1 Updated: October 6, 2010 (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 Pragma: nocache 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?
56 4.1 Problems connecting to SSL servers.
57 4.2 Why do I get problems when I use & or % in the URL?
58 4.3 How can I use {, }, [ or ] to specify multiple URLs?
59 4.4 Why do I get downloaded data even though the web page doesn't exist?
60 4.5 Why do I get return code XXX from a HTTP server?
61 4.5.1 "400 Bad Request"
62 4.5.2 "401 Unauthorized"
65 4.5.5 "405 Method Not Allowed"
66 4.5.6 "301 Moved Permanently"
67 4.6 Can you tell me what error code 142 means?
68 4.7 How do I keep user names and passwords secret in Curl command lines?
70 4.9 Curl can't authenticate to the server that requires NTLM?
71 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
72 4.11 Why does my HTTP range requests return the full document?
73 4.12 Why do I get "certificate verify failed" ?
74 4.13 Why is curl -R on Windows one hour off?
75 4.14 Redirects work in browser but not with curl!
76 4.15 FTPS doesn't work
77 4.16 My HTTP POST or PUT requests are slow!
78 4.17 Non-functional connect timeouts on Windows
79 4.18 file:// URLs containing drive letters (Windows, NetWare)
80 4.19 Why doesn't cURL return an error when the network cable is unplugged?
83 5.1 Is libcurl thread-safe?
84 5.2 How can I receive all data into a large memory chunk?
85 5.3 How do I fetch multiple files with libcurl?
86 5.4 Does libcurl do Winsock initing on win32 systems?
87 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
88 5.6 What about Keep-Alive or persistent connections?
89 5.7 Link errors when building libcurl on Windows!
90 5.8 libcurl.so.X: open failed: No such file or directory
91 5.9 How does libcurl resolve host names?
92 5.10 How do I prevent libcurl from writing the response to stdout?
93 5.11 How do I make libcurl not receive the whole HTTP response?
94 5.12 Can I make libcurl fake or hide my real IP address?
95 5.13 How do I stop an ongoing transfer?
96 5.14 Using C++ non-static functions for callbacks?
97 5.15 How do I get an FTP directory listing?
100 6.1 I have a GPL program, can I use the libcurl library?
101 6.2 I have a closed-source program, can I use the libcurl library?
102 6.3 I have a BSD licensed program, can I use the libcurl library?
103 6.4 I have a program that uses LGPL libraries, can I use libcurl?
104 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
105 6.6 Can you please change the curl/libcurl license to XXXX?
106 6.7 What are my obligations when using libcurl in my commercial apps?
109 7.1 What is PHP/CURL?
110 7.2 Who write PHP/CURL?
111 7.3 Can I perform multiple requests using the same handle?
113 ==============================================================================
119 cURL is the name of the project. The name is a play on 'Client for URLs',
120 originally with URL spelled in uppercase to make it obvious it deals with
121 URLs. The fact it can also be pronounced 'see URL' also helped, it works as
122 an abbreviation for "Client URL Request Library" or why not the recursive
123 version: "Curl URL Request Library".
125 The cURL project produces two products:
129 A free and easy-to-use client-side URL transfer library, supporting DICT,
130 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3,
131 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP.
133 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
134 kerberos, HTTP form based upload, proxies, cookies, user+password
135 authentication, file transfer resume, http proxy tunneling and more!
137 libcurl is highly portable, it builds and works identically on numerous
138 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
139 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOs, Mac
140 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF,
141 Android, Minix, IBM TPF and more...
143 libcurl is free, thread-safe, IPv6 compatible, feature rich, well
148 A command line tool for getting or sending files using URL syntax.
150 Since curl uses libcurl, curl supports the same wide range of common
151 Internet protocols that libcurl does.
153 We pronounce curl and cURL with an initial k sound: [kurl].
155 There are numerous sub-projects and related projects that also use the word
156 curl in the project names in various combinations, but you should take
157 notice that this FAQ is directed at the command-line tool named curl (and
158 libcurl the library), and may therefore not be valid for other curl-related
159 projects. (There is however a small section for the PHP/CURL in this FAQ.)
163 libcurl is a reliable and portable library which provides you with an easy
164 interface to a range of common Internet protocols.
166 You can use libcurl for free in your application, be it open source,
167 commercial or closed-source.
169 libcurl is most probably the most portable, most powerful and most often
170 used C-based multi-platform file transfer library on this planet - be it
171 open source or commercial.
173 1.3 What is curl not?
175 Curl is not a wget clone. That is a common misconception. Never, during
176 curl's development, have we intended curl to replace wget or compete on its
177 market. Curl is targeted at single-shot file transfers.
179 Curl is not a web site mirroring program. If you want to use curl to mirror
180 something: fine, go ahead and write a script that wraps around curl to make
181 it reality (like curlmirror.pl does).
183 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
184 but if you want systematic and sequential behavior you should write a
185 script (or write a new program that interfaces libcurl) and do it.
187 Curl is not a PHP tool, even though it works perfectly well when used from
188 or with PHP (when using the PHP/CURL module).
190 Curl is not a program for a single operating system. Curl exists, compiles,
191 builds and runs under a wide range of operating systems, including all
192 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
195 1.4 When will you make curl do XXXX ?
197 We love suggestions of what to change in order to make curl and libcurl
198 better. We do however believe in a few rules when it comes to the future of
201 * Curl -- the command line tool -- is to remain a non-graphical command line
202 tool. If you want GUIs or fancy scripting capabilities, you should look
203 for another tool that uses libcurl.
205 * We do not add things to curl that other small and available tools already
206 do very fine at the side. Curl's output is fine to pipe into another
207 program or redirect to another file for the next program to interpret.
209 * We focus on protocol related issues and improvements. If you wanna do more
210 magic with the supported protocols than curl currently does, chances are
211 big we will agree. If you wanna add more protocols, we may very well
214 * If you want someone else to make all the work while you wait for us to
215 implement it for you, that is not a very friendly attitude. We spend a
216 considerable time already on maintaining and developing curl. In order to
217 get more out of us, you should consider trading in some of your time and
220 * If you write the code, chances are bigger that it will get into curl
225 curl and libcurl are not made by any single individual. Daniel Stenberg is
226 project leader and main developer, but other persons' submissions are
227 important and crucial. Anyone can contribute and post their changes and
228 improvements and have them inserted in the main sources (of course on the
229 condition that developers agree on that the fixes are good).
231 The full list of all contributors is found in the docs/THANKS file.
233 curl is developed by a community, with Daniel at the wheel.
235 1.6 What do you get for making curl?
237 Project cURL is entirely free and open. No person gets paid for developing
238 (lib)curl on full or even part time. We do this voluntarily on our spare
239 time. Occasionally companies pay individual developers to work on curl, but
240 that's up to each company and developer. It is not controlled by nor
241 supervised in any way by the project.
243 We still get help from companies. Haxx provides web site, bandwidth, mailing
244 lists etc and sourceforge.net hosts project services we take advantage from,
245 like the bug tracker. Also again, some companies have sponsored certain
246 parts of the development in the past and I hope some will continue to do so
249 If you want to support our project, consider a donation or a banner-program
250 or even better: by helping us coding, documenting, testing etc.
252 1.7 What about CURL from curl.com?
254 During the summer 2001, curl.com was busy advertising their client-side
255 programming language for the web, named CURL.
257 We are in no way associated with curl.com or their CURL programming
260 Our project name curl has been in effective use since 1998. We were not the
261 first computer related project to use the name "curl" and do not claim any
262 first-hand rights to the name.
264 We recognize that we will be living in parallel with curl.com and wish them
267 1.8 I have a problem who do I mail?
269 Please do not mail any single individual unless you really need to. Keep
270 curl-related questions on a suitable mailing list. All available mailing
271 lists are listed in the MANUAL document and online at
272 http://curl.haxx.se/mail/
274 Keeping curl-related questions and discussions on mailing lists allows
275 others to join in and help, to share their ideas, contribute their
276 suggestions and spread their wisdom. Keeping discussions on public mailing
277 lists also allows for others to learn from this (both current and future
278 users thanks to the web based archives of the mailing lists), thus saving us
279 from having to repeat ourselves even more. Thanks for respecting this.
281 If you have found or simply suspect a security problem in curl or libcurl,
282 mail curl-security at haxx.se (closed list of receivers, mails are not
283 disclosed) and tell. Then we can produce a fix in a timely manner before the
284 flaw is announced to the world, thus lessen the impact the problem will have
287 1.9 Where do I buy commercial support for curl?
289 curl is fully open source. It means you can hire any skilled engineer to fix
290 your curl-related problems.
292 We list available alternatives on the curl web site:
293 http://curl.haxx.se/support.html
295 1.10 How many are using curl?
297 It is impossible to tell.
299 We don't know how many users that knowingly have installed and use curl.
301 We don't know how many users that use curl without knowing that they are in
304 We don't know how many users that downloaded or installed curl and then
307 Some facts to use as input to the math:
309 curl packages are downloaded from the curl.haxx.se and mirrors over a
310 million times per year. curl is installed by default with most Linux
311 distributions. curl is installed by default with Mac OS X. curl and libcurl
312 as used by numerous applications that include libcurl binaries in their
313 distribution packages (like Adobe Acrobat Reader and Google Earth).
315 More than a hundred known named companies use curl in commercial
316 environments and products and more than a hundred known named open source
317 projects depend on (lib)curl.
319 In a poll on the curl web site mid-2005, more than 50% of the 300+ answers
320 estimated a user base of one million users or more.
322 In March 2005, the "Linux Counter project" estimated a total Linux user base
323 of some 29 millions, while Netcraft detected some 4 million "active" Linux
324 based web servers. A guess is that a fair amount of these Linux
325 installations have curl installed.
327 The Debian project maintains statistics on packages installed by people
328 who have voluntarily run their package counting application. In mid-2010,
329 libcurl3 was installed on over 55000 such systems (62% of reporting systems)
330 and was one of the 320 most popular installed packages (out of about 107000
333 All this taken together, there is no doubt that there are millions of
336 http://curl.haxx.se/docs/companies.html
337 http://curl.haxx.se/docs/programs.html
338 http://curl.haxx.se/libcurl/using/apps.html
339 http://counter.li.org/estimates.php
340 http://news.netcraft.com/archives/2005/03/14/fedora_makes_rapid_progress.html
341 http://qa.debian.org/popcon.php?package=curl
343 1.11 Why don't you update ca-bundle.crt
345 The ca-bundle.crt file that used to be bundled with curl was very outdated
346 (it being last modified year 2000 should tell) and must be replaced with a
347 much more modern and up-to-date version by anyone who wants to verify peers
348 anyway. It is no longer provided, the last curl release that shipped it was
351 In the cURL project we've decided not to attempt to keep this file updated
352 (or even present anymore) since deciding what to add to a ca cert bundle is
353 an undertaking we've not been ready to accept, and the one we can get from
354 Mozilla is perfectly fine so there's no need to duplicate that work.
356 Today, with many services performed over HTTPS, every operating system
357 should come with a default ca cert bundle that can be deemed somewhat
358 trustworthy and that collection (if reasonably updated) should be deemed to
359 be a lot better than a private curl version.
361 If you want the most recent collection of ca certs that Mozilla Firefox
362 uses, we recommend that you extract the collection yourself from Mozilla
363 Firefox (by running 'make ca-bundle), or by using our online service setup
364 for this purpose: http://curl.haxx.se/docs/caextract.html
366 1.12 I have a problem who can I chat with?
368 There's a bunch of friendly people hanging out in the #curl channel on the
369 IRC network irc.freenode.net. If you're polite and nice, chances are big
370 that you can get -- or provide -- help instantly.
372 1.13 curl's ECCN number?
374 The US government restricts exports of software that contains or uses
375 cryptography. When doing so, the Export Control Classification Number (ECCN)
376 is used to identify the level of export control etc.
378 ASF gives a good explanation at http://www.apache.org/dev/crypto.html
380 We believe curl's number might be ECCN 5D002, another possibility is
381 5D992. It seems necessary to write them, asking to confirm.
383 Comprehensible explanations of the meaning of such numbers and how to
384 obtain them (resp.) are here
386 http://www.bis.doc.gov/licensing/exportingbasics.htm
387 http://www.bis.doc.gov/licensing/do_i_needaneccn.html
389 An incomprehensible description of the two numbers above is here
390 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
392 1.14 How do I submit my patch?
394 When you have made a patch or a change of whatever sort, and want to submit
395 that to the project, there are a few different ways we prefer:
397 o send a patch to the curl-library mailing list. We're many subscribers
398 there and there are lots of people who can review patches, comment on them
399 and "receive" them properly.
401 o if your patch changes or fixes a bug, you can also opt to submit a bug
402 report in the bug tracker and attach your patch there. There are less
403 people involved there.
405 Lots of more details are found in the CONTRIBUTE and INTERNALS docs.
408 2. Install Related Problems
410 2.1 configure doesn't find OpenSSL even when it is installed
412 This may be because of several reasons.
414 2.1.1 native linker doesn't find openssl
417 Solaris (native cc compiler)
418 HPUX (native cc compiler)
419 SGI IRIX (native cc compiler)
420 SCO UNIX (native cc compiler)
422 When configuring curl, I specify --with-ssl. OpenSSL is installed in
423 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
424 CRYPTO_lock in -lcrypto
426 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
427 -lcrypto, so ld can't find the library. This is due to a bug in the GNU
430 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
431 ./configure places the -L/usr/local/ssl/lib early enough in the command
432 line to make things work
434 2.1.2 only the libssl lib is missing
436 If all include files and the libcrypto lib is present, with only the
437 libssl being missing according to configure, this is mostly likely because
438 a few functions are left out from the libssl.
440 If the function names missing include RSA or RSAREF you can be certain
441 that this is because libssl requires the RSA and RSAREF libs to build.
443 See the INSTALL file section that explains how to add those libs to
444 configure. Make sure that you remove the config.cache file before you
445 rerun configure with the new flags.
447 2.2 Does curl work/build with other SSL libraries?
449 Curl has been written to use OpenSSL, GnuTLS, yassl, NSS or PolarSSL,
450 although there should not be many problems using a different library. If
451 anyone does "port" curl to use a different SSL library, we are of course
452 very interested in getting the patch!
454 2.3 Where can I find a copy of LIBEAY32.DLL?
456 That is an OpenSSL binary built for Windows.
458 Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
459 on a windows machine to do https://. Check out the curl web site to find
460 accurate and up-to-date pointers to recent OpenSSL DLLs and other binary
463 2.4 Does curl support SOCKS (RFC 1928) ?
465 Yes, SOCKS 4 and 5 are supported.
470 3.1 curl: (1) SSL is disabled, https: not supported
472 If you get this output when trying to get anything from a https:// server,
473 it means that the configure script couldn't find all libs and include files
474 it requires for SSL to work. If the configure script fails to find them,
475 curl is simply built without SSL support.
477 To get the https:// support into a curl that was previously built but that
478 reports that https:// is not supported, you should dig through the document
479 and logs and check out why the configure script doesn't find the SSL libs
480 and/or include files.
482 Also, check out the other paragraph in this FAQ labelled "configure doesn't
483 find OpenSSL even when it is installed".
485 3.2 How do I tell curl to resume a transfer?
487 Curl supports resumed transfers both ways on both FTP and HTTP.
491 3.3 Why doesn't my posting using -F work?
493 You can't simply use -F or -d at your choice. The web server that will
494 receive your post assumes one of the formats. If the form you're trying to
495 "fake" sets the type to 'multipart/form-data', then and only then you must
496 use the -F type. In all the most common cases, you should use -d which then
497 causes a posting with the type 'application/x-www-form-urlencoded'.
499 This is described in some detail in the MANUAL and TheArtOfHttpScripting
500 documents, and if you don't understand it the first time, read it again
501 before you post questions about this to the mailing list. Also, try reading
502 through the mailing list archives for old postings and questions regarding
505 3.4 How do I tell curl to run custom FTP commands?
507 You can tell curl to perform optional commands both before and/or after a
508 file transfer. Study the -Q/--quote option.
510 Since curl is used for file transfers, you don't use curl to just perform
511 FTP commands without transferring anything. Therefore you must always specify
512 a URL to transfer to/from even when doing custom FTP commands.
514 3.5 How can I disable the Pragma: nocache header?
516 You can change all internally generated headers by adding a replacement with
517 the -H/--header option. By adding a header with empty contents you safely
518 disable that one. Use -H "Pragma:" to disable that specific header.
520 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
522 To curl, all contents are alike. It doesn't matter how the page was
523 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain
524 HTML-files. There's no difference to curl and it doesn't even know what kind
525 of language that generated the page.
527 See also item 3.14 regarding javascript.
529 3.7 Can I use curl to delete/rename a file through FTP?
531 Yes. You specify custom FTP commands with -Q/--quote.
533 One example would be to delete a file after you have downloaded it:
535 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
537 or rename a file after upload:
539 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
541 3.8 How do I tell curl to follow HTTP redirects?
543 Curl does not follow so-called redirects by default. The Location: header
544 that informs the client about this is only interpreted if you're using the
545 -L/--location option. As in:
547 curl -L http://redirector.com
549 Not all redirects are HTTP ones, see 4.14
551 3.9 How do I use curl in my favorite programming language?
553 There exist many language interfaces/bindings for curl that integrates it
554 better with various languages. If you are fluid in a script language, you
555 may very well opt to use such an interface instead of using the command line
558 Find out more about which languages that support curl directly, and how to
559 install and use them, in the libcurl section of the curl web site:
560 http://curl.haxx.se/libcurl/
562 In October 2009, there were interfaces available for the following
563 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
564 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
565 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
566 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
567 Q, wxwidgets and XBLite. By the time you read this, additional ones may have
570 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
572 Curl adheres to the HTTP spec, which basically means you can play with *any*
573 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
574 XML-RPC are all such ones. You can use -X to set custom requests and -H to
575 set custom headers (or replace internally generated ones).
577 Using libcurl is of course just as fine and you'd just use the proper
578 library options to do the same.
580 3.11 How do I POST with a different Content-Type?
582 You can always replace the internally generated headers with -H/--header.
583 To make a simple HTTP POST with text/xml as content-type, do something like:
585 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
587 3.12 Why do FTP specific features over HTTP proxy fail?
589 Because when you use a HTTP proxy, the protocol spoken on the network will
590 be HTTP, even if you specify a FTP URL. This effectively means that you
591 normally can't use FTP specific features such as FTP upload and FTP quote
594 There is one exception to this rule, and that is if you can "tunnel through"
595 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
596 and is generally not available as proxy admins usually disable tunneling to
597 other ports than 443 (which is used for HTTPS access through proxies).
599 3.13 Why does my single/double quotes fail?
601 To specify a command line option that includes spaces, you might need to
602 put the entire option within quotes. Like in:
604 curl -d " with spaces " url.com
608 curl -d ' with spaces ' url.com
610 Exactly what kind of quotes and how to do this is entirely up to the shell
611 or command line interpreter that you are using. For most unix shells, you
612 can more or less pick either single (') or double (") quotes. For
613 Windows/DOS prompts I believe you're forced to use double (") quotes.
615 Please study the documentation for your particular environment. Examples in
616 the curl docs will use a mix of both these ones as shown above. You must
617 adjust them to work in your environment.
619 Remember that curl works and runs on more operating systems than most single
620 individuals have ever tried.
622 3.14 Does curl support Javascript or PAC (automated proxy config)?
624 Many web pages do magic stuff using embedded Javascript. Curl and libcurl
625 have no built-in support for that, so it will be treated just like any other
628 .pac files are a netscape invention and are sometimes used by organizations
629 to allow them to differentiate which proxies to use. The .pac contents is
630 just a Javascript program that gets invoked by the browser and that returns
631 the name of the proxy to connect to. Since curl doesn't support Javascript,
632 it can't support .pac proxy configuration either.
634 Some workarounds usually suggested to overcome this Javascript dependency:
636 - Depending on the Javascript complexity, write up a script that
637 translates it to another language and execute that.
639 - Read the Javascript code and rewrite the same logic in another language.
641 - Implement a Javascript interpreter, people have successfully used the
642 Mozilla Javascript engine in the past.
644 - Ask your admins to stop this, for a static proxy setup or similar.
646 3.15 Can I do recursive fetches with curl?
648 No. curl itself has no code that performs recursive operations, such as
649 those performed by wget and similar tools.
651 There exist wrapper scripts with that functionality (for example the
652 curlmirror perl script), and you can write programs based on libcurl to do
653 it, but the command line tool curl itself cannot.
655 3.16 What certificates do I need when I use SSL?
657 There are three different kinds of "certificates" to keep track of when we
658 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
660 - Client certificate. The server you communicate may require that you can
661 provide this in order to prove that you actually are who you claim to be.
662 If the server doesn't require this, you don't need a client certificate.
664 A client certificate is always used together with a private key, and the
665 private key has a pass phrase that protects it.
667 - Server certificate. The server you communicate with has a server
668 certificate. You can and should verify this certificate to make sure that
669 you are truly talking to the real server and not a server impersonating
672 - Certificate Authority certificate ("CA cert"). You often have several CA
673 certs in a CA cert bundle that can be used to verify a server certificate
674 that was signed by one of the authorities in the bundle. curl does not
675 come with a CA cert bundle but most curl installs provide one. You can
676 also override the default.
678 The server certificate verification process is made by using a Certificate
679 Authority certificate ("CA cert") that was used to sign the server
680 certificate. Server certificate verification is enabled by default in curl
681 and libcurl and is often the reason for problems as explained in FAQ entry
682 4.12 and the SSLCERTS document
683 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
684 "self-signed" or otherwise signed by a CA that you do not have a CA cert
685 for, cannot be verified. If the verification during a connect fails, you
686 are refused access. You then need to explicitly disable the verification
687 to connect to the server.
689 3.17 How do I list the root dir of an FTP server?
691 There are two ways. The way defined in the RFC is to use an encoded slash
692 in the first path part. List the "/tmp" dir like this:
694 curl ftp://ftp.sunet.se/%2ftmp/
696 or the not-quite-kosher-but-more-readable way, by simply starting the path
697 section of the URL with a slash:
699 curl ftp://ftp.sunet.se//tmp/
701 3.18 Can I use curl to send a POST/PUT and not wait for a response?
705 But you could easily write your own program using libcurl to do such stunts.
707 3.19 How do I get HTTP from a host using a specific IP address?
709 For example, you may be trying out a web site installation that isn't yet in
710 the DNS. Or you have a site using multiple IP addresses for a given host
711 name and you want to address a specific one out of the set.
713 Set a custom Host: header that identifies the server name you want to reach
714 but use the target IP address in the URL:
716 curl --header "Host: www.example.com" http://127.0.0.1/
721 4.1 Problems connecting to SSL servers.
723 It took a very long time before we could sort out why curl had problems to
724 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
725 error sometimes showed up similar to:
727 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
729 It turned out to be because many older SSL servers don't deal with SSLv3
730 requests properly. To correct this problem, tell curl to select SSLv2 from
731 the command line (-2/--sslv2).
733 There have also been examples where the remote server didn't like the SSLv2
734 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
736 4.2 Why do I get problems when I use & or % in the URL?
738 In general unix shells, the & symbol is treated specially and when used, it
739 runs the specified command in the background. To safely send the & as a part
740 of a URL, you should quote the entire URL by using single (') or double (")
741 quotes around it. Similar problems can also occur on some shells with other
742 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
744 An example that would invoke a remote CGI that uses &-symbols could be:
746 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
748 In Windows, the standard DOS shell treats the %-symbol specially and you
749 need to use TWO %-symbols for each single one you want to use in the URL.
751 Also note that if you want the literal %-symbol to be part of the data you
752 pass in a POST using -d/--data you must encode it as '%25' (which then also
753 needs the %-symbol doubled on Windows machines).
755 4.3 How can I use {, }, [ or ] to specify multiple URLs?
757 Because those letters have a special meaning to the shell, and to be used in
758 a URL specified to curl you must quote them.
760 An example that downloads two URLs (sequentially) would do:
762 curl '{curl,www}.haxx.se'
764 To be able to use those letters as actual parts of the URL (without using
765 them for the curl URL "globbing" system), use the -g/--globoff option:
767 curl -g 'www.site.com/weirdname[].html'
769 4.4 Why do I get downloaded data even though the web page doesn't exist?
771 Curl asks remote servers for the page you specify. If the page doesn't exist
772 at the server, the HTTP protocol defines how the server should respond and
773 that means that headers and a "page" will be returned. That's simply how
776 By using the --fail option you can tell curl explicitly to not get any data
777 if the HTTP return code doesn't say success.
779 4.5 Why do I get return code XXX from a HTTP server?
781 RFC2616 clearly explains the return codes. This is a short transcript. Go
782 read the RFC for exact details:
784 4.5.1 "400 Bad Request"
786 The request could not be understood by the server due to malformed
787 syntax. The client SHOULD NOT repeat the request without modifications.
789 4.5.2 "401 Unauthorized"
791 The request requires user authentication.
793 4.5.3 "403 Forbidden"
795 The server understood the request, but is refusing to fulfill it.
796 Authorization will not help and the request SHOULD NOT be repeated.
798 4.5.4 "404 Not Found"
800 The server has not found anything matching the Request-URI. No indication
801 is given of whether the condition is temporary or permanent.
803 4.5.5 "405 Method Not Allowed"
805 The method specified in the Request-Line is not allowed for the resource
806 identified by the Request-URI. The response MUST include an Allow header
807 containing a list of valid methods for the requested resource.
809 4.5.6 "301 Moved Permanently"
811 If you get this return code and an HTML output similar to this:
813 <H1>Moved Permanently</H1> The document has moved <A
814 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
816 it might be because you request a directory URL but without the trailing
817 slash. Try the same operation again _with_ the trailing URL, or use the
818 -L/--location option to follow the redirection.
820 4.6 Can you tell me what error code 142 means?
822 All curl error codes are described at the end of the man page, in the
823 section called "EXIT CODES".
825 Error codes that are larger than the highest documented error code means
826 that curl has exited due to a crash. This is a serious error, and we
827 appreciate a detailed bug report from you that describes how we could go
828 ahead and repeat this!
830 4.7 How do I keep user names and passwords secret in Curl command lines?
832 This problem has two sides:
834 The first part is to avoid having clear-text passwords in the command line
835 so that they don't appear in 'ps' outputs and similar. That is easily
836 avoided by using the "-K" option to tell curl to read parameters from a file
837 or stdin to which you can pass the secret info. curl itself will also
838 attempt to "hide" the given password by blanking out the option - this
839 doesn't work on all platforms.
841 To keep the passwords in your account secret from the rest of the world is
842 not a task that curl addresses. You could of course encrypt them somehow to
843 at least hide them from being read by human eyes, but that is not what
844 anyone would call security.
846 Also note that regular HTTP (using Basic authentication) and FTP passwords
847 are sent in clear across the network. All it takes for anyone to fetch them
848 is to listen on the network. Eavesdropping is very easy. Use more secure
849 authentication methods (like Digest, Negotiate or even NTLM) or consider the
850 SSL-based alternatives HTTPS and FTPS.
854 It is not a bug if the behavior is documented. Read the docs first.
855 Especially check out the KNOWN_BUGS file, it may be a documented bug!
857 If it is a problem with a binary you've downloaded or a package for your
858 particular platform, try contacting the person who built the package/archive
861 If there is a bug, read the BUGS document first. Then report it as described
864 4.9 Curl can't authenticate to the server that requires NTLM?
866 NTLM support requires OpenSSL, GnuTLS, NSS or Microsoft Windows libraries at
867 build-time to provide this functionality.
869 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
870 should not use such ones.
872 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
874 Many web servers allow or demand that the administrator configures the
875 server properly for these requests to work on the web server.
877 Some servers seem to support HEAD only on certain kinds of URLs.
879 To fully grasp this, try the documentation for the particular server
880 software you're trying to interact with. This is not anything curl can do
883 4.11 Why does my HTTP range requests return the full document?
885 Because the range may not be supported by the server, or the server may
886 choose to ignore it and return the full document anyway.
888 4.12 Why do I get "certificate verify failed" ?
890 You invoke curl 7.10 or later to communicate on a https:// URL and get an
891 error back looking something similar to this:
893 curl: (35) SSL: error:14090086:SSL routines:
894 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
896 Then it means that curl couldn't verify that the server's certificate was
897 good. Curl verifies the certificate using the CA cert bundle that comes with
898 the curl installation.
900 To disable the verification (which makes it act like curl did before 7.10),
901 use -k. This does however enable man-in-the-middle attacks.
903 If you get this failure but are having a CA cert bundle installed and used,
904 the server's certificate is not signed by one of the CA's in the bundle. It
905 might for example be self-signed. You then correct this problem by obtaining
906 a valid CA cert for the server. Or again, decrease the security by disabling
909 Details are also in the SSLCERTS file in the release archives, found online
910 here: http://curl.haxx.se/docs/sslcerts.html
912 4.13 Why is curl -R on Windows one hour off?
914 During daylight savings time, when -R is used, curl will set a time that
915 appears one hour off. This happens due to a flaw in how Windows stores and
916 uses file modification times and it is not easily worked around. For details
917 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
919 4.14 Redirects work in browser but not with curl!
921 curl supports HTTP redirects fine (see item 3.8). Browsers generally support
922 at least two other ways to perform directs that curl does not:
924 - Meta tags. You can write a HTML tag that will cause the browser to
925 redirect to another given URL after a certain time.
927 - Javascript. You can write a Javascript program embedded in a HTML page
928 that redirects the browser to another given URL.
930 There is no way to make curl follow these redirects. You must either
931 manually figure out what the page is set to do, or you write a script that
932 parses the results and fetches the new URL.
934 4.15 FTPS doesn't work
936 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
939 When a URL is used that starts with FTPS://, curl assumes implicit SSL on
940 the control connection and will therefore immediately connect and try to
941 speak SSL. FTPS:// connections default to port 990.
943 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
944 of its related flavours). This is the most common method, and the one
945 mandated by RFC4217. This kind of connection then of course uses the
946 standard FTP port 21 by default.
948 4.16 My HTTP POST or PUT requests are slow!
950 libcurl makes all POST and PUT requests (except for POST requests with a
951 very tiny request body) use the "Expect: 100-continue" header. This header
952 allows the server to deny the operation early so that libcurl can bail out
953 already before having to send any data. This is useful in authentication
956 However, many servers don't implement the Expect: stuff properly and if the
957 server doesn't respond (positively) within 1 second libcurl will continue
958 and send off the data anyway.
960 You can disable libcurl's use of the Expect: header the same way you disable
961 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
963 4.17 Non-functional connect timeouts
965 In most Windows setups having a timeout longer than 21 seconds make no
966 difference, as it will only send 3 TCP SYN packets and no more. The second
967 packet sent three seconds after the first and the third six seconds after
968 the second. No more than three packets are sent, no matter how long the
971 See option TcpMaxConnectRetransmissions on this page:
972 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
974 Also, even on non-Windows systems there may run a firewall or anti-virus
975 software or similar that accepts the connection but does not actually do
976 anything else. This will make (lib)curl to consider the connection connected
977 and thus the connect timeout won't trigger.
979 4.18 file:// URLs containing drive letters (Windows, NetWare)
981 When using cURL to try to download a local file, one might use a URL
986 You'll find that even if D:\blah.txt does exist, cURL returns a 'file
989 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
990 file:// URLs must contain a host component, but it is ignored by
991 most implementations. In the above example, 'D:' is treated as the
992 host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
993 If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
994 and if that doesn't exist you will get the not found error.
996 To fix this problem, use file:// URLs with *three* leading slashes:
1000 Alternatively, if it makes more sense, specify 'localhost' as the host
1003 file://localhost/D:/blah.txt
1005 In either case, cURL should now be looking for the correct file.
1007 4.19 Why doesn't cURL return an error when the network cable is unplugged?
1009 Unplugging the cable is not an error situation. The TCP/IP protocol stack
1010 was designed to be fault tolerant, so even though there may be a physical
1011 break somewhere the connection shouldn't be affected, just possibly
1012 delayed. Eventually, the physical break will be fixed or the data will be
1013 re-routed around the physical problem.
1015 In such cases, the TCP/IP stack is responsible for detecting when the
1016 network connection is irrevocably lost. Since with some protocols it is
1017 perfectly legal for the client wait indefinitely for data, the stack may
1018 never report a problem, and even when it does, it can take up to 20 minutes
1019 for it to detect an issue. The curl option --keepalive-time enables
1020 keep-alive support in the TCP/IP stack which makes it periodically probe the
1021 connection to make sure it is still available to send data. That should
1022 reliably detect any TCP/IP network failure.
1024 But even that won't detect the network going down before the TCP/IP
1025 connection is established (e.g. during a DNS lookup) or using protocols that
1026 don't use TCP. To handle those situations, curl offers a number of timeouts
1027 on its own. --speed-limit/--speed-time will abort if the data transfer rate
1028 falls too low, and --connect-timeout and --max-time can be used to put an
1029 overall timeout on the connection phase or the entire transfer.
1034 5.1 Is libcurl thread-safe?
1038 We have written the libcurl code specifically adjusted for multi-threaded
1039 programs. libcurl will use thread-safe functions instead of non-safe ones if
1040 your system has such.
1042 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
1043 need to provide one or two locking functions:
1045 http://www.openssl.org/docs/crypto/threads.html
1047 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
1048 need to provide locking function(s) for libgcrypt (which is used by GnuTLS
1049 for the crypto functions).
1051 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
1053 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
1055 5.2 How can I receive all data into a large memory chunk?
1057 [ See also the examples/getinmemory.c source ]
1059 You are in full control of the callback function that gets called every time
1060 there is data received from the remote server. You can make that callback do
1061 whatever you want. You do not have to write the received data to a file.
1063 One solution to this problem could be to have a pointer to a struct that you
1064 pass to the callback function. You set the pointer using the
1065 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
1066 instead of a FILE * to a file:
1068 /* imaginary struct */
1069 struct MemoryStruct {
1074 /* imaginary callback function */
1076 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
1078 size_t realsize = size * nmemb;
1079 struct MemoryStruct *mem = (struct MemoryStruct *)data;
1081 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
1083 memcpy(&(mem->memory[mem->size]), ptr, realsize);
1084 mem->size += realsize;
1085 mem->memory[mem->size] = 0;
1090 5.3 How do I fetch multiple files with libcurl?
1092 libcurl has excellent support for transferring multiple files. You should
1093 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
1094 with curl_easy_perform(). The handle you get from curl_easy_init() is not
1095 only reusable, but you're even encouraged to reuse it if you can, as that
1096 will enable libcurl to use persistent connections.
1098 5.4 Does libcurl do Winsock initialization on win32 systems?
1100 Yes, if told to in the curl_global_init() call.
1102 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
1104 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
1105 that DLL use the FILE * (as the DLL and the client application cannot access
1106 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
1107 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
1108 file, even if that simply writes the data to the specified FILE *.
1109 Similarly, if you use CURLOPT_READDATA you must also specify
1110 CURLOPT_READFUNCTION.
1112 5.6 What about Keep-Alive or persistent connections?
1114 curl and libcurl have excellent support for persistent connections when
1115 transferring several files from the same server. Curl will attempt to reuse
1116 connections for all URLs specified on the same command line/config file, and
1117 libcurl will reuse connections for all transfers that are made using the
1118 same libcurl handle.
1120 5.7 Link errors when building libcurl on Windows!
1122 You need to make sure that your project, and all the libraries (both static
1123 and dynamic) that it links against, are compiled/linked against the same run
1126 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
1127 options to the command line compiler. /MD (linking against MSVCRT dll) seems
1128 to be the most commonly used option.
1130 When building an application that uses the static libcurl library, you must
1131 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
1132 dynamic import symbols. If you're using Visual Studio, you need to instead
1133 add CURL_STATICLIB in the "Preprocessor Definitions" section.
1135 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
1136 have linked against the wrong (static) library. If you want to use the
1137 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
1138 the import libraries below. These are the libraries produced by the various
1139 lib/Makefile.* files:
1141 Target: static lib. import lib for libcurl*.dll.
1142 -----------------------------------------------------------
1143 MingW: libcurl.a libcurldll.a
1144 MSVC (release): libcurl.lib libcurl_imp.lib
1145 MSVC (debug): libcurld.lib libcurld_imp.lib
1146 Borland: libcurl.lib libcurl_imp.lib
1149 5.8 libcurl.so.X: open failed: No such file or directory
1151 This is an error message you might get when you try to run a program linked
1152 with a shared version of libcurl and your run-time linker (ld.so) couldn't
1153 find the shared library named libcurl.so.X. (Where X is the number of the
1154 current libcurl ABI, typically 3 or 4).
1156 You need to make sure that ld.so finds libcurl.so.X. You can do that
1157 multiple ways, and it differs somewhat between different operating systems,
1158 but they are usually:
1160 * Add an option to the linker command line that specify the hard-coded path
1161 the run-time linker should check for the lib (usually -R)
1163 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
1164 should check for libs
1166 * Adjust the system's config to check for libs in the directory where you've
1167 put the dir (like Linux's /etc/ld.so.conf)
1169 'man ld.so' and 'man ld' will tell you more details
1171 5.9 How does libcurl resolve host names?
1173 libcurl supports a large a number of different name resolve functions. One
1174 of them is picked at build-time and will be used unconditionally. Thus, if
1175 you want to change name resolver function you must rebuild libcurl and tell
1176 it to use a different function.
1178 - The non-ipv6 resolver that can use one out of four host name resolve calls
1179 (depending on what your system supports):
1182 B - gethostbyname_r() with 3 arguments
1183 C - gethostbyname_r() with 5 arguments
1184 D - gethostbyname_r() with 6 arguments
1186 - The ipv6-resolver that uses getaddrinfo()
1188 - The c-ares based name resolver that uses the c-ares library for resolves.
1189 Using this offers asynchronous name resolves but it currently has no IPv6
1192 - The threaded resolver (default option on Windows). It uses:
1194 A - gethostbyname() on plain ipv4 hosts
1195 B - getaddrinfo() on ipv6-enabled hosts
1197 Also note that libcurl never resolves or reverse-lookups addresses given as
1198 pure numbers, such as 127.0.0.1 or ::1.
1200 5.10 How do I prevent libcurl from writing the response to stdout?
1202 libcurl provides a default built-in write function that writes received data
1203 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
1204 set CURLOPT_WRITEDATA to a different FILE * handle.
1206 5.11 How do I make libcurl not receive the whole HTTP response?
1208 You make the write callback (or progress callback) return an error and
1209 libcurl will then abort the transfer.
1211 5.12 Can I make libcurl fake or hide my real IP address?
1213 No. libcurl operates on a higher level than so. Besides, faking IP address
1214 would imply sending IP packages with a made-up source address, and then you
1215 normally get a problem with intercepting the packages sent back as they
1216 would then not be routed to you!
1218 If you use a proxy to access remote sites, the sites will not see your local
1219 IP address but instead the address of the proxy.
1221 Also note that on many networks NATs or other IP-munging techniques are used
1222 that makes you see and use a different IP address locally than what the
1223 remote server will see you coming from.
1225 5.13 How do I stop an ongoing transfer?
1227 There are several ways, but none of them are instant. There is no function
1228 you can call from another thread or similar that will stop it immediately.
1229 Instead you need to make sure that one of the callbacks you use return an
1230 appropriate value that will stop the transfer.
1232 Suitable callbacks that you can do this with include the progress callback,
1233 the read callback and the write callback.
1235 If you're using the multi interface, you also stop a transfer by removing
1236 the particular easy handle from the multi stack.
1238 5.14 Using C++ non-static functions for callbacks?
1240 libcurl is a C library, it doesn't know anything about C++ member functions.
1242 You can overcome this "limitation" with a relative ease using a static
1243 member function that is passed a pointer to the class:
1245 // f is the pointer to your object.
1246 static YourClass::staticFunction(void *buffer, size_t sz, size_t n, void *f)
1248 // Call non-static member function.
1249 static_cast<YourClass*>(f)->nonStaticFunction();
1252 // This is how you pass pointer to the static function:
1253 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:staticFunction);
1254 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
1256 5.15 How do I get an FTP directory listing?
1258 If you end the FTP URL you request with a slash, libcurl will provide you
1259 with a directory listing of that given directory. You can also set
1260 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
1263 The follow-up question that tend to follow the previous one, is how a
1264 program is supposed to parse the directory listing. How does it know what's
1265 a file and what's a dir and what's a symlink etc. The harsh reality is that
1266 FTP provides no such fine and easy-to-parse output. The output format FTP
1267 servers respond to LIST commands are entirely at the server's own liking and
1268 the NLST output doesn't reveal any types and in many cases don't even
1269 include all the directory entries. Also, both LIST and NLST tend to hide
1270 unix-style hidden files (those that start with a dot) by default so you need
1271 to do "LIST -a" or similar to see them.
1273 The application thus needs to parse the LIST output. One such existing
1274 list parser is available at http://cr.yp.to/ftpparse.html Versions of
1275 libcurl since 7.21.0 also provide the ability to specify a wildcard to
1276 download multiple files from one FTP directory.
1281 Curl and libcurl are released under a MIT/X derivate license. The license is
1282 very liberal and should not impose a problem for your project. This section
1283 is just a brief summary for the cases we get the most questions. (Parts of
1284 this section was much enhanced by Bjorn Reese.)
1286 We are not lawyers and this is not legal advice. You should probably consult
1287 one if you want true and accurate legal insights without our prejudice. Note
1288 especially that this section concerns the libcurl license only; compiling in
1289 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
1290 the licensing obligations of your application.
1292 6.1 I have a GPL program, can I use the libcurl library?
1296 Since libcurl may be distributed under the MIT/X derivate license, it can be
1297 used together with GPL in any software.
1299 6.2 I have a closed-source program, can I use the libcurl library?
1303 libcurl does not put any restrictions on the program that uses the library.
1305 6.3 I have a BSD licensed program, can I use the libcurl library?
1309 libcurl does not put any restrictions on the program that uses the library.
1311 6.4 I have a program that uses LGPL libraries, can I use libcurl?
1315 The LGPL license doesn't clash with other licenses.
1317 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
1321 The MIT/X derivate license practically allows you to do almost anything with
1322 the sources, on the condition that the copyright texts in the sources are
1325 6.6 Can you please change the curl/libcurl license to XXXX?
1329 We have carefully picked this license after years of development and
1330 discussions and a large amount of people have contributed with source code
1331 knowing that this is the license we use. This license puts the restrictions
1332 we want on curl/libcurl and it does not spread to other programs or
1333 libraries that use it. It should be possible for everyone to use libcurl or
1334 curl in their projects, no matter what license they already have in use.
1336 6.7 What are my obligations when using libcurl in my commercial apps?
1338 Next to none. All you need to adhere to is the MIT-style license (stated in
1339 the COPYING file) which basically says you have to include the copyright
1340 notice in "all copies" and that you may not use the copyright holder's name
1341 when promoting your software.
1343 You do not have to release any of your source code.
1345 You do not have to reveal or make public any changes to the libcurl source
1348 You do not have to reveal or make public that you are using libcurl within
1351 As can be seen here: http://curl.haxx.se/docs/companies.html and
1352 elsewhere, more and more companies are discovering the power
1353 of libcurl and take advantage of it even in commercial environments.
1358 7.1 What is PHP/CURL?
1360 The module for PHP that makes it possible for PHP programs to access curl-
1361 functions from within PHP.
1363 In the cURL project we call this module PHP/CURL to differentiate it from
1364 curl the command line tool and libcurl the library. The PHP team however
1365 does not refer to it like this (for unknown reasons). They call it plain
1366 CURL (often using all caps) or sometimes ext/curl, but both cause much
1367 confusion to users which in turn gives us a higher question load.
1369 7.2 Who write PHP/CURL?
1371 PHP/CURL is a module that comes with the regular PHP package. It depends and
1372 uses libcurl, so you need to have libcurl installed properly first before
1373 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
1375 7.3 Can I perform multiple requests using the same handle?
1377 Yes - at least in PHP version 4.3.8 and later (this has been known to not
1378 work in earlier versions, but the exact version when it started to work is
1381 After a transfer, you just set new options in the handle and make another
1382 transfer. This will make libcurl to re-use the same connection if it can.