1 Updated: December 7, 2011 (http://curl.haxx.se/docs/faq.html)
6 \___|\___/|_| \_\_____|
14 1.4 When will you make curl do XXXX ?
16 1.6 What do you get for making curl?
17 1.7 What about CURL from curl.com?
18 1.8 I have a problem who do I mail?
19 1.9 Where do I buy commercial support for curl?
20 1.10 How many are using curl?
21 1.11 Why don't you update ca-bundle.crt
22 1.12 I have a problem who can I chat with?
23 1.13 curl's ECCN number?
24 1.14 How do I submit my patch?
26 2. Install Related Problems
27 2.1 configure doesn't find OpenSSL even when it is installed
28 2.1.1 native linker doesn't find OpenSSL
29 2.1.2 only the libssl lib is missing
30 2.2 Does curl work/build with other SSL libraries?
31 2.3 Where can I find a copy of LIBEAY32.DLL?
32 2.4 Does curl support SOCKS (RFC 1928) ?
35 3.1 curl: (1) SSL is disabled, https: not supported
36 3.2 How do I tell curl to resume a transfer?
37 3.3 Why doesn't my posting using -F work?
38 3.4 How do I tell curl to run custom FTP commands?
39 3.5 How can I disable the Accept: */* header?
40 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
41 3.7 Can I use curl to delete/rename a file through FTP?
42 3.8 How do I tell curl to follow HTTP redirects?
43 3.9 How do I use curl in my favorite programming language?
44 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
45 3.11 How do I POST with a different Content-Type?
46 3.12 Why do FTP specific features over HTTP proxy fail?
47 3.13 Why does my single/double quotes fail?
48 3.14 Does curl support Javascript or PAC (automated proxy config)?
49 3.15 Can I do recursive fetches with curl?
50 3.16 What certificates do I need when I use SSL?
51 3.17 How do I list the root dir of an FTP server?
52 3.18 Can I use curl to send a POST/PUT and not wait for a response?
53 3.19 How do I get HTTP from a host using a specific IP address?
54 3.20 How to SFTP from my user's home directory?
55 3.21 Protocol xxx not supported or disabled in libcurl
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!
103 6.1 I have a GPL program, can I use the libcurl library?
104 6.2 I have a closed-source program, can I use the libcurl library?
105 6.3 I have a BSD licensed program, can I use the libcurl library?
106 6.4 I have a program that uses LGPL libraries, can I use libcurl?
107 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
108 6.6 Can you please change the curl/libcurl license to XXXX?
109 6.7 What are my obligations when using libcurl in my commercial apps?
112 7.1 What is PHP/CURL?
113 7.2 Who wrote PHP/CURL?
114 7.3 Can I perform multiple requests using the same handle?
116 ==============================================================================
122 cURL is the name of the project. The name is a play on 'Client for URLs',
123 originally with URL spelled in uppercase to make it obvious it deals with
124 URLs. The fact it can also be pronounced 'see URL' also helped, it works as
125 an abbreviation for "Client URL Request Library" or why not the recursive
126 version: "Curl URL Request Library".
128 The cURL project produces two products:
132 A free and easy-to-use client-side URL transfer library, supporting DICT,
133 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3,
134 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP.
136 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
137 kerberos, HTTP form based upload, proxies, cookies, user+password
138 authentication, file transfer resume, http proxy tunneling and more!
140 libcurl is highly portable, it builds and works identically on numerous
141 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
142 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac
143 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF,
144 Android, Minix, IBM TPF and more...
146 libcurl is free, thread-safe, IPv6 compatible, feature rich, well
151 A command line tool for getting or sending files using URL syntax.
153 Since curl uses libcurl, curl supports the same wide range of common
154 Internet protocols that libcurl does.
156 We pronounce curl and cURL with an initial k sound: [kurl].
158 There are numerous sub-projects and related projects that also use the word
159 curl in the project names in various combinations, but you should take
160 notice that this FAQ is directed at the command-line tool named curl (and
161 libcurl the library), and may therefore not be valid for other curl-related
162 projects. (There is however a small section for the PHP/CURL in this FAQ.)
166 libcurl is a reliable and portable library which provides you with an easy
167 interface to a range of common Internet protocols.
169 You can use libcurl for free in your application, be it open source,
170 commercial or closed-source.
172 libcurl is most probably the most portable, most powerful and most often
173 used C-based multi-platform file transfer library on this planet - be it
174 open source or commercial.
176 1.3 What is curl not?
178 Curl is not a wget clone. That is a common misconception. Never, during
179 curl's development, have we intended curl to replace wget or compete on its
180 market. Curl is targeted at single-shot file transfers.
182 Curl is not a web site mirroring program. If you want to use curl to mirror
183 something: fine, go ahead and write a script that wraps around curl to make
184 it reality (like curlmirror.pl does).
186 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
187 but if you want systematic and sequential behavior you should write a
188 script (or write a new program that interfaces libcurl) and do it.
190 Curl is not a PHP tool, even though it works perfectly well when used from
191 or with PHP (when using the PHP/CURL module).
193 Curl is not a program for a single operating system. Curl exists, compiles,
194 builds and runs under a wide range of operating systems, including all
195 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
198 1.4 When will you make curl do XXXX ?
200 We love suggestions of what to change in order to make curl and libcurl
201 better. We do however believe in a few rules when it comes to the future of
204 * Curl -- the command line tool -- is to remain a non-graphical command line
205 tool. If you want GUIs or fancy scripting capabilities, you should look
206 for another tool that uses libcurl.
208 * We do not add things to curl that other small and available tools already
209 do very fine at the side. Curl's output is fine to pipe into another
210 program or redirect to another file for the next program to interpret.
212 * We focus on protocol related issues and improvements. If you wanna do more
213 magic with the supported protocols than curl currently does, chances are
214 big we will agree. If you wanna add more protocols, we may very well
217 * If you want someone else to make all the work while you wait for us to
218 implement it for you, that is not a very friendly attitude. We spend a
219 considerable time already on maintaining and developing curl. In order to
220 get more out of us, you should consider trading in some of your time and
223 * If you write the code, chances are bigger that it will get into curl
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 and sourceforge.net hosts project services we take advantage from,
248 like the bug tracker. Also again, some companies have sponsored certain
249 parts of the development in the past and I hope some will continue to do so
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
265 first-hand rights to the name.
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. 300 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-bundle.crt file that used to be bundled with curl was very outdated
318 (it being last modified year 2000 should tell) and must be replaced with a
319 much more modern and up-to-date version by anyone who wants to verify peers
320 anyway. It is no longer provided, the last curl release that shipped it was
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 OpenSSL, GnuTLS, yassl, NSS, PolarSSL, axTLS or
422 qssl, although there should not be many problems using a different
423 library. If anyone does "port" curl to use a different SSL library, we are
424 of course very interested in getting the patch!
426 2.3 Where can I find a copy of LIBEAY32.DLL?
428 That is an OpenSSL binary built for Windows.
430 Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
431 on a windows machine to do https://. Check out the curl web site to find
432 accurate and up-to-date pointers to recent OpenSSL DLLs and other binary
435 2.4 Does curl support SOCKS (RFC 1928) ?
437 Yes, SOCKS 4 and 5 are supported.
442 3.1 curl: (1) SSL is disabled, https: not supported
444 If you get this output when trying to get anything from a https:// server,
445 it means that the instance of curl/libcurl that you're using was built
446 without support for this protocol.
448 This could've happened if the configure script that was run at build time
449 couldn't find all libs and include files curl requires for SSL to work. If
450 the configure script fails to find them, curl is simply built without SSL
453 To get the https:// support into a curl that was previously built but that
454 reports that https:// is not supported, you should dig through the document
455 and logs and check out why the configure script doesn't find the SSL libs
456 and/or include files.
458 Also, check out the other paragraph in this FAQ labelled "configure doesn't
459 find OpenSSL even when it is installed".
461 3.2 How do I tell curl to resume a transfer?
463 Curl supports resumed transfers both ways on both FTP and HTTP.
466 3.3 Why doesn't my posting using -F work?
468 You can't simply use -F or -d at your choice. The web server that will
469 receive your post assumes one of the formats. If the form you're trying to
470 "fake" sets the type to 'multipart/form-data', then and only then you must
471 use the -F type. In all the most common cases, you should use -d which then
472 causes a posting with the type 'application/x-www-form-urlencoded'.
474 This is described in some detail in the MANUAL and TheArtOfHttpScripting
475 documents, and if you don't understand it the first time, read it again
476 before you post questions about this to the mailing list. Also, try reading
477 through the mailing list archives for old postings and questions regarding
480 3.4 How do I tell curl to run custom FTP commands?
482 You can tell curl to perform optional commands both before and/or after a
483 file transfer. Study the -Q/--quote option.
485 Since curl is used for file transfers, you don't use curl to just perform
486 FTP commands without transferring anything. Therefore you must always specify
487 a URL to transfer to/from even when doing custom FTP commands.
489 3.5 How can I disable the Accept: */* header?
491 You can change all internally generated headers by adding a replacement with
492 the -H/--header option. By adding a header with empty contents you safely
493 disable that one. Use -H "Accept:" to disable that specific header.
495 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
497 To curl, all contents are alike. It doesn't matter how the page was
498 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain
499 HTML-files. There's no difference to curl and it doesn't even know what kind
500 of language that generated the page.
502 See also item 3.14 regarding javascript.
504 3.7 Can I use curl to delete/rename a file through FTP?
506 Yes. You specify custom FTP commands with -Q/--quote.
508 One example would be to delete a file after you have downloaded it:
510 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
512 or rename a file after upload:
514 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
516 3.8 How do I tell curl to follow HTTP redirects?
518 Curl does not follow so-called redirects by default. The Location: header
519 that informs the client about this is only interpreted if you're using the
520 -L/--location option. As in:
522 curl -L http://redirector.com
524 Not all redirects are HTTP ones, see 4.14
526 3.9 How do I use curl in my favorite programming language?
528 There exist many language interfaces/bindings for curl that integrates it
529 better with various languages. If you are fluid in a script language, you
530 may very well opt to use such an interface instead of using the command line
533 Find out more about which languages that support curl directly, and how to
534 install and use them, in the libcurl section of the curl web site:
535 http://curl.haxx.se/libcurl/
537 All the various bindings to libcurl are made by other projects and people,
538 outside of the cURL project. The cURL project itself only produces libcurl
539 with its plain C API. If you don't find anywhere else to ask you can ask
540 about bindings on the curl-library list too, but be prepared that people on
541 that list may not know anything about bindings.
543 In October 2009, there were interfaces available for the following
544 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
545 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
546 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
547 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
548 Q, wxwidgets and XBLite. By the time you read this, additional ones may have
551 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
553 Curl adheres to the HTTP spec, which basically means you can play with *any*
554 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
555 XML-RPC are all such ones. You can use -X to set custom requests and -H to
556 set custom headers (or replace internally generated ones).
558 Using libcurl is of course just as fine and you'd just use the proper
559 library options to do the same.
561 3.11 How do I POST with a different Content-Type?
563 You can always replace the internally generated headers with -H/--header.
564 To make a simple HTTP POST with text/xml as content-type, do something like:
566 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
568 3.12 Why do FTP specific features over HTTP proxy fail?
570 Because when you use a HTTP proxy, the protocol spoken on the network will
571 be HTTP, even if you specify a FTP URL. This effectively means that you
572 normally can't use FTP specific features such as FTP upload and FTP quote
575 There is one exception to this rule, and that is if you can "tunnel through"
576 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
577 and is generally not available as proxy admins usually disable tunneling to
578 other ports than 443 (which is used for HTTPS access through proxies).
580 3.13 Why does my single/double quotes fail?
582 To specify a command line option that includes spaces, you might need to
583 put the entire option within quotes. Like in:
585 curl -d " with spaces " url.com
589 curl -d ' with spaces ' url.com
591 Exactly what kind of quotes and how to do this is entirely up to the shell
592 or command line interpreter that you are using. For most unix shells, you
593 can more or less pick either single (') or double (") quotes. For
594 Windows/DOS prompts I believe you're forced to use double (") quotes.
596 Please study the documentation for your particular environment. Examples in
597 the curl docs will use a mix of both these ones as shown above. You must
598 adjust them to work in your environment.
600 Remember that curl works and runs on more operating systems than most single
601 individuals have ever tried.
603 3.14 Does curl support Javascript or PAC (automated proxy config)?
605 Many web pages do magic stuff using embedded Javascript. Curl and libcurl
606 have no built-in support for that, so it will be treated just like any other
609 .pac files are a netscape invention and are sometimes used by organizations
610 to allow them to differentiate which proxies to use. The .pac contents is
611 just a Javascript program that gets invoked by the browser and that returns
612 the name of the proxy to connect to. Since curl doesn't support Javascript,
613 it can't support .pac proxy configuration either.
615 Some workarounds usually suggested to overcome this Javascript dependency:
617 - Depending on the Javascript complexity, write up a script that
618 translates it to another language and execute that.
620 - Read the Javascript code and rewrite the same logic in another language.
622 - Implement a Javascript interpreter, people have successfully used the
623 Mozilla Javascript engine in the past.
625 - Ask your admins to stop this, for a static proxy setup or similar.
627 3.15 Can I do recursive fetches with curl?
629 No. curl itself has no code that performs recursive operations, such as
630 those performed by wget and similar tools.
632 There exist wrapper scripts with that functionality (for example the
633 curlmirror perl script), and you can write programs based on libcurl to do
634 it, but the command line tool curl itself cannot.
636 3.16 What certificates do I need when I use SSL?
638 There are three different kinds of "certificates" to keep track of when we
639 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
641 - Client certificate. The server you communicate may require that you can
642 provide this in order to prove that you actually are who you claim to be.
643 If the server doesn't require this, you don't need a client certificate.
645 A client certificate is always used together with a private key, and the
646 private key has a pass phrase that protects it.
648 - Server certificate. The server you communicate with has a server
649 certificate. You can and should verify this certificate to make sure that
650 you are truly talking to the real server and not a server impersonating
653 - Certificate Authority certificate ("CA cert"). You often have several CA
654 certs in a CA cert bundle that can be used to verify a server certificate
655 that was signed by one of the authorities in the bundle. curl does not
656 come with a CA cert bundle but most curl installs provide one. You can
657 also override the default.
659 The server certificate verification process is made by using a Certificate
660 Authority certificate ("CA cert") that was used to sign the server
661 certificate. Server certificate verification is enabled by default in curl
662 and libcurl and is often the reason for problems as explained in FAQ entry
663 4.12 and the SSLCERTS document
664 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
665 "self-signed" or otherwise signed by a CA that you do not have a CA cert
666 for, cannot be verified. If the verification during a connect fails, you
667 are refused access. You then need to explicitly disable the verification
668 to connect to the server.
670 3.17 How do I list the root dir of an FTP server?
672 There are two ways. The way defined in the RFC is to use an encoded slash
673 in the first path part. List the "/tmp" dir like this:
675 curl ftp://ftp.sunet.se/%2ftmp/
677 or the not-quite-kosher-but-more-readable way, by simply starting the path
678 section of the URL with a slash:
680 curl ftp://ftp.sunet.se//tmp/
682 3.18 Can I use curl to send a POST/PUT and not wait for a response?
686 But you could easily write your own program using libcurl to do such stunts.
688 3.19 How do I get HTTP from a host using a specific IP address?
690 For example, you may be trying out a web site installation that isn't yet in
691 the DNS. Or you have a site using multiple IP addresses for a given host
692 name and you want to address a specific one out of the set.
694 Set a custom Host: header that identifies the server name you want to reach
695 but use the target IP address in the URL:
697 curl --header "Host: www.example.com" http://127.0.0.1/
699 You can also opt to add faked host name entries to curl with the --resolve
700 option. That has the added benefit that things like redirects will also work
701 properly. The above operation would instead be done as:
703 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/
705 3.20 How to SFTP from my user's home directory?
707 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to
708 work with. It means that if you don't specify that you want the user's home
709 directory, you get the actual root directory.
711 To specify a file in your user's home directory, you need to use the correct
712 URL syntax which for sftp might look similar to:
714 curl -O -u user:password sftp://example.com/~/file.txt
716 and for SCP it is just a different protocol prefix:
718 curl -O -u user:password scp://example.com/~/file.txt
720 3.21 Protocol xxx not supported or disabled in libcurl
722 When passing on a URL to curl to use, it may respond that the particular
723 protocol is not supported or disabled. The particular way this error message
724 is phrased is because curl doesn't make a distinction internally of whether
725 a particular protocol is not supported (ie never got any code added that
726 knows how to speak that protocol) or if it was explicitly disabled. curl can
727 be built to only support a given set of protocols, and the rest would then
728 be disabled or not supported.
730 Note that this error will also occur if you pass a wrongly spelled protocol
731 part as in "htpt://example.com" or as in the less evident case if you prefix
732 the protocol part with a space as in " http://example.com/".
737 4.1 Problems connecting to SSL servers.
739 It took a very long time before we could sort out why curl had problems to
740 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
741 error sometimes showed up similar to:
743 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
745 It turned out to be because many older SSL servers don't deal with SSLv3
746 requests properly. To correct this problem, tell curl to select SSLv2 from
747 the command line (-2/--sslv2).
749 There have also been examples where the remote server didn't like the SSLv2
750 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
752 4.2 Why do I get problems when I use & or % in the URL?
754 In general unix shells, the & symbol is treated specially and when used, it
755 runs the specified command in the background. To safely send the & as a part
756 of a URL, you should quote the entire URL by using single (') or double (")
757 quotes around it. Similar problems can also occur on some shells with other
758 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
760 An example that would invoke a remote CGI that uses &-symbols could be:
762 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
764 In Windows, the standard DOS shell treats the %-symbol specially and you
765 need to use TWO %-symbols for each single one you want to use in the URL.
767 Also note that if you want the literal %-symbol to be part of the data you
768 pass in a POST using -d/--data you must encode it as '%25' (which then also
769 needs the %-symbol doubled on Windows machines).
771 4.3 How can I use {, }, [ or ] to specify multiple URLs?
773 Because those letters have a special meaning to the shell, and to be used in
774 a URL specified to curl you must quote them.
776 An example that downloads two URLs (sequentially) would do:
778 curl '{curl,www}.haxx.se'
780 To be able to use those letters as actual parts of the URL (without using
781 them for the curl URL "globbing" system), use the -g/--globoff option:
783 curl -g 'www.site.com/weirdname[].html'
785 4.4 Why do I get downloaded data even though the web page doesn't exist?
787 Curl asks remote servers for the page you specify. If the page doesn't exist
788 at the server, the HTTP protocol defines how the server should respond and
789 that means that headers and a "page" will be returned. That's simply how
792 By using the --fail option you can tell curl explicitly to not get any data
793 if the HTTP return code doesn't say success.
795 4.5 Why do I get return code XXX from a HTTP server?
797 RFC2616 clearly explains the return codes. This is a short transcript. Go
798 read the RFC for exact details:
800 4.5.1 "400 Bad Request"
802 The request could not be understood by the server due to malformed
803 syntax. The client SHOULD NOT repeat the request without modifications.
805 4.5.2 "401 Unauthorized"
807 The request requires user authentication.
809 4.5.3 "403 Forbidden"
811 The server understood the request, but is refusing to fulfil it.
812 Authorization will not help and the request SHOULD NOT be repeated.
814 4.5.4 "404 Not Found"
816 The server has not found anything matching the Request-URI. No indication
817 is given of whether the condition is temporary or permanent.
819 4.5.5 "405 Method Not Allowed"
821 The method specified in the Request-Line is not allowed for the resource
822 identified by the Request-URI. The response MUST include an Allow header
823 containing a list of valid methods for the requested resource.
825 4.5.6 "301 Moved Permanently"
827 If you get this return code and an HTML output similar to this:
829 <H1>Moved Permanently</H1> The document has moved <A
830 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
832 it might be because you request a directory URL but without the trailing
833 slash. Try the same operation again _with_ the trailing URL, or use the
834 -L/--location option to follow the redirection.
836 4.6 Can you tell me what error code 142 means?
838 All curl error codes are described at the end of the man page, in the
839 section called "EXIT CODES".
841 Error codes that are larger than the highest documented error code means
842 that curl has exited due to a crash. This is a serious error, and we
843 appreciate a detailed bug report from you that describes how we could go
844 ahead and repeat this!
846 4.7 How do I keep user names and passwords secret in Curl command lines?
848 This problem has two sides:
850 The first part is to avoid having clear-text passwords in the command line
851 so that they don't appear in 'ps' outputs and similar. That is easily
852 avoided by using the "-K" option to tell curl to read parameters from a file
853 or stdin to which you can pass the secret info. curl itself will also
854 attempt to "hide" the given password by blanking out the option - this
855 doesn't work on all platforms.
857 To keep the passwords in your account secret from the rest of the world is
858 not a task that curl addresses. You could of course encrypt them somehow to
859 at least hide them from being read by human eyes, but that is not what
860 anyone would call security.
862 Also note that regular HTTP (using Basic authentication) and FTP passwords
863 are sent in clear across the network. All it takes for anyone to fetch them
864 is to listen on the network. Eavesdropping is very easy. Use more secure
865 authentication methods (like Digest, Negotiate or even NTLM) or consider the
866 SSL-based alternatives HTTPS and FTPS.
870 It is not a bug if the behavior is documented. Read the docs first.
871 Especially check out the KNOWN_BUGS file, it may be a documented bug!
873 If it is a problem with a binary you've downloaded or a package for your
874 particular platform, try contacting the person who built the package/archive
877 If there is a bug, read the BUGS document first. Then report it as described
880 4.9 Curl can't authenticate to the server that requires NTLM?
882 NTLM support requires OpenSSL, GnuTLS, NSS or Microsoft Windows libraries at
883 build-time to provide this functionality.
885 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
886 should not use such ones.
888 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
890 Many web servers allow or demand that the administrator configures the
891 server properly for these requests to work on the web server.
893 Some servers seem to support HEAD only on certain kinds of URLs.
895 To fully grasp this, try the documentation for the particular server
896 software you're trying to interact with. This is not anything curl can do
899 4.11 Why does my HTTP range requests return the full document?
901 Because the range may not be supported by the server, or the server may
902 choose to ignore it and return the full document anyway.
904 4.12 Why do I get "certificate verify failed" ?
906 You invoke curl 7.10 or later to communicate on a https:// URL and get an
907 error back looking something similar to this:
909 curl: (35) SSL: error:14090086:SSL routines:
910 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
912 Then it means that curl couldn't verify that the server's certificate was
913 good. Curl verifies the certificate using the CA cert bundle that comes with
914 the curl installation.
916 To disable the verification (which makes it act like curl did before 7.10),
917 use -k. This does however enable man-in-the-middle attacks.
919 If you get this failure but are having a CA cert bundle installed and used,
920 the server's certificate is not signed by one of the CA's in the bundle. It
921 might for example be self-signed. You then correct this problem by obtaining
922 a valid CA cert for the server. Or again, decrease the security by disabling
925 Details are also in the SSLCERTS file in the release archives, found online
926 here: http://curl.haxx.se/docs/sslcerts.html
928 4.13 Why is curl -R on Windows one hour off?
930 During daylight savings time, when -R is used, curl will set a time that
931 appears one hour off. This happens due to a flaw in how Windows stores and
932 uses file modification times and it is not easily worked around. For details
933 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
935 4.14 Redirects work in browser but not with curl!
937 curl supports HTTP redirects fine (see item 3.8). Browsers generally support
938 at least two other ways to perform directs that curl does not:
940 - Meta tags. You can write a HTML tag that will cause the browser to
941 redirect to another given URL after a certain time.
943 - Javascript. You can write a Javascript program embedded in a HTML page
944 that redirects the browser to another given URL.
946 There is no way to make curl follow these redirects. You must either
947 manually figure out what the page is set to do, or you write a script that
948 parses the results and fetches the new URL.
950 4.15 FTPS doesn't work
952 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
955 When a URL is used that starts with FTPS://, curl assumes implicit SSL on
956 the control connection and will therefore immediately connect and try to
957 speak SSL. FTPS:// connections default to port 990.
959 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
960 of its related flavours). This is the most common method, and the one
961 mandated by RFC4217. This kind of connection then of course uses the
962 standard FTP port 21 by default.
964 4.16 My HTTP POST or PUT requests are slow!
966 libcurl makes all POST and PUT requests (except for POST requests with a
967 very tiny request body) use the "Expect: 100-continue" header. This header
968 allows the server to deny the operation early so that libcurl can bail out
969 already before having to send any data. This is useful in authentication
972 However, many servers don't implement the Expect: stuff properly and if the
973 server doesn't respond (positively) within 1 second libcurl will continue
974 and send off the data anyway.
976 You can disable libcurl's use of the Expect: header the same way you disable
977 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
979 4.17 Non-functional connect timeouts
981 In most Windows setups having a timeout longer than 21 seconds make no
982 difference, as it will only send 3 TCP SYN packets and no more. The second
983 packet sent three seconds after the first and the third six seconds after
984 the second. No more than three packets are sent, no matter how long the
987 See option TcpMaxConnectRetransmissions on this page:
988 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
990 Also, even on non-Windows systems there may run a firewall or anti-virus
991 software or similar that accepts the connection but does not actually do
992 anything else. This will make (lib)curl to consider the connection connected
993 and thus the connect timeout won't trigger.
995 4.18 file:// URLs containing drive letters (Windows, NetWare)
997 When using cURL to try to download a local file, one might use a URL
1002 You'll find that even if D:\blah.txt does exist, cURL returns a 'file
1005 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
1006 file:// URLs must contain a host component, but it is ignored by
1007 most implementations. In the above example, 'D:' is treated as the
1008 host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
1009 If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
1010 and if that doesn't exist you will get the not found error.
1012 To fix this problem, use file:// URLs with *three* leading slashes:
1016 Alternatively, if it makes more sense, specify 'localhost' as the host
1019 file://localhost/D:/blah.txt
1021 In either case, cURL should now be looking for the correct file.
1023 4.19 Why doesn't cURL return an error when the network cable is unplugged?
1025 Unplugging the cable is not an error situation. The TCP/IP protocol stack
1026 was designed to be fault tolerant, so even though there may be a physical
1027 break somewhere the connection shouldn't be affected, just possibly
1028 delayed. Eventually, the physical break will be fixed or the data will be
1029 re-routed around the physical problem.
1031 In such cases, the TCP/IP stack is responsible for detecting when the
1032 network connection is irrevocably lost. Since with some protocols it is
1033 perfectly legal for the client wait indefinitely for data, the stack may
1034 never report a problem, and even when it does, it can take up to 20 minutes
1035 for it to detect an issue. The curl option --keepalive-time enables
1036 keep-alive support in the TCP/IP stack which makes it periodically probe the
1037 connection to make sure it is still available to send data. That should
1038 reliably detect any TCP/IP network failure.
1040 But even that won't detect the network going down before the TCP/IP
1041 connection is established (e.g. during a DNS lookup) or using protocols that
1042 don't use TCP. To handle those situations, curl offers a number of timeouts
1043 on its own. --speed-limit/--speed-time will abort if the data transfer rate
1044 falls too low, and --connect-timeout and --max-time can be used to put an
1045 overall timeout on the connection phase or the entire transfer.
1050 5.1 Is libcurl thread-safe?
1054 We have written the libcurl code specifically adjusted for multi-threaded
1055 programs. libcurl will use thread-safe functions instead of non-safe ones if
1056 your system has such.
1058 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
1059 need to provide one or two locking functions:
1061 http://www.openssl.org/docs/crypto/threads.html
1063 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
1064 need to provide locking function(s) for libgcrypt (which is used by GnuTLS
1065 for the crypto functions).
1067 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
1069 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
1071 5.2 How can I receive all data into a large memory chunk?
1073 [ See also the examples/getinmemory.c source ]
1075 You are in full control of the callback function that gets called every time
1076 there is data received from the remote server. You can make that callback do
1077 whatever you want. You do not have to write the received data to a file.
1079 One solution to this problem could be to have a pointer to a struct that you
1080 pass to the callback function. You set the pointer using the
1081 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
1082 instead of a FILE * to a file:
1084 /* imaginary struct */
1085 struct MemoryStruct {
1090 /* imaginary callback function */
1092 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
1094 size_t realsize = size * nmemb;
1095 struct MemoryStruct *mem = (struct MemoryStruct *)data;
1097 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
1099 memcpy(&(mem->memory[mem->size]), ptr, realsize);
1100 mem->size += realsize;
1101 mem->memory[mem->size] = 0;
1106 5.3 How do I fetch multiple files with libcurl?
1108 libcurl has excellent support for transferring multiple files. You should
1109 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
1110 with curl_easy_perform(). The handle you get from curl_easy_init() is not
1111 only reusable, but you're even encouraged to reuse it if you can, as that
1112 will enable libcurl to use persistent connections.
1114 5.4 Does libcurl do Winsock initialization on win32 systems?
1116 Yes, if told to in the curl_global_init() call.
1118 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
1120 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
1121 that DLL use the FILE * (as the DLL and the client application cannot access
1122 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
1123 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
1124 file, even if that simply writes the data to the specified FILE *.
1125 Similarly, if you use CURLOPT_READDATA you must also specify
1126 CURLOPT_READFUNCTION.
1128 5.6 What about Keep-Alive or persistent connections?
1130 curl and libcurl have excellent support for persistent connections when
1131 transferring several files from the same server. Curl will attempt to reuse
1132 connections for all URLs specified on the same command line/config file, and
1133 libcurl will reuse connections for all transfers that are made using the
1134 same libcurl handle.
1136 When you use the easy interface, the connection cache is kept within the
1137 easy handle. If you instead use the multi interface, the connection cache
1138 will be kept within the multi handle and will be shared among all the easy
1139 handles that are used within the same multi handle.
1141 5.7 Link errors when building libcurl on Windows!
1143 You need to make sure that your project, and all the libraries (both static
1144 and dynamic) that it links against, are compiled/linked against the same run
1147 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
1148 options to the command line compiler. /MD (linking against MSVCRT dll) seems
1149 to be the most commonly used option.
1151 When building an application that uses the static libcurl library, you must
1152 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
1153 dynamic import symbols. If you're using Visual Studio, you need to instead
1154 add CURL_STATICLIB in the "Preprocessor Definitions" section.
1156 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
1157 have linked against the wrong (static) library. If you want to use the
1158 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
1159 the import libraries below. These are the libraries produced by the various
1160 lib/Makefile.* files:
1162 Target: static lib. import lib for libcurl*.dll.
1163 -----------------------------------------------------------
1164 MingW: libcurl.a libcurldll.a
1165 MSVC (release): libcurl.lib libcurl_imp.lib
1166 MSVC (debug): libcurld.lib libcurld_imp.lib
1167 Borland: libcurl.lib libcurl_imp.lib
1169 5.8 libcurl.so.X: open failed: No such file or directory
1171 This is an error message you might get when you try to run a program linked
1172 with a shared version of libcurl and your run-time linker (ld.so) couldn't
1173 find the shared library named libcurl.so.X. (Where X is the number of the
1174 current libcurl ABI, typically 3 or 4).
1176 You need to make sure that ld.so finds libcurl.so.X. You can do that
1177 multiple ways, and it differs somewhat between different operating systems,
1178 but they are usually:
1180 * Add an option to the linker command line that specify the hard-coded path
1181 the run-time linker should check for the lib (usually -R)
1183 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
1184 should check for libs
1186 * Adjust the system's config to check for libs in the directory where you've
1187 put the dir (like Linux's /etc/ld.so.conf)
1189 'man ld.so' and 'man ld' will tell you more details
1191 5.9 How does libcurl resolve host names?
1193 libcurl supports a large a number of different name resolve functions. One
1194 of them is picked at build-time and will be used unconditionally. Thus, if
1195 you want to change name resolver function you must rebuild libcurl and tell
1196 it to use a different function.
1198 - The non-ipv6 resolver that can use one out of four host name resolve calls
1199 (depending on what your system supports):
1202 B - gethostbyname_r() with 3 arguments
1203 C - gethostbyname_r() with 5 arguments
1204 D - gethostbyname_r() with 6 arguments
1206 - The ipv6-resolver that uses getaddrinfo()
1208 - The c-ares based name resolver that uses the c-ares library for resolves.
1209 Using this offers asynchronous name resolves.
1211 - The threaded resolver (default option on Windows). It uses:
1213 A - gethostbyname() on plain ipv4 hosts
1214 B - getaddrinfo() on ipv6-enabled hosts
1216 Also note that libcurl never resolves or reverse-lookups addresses given as
1217 pure numbers, such as 127.0.0.1 or ::1.
1219 5.10 How do I prevent libcurl from writing the response to stdout?
1221 libcurl provides a default built-in write function that writes received data
1222 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
1223 set CURLOPT_WRITEDATA to a different FILE * handle.
1225 5.11 How do I make libcurl not receive the whole HTTP response?
1227 You make the write callback (or progress callback) return an error and
1228 libcurl will then abort the transfer.
1230 5.12 Can I make libcurl fake or hide my real IP address?
1232 No. libcurl operates on a higher level than so. Besides, faking IP address
1233 would imply sending IP packages with a made-up source address, and then you
1234 normally get a problem with intercepting the packages sent back as they
1235 would then not be routed to you!
1237 If you use a proxy to access remote sites, the sites will not see your local
1238 IP address but instead the address of the proxy.
1240 Also note that on many networks NATs or other IP-munging techniques are used
1241 that makes you see and use a different IP address locally than what the
1242 remote server will see you coming from.
1244 5.13 How do I stop an ongoing transfer?
1246 With the easy interface you make sure to return the correct error code from
1247 one of the callbacks, but none of them are instant. There is no function you
1248 can call from another thread or similar that will stop it immediately.
1249 Instead, you need to make sure that one of the callbacks you use returns an
1250 appropriate value that will stop the transfer. Suitable callbacks that you
1251 can do this with include the progress callback, the read callback and the
1254 If you're using the multi interface, you can also stop a transfer by
1255 removing the particular easy handle from the multi stack at any moment you
1256 think the transfer is done.
1258 5.14 Using C++ non-static functions for callbacks?
1260 libcurl is a C library, it doesn't know anything about C++ member functions.
1262 You can overcome this "limitation" with a relative ease using a static
1263 member function that is passed a pointer to the class:
1265 // f is the pointer to your object.
1266 static YourClass::func(void *buffer, size_t sz, size_t n, void *f)
1268 // Call non-static member function.
1269 static_cast<YourClass*>(f)->nonStaticFunction();
1272 // This is how you pass pointer to the static function:
1273 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func);
1274 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
1276 5.15 How do I get an FTP directory listing?
1278 If you end the FTP URL you request with a slash, libcurl will provide you
1279 with a directory listing of that given directory. You can also set
1280 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
1283 The follow-up question that tend to follow the previous one, is how a
1284 program is supposed to parse the directory listing. How does it know what's
1285 a file and what's a dir and what's a symlink etc. The harsh reality is that
1286 FTP provides no such fine and easy-to-parse output. The output format FTP
1287 servers respond to LIST commands are entirely at the server's own liking and
1288 the NLST output doesn't reveal any types and in many cases don't even
1289 include all the directory entries. Also, both LIST and NLST tend to hide
1290 unix-style hidden files (those that start with a dot) by default so you need
1291 to do "LIST -a" or similar to see them.
1293 The application thus needs to parse the LIST output. One such existing
1294 list parser is available at http://cr.yp.to/ftpparse.html Versions of
1295 libcurl since 7.21.0 also provide the ability to specify a wildcard to
1296 download multiple files from one FTP directory.
1298 5.16 I want a different time-out!
1300 Time and time again users realize that CURLOPT_TIMEOUT and
1301 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all
1302 the various use cases and scenarios applications end up with.
1304 libcurl offers many more ways to time-out operations. A common alternative
1305 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to
1306 specify the lowest possible speed to accept before to consider the transfer
1309 The most flexible way is by writing your own time-out logic and using
1310 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and
1311 use that to figure out exactly when the right condition is met when the
1312 transfer should get stopped.
1317 Curl and libcurl are released under a MIT/X derivate license. The license is
1318 very liberal and should not impose a problem for your project. This section
1319 is just a brief summary for the cases we get the most questions. (Parts of
1320 this section was much enhanced by Bjorn Reese.)
1322 We are not lawyers and this is not legal advice. You should probably consult
1323 one if you want true and accurate legal insights without our prejudice. Note
1324 especially that this section concerns the libcurl license only; compiling in
1325 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
1326 the licensing obligations of your application.
1328 6.1 I have a GPL program, can I use the libcurl library?
1332 Since libcurl may be distributed under the MIT/X derivate license, it can be
1333 used together with GPL in any software.
1335 6.2 I have a closed-source program, can I use the libcurl library?
1339 libcurl does not put any restrictions on the program that uses the library.
1341 6.3 I have a BSD licensed program, can I use the libcurl library?
1345 libcurl does not put any restrictions on the program that uses the library.
1347 6.4 I have a program that uses LGPL libraries, can I use libcurl?
1351 The LGPL license doesn't clash with other licenses.
1353 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
1357 The MIT/X derivate license practically allows you to do almost anything with
1358 the sources, on the condition that the copyright texts in the sources are
1361 6.6 Can you please change the curl/libcurl license to XXXX?
1365 We have carefully picked this license after years of development and
1366 discussions and a large amount of people have contributed with source code
1367 knowing that this is the license we use. This license puts the restrictions
1368 we want on curl/libcurl and it does not spread to other programs or
1369 libraries that use it. It should be possible for everyone to use libcurl or
1370 curl in their projects, no matter what license they already have in use.
1372 6.7 What are my obligations when using libcurl in my commercial apps?
1374 Next to none. All you need to adhere to is the MIT-style license (stated in
1375 the COPYING file) which basically says you have to include the copyright
1376 notice in "all copies" and that you may not use the copyright holder's name
1377 when promoting your software.
1379 You do not have to release any of your source code.
1381 You do not have to reveal or make public any changes to the libcurl source
1384 You do not have to broadcast to the world that you are using libcurl within
1387 All we ask is that you disclose "the copyright notice and this permission
1388 notice" somewhere. Most probably like in the documentation or in the section
1389 where other third party dependencies already are mentioned and acknowledged.
1391 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere,
1392 more and more companies are discovering the power of libcurl and take
1393 advantage of it even in commercial environments.
1398 7.1 What is PHP/CURL?
1400 The module for PHP that makes it possible for PHP programs to access curl-
1401 functions from within PHP.
1403 In the cURL project we call this module PHP/CURL to differentiate it from
1404 curl the command line tool and libcurl the library. The PHP team however
1405 does not refer to it like this (for unknown reasons). They call it plain
1406 CURL (often using all caps) or sometimes ext/curl, but both cause much
1407 confusion to users which in turn gives us a higher question load.
1409 7.2 Who wrote PHP/CURL?
1411 PHP/CURL is a module that comes with the regular PHP package. It depends and
1412 uses libcurl, so you need to have libcurl installed properly first before
1413 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
1415 7.3 Can I perform multiple requests using the same handle?
1417 Yes - at least in PHP version 4.3.8 and later (this has been known to not
1418 work in earlier versions, but the exact version when it started to work is
1421 After a transfer, you just set new options in the handle and make another
1422 transfer. This will make libcurl to re-use the same connection if it can.