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+Updated: October 6, 2010 (http://curl.haxx.se/docs/faq.html)
+ _ _ ____ _
+ ___| | | | _ \| |
+ / __| | | | |_) | |
+ | (__| |_| | _ <| |___
+ \___|\___/|_| \_\_____|
+
+FAQ
+
+ 1. Philosophy
+ 1.1 What is cURL?
+ 1.2 What is libcurl?
+ 1.3 What is curl not?
+ 1.4 When will you make curl do XXXX ?
+ 1.5 Who makes curl?
+ 1.6 What do you get for making curl?
+ 1.7 What about CURL from curl.com?
+ 1.8 I have a problem who do I mail?
+ 1.9 Where do I buy commercial support for curl?
+ 1.10 How many are using curl?
+ 1.11 Why don't you update ca-bundle.crt
+ 1.12 I have a problem who can I chat with?
+ 1.13 curl's ECCN number?
+ 1.14 How do I submit my patch?
+
+ 2. Install Related Problems
+ 2.1 configure doesn't find OpenSSL even when it is installed
+ 2.1.1 native linker doesn't find OpenSSL
+ 2.1.2 only the libssl lib is missing
+ 2.2 Does curl work/build with other SSL libraries?
+ 2.3 Where can I find a copy of LIBEAY32.DLL?
+ 2.4 Does curl support SOCKS (RFC 1928) ?
+
+ 3. Usage Problems
+ 3.1 curl: (1) SSL is disabled, https: not supported
+ 3.2 How do I tell curl to resume a transfer?
+ 3.3 Why doesn't my posting using -F work?
+ 3.4 How do I tell curl to run custom FTP commands?
+ 3.5 How can I disable the Pragma: nocache header?
+ 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
+ 3.7 Can I use curl to delete/rename a file through FTP?
+ 3.8 How do I tell curl to follow HTTP redirects?
+ 3.9 How do I use curl in my favorite programming language?
+ 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
+ 3.11 How do I POST with a different Content-Type?
+ 3.12 Why do FTP specific features over HTTP proxy fail?
+ 3.13 Why does my single/double quotes fail?
+ 3.14 Does curl support Javascript or PAC (automated proxy config)?
+ 3.15 Can I do recursive fetches with curl?
+ 3.16 What certificates do I need when I use SSL?
+ 3.17 How do I list the root dir of an FTP server?
+ 3.18 Can I use curl to send a POST/PUT and not wait for a response?
+ 3.19 How do I get HTTP from a host using a specific IP address?
+
+ 4. Running Problems
+ 4.1 Problems connecting to SSL servers.
+ 4.2 Why do I get problems when I use & or % in the URL?
+ 4.3 How can I use {, }, [ or ] to specify multiple URLs?
+ 4.4 Why do I get downloaded data even though the web page doesn't exist?
+ 4.5 Why do I get return code XXX from a HTTP server?
+ 4.5.1 "400 Bad Request"
+ 4.5.2 "401 Unauthorized"
+ 4.5.3 "403 Forbidden"
+ 4.5.4 "404 Not Found"
+ 4.5.5 "405 Method Not Allowed"
+ 4.5.6 "301 Moved Permanently"
+ 4.6 Can you tell me what error code 142 means?
+ 4.7 How do I keep user names and passwords secret in Curl command lines?
+ 4.8 I found a bug!
+ 4.9 Curl can't authenticate to the server that requires NTLM?
+ 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
+ 4.11 Why does my HTTP range requests return the full document?
+ 4.12 Why do I get "certificate verify failed" ?
+ 4.13 Why is curl -R on Windows one hour off?
+ 4.14 Redirects work in browser but not with curl!
+ 4.15 FTPS doesn't work
+ 4.16 My HTTP POST or PUT requests are slow!
+ 4.17 Non-functional connect timeouts on Windows
+ 4.18 file:// URLs containing drive letters (Windows, NetWare)
+ 4.19 Why doesn't cURL return an error when the network cable is unplugged?
+
+ 5. libcurl Issues
+ 5.1 Is libcurl thread-safe?
+ 5.2 How can I receive all data into a large memory chunk?
+ 5.3 How do I fetch multiple files with libcurl?
+ 5.4 Does libcurl do Winsock initing on win32 systems?
+ 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
+ 5.6 What about Keep-Alive or persistent connections?
+ 5.7 Link errors when building libcurl on Windows!
+ 5.8 libcurl.so.X: open failed: No such file or directory
+ 5.9 How does libcurl resolve host names?
+ 5.10 How do I prevent libcurl from writing the response to stdout?
+ 5.11 How do I make libcurl not receive the whole HTTP response?
+ 5.12 Can I make libcurl fake or hide my real IP address?
+ 5.13 How do I stop an ongoing transfer?
+ 5.14 Using C++ non-static functions for callbacks?
+ 5.15 How do I get an FTP directory listing?
+
+ 6. License Issues
+ 6.1 I have a GPL program, can I use the libcurl library?
+ 6.2 I have a closed-source program, can I use the libcurl library?
+ 6.3 I have a BSD licensed program, can I use the libcurl library?
+ 6.4 I have a program that uses LGPL libraries, can I use libcurl?
+ 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
+ 6.6 Can you please change the curl/libcurl license to XXXX?
+ 6.7 What are my obligations when using libcurl in my commercial apps?
+
+ 7. PHP/CURL Issues
+ 7.1 What is PHP/CURL?
+ 7.2 Who write PHP/CURL?
+ 7.3 Can I perform multiple requests using the same handle?
+
+==============================================================================
+
+1. Philosophy
+
+ 1.1 What is cURL?
+
+ cURL is the name of the project. The name is a play on 'Client for URLs',
+ originally with URL spelled in uppercase to make it obvious it deals with
+ URLs. The fact it can also be pronounced 'see URL' also helped, it works as
+ an abbreviation for "Client URL Request Library" or why not the recursive
+ version: "Curl URL Request Library".
+
+ The cURL project produces two products:
+
+ libcurl
+
+ A free and easy-to-use client-side URL transfer library, supporting DICT,
+ FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3,
+ POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP.
+
+ libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
+ kerberos, HTTP form based upload, proxies, cookies, user+password
+ authentication, file transfer resume, http proxy tunneling and more!
+
+ libcurl is highly portable, it builds and works identically on numerous
+ platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX,
+ IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOs, Mac
+ OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF,
+ Android, Minix, IBM TPF and more...
+
+ libcurl is free, thread-safe, IPv6 compatible, feature rich, well
+ supported and fast.
+
+ curl
+
+ A command line tool for getting or sending files using URL syntax.
+
+ Since curl uses libcurl, curl supports the same wide range of common
+ Internet protocols that libcurl does.
+
+ We pronounce curl and cURL with an initial k sound: [kurl].
+
+ There are numerous sub-projects and related projects that also use the word
+ curl in the project names in various combinations, but you should take
+ notice that this FAQ is directed at the command-line tool named curl (and
+ libcurl the library), and may therefore not be valid for other curl-related
+ projects. (There is however a small section for the PHP/CURL in this FAQ.)
+
+ 1.2 What is libcurl?
+
+ libcurl is a reliable and portable library which provides you with an easy
+ interface to a range of common Internet protocols.
+
+ You can use libcurl for free in your application, be it open source,
+ commercial or closed-source.
+
+ libcurl is most probably the most portable, most powerful and most often
+ used C-based multi-platform file transfer library on this planet - be it
+ open source or commercial.
+
+ 1.3 What is curl not?
+
+ Curl is not a wget clone. That is a common misconception. Never, during
+ curl's development, have we intended curl to replace wget or compete on its
+ market. Curl is targeted at single-shot file transfers.
+
+ Curl is not a web site mirroring program. If you want to use curl to mirror
+ something: fine, go ahead and write a script that wraps around curl to make
+ it reality (like curlmirror.pl does).
+
+ Curl is not an FTP site mirroring program. Sure, get and send FTP with curl
+ but if you want systematic and sequential behavior you should write a
+ script (or write a new program that interfaces libcurl) and do it.
+
+ Curl is not a PHP tool, even though it works perfectly well when used from
+ or with PHP (when using the PHP/CURL module).
+
+ Curl is not a program for a single operating system. Curl exists, compiles,
+ builds and runs under a wide range of operating systems, including all
+ modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2,
+ OS X, QNX etc.
+
+ 1.4 When will you make curl do XXXX ?
+
+ We love suggestions of what to change in order to make curl and libcurl
+ better. We do however believe in a few rules when it comes to the future of
+ curl:
+
+ * Curl -- the command line tool -- is to remain a non-graphical command line
+ tool. If you want GUIs or fancy scripting capabilities, you should look
+ for another tool that uses libcurl.
+
+ * We do not add things to curl that other small and available tools already
+ do very fine at the side. Curl's output is fine to pipe into another
+ program or redirect to another file for the next program to interpret.
+
+ * We focus on protocol related issues and improvements. If you wanna do more
+ magic with the supported protocols than curl currently does, chances are
+ big we will agree. If you wanna add more protocols, we may very well
+ agree.
+
+ * If you want someone else to make all the work while you wait for us to
+ implement it for you, that is not a very friendly attitude. We spend a
+ considerable time already on maintaining and developing curl. In order to
+ get more out of us, you should consider trading in some of your time and
+ efforts in return.
+
+ * If you write the code, chances are bigger that it will get into curl
+ faster.
+
+ 1.5 Who makes curl?
+
+ curl and libcurl are not made by any single individual. Daniel Stenberg is
+ project leader and main developer, but other persons' submissions are
+ important and crucial. Anyone can contribute and post their changes and
+ improvements and have them inserted in the main sources (of course on the
+ condition that developers agree on that the fixes are good).
+
+ The full list of all contributors is found in the docs/THANKS file.
+
+ curl is developed by a community, with Daniel at the wheel.
+
+ 1.6 What do you get for making curl?
+
+ Project cURL is entirely free and open. No person gets paid for developing
+ (lib)curl on full or even part time. We do this voluntarily on our spare
+ time. Occasionally companies pay individual developers to work on curl, but
+ that's up to each company and developer. It is not controlled by nor
+ supervised in any way by the project.
+
+ We still get help from companies. Haxx provides web site, bandwidth, mailing
+ lists etc and sourceforge.net hosts project services we take advantage from,
+ like the bug tracker. Also again, some companies have sponsored certain
+ parts of the development in the past and I hope some will continue to do so
+ in the future.
+
+ If you want to support our project, consider a donation or a banner-program
+ or even better: by helping us coding, documenting, testing etc.
+
+ 1.7 What about CURL from curl.com?
+
+ During the summer 2001, curl.com was busy advertising their client-side
+ programming language for the web, named CURL.
+
+ We are in no way associated with curl.com or their CURL programming
+ language.
+
+ Our project name curl has been in effective use since 1998. We were not the
+ first computer related project to use the name "curl" and do not claim any
+ first-hand rights to the name.
+
+ We recognize that we will be living in parallel with curl.com and wish them
+ every success.
+
+ 1.8 I have a problem who do I mail?
+
+ Please do not mail any single individual unless you really need to. Keep
+ curl-related questions on a suitable mailing list. All available mailing
+ lists are listed in the MANUAL document and online at
+ http://curl.haxx.se/mail/
+
+ Keeping curl-related questions and discussions on mailing lists allows
+ others to join in and help, to share their ideas, contribute their
+ suggestions and spread their wisdom. Keeping discussions on public mailing
+ lists also allows for others to learn from this (both current and future
+ users thanks to the web based archives of the mailing lists), thus saving us
+ from having to repeat ourselves even more. Thanks for respecting this.
+
+ If you have found or simply suspect a security problem in curl or libcurl,
+ mail curl-security at haxx.se (closed list of receivers, mails are not
+ disclosed) and tell. Then we can produce a fix in a timely manner before the
+ flaw is announced to the world, thus lessen the impact the problem will have
+ on existing users.
+
+ 1.9 Where do I buy commercial support for curl?
+
+ curl is fully open source. It means you can hire any skilled engineer to fix
+ your curl-related problems.
+
+ We list available alternatives on the curl web site:
+ http://curl.haxx.se/support.html
+
+ 1.10 How many are using curl?
+
+ It is impossible to tell.
+
+ We don't know how many users that knowingly have installed and use curl.
+
+ We don't know how many users that use curl without knowing that they are in
+ fact using it.
+
+ We don't know how many users that downloaded or installed curl and then
+ never use it.
+
+ Some facts to use as input to the math:
+
+ curl packages are downloaded from the curl.haxx.se and mirrors over a
+ million times per year. curl is installed by default with most Linux
+ distributions. curl is installed by default with Mac OS X. curl and libcurl
+ as used by numerous applications that include libcurl binaries in their
+ distribution packages (like Adobe Acrobat Reader and Google Earth).
+
+ More than a hundred known named companies use curl in commercial
+ environments and products and more than a hundred known named open source
+ projects depend on (lib)curl.
+
+ In a poll on the curl web site mid-2005, more than 50% of the 300+ answers
+ estimated a user base of one million users or more.
+
+ In March 2005, the "Linux Counter project" estimated a total Linux user base
+ of some 29 millions, while Netcraft detected some 4 million "active" Linux
+ based web servers. A guess is that a fair amount of these Linux
+ installations have curl installed.
+
+ The Debian project maintains statistics on packages installed by people
+ who have voluntarily run their package counting application. In mid-2010,
+ libcurl3 was installed on over 55000 such systems (62% of reporting systems)
+ and was one of the 320 most popular installed packages (out of about 107000
+ possible packages).
+
+ All this taken together, there is no doubt that there are millions of
+ (lib)curl users.
+
+ http://curl.haxx.se/docs/companies.html
+ http://curl.haxx.se/docs/programs.html
+ http://curl.haxx.se/libcurl/using/apps.html
+ http://counter.li.org/estimates.php
+ http://news.netcraft.com/archives/2005/03/14/fedora_makes_rapid_progress.html
+ http://qa.debian.org/popcon.php?package=curl
+
+ 1.11 Why don't you update ca-bundle.crt
+
+ The ca-bundle.crt file that used to be bundled with curl was very outdated
+ (it being last modified year 2000 should tell) and must be replaced with a
+ much more modern and up-to-date version by anyone who wants to verify peers
+ anyway. It is no longer provided, the last curl release that shipped it was
+ curl 7.18.0.
+
+ In the cURL project we've decided not to attempt to keep this file updated
+ (or even present anymore) since deciding what to add to a ca cert bundle is
+ an undertaking we've not been ready to accept, and the one we can get from
+ Mozilla is perfectly fine so there's no need to duplicate that work.
+
+ Today, with many services performed over HTTPS, every operating system
+ should come with a default ca cert bundle that can be deemed somewhat
+ trustworthy and that collection (if reasonably updated) should be deemed to
+ be a lot better than a private curl version.
+
+ If you want the most recent collection of ca certs that Mozilla Firefox
+ uses, we recommend that you extract the collection yourself from Mozilla
+ Firefox (by running 'make ca-bundle), or by using our online service setup
+ for this purpose: http://curl.haxx.se/docs/caextract.html
+
+ 1.12 I have a problem who can I chat with?
+
+ There's a bunch of friendly people hanging out in the #curl channel on the
+ IRC network irc.freenode.net. If you're polite and nice, chances are big
+ that you can get -- or provide -- help instantly.
+
+ 1.13 curl's ECCN number?
+
+ The US government restricts exports of software that contains or uses
+ cryptography. When doing so, the Export Control Classification Number (ECCN)
+ is used to identify the level of export control etc.
+
+ ASF gives a good explanation at http://www.apache.org/dev/crypto.html
+
+ We believe curl's number might be ECCN 5D002, another possibility is
+ 5D992. It seems necessary to write them, asking to confirm.
+
+ Comprehensible explanations of the meaning of such numbers and how to
+ obtain them (resp.) are here
+
+ http://www.bis.doc.gov/licensing/exportingbasics.htm
+ http://www.bis.doc.gov/licensing/do_i_needaneccn.html
+
+ An incomprehensible description of the two numbers above is here
+ http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf
+
+ 1.14 How do I submit my patch?
+
+ When you have made a patch or a change of whatever sort, and want to submit
+ that to the project, there are a few different ways we prefer:
+
+ o send a patch to the curl-library mailing list. We're many subscribers
+ there and there are lots of people who can review patches, comment on them
+ and "receive" them properly.
+
+ o if your patch changes or fixes a bug, you can also opt to submit a bug
+ report in the bug tracker and attach your patch there. There are less
+ people involved there.
+
+ Lots of more details are found in the CONTRIBUTE and INTERNALS docs.
+
+
+2. Install Related Problems
+
+ 2.1 configure doesn't find OpenSSL even when it is installed
+
+ This may be because of several reasons.
+
+ 2.1.1 native linker doesn't find openssl
+
+ Affected platforms:
+ Solaris (native cc compiler)
+ HPUX (native cc compiler)
+ SGI IRIX (native cc compiler)
+ SCO UNIX (native cc compiler)
+
+ When configuring curl, I specify --with-ssl. OpenSSL is installed in
+ /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
+ CRYPTO_lock in -lcrypto
+
+ Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
+ -lcrypto, so ld can't find the library. This is due to a bug in the GNU
+ autoconf tool.
+
+ Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
+ ./configure places the -L/usr/local/ssl/lib early enough in the command
+ line to make things work
+
+ 2.1.2 only the libssl lib is missing
+
+ If all include files and the libcrypto lib is present, with only the
+ libssl being missing according to configure, this is mostly likely because
+ a few functions are left out from the libssl.
+
+ If the function names missing include RSA or RSAREF you can be certain
+ that this is because libssl requires the RSA and RSAREF libs to build.
+
+ See the INSTALL file section that explains how to add those libs to
+ configure. Make sure that you remove the config.cache file before you
+ rerun configure with the new flags.
+
+ 2.2 Does curl work/build with other SSL libraries?
+
+ Curl has been written to use OpenSSL, GnuTLS, yassl, NSS or PolarSSL,
+ although there should not be many problems using a different library. If
+ anyone does "port" curl to use a different SSL library, we are of course
+ very interested in getting the patch!
+
+ 2.3 Where can I find a copy of LIBEAY32.DLL?
+
+ That is an OpenSSL binary built for Windows.
+
+ Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
+ on a windows machine to do https://. Check out the curl web site to find
+ accurate and up-to-date pointers to recent OpenSSL DLLs and other binary
+ packages.
+
+ 2.4 Does curl support SOCKS (RFC 1928) ?
+
+ Yes, SOCKS 4 and 5 are supported.
+
+
+3. Usage problems
+
+ 3.1 curl: (1) SSL is disabled, https: not supported
+
+ If you get this output when trying to get anything from a https:// server,
+ it means that the configure script couldn't find all libs and include files
+ it requires for SSL to work. If the configure script fails to find them,
+ curl is simply built without SSL support.
+
+ To get the https:// support into a curl that was previously built but that
+ reports that https:// is not supported, you should dig through the document
+ and logs and check out why the configure script doesn't find the SSL libs
+ and/or include files.
+
+ Also, check out the other paragraph in this FAQ labelled "configure doesn't
+ find OpenSSL even when it is installed".
+
+ 3.2 How do I tell curl to resume a transfer?
+
+ Curl supports resumed transfers both ways on both FTP and HTTP.
+
+ Try the -C option.
+
+ 3.3 Why doesn't my posting using -F work?
+
+ You can't simply use -F or -d at your choice. The web server that will
+ receive your post assumes one of the formats. If the form you're trying to
+ "fake" sets the type to 'multipart/form-data', then and only then you must
+ use the -F type. In all the most common cases, you should use -d which then
+ causes a posting with the type 'application/x-www-form-urlencoded'.
+
+ This is described in some detail in the MANUAL and TheArtOfHttpScripting
+ documents, and if you don't understand it the first time, read it again
+ before you post questions about this to the mailing list. Also, try reading
+ through the mailing list archives for old postings and questions regarding
+ this.
+
+ 3.4 How do I tell curl to run custom FTP commands?
+
+ You can tell curl to perform optional commands both before and/or after a
+ file transfer. Study the -Q/--quote option.
+
+ Since curl is used for file transfers, you don't use curl to just perform
+ FTP commands without transferring anything. Therefore you must always specify
+ a URL to transfer to/from even when doing custom FTP commands.
+
+ 3.5 How can I disable the Pragma: nocache header?
+
+ You can change all internally generated headers by adding a replacement with
+ the -H/--header option. By adding a header with empty contents you safely
+ disable that one. Use -H "Pragma:" to disable that specific header.
+
+ 3.6 Does curl support ASP, XML, XHTML or HTML version Y?
+
+ To curl, all contents are alike. It doesn't matter how the page was
+ generated. It may be ASP, PHP, Perl, shell-script, SSI or plain
+ HTML-files. There's no difference to curl and it doesn't even know what kind
+ of language that generated the page.
+
+ See also item 3.14 regarding javascript.
+
+ 3.7 Can I use curl to delete/rename a file through FTP?
+
+ Yes. You specify custom FTP commands with -Q/--quote.
+
+ One example would be to delete a file after you have downloaded it:
+
+ curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
+
+ or rename a file after upload:
+
+ curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname"
+
+ 3.8 How do I tell curl to follow HTTP redirects?
+
+ Curl does not follow so-called redirects by default. The Location: header
+ that informs the client about this is only interpreted if you're using the
+ -L/--location option. As in:
+
+ curl -L http://redirector.com
+
+ Not all redirects are HTTP ones, see 4.14
+
+ 3.9 How do I use curl in my favorite programming language?
+
+ There exist many language interfaces/bindings for curl that integrates it
+ better with various languages. If you are fluid in a script language, you
+ may very well opt to use such an interface instead of using the command line
+ tool.
+
+ Find out more about which languages that support curl directly, and how to
+ install and use them, in the libcurl section of the curl web site:
+ http://curl.haxx.se/libcurl/
+
+ In October 2009, there were interfaces available for the following
+ languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria,
+ Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET,
+ Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby,
+ Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro,
+ Q, wxwidgets and XBLite. By the time you read this, additional ones may have
+ appeared!
+
+ 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP?
+
+ Curl adheres to the HTTP spec, which basically means you can play with *any*
+ protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and
+ XML-RPC are all such ones. You can use -X to set custom requests and -H to
+ set custom headers (or replace internally generated ones).
+
+ Using libcurl is of course just as fine and you'd just use the proper
+ library options to do the same.
+
+ 3.11 How do I POST with a different Content-Type?
+
+ You can always replace the internally generated headers with -H/--header.
+ To make a simple HTTP POST with text/xml as content-type, do something like:
+
+ curl -d "datatopost" -H "Content-Type: text/xml" [URL]
+
+ 3.12 Why do FTP specific features over HTTP proxy fail?
+
+ Because when you use a HTTP proxy, the protocol spoken on the network will
+ be HTTP, even if you specify a FTP URL. This effectively means that you
+ normally can't use FTP specific features such as FTP upload and FTP quote
+ etc.
+
+ There is one exception to this rule, and that is if you can "tunnel through"
+ the given HTTP proxy. Proxy tunneling is enabled with a special option (-p)
+ and is generally not available as proxy admins usually disable tunneling to
+ other ports than 443 (which is used for HTTPS access through proxies).
+
+ 3.13 Why does my single/double quotes fail?
+
+ To specify a command line option that includes spaces, you might need to
+ put the entire option within quotes. Like in:
+
+ curl -d " with spaces " url.com
+
+ or perhaps
+
+ curl -d ' with spaces ' url.com
+
+ Exactly what kind of quotes and how to do this is entirely up to the shell
+ or command line interpreter that you are using. For most unix shells, you
+ can more or less pick either single (') or double (") quotes. For
+ Windows/DOS prompts I believe you're forced to use double (") quotes.
+
+ Please study the documentation for your particular environment. Examples in
+ the curl docs will use a mix of both these ones as shown above. You must
+ adjust them to work in your environment.
+
+ Remember that curl works and runs on more operating systems than most single
+ individuals have ever tried.
+
+ 3.14 Does curl support Javascript or PAC (automated proxy config)?
+
+ Many web pages do magic stuff using embedded Javascript. Curl and libcurl
+ have no built-in support for that, so it will be treated just like any other
+ contents.
+
+ .pac files are a netscape invention and are sometimes used by organizations
+ to allow them to differentiate which proxies to use. The .pac contents is
+ just a Javascript program that gets invoked by the browser and that returns
+ the name of the proxy to connect to. Since curl doesn't support Javascript,
+ it can't support .pac proxy configuration either.
+
+ Some workarounds usually suggested to overcome this Javascript dependency:
+
+ - Depending on the Javascript complexity, write up a script that
+ translates it to another language and execute that.
+
+ - Read the Javascript code and rewrite the same logic in another language.
+
+ - Implement a Javascript interpreter, people have successfully used the
+ Mozilla Javascript engine in the past.
+
+ - Ask your admins to stop this, for a static proxy setup or similar.
+
+ 3.15 Can I do recursive fetches with curl?
+
+ No. curl itself has no code that performs recursive operations, such as
+ those performed by wget and similar tools.
+
+ There exist wrapper scripts with that functionality (for example the
+ curlmirror perl script), and you can write programs based on libcurl to do
+ it, but the command line tool curl itself cannot.
+
+ 3.16 What certificates do I need when I use SSL?
+
+ There are three different kinds of "certificates" to keep track of when we
+ talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl.
+
+ - Client certificate. The server you communicate may require that you can
+ provide this in order to prove that you actually are who you claim to be.
+ If the server doesn't require this, you don't need a client certificate.
+
+ A client certificate is always used together with a private key, and the
+ private key has a pass phrase that protects it.
+
+ - Server certificate. The server you communicate with has a server
+ certificate. You can and should verify this certificate to make sure that
+ you are truly talking to the real server and not a server impersonating
+ it.
+
+ - Certificate Authority certificate ("CA cert"). You often have several CA
+ certs in a CA cert bundle that can be used to verify a server certificate
+ that was signed by one of the authorities in the bundle. curl does not
+ come with a CA cert bundle but most curl installs provide one. You can
+ also override the default.
+
+ The server certificate verification process is made by using a Certificate
+ Authority certificate ("CA cert") that was used to sign the server
+ certificate. Server certificate verification is enabled by default in curl
+ and libcurl and is often the reason for problems as explained in FAQ entry
+ 4.12 and the SSLCERTS document
+ (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are
+ "self-signed" or otherwise signed by a CA that you do not have a CA cert
+ for, cannot be verified. If the verification during a connect fails, you
+ are refused access. You then need to explicitly disable the verification
+ to connect to the server.
+
+ 3.17 How do I list the root dir of an FTP server?
+
+ There are two ways. The way defined in the RFC is to use an encoded slash
+ in the first path part. List the "/tmp" dir like this:
+
+ curl ftp://ftp.sunet.se/%2ftmp/
+
+ or the not-quite-kosher-but-more-readable way, by simply starting the path
+ section of the URL with a slash:
+
+ curl ftp://ftp.sunet.se//tmp/
+
+ 3.18 Can I use curl to send a POST/PUT and not wait for a response?
+
+ No.
+
+ But you could easily write your own program using libcurl to do such stunts.
+
+ 3.19 How do I get HTTP from a host using a specific IP address?
+
+ For example, you may be trying out a web site installation that isn't yet in
+ the DNS. Or you have a site using multiple IP addresses for a given host
+ name and you want to address a specific one out of the set.
+
+ Set a custom Host: header that identifies the server name you want to reach
+ but use the target IP address in the URL:
+
+ curl --header "Host: www.example.com" http://127.0.0.1/
+
+
+4. Running Problems
+
+ 4.1 Problems connecting to SSL servers.
+
+ It took a very long time before we could sort out why curl had problems to
+ connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The
+ error sometimes showed up similar to:
+
+ 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
+
+ It turned out to be because many older SSL servers don't deal with SSLv3
+ requests properly. To correct this problem, tell curl to select SSLv2 from
+ the command line (-2/--sslv2).
+
+ There have also been examples where the remote server didn't like the SSLv2
+ request and instead you had to force curl to use SSLv3 with -3/--sslv3.
+
+ 4.2 Why do I get problems when I use & or % in the URL?
+
+ In general unix shells, the & symbol is treated specially and when used, it
+ runs the specified command in the background. To safely send the & as a part
+ of a URL, you should quote the entire URL by using single (') or double (")
+ quotes around it. Similar problems can also occur on some shells with other
+ characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL.
+
+ An example that would invoke a remote CGI that uses &-symbols could be:
+
+ curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
+
+ In Windows, the standard DOS shell treats the %-symbol specially and you
+ need to use TWO %-symbols for each single one you want to use in the URL.
+
+ Also note that if you want the literal %-symbol to be part of the data you
+ pass in a POST using -d/--data you must encode it as '%25' (which then also
+ needs the %-symbol doubled on Windows machines).
+
+ 4.3 How can I use {, }, [ or ] to specify multiple URLs?
+
+ Because those letters have a special meaning to the shell, and to be used in
+ a URL specified to curl you must quote them.
+
+ An example that downloads two URLs (sequentially) would do:
+
+ curl '{curl,www}.haxx.se'
+
+ To be able to use those letters as actual parts of the URL (without using
+ them for the curl URL "globbing" system), use the -g/--globoff option:
+
+ curl -g 'www.site.com/weirdname[].html'
+
+ 4.4 Why do I get downloaded data even though the web page doesn't exist?
+
+ Curl asks remote servers for the page you specify. If the page doesn't exist
+ at the server, the HTTP protocol defines how the server should respond and
+ that means that headers and a "page" will be returned. That's simply how
+ HTTP works.
+
+ By using the --fail option you can tell curl explicitly to not get any data
+ if the HTTP return code doesn't say success.
+
+ 4.5 Why do I get return code XXX from a HTTP server?
+
+ RFC2616 clearly explains the return codes. This is a short transcript. Go
+ read the RFC for exact details:
+
+ 4.5.1 "400 Bad Request"
+
+ The request could not be understood by the server due to malformed
+ syntax. The client SHOULD NOT repeat the request without modifications.
+
+ 4.5.2 "401 Unauthorized"
+
+ The request requires user authentication.
+
+ 4.5.3 "403 Forbidden"
+
+ The server understood the request, but is refusing to fulfill it.
+ Authorization will not help and the request SHOULD NOT be repeated.
+
+ 4.5.4 "404 Not Found"
+
+ The server has not found anything matching the Request-URI. No indication
+ is given of whether the condition is temporary or permanent.
+
+ 4.5.5 "405 Method Not Allowed"
+
+ The method specified in the Request-Line is not allowed for the resource
+ identified by the Request-URI. The response MUST include an Allow header
+ containing a list of valid methods for the requested resource.
+
+ 4.5.6 "301 Moved Permanently"
+
+ If you get this return code and an HTML output similar to this:
+
+ <H1>Moved Permanently</H1> The document has moved <A
+ HREF="http://same_url_now_with_a_trailing_slash/">here</A>.
+
+ it might be because you request a directory URL but without the trailing
+ slash. Try the same operation again _with_ the trailing URL, or use the
+ -L/--location option to follow the redirection.
+
+ 4.6 Can you tell me what error code 142 means?
+
+ All curl error codes are described at the end of the man page, in the
+ section called "EXIT CODES".
+
+ Error codes that are larger than the highest documented error code means
+ that curl has exited due to a crash. This is a serious error, and we
+ appreciate a detailed bug report from you that describes how we could go
+ ahead and repeat this!
+
+ 4.7 How do I keep user names and passwords secret in Curl command lines?
+
+ This problem has two sides:
+
+ The first part is to avoid having clear-text passwords in the command line
+ so that they don't appear in 'ps' outputs and similar. That is easily
+ avoided by using the "-K" option to tell curl to read parameters from a file
+ or stdin to which you can pass the secret info. curl itself will also
+ attempt to "hide" the given password by blanking out the option - this
+ doesn't work on all platforms.
+
+ To keep the passwords in your account secret from the rest of the world is
+ not a task that curl addresses. You could of course encrypt them somehow to
+ at least hide them from being read by human eyes, but that is not what
+ anyone would call security.
+
+ Also note that regular HTTP (using Basic authentication) and FTP passwords
+ are sent in clear across the network. All it takes for anyone to fetch them
+ is to listen on the network. Eavesdropping is very easy. Use more secure
+ authentication methods (like Digest, Negotiate or even NTLM) or consider the
+ SSL-based alternatives HTTPS and FTPS.
+
+ 4.8 I found a bug!
+
+ It is not a bug if the behavior is documented. Read the docs first.
+ Especially check out the KNOWN_BUGS file, it may be a documented bug!
+
+ If it is a problem with a binary you've downloaded or a package for your
+ particular platform, try contacting the person who built the package/archive
+ you have.
+
+ If there is a bug, read the BUGS document first. Then report it as described
+ in there.
+
+ 4.9 Curl can't authenticate to the server that requires NTLM?
+
+ NTLM support requires OpenSSL, GnuTLS, NSS or Microsoft Windows libraries at
+ build-time to provide this functionality.
+
+ NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You
+ should not use such ones.
+
+ 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work!
+
+ Many web servers allow or demand that the administrator configures the
+ server properly for these requests to work on the web server.
+
+ Some servers seem to support HEAD only on certain kinds of URLs.
+
+ To fully grasp this, try the documentation for the particular server
+ software you're trying to interact with. This is not anything curl can do
+ anything about.
+
+ 4.11 Why does my HTTP range requests return the full document?
+
+ Because the range may not be supported by the server, or the server may
+ choose to ignore it and return the full document anyway.
+
+ 4.12 Why do I get "certificate verify failed" ?
+
+ You invoke curl 7.10 or later to communicate on a https:// URL and get an
+ error back looking something similar to this:
+
+ curl: (35) SSL: error:14090086:SSL routines:
+ SSL3_GET_SERVER_CERTIFICATE:certificate verify failed
+
+ Then it means that curl couldn't verify that the server's certificate was
+ good. Curl verifies the certificate using the CA cert bundle that comes with
+ the curl installation.
+
+ To disable the verification (which makes it act like curl did before 7.10),
+ use -k. This does however enable man-in-the-middle attacks.
+
+ If you get this failure but are having a CA cert bundle installed and used,
+ the server's certificate is not signed by one of the CA's in the bundle. It
+ might for example be self-signed. You then correct this problem by obtaining
+ a valid CA cert for the server. Or again, decrease the security by disabling
+ this check.
+
+ Details are also in the SSLCERTS file in the release archives, found online
+ here: http://curl.haxx.se/docs/sslcerts.html
+
+ 4.13 Why is curl -R on Windows one hour off?
+
+ During daylight savings time, when -R is used, curl will set a time that
+ appears one hour off. This happens due to a flaw in how Windows stores and
+ uses file modification times and it is not easily worked around. For details
+ on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp
+
+ 4.14 Redirects work in browser but not with curl!
+
+ curl supports HTTP redirects fine (see item 3.8). Browsers generally support
+ at least two other ways to perform directs that curl does not:
+
+ - Meta tags. You can write a HTML tag that will cause the browser to
+ redirect to another given URL after a certain time.
+
+ - Javascript. You can write a Javascript program embedded in a HTML page
+ that redirects the browser to another given URL.
+
+ There is no way to make curl follow these redirects. You must either
+ manually figure out what the page is set to do, or you write a script that
+ parses the results and fetches the new URL.
+
+ 4.15 FTPS doesn't work
+
+ curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit
+ mode.
+
+ When a URL is used that starts with FTPS://, curl assumes implicit SSL on
+ the control connection and will therefore immediately connect and try to
+ speak SSL. FTPS:// connections default to port 990.
+
+ To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one
+ of its related flavours). This is the most common method, and the one
+ mandated by RFC4217. This kind of connection then of course uses the
+ standard FTP port 21 by default.
+
+ 4.16 My HTTP POST or PUT requests are slow!
+
+ libcurl makes all POST and PUT requests (except for POST requests with a
+ very tiny request body) use the "Expect: 100-continue" header. This header
+ allows the server to deny the operation early so that libcurl can bail out
+ already before having to send any data. This is useful in authentication
+ cases and others.
+
+ However, many servers don't implement the Expect: stuff properly and if the
+ server doesn't respond (positively) within 1 second libcurl will continue
+ and send off the data anyway.
+
+ You can disable libcurl's use of the Expect: header the same way you disable
+ any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0.
+
+ 4.17 Non-functional connect timeouts
+
+ In most Windows setups having a timeout longer than 21 seconds make no
+ difference, as it will only send 3 TCP SYN packets and no more. The second
+ packet sent three seconds after the first and the third six seconds after
+ the second. No more than three packets are sent, no matter how long the
+ timeout is set.
+
+ See option TcpMaxConnectRetransmissions on this page:
+ http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7
+
+ Also, even on non-Windows systems there may run a firewall or anti-virus
+ software or similar that accepts the connection but does not actually do
+ anything else. This will make (lib)curl to consider the connection connected
+ and thus the connect timeout won't trigger.
+
+ 4.18 file:// URLs containing drive letters (Windows, NetWare)
+
+ When using cURL to try to download a local file, one might use a URL
+ in this format:
+
+ file://D:/blah.txt
+
+ You'll find that even if D:\blah.txt does exist, cURL returns a 'file
+ not found' error.
+
+ According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html),
+ file:// URLs must contain a host component, but it is ignored by
+ most implementations. In the above example, 'D:' is treated as the
+ host component, and is taken away. Thus, cURL tries to open '/blah.txt'.
+ If your system is installed to drive C:, that will resolve to 'C:\blah.txt',
+ and if that doesn't exist you will get the not found error.
+
+ To fix this problem, use file:// URLs with *three* leading slashes:
+
+ file:///D:/blah.txt
+
+ Alternatively, if it makes more sense, specify 'localhost' as the host
+ component:
+
+ file://localhost/D:/blah.txt
+
+ In either case, cURL should now be looking for the correct file.
+
+ 4.19 Why doesn't cURL return an error when the network cable is unplugged?
+
+ Unplugging the cable is not an error situation. The TCP/IP protocol stack
+ was designed to be fault tolerant, so even though there may be a physical
+ break somewhere the connection shouldn't be affected, just possibly
+ delayed. Eventually, the physical break will be fixed or the data will be
+ re-routed around the physical problem.
+
+ In such cases, the TCP/IP stack is responsible for detecting when the
+ network connection is irrevocably lost. Since with some protocols it is
+ perfectly legal for the client wait indefinitely for data, the stack may
+ never report a problem, and even when it does, it can take up to 20 minutes
+ for it to detect an issue. The curl option --keepalive-time enables
+ keep-alive support in the TCP/IP stack which makes it periodically probe the
+ connection to make sure it is still available to send data. That should
+ reliably detect any TCP/IP network failure.
+
+ But even that won't detect the network going down before the TCP/IP
+ connection is established (e.g. during a DNS lookup) or using protocols that
+ don't use TCP. To handle those situations, curl offers a number of timeouts
+ on its own. --speed-limit/--speed-time will abort if the data transfer rate
+ falls too low, and --connect-timeout and --max-time can be used to put an
+ overall timeout on the connection phase or the entire transfer.
+
+
+5. libcurl Issues
+
+ 5.1 Is libcurl thread-safe?
+
+ Yes.
+
+ We have written the libcurl code specifically adjusted for multi-threaded
+ programs. libcurl will use thread-safe functions instead of non-safe ones if
+ your system has such.
+
+ If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
+ need to provide one or two locking functions:
+
+ http://www.openssl.org/docs/crypto/threads.html
+
+ If you use a GnuTLS-powered libcurl in a multi-threaded environment, you
+ need to provide locking function(s) for libgcrypt (which is used by GnuTLS
+ for the crypto functions).
+
+ http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html
+
+ No special locking is needed with a NSS-powered libcurl. NSS is thread-safe.
+
+ 5.2 How can I receive all data into a large memory chunk?
+
+ [ See also the examples/getinmemory.c source ]
+
+ You are in full control of the callback function that gets called every time
+ there is data received from the remote server. You can make that callback do
+ whatever you want. You do not have to write the received data to a file.
+
+ One solution to this problem could be to have a pointer to a struct that you
+ pass to the callback function. You set the pointer using the
+ CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback
+ instead of a FILE * to a file:
+
+ /* imaginary struct */
+ struct MemoryStruct {
+ char *memory;
+ size_t size;
+ };
+
+ /* imaginary callback function */
+ size_t
+ WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data)
+ {
+ size_t realsize = size * nmemb;
+ struct MemoryStruct *mem = (struct MemoryStruct *)data;
+
+ mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
+ if (mem->memory) {
+ memcpy(&(mem->memory[mem->size]), ptr, realsize);
+ mem->size += realsize;
+ mem->memory[mem->size] = 0;
+ }
+ return realsize;
+ }
+
+ 5.3 How do I fetch multiple files with libcurl?
+
+ libcurl has excellent support for transferring multiple files. You should
+ just repeatedly set new URLs with curl_easy_setopt() and then transfer it
+ with curl_easy_perform(). The handle you get from curl_easy_init() is not
+ only reusable, but you're even encouraged to reuse it if you can, as that
+ will enable libcurl to use persistent connections.
+
+ 5.4 Does libcurl do Winsock initialization on win32 systems?
+
+ Yes, if told to in the curl_global_init() call.
+
+ 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ?
+
+ Yes, but you cannot open a FILE * and pass the pointer to a DLL and have
+ that DLL use the FILE * (as the DLL and the client application cannot access
+ each others' variable memory areas). If you set CURLOPT_WRITEDATA you must
+ also use CURLOPT_WRITEFUNCTION as well to set a function that writes the
+ file, even if that simply writes the data to the specified FILE *.
+ Similarly, if you use CURLOPT_READDATA you must also specify
+ CURLOPT_READFUNCTION.
+
+ 5.6 What about Keep-Alive or persistent connections?
+
+ curl and libcurl have excellent support for persistent connections when
+ transferring several files from the same server. Curl will attempt to reuse
+ connections for all URLs specified on the same command line/config file, and
+ libcurl will reuse connections for all transfers that are made using the
+ same libcurl handle.
+
+ 5.7 Link errors when building libcurl on Windows!
+
+ You need to make sure that your project, and all the libraries (both static
+ and dynamic) that it links against, are compiled/linked against the same run
+ time library.
+
+ This is determined by the /MD, /ML, /MT (and their corresponding /M?d)
+ options to the command line compiler. /MD (linking against MSVCRT dll) seems
+ to be the most commonly used option.
+
+ When building an application that uses the static libcurl library, you must
+ add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for
+ dynamic import symbols. If you're using Visual Studio, you need to instead
+ add CURL_STATICLIB in the "Preprocessor Definitions" section.
+
+ If you get linker error like "unknown symbol __imp__curl_easy_init ..." you
+ have linked against the wrong (static) library. If you want to use the
+ libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of
+ the import libraries below. These are the libraries produced by the various
+ lib/Makefile.* files:
+
+ Target: static lib. import lib for libcurl*.dll.
+ -----------------------------------------------------------
+ MingW: libcurl.a libcurldll.a
+ MSVC (release): libcurl.lib libcurl_imp.lib
+ MSVC (debug): libcurld.lib libcurld_imp.lib
+ Borland: libcurl.lib libcurl_imp.lib
+
+
+ 5.8 libcurl.so.X: open failed: No such file or directory
+
+ This is an error message you might get when you try to run a program linked
+ with a shared version of libcurl and your run-time linker (ld.so) couldn't
+ find the shared library named libcurl.so.X. (Where X is the number of the
+ current libcurl ABI, typically 3 or 4).
+
+ You need to make sure that ld.so finds libcurl.so.X. You can do that
+ multiple ways, and it differs somewhat between different operating systems,
+ but they are usually:
+
+ * Add an option to the linker command line that specify the hard-coded path
+ the run-time linker should check for the lib (usually -R)
+
+ * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so
+ should check for libs
+
+ * Adjust the system's config to check for libs in the directory where you've
+ put the dir (like Linux's /etc/ld.so.conf)
+
+ 'man ld.so' and 'man ld' will tell you more details
+
+ 5.9 How does libcurl resolve host names?
+
+ libcurl supports a large a number of different name resolve functions. One
+ of them is picked at build-time and will be used unconditionally. Thus, if
+ you want to change name resolver function you must rebuild libcurl and tell
+ it to use a different function.
+
+ - The non-ipv6 resolver that can use one out of four host name resolve calls
+ (depending on what your system supports):
+
+ A - gethostbyname()
+ B - gethostbyname_r() with 3 arguments
+ C - gethostbyname_r() with 5 arguments
+ D - gethostbyname_r() with 6 arguments
+
+ - The ipv6-resolver that uses getaddrinfo()
+
+ - The c-ares based name resolver that uses the c-ares library for resolves.
+ Using this offers asynchronous name resolves but it currently has no IPv6
+ support.
+
+ - The threaded resolver (default option on Windows). It uses:
+
+ A - gethostbyname() on plain ipv4 hosts
+ B - getaddrinfo() on ipv6-enabled hosts
+
+ Also note that libcurl never resolves or reverse-lookups addresses given as
+ pure numbers, such as 127.0.0.1 or ::1.
+
+ 5.10 How do I prevent libcurl from writing the response to stdout?
+
+ libcurl provides a default built-in write function that writes received data
+ to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly
+ set CURLOPT_WRITEDATA to a different FILE * handle.
+
+ 5.11 How do I make libcurl not receive the whole HTTP response?
+
+ You make the write callback (or progress callback) return an error and
+ libcurl will then abort the transfer.
+
+ 5.12 Can I make libcurl fake or hide my real IP address?
+
+ No. libcurl operates on a higher level than so. Besides, faking IP address
+ would imply sending IP packages with a made-up source address, and then you
+ normally get a problem with intercepting the packages sent back as they
+ would then not be routed to you!
+
+ If you use a proxy to access remote sites, the sites will not see your local
+ IP address but instead the address of the proxy.
+
+ Also note that on many networks NATs or other IP-munging techniques are used
+ that makes you see and use a different IP address locally than what the
+ remote server will see you coming from.
+
+ 5.13 How do I stop an ongoing transfer?
+
+ There are several ways, but none of them are instant. There is no function
+ you can call from another thread or similar that will stop it immediately.
+ Instead you need to make sure that one of the callbacks you use return an
+ appropriate value that will stop the transfer.
+
+ Suitable callbacks that you can do this with include the progress callback,
+ the read callback and the write callback.
+
+ If you're using the multi interface, you also stop a transfer by removing
+ the particular easy handle from the multi stack.
+
+ 5.14 Using C++ non-static functions for callbacks?
+
+ libcurl is a C library, it doesn't know anything about C++ member functions.
+
+ You can overcome this "limitation" with a relative ease using a static
+ member function that is passed a pointer to the class:
+
+ // f is the pointer to your object.
+ static YourClass::staticFunction(void *buffer, size_t sz, size_t n, void *f)
+ {
+ // Call non-static member function.
+ static_cast<YourClass*>(f)->nonStaticFunction();
+ }
+
+ // This is how you pass pointer to the static function:
+ curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:staticFunction);
+ curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
+
+ 5.15 How do I get an FTP directory listing?
+
+ If you end the FTP URL you request with a slash, libcurl will provide you
+ with a directory listing of that given directory. You can also set
+ CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use
+ to list the files.
+
+ The follow-up question that tend to follow the previous one, is how a
+ program is supposed to parse the directory listing. How does it know what's
+ a file and what's a dir and what's a symlink etc. The harsh reality is that
+ FTP provides no such fine and easy-to-parse output. The output format FTP
+ servers respond to LIST commands are entirely at the server's own liking and
+ the NLST output doesn't reveal any types and in many cases don't even
+ include all the directory entries. Also, both LIST and NLST tend to hide
+ unix-style hidden files (those that start with a dot) by default so you need
+ to do "LIST -a" or similar to see them.
+
+ The application thus needs to parse the LIST output. One such existing
+ list parser is available at http://cr.yp.to/ftpparse.html Versions of
+ libcurl since 7.21.0 also provide the ability to specify a wildcard to
+ download multiple files from one FTP directory.
+
+
+6. License Issues
+
+ Curl and libcurl are released under a MIT/X derivate license. The license is
+ very liberal and should not impose a problem for your project. This section
+ is just a brief summary for the cases we get the most questions. (Parts of
+ this section was much enhanced by Bjorn Reese.)
+
+ We are not lawyers and this is not legal advice. You should probably consult
+ one if you want true and accurate legal insights without our prejudice.
+
+ 6.1 I have a GPL program, can I use the libcurl library?
+
+ Yes!
+
+ Since libcurl may be distributed under the MIT/X derivate license, it can be
+ used together with GPL in any software.
+
+ 6.2 I have a closed-source program, can I use the libcurl library?
+
+ Yes!
+
+ libcurl does not put any restrictions on the program that uses the library.
+
+ 6.3 I have a BSD licensed program, can I use the libcurl library?
+
+ Yes!
+
+ libcurl does not put any restrictions on the program that uses the library.
+
+ 6.4 I have a program that uses LGPL libraries, can I use libcurl?
+
+ Yes!
+
+ The LGPL license doesn't clash with other licenses.
+
+ 6.5 Can I modify curl/libcurl for my program and keep the changes secret?
+
+ Yes!
+
+ The MIT/X derivate license practically allows you to do almost anything with
+ the sources, on the condition that the copyright texts in the sources are
+ left intact.
+
+ 6.6 Can you please change the curl/libcurl license to XXXX?
+
+ No.
+
+ We have carefully picked this license after years of development and
+ discussions and a large amount of people have contributed with source code
+ knowing that this is the license we use. This license puts the restrictions
+ we want on curl/libcurl and it does not spread to other programs or
+ libraries that use it. It should be possible for everyone to use libcurl or
+ curl in their projects, no matter what license they already have in use.
+
+ 6.7 What are my obligations when using libcurl in my commercial apps?
+
+ Next to none. All you need to adhere to is the MIT-style license (stated in
+ the COPYING file) which basically says you have to include the copyright
+ notice in "all copies" and that you may not use the copyright holder's name
+ when promoting your software.
+
+ You do not have to release any of your source code.
+
+ You do not have to reveal or make public any changes to the libcurl source
+ code.
+
+ You do not have to reveal or make public that you are using libcurl within
+ your app.
+
+ As can be seen here: http://curl.haxx.se/docs/companies.html and
+ elsewhere, more and more companies are discovering the power
+ of libcurl and take advantage of it even in commercial environments.
+
+
+7. PHP/CURL Issues
+
+ 7.1 What is PHP/CURL?
+
+ The module for PHP that makes it possible for PHP programs to access curl-
+ functions from within PHP.
+
+ In the cURL project we call this module PHP/CURL to differentiate it from
+ curl the command line tool and libcurl the library. The PHP team however
+ does not refer to it like this (for unknown reasons). They call it plain
+ CURL (often using all caps) or sometimes ext/curl, but both cause much
+ confusion to users which in turn gives us a higher question load.
+
+ 7.2 Who write PHP/CURL?
+
+ PHP/CURL is a module that comes with the regular PHP package. It depends and
+ uses libcurl, so you need to have libcurl installed properly first before
+ PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes.
+
+ 7.3 Can I perform multiple requests using the same handle?
+
+ Yes - at least in PHP version 4.3.8 and later (this has been known to not
+ work in earlier versions, but the exact version when it started to work is
+ unknown to me).
+
+ After a transfer, you just set new options in the handle and make another
+ transfer. This will make libcurl to re-use the same connection if it can.