5 \___|\___/|_| \_\_____|
13 1.4 When will you make curl do XXXX ?
15 1.6 What do you get for making curl?
16 1.7 What about CURL from curl.com?
17 1.8 I have a problem who do I mail?
18 1.9 Where do I buy commercial support for curl?
19 1.10 How many are using curl?
20 1.11 Why don't you update ca-bundle.crt
21 1.12 I have a problem who can I chat with?
22 1.13 curl's ECCN number?
23 1.14 How do I submit my patch?
25 2. Install Related Problems
26 2.1 configure doesn't find OpenSSL even when it is installed
27 2.1.1 native linker doesn't find OpenSSL
28 2.1.2 only the libssl lib is missing
29 2.2 Does curl work/build with other SSL libraries?
30 2.3 Where can I find a copy of LIBEAY32.DLL?
31 2.4 Does curl support SOCKS (RFC 1928) ?
34 3.1 curl: (1) SSL is disabled, https: not supported
35 3.2 How do I tell curl to resume a transfer?
36 3.3 Why doesn't my posting using -F work?
37 3.4 How do I tell curl to run custom FTP commands?
38 3.5 How can I disable the Accept: */* header?
39 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
40 3.7 Can I use curl to delete/rename a file through FTP?
41 3.8 How do I tell curl to follow HTTP redirects?
42 3.9 How do I use curl in my favorite programming language?
43 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
44 3.11 How do I POST with a different Content-Type?
45 3.12 Why do FTP specific features over HTTP proxy fail?
46 3.13 Why does my single/double quotes fail?
47 3.14 Does curl support Javascript or PAC (automated proxy config)?
48 3.15 Can I do recursive fetches with curl?
49 3.16 What certificates do I need when I use SSL?
50 3.17 How do I list the root dir of an FTP server?
51 3.18 Can I use curl to send a POST/PUT and not wait for a response?
52 3.19 How do I get HTTP from a host using a specific IP address?
53 3.20 How to SFTP from my user's home directory?
54 3.21 Protocol xxx not supported or disabled in libcurl
57 4.1 Problems connecting to SSL servers.
58 4.2 Why do I get problems when I use & or % in the URL?
59 4.3 How can I use {, }, [ or ] to specify multiple URLs?
60 4.4 Why do I get downloaded data even though the web page doesn't exist?
61 4.5 Why do I get return code XXX from a HTTP server?
62 4.5.1 "400 Bad Request"
63 4.5.2 "401 Unauthorized"
66 4.5.5 "405 Method Not Allowed"
67 4.5.6 "301 Moved Permanently"
68 4.6 Can you tell me what error code 142 means?
69 4.7 How do I keep user names and passwords secret in Curl command lines?
71 4.9 Curl can't authenticate to the server that requires NTLM?
72 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
73 4.11 Why does my HTTP range requests return the full document?
74 4.12 Why do I get "certificate verify failed" ?
75 4.13 Why is curl -R on Windows one hour off?
76 4.14 Redirects work in browser but not with curl!
77 4.15 FTPS doesn't work
78 4.16 My HTTP POST or PUT requests are slow!
79 4.17 Non-functional connect timeouts on Windows
80 4.18 file:// URLs containing drive letters (Windows, NetWare)
81 4.19 Why doesn't cURL return an error when the network cable is unplugged?
84 5.1 Is libcurl thread-safe?
85 5.2 How can I receive all data into a large memory chunk?
86 5.3 How do I fetch multiple files with libcurl?
87 5.4 Does libcurl do Winsock initing on win32 systems?
88 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
89 5.6 What about Keep-Alive or persistent connections?
90 5.7 Link errors when building libcurl on Windows!
91 5.8 libcurl.so.X: open failed: No such file or directory
92 5.9 How does libcurl resolve host names?
93 5.10 How do I prevent libcurl from writing the response to stdout?
94 5.11 How do I make libcurl not receive the whole HTTP response?
95 5.12 Can I make libcurl fake or hide my real IP address?
96 5.13 How do I stop an ongoing transfer?
97 5.14 Using C++ non-static functions for callbacks?
98 5.15 How do I get an FTP directory listing?
99 5.16 I want a different time-out!
102 6.1 I have a GPL program, can I use the libcurl library?
103 6.2 I have a closed-source program, can I use the libcurl library?
104 6.3 I have a BSD licensed program, can I use the libcurl library?
105 6.4 I have a program that uses LGPL libraries, can I use libcurl?
106 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
107 6.6 Can you please change the curl/libcurl license to XXXX?
108 6.7 What are my obligations when using libcurl in my commercial apps?
111 7.1 What is PHP/CURL?
112 7.2 Who wrote PHP/CURL?
113 7.3 Can I perform multiple requests using the same handle?
115 ==============================================================================
121 cURL is the name of the project. The name is a play on 'Client for URLs',
122 originally with URL spelled in uppercase to make it obvious it deals with
123 URLs. The fact it can also be pronounced 'see URL' also helped, it works as
124 an abbreviation for "Client URL Request Library" or why not the recursive
125 version: "Curl URL Request Library".
127 The cURL project produces two products:
131 A free and easy-to-use client-side URL transfer library, supporting DICT,
132 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3,
133 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP.
135 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
136 kerberos, HTTP form based upload, proxies, cookies, user+password
137 authentication, file transfer resume, http proxy tunneling and more!
139 libcurl is highly portable, it builds and works identically on numerous
140 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
141 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac
142 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF,
143 Android, Minix, IBM TPF and more...
145 libcurl is free, thread-safe, IPv6 compatible, feature rich, well
150 A command line tool for getting or sending files using URL syntax.
152 Since curl uses libcurl, curl supports the same wide range of common
153 Internet protocols that libcurl does.
155 We pronounce curl and cURL with an initial k sound: [kurl].
157 There are numerous sub-projects and related projects that also use the word
158 curl in the project names in various combinations, but you should take
159 notice that this FAQ is directed at the command-line tool named curl (and
160 libcurl the library), and may therefore not be valid for other curl-related
161 projects. (There is however a small section for the PHP/CURL in this FAQ.)
165 libcurl is a reliable and portable library which provides you with an easy
166 interface to a range of common Internet protocols.
168 You can use libcurl for free in your application, be it open source,
169 commercial or closed-source.
171 libcurl is most probably the most portable, most powerful and most often
172 used C-based multi-platform file transfer library on this planet - be it
173 open source or commercial.
175 1.3 What is curl not?
177 Curl is not a wget clone. That is a common misconception. Never, during
178 curl's development, have we intended curl to replace wget or compete on its
179 market. Curl is targeted at single-shot file transfers.
181 Curl is not a web site mirroring program. If you want to use curl to mirror
182 something: fine, go ahead and write a script that wraps around curl to make
183 it reality (like curlmirror.pl does).
185 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
186 but if you want systematic and sequential behavior you should write a
187 script (or write a new program that interfaces libcurl) and do it.
189 Curl is not a PHP tool, even though it works perfectly well when used from
190 or with PHP (when using the PHP/CURL module).
192 Curl is not a program for a single operating system. Curl exists, compiles,
193 builds and runs under a wide range of operating systems, including all
194 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
197 1.4 When will you make curl do XXXX ?
199 We love suggestions of what to change in order to make curl and libcurl
200 better. We do however believe in a few rules when it comes to the future of
203 * Curl -- the command line tool -- is to remain a non-graphical command line
204 tool. If you want GUIs or fancy scripting capabilities, you should look
205 for another tool that uses libcurl.
207 * We do not add things to curl that other small and available tools already
208 do very fine at the side. Curl's output is fine to pipe into another
209 program or redirect to another file for the next program to interpret.
211 * We focus on protocol related issues and improvements. If you wanna do more
212 magic with the supported protocols than curl currently does, chances are
213 big we will agree. If you wanna add more protocols, we may very well
216 * If you want someone else to make all the work while you wait for us to
217 implement it for you, that is not a very friendly attitude. We spend a
218 considerable time already on maintaining and developing curl. In order to
219 get more out of us, you should consider trading in some of your time and
222 * If you write the code, chances are bigger that it will get into curl
227 curl and libcurl are not made by any single individual. Daniel Stenberg is
228 project leader and main developer, but other persons' submissions are
229 important and crucial. Anyone can contribute and post their changes and
230 improvements and have them inserted in the main sources (of course on the
231 condition that developers agree on that the fixes are good).
233 The full list of all contributors is found in the docs/THANKS file.
235 curl is developed by a community, with Daniel at the wheel.
237 1.6 What do you get for making curl?
239 Project cURL is entirely free and open. No person gets paid for developing
240 (lib)curl on full or even part time. We do this voluntarily on our spare
241 time. Occasionally companies pay individual developers to work on curl, but
242 that's up to each company and developer. It is not controlled by nor
243 supervised in any way by the project.
245 We still get help from companies. Haxx provides web site, bandwidth, mailing
246 lists etc and sourceforge.net hosts project services we take advantage from,
247 like the bug tracker. Also again, some companies have sponsored certain
248 parts of the development in the past and I hope some will continue to do so
251 If you want to support our project, consider a donation or a banner-program
252 or even better: by helping us coding, documenting, testing etc.
254 1.7 What about CURL from curl.com?
256 During the summer 2001, curl.com was busy advertising their client-side
257 programming language for the web, named CURL.
259 We are in no way associated with curl.com or their CURL programming
262 Our project name curl has been in effective use since 1998. We were not the
263 first computer related project to use the name "curl" and do not claim any
264 first-hand rights to the name.
266 We recognize that we will be living in parallel with curl.com and wish them
269 1.8 I have a problem who do I mail?
271 Please do not mail any single individual unless you really need to. Keep
272 curl-related questions on a suitable mailing list. All available mailing
273 lists are listed in the MANUAL document and online at
274 http://curl.haxx.se/mail/
276 Keeping curl-related questions and discussions on mailing lists allows
277 others to join in and help, to share their ideas, contribute their
278 suggestions and spread their wisdom. Keeping discussions on public mailing
279 lists also allows for others to learn from this (both current and future
280 users thanks to the web based archives of the mailing lists), thus saving us
281 from having to repeat ourselves even more. Thanks for respecting this.
283 If you have found or simply suspect a security problem in curl or libcurl,
284 mail curl-security at haxx.se (closed list of receivers, mails are not
285 disclosed) and tell. Then we can produce a fix in a timely manner before the
286 flaw is announced to the world, thus lessen the impact the problem will have
289 1.9 Where do I buy commercial support for curl?
291 curl is fully open source. It means you can hire any skilled engineer to fix
292 your curl-related problems.
294 We list available alternatives on the curl web site:
295 http://curl.haxx.se/support.html
297 1.10 How many are using curl?
299 It is impossible to tell.
301 We don't know how many users that knowingly have installed and use curl.
303 We don't know how many users that use curl without knowing that they are in
306 We don't know how many users that downloaded or installed curl and then
309 In May 2012 Daniel did a counting game and came up with a number that may
310 be completely wrong or somewhat accurate. 300 million!
312 See http://daniel.haxx.se/blog/2012/05/16/300m-users/
314 1.11 Why don't you update ca-bundle.crt
316 The ca-bundle.crt file that used to be bundled with curl was very outdated
317 (it being last modified year 2000 should tell) and must be replaced with a
318 much more modern and up-to-date version by anyone who wants to verify peers
319 anyway. It is no longer provided, the last curl release that shipped it was
322 In the cURL project we've decided not to attempt to keep this file updated
323 (or even present anymore) since deciding what to add to a ca cert bundle is
324 an undertaking we've not been ready to accept, and the one we can get from
325 Mozilla is perfectly fine so there's no need to duplicate that work.
327 Today, with many services performed over HTTPS, every operating system
328 should come with a default ca cert bundle that can be deemed somewhat
329 trustworthy and that collection (if reasonably updated) should be deemed to
330 be a lot better than a private curl version.
332 If you want the most recent collection of ca certs that Mozilla Firefox
333 uses, we recommend that you extract the collection yourself from Mozilla
334 Firefox (by running 'make ca-bundle), or by using our online service setup
335 for this purpose: http://curl.haxx.se/docs/caextract.html
337 1.12 I have a problem who can I chat with?
339 There's a bunch of friendly people hanging out in the #curl channel on the
340 IRC network irc.freenode.net. If you're polite and nice, chances are big
341 that you can get -- or provide -- help instantly.
343 1.13 curl's ECCN number?
345 The US government restricts exports of software that contains or uses
346 cryptography. When doing so, the Export Control Classification Number (ECCN)
347 is used to identify the level of export control etc.
349 ASF gives a good explanation at http://www.apache.org/dev/crypto.html
351 We believe curl's number might be ECCN 5D002, another possibility is
352 5D992. It seems necessary to write them, asking to confirm.
354 Comprehensible explanations of the meaning of such numbers and how to
355 obtain them (resp.) are here
357 http://www.bis.doc.gov/licensing/exportingbasics.htm
358 http://www.bis.doc.gov/licensing/do_i_needaneccn.html
360 An incomprehensible description of the two numbers above is here
361 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
363 1.14 How do I submit my patch?
365 When you have made a patch or a change of whatever sort, and want to submit
366 that to the project, there are a few different ways we prefer:
368 o send a patch to the curl-library mailing list. We're many subscribers
369 there and there are lots of people who can review patches, comment on them
370 and "receive" them properly.
372 o if your patch changes or fixes a bug, you can also opt to submit a bug
373 report in the bug tracker and attach your patch there. There are less
374 people involved there.
376 Lots of more details are found in the CONTRIBUTE and INTERNALS docs.
379 2. Install Related Problems
381 2.1 configure doesn't find OpenSSL even when it is installed
383 This may be because of several reasons.
385 2.1.1 native linker doesn't find openssl
388 Solaris (native cc compiler)
389 HPUX (native cc compiler)
390 SGI IRIX (native cc compiler)
391 SCO UNIX (native cc compiler)
393 When configuring curl, I specify --with-ssl. OpenSSL is installed in
394 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
395 CRYPTO_lock in -lcrypto
397 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
398 -lcrypto, so ld can't find the library. This is due to a bug in the GNU
401 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
402 ./configure places the -L/usr/local/ssl/lib early enough in the command
403 line to make things work
405 2.1.2 only the libssl lib is missing
407 If all include files and the libcrypto lib is present, with only the
408 libssl being missing according to configure, this is mostly likely because
409 a few functions are left out from the libssl.
411 If the function names missing include RSA or RSAREF you can be certain
412 that this is because libssl requires the RSA and RSAREF libs to build.
414 See the INSTALL file section that explains how to add those libs to
415 configure. Make sure that you remove the config.cache file before you
416 rerun configure with the new flags.
418 2.2 Does curl work/build with other SSL libraries?
420 Curl has been written to use OpenSSL, GnuTLS, yassl, NSS, PolarSSL, axTLS or
421 qssl, although there should not be many problems using a different
422 library. If anyone does "port" curl to use a different SSL library, we are
423 of course very interested in getting the patch!
425 2.3 Where can I find a copy of LIBEAY32.DLL?
427 That is an OpenSSL binary built for Windows.
429 Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
430 on a windows machine to do https://. Check out the curl web site to find
431 accurate and up-to-date pointers to recent OpenSSL DLLs and other binary
434 2.4 Does curl support SOCKS (RFC 1928) ?
436 Yes, SOCKS 4 and 5 are supported.
441 3.1 curl: (1) SSL is disabled, https: not supported
443 If you get this output when trying to get anything from a https:// server,
444 it means that the instance of curl/libcurl that you're using was built
445 without support for this protocol.
447 This could've happened if the configure script that was run at build time
448 couldn't find all libs and include files curl requires for SSL to work. If
449 the configure script fails to find them, curl is simply built without SSL
452 To get the https:// support into a curl that was previously built but that
453 reports that https:// is not supported, you should dig through the document
454 and logs and check out why the configure script doesn't find the SSL libs
455 and/or include files.
457 Also, check out the other paragraph in this FAQ labelled "configure doesn't
458 find OpenSSL even when it is installed".
460 3.2 How do I tell curl to resume a transfer?
462 Curl supports resumed transfers both ways on both FTP and HTTP.
465 3.3 Why doesn't my posting using -F work?
467 You can't simply use -F or -d at your choice. The web server that will
468 receive your post assumes one of the formats. If the form you're trying to
469 "fake" sets the type to 'multipart/form-data', then and only then you must
470 use the -F type. In all the most common cases, you should use -d which then
471 causes a posting with the type 'application/x-www-form-urlencoded'.
473 This is described in some detail in the MANUAL and TheArtOfHttpScripting
474 documents, and if you don't understand it the first time, read it again
475 before you post questions about this to the mailing list. Also, try reading
476 through the mailing list archives for old postings and questions regarding
479 3.4 How do I tell curl to run custom FTP commands?
481 You can tell curl to perform optional commands both before and/or after a
482 file transfer. Study the -Q/--quote option.
484 Since curl is used for file transfers, you don't use curl to just perform
485 FTP commands without transferring anything. Therefore you must always specify
486 a URL to transfer to/from even when doing custom FTP commands.
488 3.5 How can I disable the Accept: */* header?
490 You can change all internally generated headers by adding a replacement with
491 the -H/--header option. By adding a header with empty contents you safely
492 disable that one. Use -H "Accept:" to disable that specific header.
494 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
496 To curl, all contents are alike. It doesn't matter how the page was
497 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain
498 HTML-files. There's no difference to curl and it doesn't even know what kind
499 of language that generated the page.
501 See also item 3.14 regarding javascript.
503 3.7 Can I use curl to delete/rename a file through FTP?
505 Yes. You specify custom FTP commands with -Q/--quote.
507 One example would be to delete a file after you have downloaded it:
509 curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
511 or rename a file after upload:
513 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
515 3.8 How do I tell curl to follow HTTP redirects?
517 Curl does not follow so-called redirects by default. The Location: header
518 that informs the client about this is only interpreted if you're using the
519 -L/--location option. As in:
521 curl -L http://redirector.com
523 Not all redirects are HTTP ones, see 4.14
525 3.9 How do I use curl in my favorite programming language?
527 There exist many language interfaces/bindings for curl that integrates it
528 better with various languages. If you are fluid in a script language, you
529 may very well opt to use such an interface instead of using the command line
532 Find out more about which languages that support curl directly, and how to
533 install and use them, in the libcurl section of the curl web site:
534 http://curl.haxx.se/libcurl/
536 All the various bindings to libcurl are made by other projects and people,
537 outside of the cURL project. The cURL project itself only produces libcurl
538 with its plain C API. If you don't find anywhere else to ask you can ask
539 about bindings on the curl-library list too, but be prepared that people on
540 that list may not know anything about bindings.
542 In October 2009, there were interfaces available for the following
543 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
544 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
545 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
546 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
547 Q, wxwidgets and XBLite. By the time you read this, additional ones may have
550 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
552 Curl adheres to the HTTP spec, which basically means you can play with *any*
553 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
554 XML-RPC are all such ones. You can use -X to set custom requests and -H to
555 set custom headers (or replace internally generated ones).
557 Using libcurl is of course just as fine and you'd just use the proper
558 library options to do the same.
560 3.11 How do I POST with a different Content-Type?
562 You can always replace the internally generated headers with -H/--header.
563 To make a simple HTTP POST with text/xml as content-type, do something like:
565 curl -d "datatopost" -H "Content-Type: text/xml" [URL]
567 3.12 Why do FTP specific features over HTTP proxy fail?
569 Because when you use a HTTP proxy, the protocol spoken on the network will
570 be HTTP, even if you specify a FTP URL. This effectively means that you
571 normally can't use FTP specific features such as FTP upload and FTP quote
574 There is one exception to this rule, and that is if you can "tunnel through"
575 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
576 and is generally not available as proxy admins usually disable tunneling to
577 other ports than 443 (which is used for HTTPS access through proxies).
579 3.13 Why does my single/double quotes fail?
581 To specify a command line option that includes spaces, you might need to
582 put the entire option within quotes. Like in:
584 curl -d " with spaces " url.com
588 curl -d ' with spaces ' url.com
590 Exactly what kind of quotes and how to do this is entirely up to the shell
591 or command line interpreter that you are using. For most unix shells, you
592 can more or less pick either single (') or double (") quotes. For
593 Windows/DOS prompts I believe you're forced to use double (") quotes.
595 Please study the documentation for your particular environment. Examples in
596 the curl docs will use a mix of both these ones as shown above. You must
597 adjust them to work in your environment.
599 Remember that curl works and runs on more operating systems than most single
600 individuals have ever tried.
602 3.14 Does curl support Javascript or PAC (automated proxy config)?
604 Many web pages do magic stuff using embedded Javascript. Curl and libcurl
605 have no built-in support for that, so it will be treated just like any other
608 .pac files are a netscape invention and are sometimes used by organizations
609 to allow them to differentiate which proxies to use. The .pac contents is
610 just a Javascript program that gets invoked by the browser and that returns
611 the name of the proxy to connect to. Since curl doesn't support Javascript,
612 it can't support .pac proxy configuration either.
614 Some workarounds usually suggested to overcome this Javascript dependency:
616 - Depending on the Javascript complexity, write up a script that
617 translates it to another language and execute that.
619 - Read the Javascript code and rewrite the same logic in another language.
621 - Implement a Javascript interpreter, people have successfully used the
622 Mozilla Javascript engine in the past.
624 - Ask your admins to stop this, for a static proxy setup or similar.
626 3.15 Can I do recursive fetches with curl?
628 No. curl itself has no code that performs recursive operations, such as
629 those performed by wget and similar tools.
631 There exist wrapper scripts with that functionality (for example the
632 curlmirror perl script), and you can write programs based on libcurl to do
633 it, but the command line tool curl itself cannot.
635 3.16 What certificates do I need when I use SSL?
637 There are three different kinds of "certificates" to keep track of when we
638 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
640 - Client certificate. The server you communicate may require that you can
641 provide this in order to prove that you actually are who you claim to be.
642 If the server doesn't require this, you don't need a client certificate.
644 A client certificate is always used together with a private key, and the
645 private key has a pass phrase that protects it.
647 - Server certificate. The server you communicate with has a server
648 certificate. You can and should verify this certificate to make sure that
649 you are truly talking to the real server and not a server impersonating
652 - Certificate Authority certificate ("CA cert"). You often have several CA
653 certs in a CA cert bundle that can be used to verify a server certificate
654 that was signed by one of the authorities in the bundle. curl does not
655 come with a CA cert bundle but most curl installs provide one. You can
656 also override the default.
658 The server certificate verification process is made by using a Certificate
659 Authority certificate ("CA cert") that was used to sign the server
660 certificate. Server certificate verification is enabled by default in curl
661 and libcurl and is often the reason for problems as explained in FAQ entry
662 4.12 and the SSLCERTS document
663 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
664 "self-signed" or otherwise signed by a CA that you do not have a CA cert
665 for, cannot be verified. If the verification during a connect fails, you
666 are refused access. You then need to explicitly disable the verification
667 to connect to the server.
669 3.17 How do I list the root dir of an FTP server?
671 There are two ways. The way defined in the RFC is to use an encoded slash
672 in the first path part. List the "/tmp" dir like this:
674 curl ftp://ftp.sunet.se/%2ftmp/
676 or the not-quite-kosher-but-more-readable way, by simply starting the path
677 section of the URL with a slash:
679 curl ftp://ftp.sunet.se//tmp/
681 3.18 Can I use curl to send a POST/PUT and not wait for a response?
685 But you could easily write your own program using libcurl to do such stunts.
687 3.19 How do I get HTTP from a host using a specific IP address?
689 For example, you may be trying out a web site installation that isn't yet in
690 the DNS. Or you have a site using multiple IP addresses for a given host
691 name and you want to address a specific one out of the set.
693 Set a custom Host: header that identifies the server name you want to reach
694 but use the target IP address in the URL:
696 curl --header "Host: www.example.com" http://127.0.0.1/
698 You can also opt to add faked host name entries to curl with the --resolve
699 option. That has the added benefit that things like redirects will also work
700 properly. The above operation would instead be done as:
702 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/
704 3.20 How to SFTP from my user's home directory?
706 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to
707 work with. It means that if you don't specify that you want the user's home
708 directory, you get the actual root directory.
710 To specify a file in your user's home directory, you need to use the correct
711 URL syntax which for sftp might look similar to:
713 curl -O -u user:password sftp://example.com/~/file.txt
715 and for SCP it is just a different protocol prefix:
717 curl -O -u user:password scp://example.com/~/file.txt
719 3.21 Protocol xxx not supported or disabled in libcurl
721 When passing on a URL to curl to use, it may respond that the particular
722 protocol is not supported or disabled. The particular way this error message
723 is phrased is because curl doesn't make a distinction internally of whether
724 a particular protocol is not supported (ie never got any code added that
725 knows how to speak that protocol) or if it was explicitly disabled. curl can
726 be built to only support a given set of protocols, and the rest would then
727 be disabled or not supported.
729 Note that this error will also occur if you pass a wrongly spelled protocol
730 part as in "htpt://example.com" or as in the less evident case if you prefix
731 the protocol part with a space as in " http://example.com/".
736 4.1 Problems connecting to SSL servers.
738 It took a very long time before we could sort out why curl had problems to
739 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
740 error sometimes showed up similar to:
742 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
744 It turned out to be because many older SSL servers don't deal with SSLv3
745 requests properly. To correct this problem, tell curl to select SSLv2 from
746 the command line (-2/--sslv2).
748 There have also been examples where the remote server didn't like the SSLv2
749 request and instead you had to force curl to use SSLv3 with -3/--sslv3.
751 4.2 Why do I get problems when I use & or % in the URL?
753 In general unix shells, the & symbol is treated specially and when used, it
754 runs the specified command in the background. To safely send the & as a part
755 of a URL, you should quote the entire URL by using single (') or double (")
756 quotes around it. Similar problems can also occur on some shells with other
757 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
759 An example that would invoke a remote CGI that uses &-symbols could be:
761 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
763 In Windows, the standard DOS shell treats the %-symbol specially and you
764 need to use TWO %-symbols for each single one you want to use in the URL.
766 Also note that if you want the literal %-symbol to be part of the data you
767 pass in a POST using -d/--data you must encode it as '%25' (which then also
768 needs the %-symbol doubled on Windows machines).
770 4.3 How can I use {, }, [ or ] to specify multiple URLs?
772 Because those letters have a special meaning to the shell, and to be used in
773 a URL specified to curl you must quote them.
775 An example that downloads two URLs (sequentially) would do:
777 curl '{curl,www}.haxx.se'
779 To be able to use those letters as actual parts of the URL (without using
780 them for the curl URL "globbing" system), use the -g/--globoff option:
782 curl -g 'www.site.com/weirdname[].html'
784 4.4 Why do I get downloaded data even though the web page doesn't exist?
786 Curl asks remote servers for the page you specify. If the page doesn't exist
787 at the server, the HTTP protocol defines how the server should respond and
788 that means that headers and a "page" will be returned. That's simply how
791 By using the --fail option you can tell curl explicitly to not get any data
792 if the HTTP return code doesn't say success.
794 4.5 Why do I get return code XXX from a HTTP server?
796 RFC2616 clearly explains the return codes. This is a short transcript. Go
797 read the RFC for exact details:
799 4.5.1 "400 Bad Request"
801 The request could not be understood by the server due to malformed
802 syntax. The client SHOULD NOT repeat the request without modifications.
804 4.5.2 "401 Unauthorized"
806 The request requires user authentication.
808 4.5.3 "403 Forbidden"
810 The server understood the request, but is refusing to fulfil it.
811 Authorization will not help and the request SHOULD NOT be repeated.
813 4.5.4 "404 Not Found"
815 The server has not found anything matching the Request-URI. No indication
816 is given of whether the condition is temporary or permanent.
818 4.5.5 "405 Method Not Allowed"
820 The method specified in the Request-Line is not allowed for the resource
821 identified by the Request-URI. The response MUST include an Allow header
822 containing a list of valid methods for the requested resource.
824 4.5.6 "301 Moved Permanently"
826 If you get this return code and an HTML output similar to this:
828 <H1>Moved Permanently</H1> The document has moved <A
829 HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
831 it might be because you request a directory URL but without the trailing
832 slash. Try the same operation again _with_ the trailing URL, or use the
833 -L/--location option to follow the redirection.
835 4.6 Can you tell me what error code 142 means?
837 All curl error codes are described at the end of the man page, in the
838 section called "EXIT CODES".
840 Error codes that are larger than the highest documented error code means
841 that curl has exited due to a crash. This is a serious error, and we
842 appreciate a detailed bug report from you that describes how we could go
843 ahead and repeat this!
845 4.7 How do I keep user names and passwords secret in Curl command lines?
847 This problem has two sides:
849 The first part is to avoid having clear-text passwords in the command line
850 so that they don't appear in 'ps' outputs and similar. That is easily
851 avoided by using the "-K" option to tell curl to read parameters from a file
852 or stdin to which you can pass the secret info. curl itself will also
853 attempt to "hide" the given password by blanking out the option - this
854 doesn't work on all platforms.
856 To keep the passwords in your account secret from the rest of the world is
857 not a task that curl addresses. You could of course encrypt them somehow to
858 at least hide them from being read by human eyes, but that is not what
859 anyone would call security.
861 Also note that regular HTTP (using Basic authentication) and FTP passwords
862 are sent in clear across the network. All it takes for anyone to fetch them
863 is to listen on the network. Eavesdropping is very easy. Use more secure
864 authentication methods (like Digest, Negotiate or even NTLM) or consider the
865 SSL-based alternatives HTTPS and FTPS.
869 It is not a bug if the behavior is documented. Read the docs first.
870 Especially check out the KNOWN_BUGS file, it may be a documented bug!
872 If it is a problem with a binary you've downloaded or a package for your
873 particular platform, try contacting the person who built the package/archive
876 If there is a bug, read the BUGS document first. Then report it as described
879 4.9 Curl can't authenticate to the server that requires NTLM?
881 NTLM support requires OpenSSL, GnuTLS, NSS or Microsoft Windows libraries at
882 build-time to provide this functionality.
884 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
885 should not use such ones.
887 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
889 Many web servers allow or demand that the administrator configures the
890 server properly for these requests to work on the web server.
892 Some servers seem to support HEAD only on certain kinds of URLs.
894 To fully grasp this, try the documentation for the particular server
895 software you're trying to interact with. This is not anything curl can do
898 4.11 Why does my HTTP range requests return the full document?
900 Because the range may not be supported by the server, or the server may
901 choose to ignore it and return the full document anyway.
903 4.12 Why do I get "certificate verify failed" ?
905 You invoke curl 7.10 or later to communicate on a https:// URL and get an
906 error back looking something similar to this:
908 curl: (35) SSL: error:14090086:SSL routines:
909 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
911 Then it means that curl couldn't verify that the server's certificate was
912 good. Curl verifies the certificate using the CA cert bundle that comes with
913 the curl installation.
915 To disable the verification (which makes it act like curl did before 7.10),
916 use -k. This does however enable man-in-the-middle attacks.
918 If you get this failure but are having a CA cert bundle installed and used,
919 the server's certificate is not signed by one of the CA's in the bundle. It
920 might for example be self-signed. You then correct this problem by obtaining
921 a valid CA cert for the server. Or again, decrease the security by disabling
924 Details are also in the SSLCERTS file in the release archives, found online
925 here: http://curl.haxx.se/docs/sslcerts.html
927 4.13 Why is curl -R on Windows one hour off?
929 During daylight savings time, when -R is used, curl will set a time that
930 appears one hour off. This happens due to a flaw in how Windows stores and
931 uses file modification times and it is not easily worked around. For details
932 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
934 4.14 Redirects work in browser but not with curl!
936 curl supports HTTP redirects fine (see item 3.8). Browsers generally support
937 at least two other ways to perform directs that curl does not:
939 - Meta tags. You can write a HTML tag that will cause the browser to
940 redirect to another given URL after a certain time.
942 - Javascript. You can write a Javascript program embedded in a HTML page
943 that redirects the browser to another given URL.
945 There is no way to make curl follow these redirects. You must either
946 manually figure out what the page is set to do, or you write a script that
947 parses the results and fetches the new URL.
949 4.15 FTPS doesn't work
951 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
954 When a URL is used that starts with FTPS://, curl assumes implicit SSL on
955 the control connection and will therefore immediately connect and try to
956 speak SSL. FTPS:// connections default to port 990.
958 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
959 of its related flavours). This is the most common method, and the one
960 mandated by RFC4217. This kind of connection then of course uses the
961 standard FTP port 21 by default.
963 4.16 My HTTP POST or PUT requests are slow!
965 libcurl makes all POST and PUT requests (except for POST requests with a
966 very tiny request body) use the "Expect: 100-continue" header. This header
967 allows the server to deny the operation early so that libcurl can bail out
968 already before having to send any data. This is useful in authentication
971 However, many servers don't implement the Expect: stuff properly and if the
972 server doesn't respond (positively) within 1 second libcurl will continue
973 and send off the data anyway.
975 You can disable libcurl's use of the Expect: header the same way you disable
976 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
978 4.17 Non-functional connect timeouts
980 In most Windows setups having a timeout longer than 21 seconds make no
981 difference, as it will only send 3 TCP SYN packets and no more. The second
982 packet sent three seconds after the first and the third six seconds after
983 the second. No more than three packets are sent, no matter how long the
986 See option TcpMaxConnectRetransmissions on this page:
987 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
989 Also, even on non-Windows systems there may run a firewall or anti-virus
990 software or similar that accepts the connection but does not actually do
991 anything else. This will make (lib)curl to consider the connection connected
992 and thus the connect timeout won't trigger.
994 4.18 file:// URLs containing drive letters (Windows, NetWare)
996 When using cURL to try to download a local file, one might use a URL
1001 You'll find that even if D:\blah.txt does exist, cURL returns a 'file
1004 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
1005 file:// URLs must contain a host component, but it is ignored by
1006 most implementations. In the above example, 'D:' is treated as the
1007 host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
1008 If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
1009 and if that doesn't exist you will get the not found error.
1011 To fix this problem, use file:// URLs with *three* leading slashes:
1015 Alternatively, if it makes more sense, specify 'localhost' as the host
1018 file://localhost/D:/blah.txt
1020 In either case, cURL should now be looking for the correct file.
1022 4.19 Why doesn't cURL return an error when the network cable is unplugged?
1024 Unplugging the cable is not an error situation. The TCP/IP protocol stack
1025 was designed to be fault tolerant, so even though there may be a physical
1026 break somewhere the connection shouldn't be affected, just possibly
1027 delayed. Eventually, the physical break will be fixed or the data will be
1028 re-routed around the physical problem.
1030 In such cases, the TCP/IP stack is responsible for detecting when the
1031 network connection is irrevocably lost. Since with some protocols it is
1032 perfectly legal for the client wait indefinitely for data, the stack may
1033 never report a problem, and even when it does, it can take up to 20 minutes
1034 for it to detect an issue. The curl option --keepalive-time enables
1035 keep-alive support in the TCP/IP stack which makes it periodically probe the
1036 connection to make sure it is still available to send data. That should
1037 reliably detect any TCP/IP network failure.
1039 But even that won't detect the network going down before the TCP/IP
1040 connection is established (e.g. during a DNS lookup) or using protocols that
1041 don't use TCP. To handle those situations, curl offers a number of timeouts
1042 on its own. --speed-limit/--speed-time will abort if the data transfer rate
1043 falls too low, and --connect-timeout and --max-time can be used to put an
1044 overall timeout on the connection phase or the entire transfer.
1049 5.1 Is libcurl thread-safe?
1053 We have written the libcurl code specifically adjusted for multi-threaded
1054 programs. libcurl will use thread-safe functions instead of non-safe ones if
1055 your system has such.
1057 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
1058 need to provide one or two locking functions:
1060 http://www.openssl.org/docs/crypto/threads.html
1062 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
1063 need to provide locking function(s) for libgcrypt (which is used by GnuTLS
1064 for the crypto functions).
1066 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
1068 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
1070 5.2 How can I receive all data into a large memory chunk?
1072 [ See also the examples/getinmemory.c source ]
1074 You are in full control of the callback function that gets called every time
1075 there is data received from the remote server. You can make that callback do
1076 whatever you want. You do not have to write the received data to a file.
1078 One solution to this problem could be to have a pointer to a struct that you
1079 pass to the callback function. You set the pointer using the
1080 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
1081 instead of a FILE * to a file:
1083 /* imaginary struct */
1084 struct MemoryStruct {
1089 /* imaginary callback function */
1091 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
1093 size_t realsize = size * nmemb;
1094 struct MemoryStruct *mem = (struct MemoryStruct *)data;
1096 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
1098 memcpy(&(mem->memory[mem->size]), ptr, realsize);
1099 mem->size += realsize;
1100 mem->memory[mem->size] = 0;
1105 5.3 How do I fetch multiple files with libcurl?
1107 libcurl has excellent support for transferring multiple files. You should
1108 just repeatedly set new URLs with curl_easy_setopt() and then transfer it
1109 with curl_easy_perform(). The handle you get from curl_easy_init() is not
1110 only reusable, but you're even encouraged to reuse it if you can, as that
1111 will enable libcurl to use persistent connections.
1113 5.4 Does libcurl do Winsock initialization on win32 systems?
1115 Yes, if told to in the curl_global_init() call.
1117 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
1119 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
1120 that DLL use the FILE * (as the DLL and the client application cannot access
1121 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
1122 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
1123 file, even if that simply writes the data to the specified FILE *.
1124 Similarly, if you use CURLOPT_READDATA you must also specify
1125 CURLOPT_READFUNCTION.
1127 5.6 What about Keep-Alive or persistent connections?
1129 curl and libcurl have excellent support for persistent connections when
1130 transferring several files from the same server. Curl will attempt to reuse
1131 connections for all URLs specified on the same command line/config file, and
1132 libcurl will reuse connections for all transfers that are made using the
1133 same libcurl handle.
1135 When you use the easy interface, the connection cache is kept within the
1136 easy handle. If you instead use the multi interface, the connection cache
1137 will be kept within the multi handle and will be shared among all the easy
1138 handles that are used within the same multi handle.
1140 5.7 Link errors when building libcurl on Windows!
1142 You need to make sure that your project, and all the libraries (both static
1143 and dynamic) that it links against, are compiled/linked against the same run
1146 This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
1147 options to the command line compiler. /MD (linking against MSVCRT dll) seems
1148 to be the most commonly used option.
1150 When building an application that uses the static libcurl library, you must
1151 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
1152 dynamic import symbols. If you're using Visual Studio, you need to instead
1153 add CURL_STATICLIB in the "Preprocessor Definitions" section.
1155 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
1156 have linked against the wrong (static) library. If you want to use the
1157 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
1158 the import libraries below. These are the libraries produced by the various
1159 lib/Makefile.* files:
1161 Target: static lib. import lib for libcurl*.dll.
1162 -----------------------------------------------------------
1163 MingW: libcurl.a libcurldll.a
1164 MSVC (release): libcurl.lib libcurl_imp.lib
1165 MSVC (debug): libcurld.lib libcurld_imp.lib
1166 Borland: libcurl.lib libcurl_imp.lib
1168 5.8 libcurl.so.X: open failed: No such file or directory
1170 This is an error message you might get when you try to run a program linked
1171 with a shared version of libcurl and your run-time linker (ld.so) couldn't
1172 find the shared library named libcurl.so.X. (Where X is the number of the
1173 current libcurl ABI, typically 3 or 4).
1175 You need to make sure that ld.so finds libcurl.so.X. You can do that
1176 multiple ways, and it differs somewhat between different operating systems,
1177 but they are usually:
1179 * Add an option to the linker command line that specify the hard-coded path
1180 the run-time linker should check for the lib (usually -R)
1182 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
1183 should check for libs
1185 * Adjust the system's config to check for libs in the directory where you've
1186 put the dir (like Linux's /etc/ld.so.conf)
1188 'man ld.so' and 'man ld' will tell you more details
1190 5.9 How does libcurl resolve host names?
1192 libcurl supports a large a number of different name resolve functions. One
1193 of them is picked at build-time and will be used unconditionally. Thus, if
1194 you want to change name resolver function you must rebuild libcurl and tell
1195 it to use a different function.
1197 - The non-ipv6 resolver that can use one out of four host name resolve calls
1198 (depending on what your system supports):
1201 B - gethostbyname_r() with 3 arguments
1202 C - gethostbyname_r() with 5 arguments
1203 D - gethostbyname_r() with 6 arguments
1205 - The ipv6-resolver that uses getaddrinfo()
1207 - The c-ares based name resolver that uses the c-ares library for resolves.
1208 Using this offers asynchronous name resolves.
1210 - The threaded resolver (default option on Windows). It uses:
1212 A - gethostbyname() on plain ipv4 hosts
1213 B - getaddrinfo() on ipv6-enabled hosts
1215 Also note that libcurl never resolves or reverse-lookups addresses given as
1216 pure numbers, such as 127.0.0.1 or ::1.
1218 5.10 How do I prevent libcurl from writing the response to stdout?
1220 libcurl provides a default built-in write function that writes received data
1221 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
1222 set CURLOPT_WRITEDATA to a different FILE * handle.
1224 5.11 How do I make libcurl not receive the whole HTTP response?
1226 You make the write callback (or progress callback) return an error and
1227 libcurl will then abort the transfer.
1229 5.12 Can I make libcurl fake or hide my real IP address?
1231 No. libcurl operates on a higher level than so. Besides, faking IP address
1232 would imply sending IP packages with a made-up source address, and then you
1233 normally get a problem with intercepting the packages sent back as they
1234 would then not be routed to you!
1236 If you use a proxy to access remote sites, the sites will not see your local
1237 IP address but instead the address of the proxy.
1239 Also note that on many networks NATs or other IP-munging techniques are used
1240 that makes you see and use a different IP address locally than what the
1241 remote server will see you coming from.
1243 5.13 How do I stop an ongoing transfer?
1245 With the easy interface you make sure to return the correct error code from
1246 one of the callbacks, but none of them are instant. There is no function you
1247 can call from another thread or similar that will stop it immediately.
1248 Instead, you need to make sure that one of the callbacks you use returns an
1249 appropriate value that will stop the transfer. Suitable callbacks that you
1250 can do this with include the progress callback, the read callback and the
1253 If you're using the multi interface, you can also stop a transfer by
1254 removing the particular easy handle from the multi stack at any moment you
1255 think the transfer is done.
1257 5.14 Using C++ non-static functions for callbacks?
1259 libcurl is a C library, it doesn't know anything about C++ member functions.
1261 You can overcome this "limitation" with a relative ease using a static
1262 member function that is passed a pointer to the class:
1264 // f is the pointer to your object.
1265 static YourClass::func(void *buffer, size_t sz, size_t n, void *f)
1267 // Call non-static member function.
1268 static_cast<YourClass*>(f)->nonStaticFunction();
1271 // This is how you pass pointer to the static function:
1272 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func);
1273 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
1275 5.15 How do I get an FTP directory listing?
1277 If you end the FTP URL you request with a slash, libcurl will provide you
1278 with a directory listing of that given directory. You can also set
1279 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
1282 The follow-up question that tend to follow the previous one, is how a
1283 program is supposed to parse the directory listing. How does it know what's
1284 a file and what's a dir and what's a symlink etc. The harsh reality is that
1285 FTP provides no such fine and easy-to-parse output. The output format FTP
1286 servers respond to LIST commands are entirely at the server's own liking and
1287 the NLST output doesn't reveal any types and in many cases don't even
1288 include all the directory entries. Also, both LIST and NLST tend to hide
1289 unix-style hidden files (those that start with a dot) by default so you need
1290 to do "LIST -a" or similar to see them.
1292 The application thus needs to parse the LIST output. One such existing
1293 list parser is available at http://cr.yp.to/ftpparse.html Versions of
1294 libcurl since 7.21.0 also provide the ability to specify a wildcard to
1295 download multiple files from one FTP directory.
1297 5.16 I want a different time-out!
1299 Time and time again users realize that CURLOPT_TIMEOUT and
1300 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all
1301 the various use cases and scenarios applications end up with.
1303 libcurl offers many more ways to time-out operations. A common alternative
1304 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to
1305 specify the lowest possible speed to accept before to consider the transfer
1308 The most flexible way is by writing your own time-out logic and using
1309 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and
1310 use that to figure out exactly when the right condition is met when the
1311 transfer should get stopped.
1316 Curl and libcurl are released under a MIT/X derivate license. The license is
1317 very liberal and should not impose a problem for your project. This section
1318 is just a brief summary for the cases we get the most questions. (Parts of
1319 this section was much enhanced by Bjorn Reese.)
1321 We are not lawyers and this is not legal advice. You should probably consult
1322 one if you want true and accurate legal insights without our prejudice. Note
1323 especially that this section concerns the libcurl license only; compiling in
1324 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
1325 the licensing obligations of your application.
1327 6.1 I have a GPL program, can I use the libcurl library?
1331 Since libcurl may be distributed under the MIT/X derivate license, it can be
1332 used together with GPL in any software.
1334 6.2 I have a closed-source program, can I use the libcurl library?
1338 libcurl does not put any restrictions on the program that uses the library.
1340 6.3 I have a BSD licensed program, can I use the libcurl library?
1344 libcurl does not put any restrictions on the program that uses the library.
1346 6.4 I have a program that uses LGPL libraries, can I use libcurl?
1350 The LGPL license doesn't clash with other licenses.
1352 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
1356 The MIT/X derivate license practically allows you to do almost anything with
1357 the sources, on the condition that the copyright texts in the sources are
1360 6.6 Can you please change the curl/libcurl license to XXXX?
1364 We have carefully picked this license after years of development and
1365 discussions and a large amount of people have contributed with source code
1366 knowing that this is the license we use. This license puts the restrictions
1367 we want on curl/libcurl and it does not spread to other programs or
1368 libraries that use it. It should be possible for everyone to use libcurl or
1369 curl in their projects, no matter what license they already have in use.
1371 6.7 What are my obligations when using libcurl in my commercial apps?
1373 Next to none. All you need to adhere to is the MIT-style license (stated in
1374 the COPYING file) which basically says you have to include the copyright
1375 notice in "all copies" and that you may not use the copyright holder's name
1376 when promoting your software.
1378 You do not have to release any of your source code.
1380 You do not have to reveal or make public any changes to the libcurl source
1383 You do not have to broadcast to the world that you are using libcurl within
1386 All we ask is that you disclose "the copyright notice and this permission
1387 notice" somewhere. Most probably like in the documentation or in the section
1388 where other third party dependencies already are mentioned and acknowledged.
1390 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere,
1391 more and more companies are discovering the power of libcurl and take
1392 advantage of it even in commercial environments.
1397 7.1 What is PHP/CURL?
1399 The module for PHP that makes it possible for PHP programs to access curl-
1400 functions from within PHP.
1402 In the cURL project we call this module PHP/CURL to differentiate it from
1403 curl the command line tool and libcurl the library. The PHP team however
1404 does not refer to it like this (for unknown reasons). They call it plain
1405 CURL (often using all caps) or sometimes ext/curl, but both cause much
1406 confusion to users which in turn gives us a higher question load.
1408 7.2 Who wrote PHP/CURL?
1410 PHP/CURL is a module that comes with the regular PHP package. It depends and
1411 uses libcurl, so you need to have libcurl installed properly first before
1412 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
1414 7.3 Can I perform multiple requests using the same handle?
1416 Yes - at least in PHP version 4.3.8 and later (this has been known to not
1417 work in earlier versions, but the exact version when it started to work is
1420 After a transfer, you just set new options in the handle and make another
1421 transfer. This will make libcurl to re-use the same connection if it can.