4.13 Why is curl -R on Windows one hour off?
967 During daylight savings time, when -R is used, curl will set a time that
968 appears one hour off. This happens due to a flaw in how Windows stores and
969 uses file modification times and it is not easily worked around. For details
970 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
972 4.14 Redirects work in browser but not with curl!
974 curl supports HTTP redirects fine (see item 3.8). Browsers generally support
975 at least two other ways to perform redirects that curl does not:
977 Meta tags. You can write a HTML tag that will cause the browser to redirect
978 to another given URL after a certain time.
980 Javascript. You can write a Javascript program embedded in a HTML page that
981 redirects the browser to another given URL.
983 There is no way to make curl follow these redirects. You must either
984 manually figure out what the page is set to do, or you write a script that
985 parses the results and fetches the new URL.
987 4.15 FTPS doesn't work
989 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
992 When a URL is used that starts with FTPS://, curl assumes implicit SSL on
993 the control connection and will therefore immediately connect and try to
994 speak SSL. FTPS:// connections default to port 990.
996 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
997 of its related flavours). This is the most common method, and the one
998 mandated by RFC4217. This kind of connection then of course uses the
999 standard FTP port 21 by default.
1001 4.16 My HTTP POST or PUT requests are slow!
1003 libcurl makes all POST and PUT requests (except for POST requests with a
1004 very tiny request body) use the "Expect: 100-continue" header. This header
1005 allows the server to deny the operation early so that libcurl can bail out
1006 already before having to send any data. This is useful in authentication
1009 However, many servers don't implement the Expect: stuff properly and if the
1010 server doesn't respond (positively) within 1 second libcurl will continue
1011 and send off the data anyway.
1013 You can disable libcurl's use of the Expect: header the same way you disable
1014 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
1016 4.17 Non-functional connect timeouts
1018 In most Windows setups having a timeout longer than 21 seconds make no
1019 difference, as it will only send 3 TCP SYN packets and no more. The second
1020 packet sent three seconds after the first and the third six seconds after
1021 the second. No more than three packets are sent, no matter how long the
1024 See option TcpMaxConnectRetransmissions on this page:
1025 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
1027 Also, even on non-Windows systems there may run a firewall or anti-virus
1028 software or similar that accepts the connection but does not actually do
1029 anything else. This will make (lib)curl to consider the connection connected
1030 and thus the connect timeout won't trigger.
1032 4.18 file:// URLs containing drive letters (Windows, NetWare)
1034 When using cURL to try to download a local file, one might use a URL
1039 You'll find that even if D:\blah.txt does exist, cURL returns a 'file
1042 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
1043 file:// URLs must contain a host component, but it is ignored by
1044 most implementations. In the above example, 'D:' is treated as the
1045 host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
1046 If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
1047 and if that doesn't exist you will get the not found error.
1049 To fix this problem, use file:// URLs with *three* leading slashes:
1053 Alternatively, if it makes more sense, specify 'localhost' as the host
1056 file://localhost/D:/blah.txt
1058 In either case, cURL should now be looking for the correct file.
1060 4.19 Why doesn't cURL return an error when the network cable is unplugged?
1062 Unplugging a cable is not an error situation. The TCP/IP protocol stack
1063 was designed to be fault tolerant, so even though there may be a physical
1064 break somewhere the connection shouldn't be affected, just possibly
1065 delayed. Eventually, the physical break will be fixed or the data will be
1066 re-routed around the physical problem through another path.
1068 In such cases, the TCP/IP stack is responsible for detecting when the
1069 network connection is irrevocably lost. Since with some protocols it is
1070 perfectly legal for the client wait indefinitely for data, the stack may
1071 never report a problem, and even when it does, it can take up to 20 minutes
1072 for it to detect an issue. The curl option --keepalive-time enables
1073 keep-alive support in the TCP/IP stack which makes it periodically probe the
1074 connection to make sure it is still available to send data. That should
1075 reliably detect any TCP/IP network failure.
1077 But even that won't detect the network going down before the TCP/IP
1078 connection is established (e.g. during a DNS lookup) or using protocols that
1079 don't use TCP. To handle those situations, curl offers a number of timeouts
1080 on its own. --speed-limit/--speed-time will abort if the data transfer rate
1081 falls too low, and --connect-timeout and --max-time can be used to put an
1082 overall timeout on the connection phase or the entire transfer.
1084 A libcurl-using application running in a known physical environment (e.g.
1085 an embedded device with only a single network connection) may want to act
1086 immediately if its lone network connection goes down. That can be achieved
1087 by having the application monitor the network connection on its own using an
1088 OS-specific mechanism, then signalling libcurl to abort (see also item 5.13).
1093 5.1 Is libcurl thread-safe?
1097 We have written the libcurl code specifically adjusted for multi-threaded
1098 programs. libcurl will use thread-safe functions instead of non-safe ones if
1099 your system has such. Note that you must never share the same handle in
1102 libcurl's implementation of timeouts might use signals (depending on what it
1103 was built to use for name resolving), and signal handling is generally not
1104 thread-safe. Multi-threaded Applicationss that call libcurl from different
1105 threads (on different handles) might want to use CURLOPT_NOSIGNAL, e.g.:
1107 curl_easy_setopt(handle, CURLOPT_NOSIGNAL, true);
1109 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
1110 need to provide one or two locking functions:
1112 http://www.openssl.org/docs/crypto/threads.html
1114 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
1115 need to provide locking function(s) for libgcrypt (which is used by GnuTLS
1116 for the crypto functions).
1118 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
1120 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
1122 5.2 How can I receive all data into a large memory chunk?
1124 [ See also the examples/getinmemory.c source ]
1126 You are in full control of the callback function that gets called every time
1127 there is data received from the remote server. You can make that callback do
1128 whatever you want. You do not have to write the received data to a file.
1130 One solution to this problem could be to have a pointer to a struct that you
1131 pass to the callback function. You set the pointer using the
1132 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
1133 instead of a FILE * to a file:
1135 /* imaginary struct */
1136 struct MemoryStruct {
1141 /* imaginary callback function */
1143 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
1145 size_t realsize = size * nmemb;
1146 struct MemoryStruct *mem = (struct MemoryStruct *)data;
1148 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
1150 memcpy(&(mem->memory[mem->size]), ptr, realsize);
1151 mem->size += realsize;
1152 mem->memory[mem->size] = 0;
1157 5.3 How do I fetch multiple files with libcurl?
1159 libcurl has excellent support for transferring multiple files. You should
1160 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
1161 with curl_easy_perform(). The handle you get from curl_easy_init() is not
1162 only reusable, but you're even encouraged to reuse it if you can, as that
1163 will enable libcurl to use persistent connections.
1165 5.4 Does libcurl do Winsock initialization on win32 systems?
1167 Yes, if told to in the curl_global_init() call.
1169 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
1171 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
1172 that DLL use the FILE * (as the DLL and the client application cannot access
1173 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
1174 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
1175 file, even if that simply writes the data to the specified FILE *.
1176 Similarly, if you use CURLOPT_READDATA you must also specify
1177 CURLOPT_READFUNCTION.
1179 5.6 What about Keep-Alive or persistent connections?
1181 curl and libcurl have excellent support for persistent connections when
1182 transferring several files from the same server. Curl will attempt to reuse
1183 connections for all URLs specified on the same command line/config file, and
1184 libcurl will reuse connections for all transfers that are made using the
1185 same libcurl handle.
1187 When you use the easy interface, the connection cache is kept within the
1188 easy handle. If you instead use the multi interface, the connection cache
1189 will be kept within the multi handle and will be shared among all the easy
1190 handles that are used within the same multi handle.
1192 5.7 Link errors when building libcurl on Windows!
1194 You need to make sure that your project, and all the libraries (both static
1195 and dynamic) that it links against, are compiled/linked against the same run
1198 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
1199 options to the command line compiler. /MD (linking against MSVCRT dll) seems
1200 to be the most commonly used option.
1202 When building an application that uses the static libcurl library, you must
1203 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
1204 dynamic import symbols. If you're using Visual Studio, you need to instead
1205 add CURL_STATICLIB in the "Preprocessor Definitions" section.
1207 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
1208 have linked against the wrong (static) library. If you want to use the
1209 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
1210 the import libraries below. These are the libraries produced by the various
1211 lib/Makefile.* files:
1213 Target: static lib. import lib for libcurl*.dll.
1214 -----------------------------------------------------------
1215 MingW: libcurl.a libcurldll.a
1216 MSVC (release): libcurl.lib libcurl_imp.lib
1217 MSVC (debug): libcurld.lib libcurld_imp.lib
1218 Borland: libcurl.lib libcurl_imp.lib
1220 5.8 libcurl.so.X: open failed: No such file or directory
1222 This is an error message you might get when you try to run a program linked
1223 with a shared version of libcurl and your run-time linker (ld.so) couldn't
1224 find the shared library named libcurl.so.X. (Where X is the number of the
1225 current libcurl ABI, typically 3 or 4).
1227 You need to make sure that ld.so finds libcurl.so.X. You can do that
1228 multiple ways, and it differs somewhat between different operating systems,
1229 but they are usually:
1231 * Add an option to the linker command line that specify the hard-coded path
1232 the run-time linker should check for the lib (usually -R)
1234 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
1235 should check for libs
1237 * Adjust the system's config to check for libs in the directory where you've
1238 put the dir (like Linux's /etc/ld.so.conf)
1240 'man ld.so' and 'man ld' will tell you more details
1242 5.9 How does libcurl resolve host names?
1244 libcurl supports a large a number of different name resolve functions. One
1245 of them is picked at build-time and will be used unconditionally. Thus, if
1246 you want to change name resolver function you must rebuild libcurl and tell
1247 it to use a different function.
1249 - The non-ipv6 resolver that can use one out of four host name resolve calls
1250 (depending on what your system supports):
1253 B - gethostbyname_r() with 3 arguments
1254 C - gethostbyname_r() with 5 arguments
1255 D - gethostbyname_r() with 6 arguments
1257 - The ipv6-resolver that uses getaddrinfo()
1259 - The c-ares based name resolver that uses the c-ares library for resolves.
1260 Using this offers asynchronous name resolves.
1262 - The threaded resolver (default option on Windows). It uses:
1264 A - gethostbyname() on plain ipv4 hosts
1265 B - getaddrinfo() on ipv6-enabled hosts
1267 Also note that libcurl never resolves or reverse-lookups addresses given as
1268 pure numbers, such as 127.0.0.1 or ::1.
1270 5.10 How do I prevent libcurl from writing the response to stdout?
1272 libcurl provides a default built-in write function that writes received data
1273 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
1274 set CURLOPT_WRITEDATA to a different FILE * handle.
1276 5.11 How do I make libcurl not receive the whole HTTP response?
1278 You make the write callback (or progress callback) return an error and
1279 libcurl will then abort the transfer.
1281 5.12 Can I make libcurl fake or hide my real IP address?
1283 No. libcurl operates on a higher level. Besides, faking IP address would
1284 imply sending IP packet with a made-up source address, and then you normally
1285 get a problem with receiving the packet sent back as they would then not be
1288 If you use a proxy to access remote sites, the sites will not see your local
1289 IP address but instead the address of the proxy.
1291 Also note that on many networks NATs or other IP-munging techniques are used
1292 that makes you see and use a different IP address locally than what the
1293 remote server will see you coming from. You may also consider using
1294 http://www.torproject.org .
1296 5.13 How do I stop an ongoing transfer?
1298 With the easy interface you make sure to return the correct error code from
1299 one of the callbacks, but none of them are instant. There is no function you
1300 can call from another thread or similar that will stop it immediately.
1301 Instead, you need to make sure that one of the callbacks you use returns an
1302 appropriate value that will stop the transfer. Suitable callbacks that you
1303 can do this with include the progress callback, the read callback and the
1306 If you're using the multi interface, you can also stop a transfer by
1307 removing the particular easy handle from the multi stack at any moment you
1308 think the transfer is done or when you wish to abort the transfer.
1310 5.14 Using C++ non-static functions for callbacks?
1312 libcurl is a C library, it doesn't know anything about C++ member functions.
1314 You can overcome this "limitation" with a relative ease using a static
1315 member function that is passed a pointer to the class:
1317 // f is the pointer to your object.
1318 static YourClass::func(void *buffer, size_t sz, size_t n, void *f)
1320 // Call non-static member function.
1321 static_cast<YourClass*>(f)->nonStaticFunction();
1324 // This is how you pass pointer to the static function:
1325 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func);
1326 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
1328 5.15 How do I get an FTP directory listing?
1330 If you end the FTP URL you request with a slash, libcurl will provide you
1331 with a directory listing of that given directory. You can also set
1332 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
1335 The follow-up question that tend to follow the previous one, is how a
1336 program is supposed to parse the directory listing. How does it know what's
1337 a file and what's a dir and what's a symlink etc. The harsh reality is that
1338 FTP provides no such fine and easy-to-parse output. The output format FTP
1339 servers respond to LIST commands are entirely at the server's own liking and
1340 the NLST output doesn't reveal any types and in many cases don't even
1341 include all the directory entries. Also, both LIST and NLST tend to hide
1342 unix-style hidden files (those that start with a dot) by default so you need
1343 to do "LIST -a" or similar to see them.
1345 The application thus needs to parse the LIST output. One such existing
1346 list parser is available at http://cr.yp.to/ftpparse.html Versions of
1347 libcurl since 7.21.0 also provide the ability to specify a wildcard to
1348 download multiple files from one FTP directory.
1350 5.16 I want a different time-out!
1352 Time and time again users realize that CURLOPT_TIMEOUT and
1353 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all
1354 the various use cases and scenarios applications end up with.
1356 libcurl offers many more ways to time-out operations. A common alternative
1357 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to
1358 specify the lowest possible speed to accept before to consider the transfer
1361 The most flexible way is by writing your own time-out logic and using
1362 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and
1363 use that to figure out exactly when the right condition is met when the
1364 transfer should get stopped.
1366 5.17 Can I write a server with libcurl?
1368 No. libcurl offers no functions or building blocks to build any kind of
1369 internet protocol server. libcurl is only a client-side library. For server
1370 libraries, you need to continue your search elsewhere but there exist many
1371 good open source ones out there for most protocols you could possibly want a
1372 server for. And there are really good stand-alone ones that have been tested
1373 and proven for many years. There's no need for you to reinvent them!
1375 5.18 Does libcurl use threads?
1377 Put simply: no, libcurl will execute in the same thread you call it in. All
1378 callbacks will be called in the same thread as the one you call libcurl in.
1380 If you want to avoid your thread to be blocked by the libcurl call, you make
1381 sure you use the non-blocking API which will do transfers asynchronously -
1382 but still in the same single thread.
1384 libcurl will potentially internally use threads for name resolving, if it
1385 was built to work like that, but in those cases it'll create the child
1386 threads by itself and they will only be used and then killed internally by
1387 libcurl and never exposed to the outside.
1391 Curl and libcurl are released under a MIT/X derivate license. The license is
1392 very liberal and should not impose a problem for your project. This section
1393 is just a brief summary for the cases we get the most questions. (Parts of
1394 this section was much enhanced by Bjorn Reese.)
1396 We are not lawyers and this is not legal advice. You should probably consult
1397 one if you want true and accurate legal insights without our prejudice. Note
1398 especially that this section concerns the libcurl license only; compiling in
1399 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
1400 the licensing obligations of your application.
1402 6.1 I have a GPL program, can I use the libcurl library?
1406 Since libcurl may be distributed under the MIT/X derivate license, it can be
1407 used together with GPL in any software.
1409 6.2 I have a closed-source program, can I use the libcurl library?
1413 libcurl does not put any restrictions on the program that uses the library.
1415 6.3 I have a BSD licensed program, can I use the libcurl library?
1419 libcurl does not put any restrictions on the program that uses the library.
1421 6.4 I have a program that uses LGPL libraries, can I use libcurl?
1425 The LGPL license doesn't clash with other licenses.
1427 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
1431 The MIT/X derivate license practically allows you to do almost anything with
1432 the sources, on the condition that the copyright texts in the sources are
1435 6.6 Can you please change the curl/libcurl license to XXXX?
1439 We have carefully picked this license after years of development and
1440 discussions and a large amount of people have contributed with source code
1441 knowing that this is the license we use. This license puts the restrictions
1442 we want on curl/libcurl and it does not spread to other programs or
1443 libraries that use it. It should be possible for everyone to use libcurl or
1444 curl in their projects, no matter what license they already have in use.
1446 6.7 What are my obligations when using libcurl in my commercial apps?
1448 Next to none. All you need to adhere to is the MIT-style license (stated in
1449 the COPYING file) which basically says you have to include the copyright
1450 notice in "all copies" and that you may not use the copyright holder's name
1451 when promoting your software.
1453 You do not have to release any of your source code.
1455 You do not have to reveal or make public any changes to the libcurl source
1458 You do not have to broadcast to the world that you are using libcurl within
1461 All we ask is that you disclose "the copyright notice and this permission
1462 notice" somewhere. Most probably like in the documentation or in the section
1463 where other third party dependencies already are mentioned and acknowledged.
1465 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere,
1466 more and more companies are discovering the power of libcurl and take
1467 advantage of it even in commercial environments.
1472 7.1 What is PHP/CURL?
1474 The module for PHP that makes it possible for PHP programs to access curl-
1475 functions from within PHP.
1477 In the cURL project we call this module PHP/CURL to differentiate it from
1478 curl the command line tool and libcurl the library. The PHP team however
1479 does not refer to it like this (for unknown reasons). They call it plain
1480 CURL (often using all caps) or sometimes ext/curl, but both cause much
1481 confusion to users which in turn gives us a higher question load.
1483 7.2 Who wrote PHP/CURL?
1485 PHP/CURL is a module that comes with the regular PHP package. It depends and
1486 uses libcurl, so you need to have libcurl installed properly first before
1487 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
1489 7.3 Can I perform multiple requests using the same handle?
1491 Yes - at least in PHP version 4.3.8 and later (this has been known to not
1492 work in earlier versions, but the exact version when it started to work is
1495 After a transfer, you just set new options in the handle and make another
1496 transfer. This will make libcurl to re-use the same connection if it can.