-Updated: Oct 22, 2009 (http://curl.haxx.se/docs/faq.html)
_ _ ____ _
___| | | | _ \| |
/ __| | | | |_) | |
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
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?
+ 3.5 How can I disable the Accept: */* 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?
3.16 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?
+ 3.20 How to SFTP from my user's home directory?
+ 3.21 Protocol xxx not supported or disabled in libcurl
+ 3.22 curl -X gives me HTTP problems
4. Running Problems
4.1 Problems connecting to SSL servers.
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?
+ 4.20 curl doesn't return error for HTTP non-200 responses!
5. libcurl Issues
5.1 Is libcurl thread-safe?
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.3: open failed: No such file or directory
+ 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?
+ 5.15 How do I get an FTP directory listing?
+ 5.16 I want a different time-out!
+ 5.17 Can I write a server with libcurl?
+ 5.18 Does libcurl use threads?
6. License Issues
6.1 I have a GPL program, can I use the libcurl library?
7. PHP/CURL Issues
7.1 What is PHP/CURL?
- 7.2 Who write PHP/CURL?
+ 7.2 Who wrote PHP/CURL?
7.3 Can I perform multiple requests using the same handle?
==============================================================================
libcurl
- A free and easy-to-use client-side URL transfer library, supporting FTP,
- FTPS, HTTP, HTTPS, SCP, SFTP, TFTP, TELNET, DICT, FILE, LDAP and LDAPS.
+ 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, SMB, SMBS, SMTP, SMTPS, TELNET and TFTP.
+
libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading,
- kerberos, HTTP form based upload, proxies, cookies, user+password
+ Kerberos, SPNEGO, 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 and more...
+ platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HP-UX,
+ 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.
A command line tool for getting or sending files using URL syntax.
- Since curl uses libcurl, it supports a range of common Internet protocols,
- currently including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, LDAP, LDAPS,
- DICT, TELNET and FILE.
+ Since curl uses libcurl, curl supports the same wide range of common
+ Internet protocols that libcurl does.
+
+ We pronounce curl with an initial k sound. It rhymes with words like girl
+ and earl. This is a short WAV file to help you:
- We pronounce curl and cURL with an initial k sound: [kurl].
+ http://media.merriam-webster.com/soundc11/c/curl0001.wav
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
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.
+ 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 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.
+ 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 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.
+ If you write the code, chances are bigger that it will get into curl faster.
1.5 Who makes curl?
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.
+ curl on full time. We do this voluntarily, mostly on 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, CVS server 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.
+ lists etc, sourceforge.net hosts project services we take advantage from,
+ like the bug tracker and github hosts the primary git repository. 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.
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.
+ rights to the name.
We recognize that we will be living in parallel with curl.com and wish them
every success.
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 90 known named companies use curl in commercial environments and
- products. More than 100 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.
+ In May 2012 Daniel did a counting game and came up with a number that may
+ be completely wrong or somewhat accurate. Over 500 million!
- 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
+ See http://daniel.haxx.se/blog/2012/05/16/300m-users/
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.
+ The ca cert bundle that used to shipped with curl was very outdated and must
+ be replaced with an up-to-date version by anyone who wants to verify
+ peers. It is no longer provided by curl. The last curl release ever that
+ shipped a ca cert bundle 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
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
2.2 Does curl work/build with other SSL libraries?
- Curl has been written to use OpenSSL, GnuTLS, yassl or NSS, 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!
+ Curl has been written to use a generic SSL function layer internally, and
+ that SSL functionality can then be provided by one out of many different SSL
+ backends.
+
+ curl can be built to use one of the following SSL alternatives: OpenSSL,
+ GnuTLS, yassl, NSS, PolarSSL, axTLS, Secure Transport (native iOS/OS X),
+ WinSSL (native Windows) or GSKit (native IBM i). They all have their pros
+ and cons, and we try to maintain a comparison of them here:
+ http://curl.haxx.se/docs/ssl-compared.html
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.
+ Curl can be built with OpenSSL to do the SSL stuff. The LIBEAY32.DLL is then
+ what curl needs on a windows machine to do https:// etc. 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) ?
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.
+ it means that the instance of curl/libcurl that you're using was built
+ without support for this protocol.
+
+ This could've happened if the configure script that was run at build time
+ couldn't find all libs and include files curl 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 labeled "configure doesn't
+ 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
+ receive your post expects one of the formats. If the form you're trying to
+ submit uses the type '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
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.
+ Since curl is used for file transfers, you don't normally use curl to
+ perform FTP commands without transferring anything. Therefore you must
+ always specify a URL to transfer to/from even when doing custom FTP
+ commands, or use -I which implies the "no body" option sent to libcurl.
- 3.5 How can I disable the Pragma: nocache header?
+ 3.5 How can I disable the Accept: */* 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.
+ disable that one. Use -H "Accept:" 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.
+ 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.
install and use them, in the libcurl section of the curl web site:
http://curl.haxx.se/libcurl/
- In February 2007, there are interfaces available for the following
- languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Euphoria, Ferite,
- Gambas, glib/GTK+, Java, Lisp, Lua, Mono, .NET, Object-Pascal, O'Caml,
- Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby, Scheme, S-Lang,
- Smalltalk, SPL, Tcl, Visual Basic, Q, wxwidgets and XBLite. By the time you
- read this, additional ones may have appeared!
+ All the various bindings to libcurl are made by other projects and people,
+ outside of the cURL project. The cURL project itself only produces libcurl
+ with its plain C API. If you don't find anywhere else to ask you can ask
+ about bindings on the curl-library list too, but be prepared that people on
+ that list may not know anything about bindings.
+
+ 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?
the name of the proxy to connect to. Since curl doesn't support Javascript,
it can't support .pac proxy configuration either.
- Some work-arounds usually suggested to overcome this Javascript dependency:
+ 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.
+ 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.
+ 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.
+ 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.
+ Ask your admins to stop this, for a static proxy setup or similar.
3.15 Can I do recursive fetches with curl?
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.
-
- - 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 comes with a
- default CA cert bundle. You can 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.
+ 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?
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/
+
+ You can also opt to add faked host name entries to curl with the --resolve
+ option. That has the added benefit that things like redirects will also work
+ properly. The above operation would instead be done as:
+
+ curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/
+
+ 3.20 How to SFTP from my user's home directory?
+
+ Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to
+ work with. It means that if you don't specify that you want the user's home
+ directory, you get the actual root directory.
+
+ To specify a file in your user's home directory, you need to use the correct
+ URL syntax which for sftp might look similar to:
+
+ curl -O -u user:password sftp://example.com/~/file.txt
+
+ and for SCP it is just a different protocol prefix:
+
+ curl -O -u user:password scp://example.com/~/file.txt
+
+ 3.21 Protocol xxx not supported or disabled in libcurl
+
+ When passing on a URL to curl to use, it may respond that the particular
+ protocol is not supported or disabled. The particular way this error message
+ is phrased is because curl doesn't make a distinction internally of whether
+ a particular protocol is not supported (i.e. never got any code added that
+ knows how to speak that protocol) or if it was explicitly disabled. curl can
+ be built to only support a given set of protocols, and the rest would then
+ be disabled or not supported.
+
+ Note that this error will also occur if you pass a wrongly spelled protocol
+ part as in "htpt://example.com" or as in the less evident case if you prefix
+ the protocol part with a space as in " http://example.com/".
+
+ 3.22 curl -X gives me HTTP problems
+
+ In normal circumstances, -X should hardly ever be used.
+
+ By default you use curl without explicitly saying which request method to
+ use when the URL identifies a HTTP transfer. If you just pass in a URL like
+ "curl http://example.com" it will use GET. If you use -d or -F curl will use
+ POST, -I will cause a HEAD and -T will make it a PUT.
+
+ If for whatever reason you're not happy with these default choices that curl
+ does for you, you can override those request methods by specifying -X
+ [WHATEVER]. This way you can for example send a DELETE by doing "curl -X
+ DELETE [URL]".
+
+ It is thus pointless to do "curl -XGET [URL]" as GET would be used
+ anyway. In the same vein it is pointless to do "curl -X POST -d data
+ [URL]"... But you can make a fun and somewhat rare request that sends a
+ request-body in a GET request with something like "curl -X GET -d data
+ [URL]"
+
+ Note that -X doesn't change curl's behavior. It only modifies the actual
+ string sent in the request.
+
+ Accordingly, by using -XPOST on a command line that for example would follow
+ a 303 redirect, you will effectively prevent curl from behaving
+ correctly. Be aware.
+
4. Running Problems
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.
+ In Windows, the standard DOS shell treats the percent sign specially and you
+ need to use TWO percent signs 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).
+ If you want a literal percent sign 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
+ percent sign doubled on Windows machines).
4.3 How can I use {, }, [ or ] to specify multiple URLs?
4.5.3 "403 Forbidden"
- The server understood the request, but is refusing to fulfill it.
+ The server understood the request, but is refusing to fulfil it.
Authorization will not help and the request SHOULD NOT be repeated.
4.5.4 "404 Not Found"
4.9 Curl can't authenticate to the server that requires NTLM?
- This is supported in curl 7.10.6 or later. No earlier curl version knows
- of this magic. Later versions require the OpenSSL or Microsoft Windows
- libraries to provide this functionality. Using the NSS library will
- not provide NTLM authentication functionality in curl.
+ NTLM support requires OpenSSL, GnuTLS, NSS, Secure Transport, 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.
4.14 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:
+ at least two other ways to perform redirects 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.
+ 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.
+ 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
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 a 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 through another path.
+
+ 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.
+
+ A libcurl-using application running in a known physical environment (e.g.
+ an embedded device with only a single network connection) may want to act
+ immediately if its lone network connection goes down. That can be achieved
+ by having the application monitor the network connection on its own using an
+ OS-specific mechanism, then signalling libcurl to abort (see also item 5.13).
+
+ 4.20 curl doesn't return error for HTTP non-200 responses!
+
+ Correct. Unless you use -f (--fail).
+
+ When doing HTTP transfers, curl will perform exactly what you're asking it
+ to do and if successful it will not return an error. You can use curl to
+ test your web server's "file not found" page (that gets 404 back), you can
+ use it to check your authentication protected web pages (that get a 401
+ back) and so on.
+
+ The specific HTTP response code does not constitute a problem or error for
+ curl. It simply sends and delivers HTTP as you asked and if that worked,
+ everything is fine and dandy. The response code is generally providing more
+ higher level error information that curl doesn't care about. The error was
+ not in the HTTP transfer.
+
+ If you want your command line to treat error codes in the 400 and up range
+ as errors and thus return a non-zero value and possibly show an error
+ message, curl has a dedicated option for that: -f (CURLOPT_FAILONERROR in
+ libcurl speak).
+
+ You can also use the -w option and the variable %{response_code} to extract
+ the exact response code that was return in the response.
+
5. libcurl Issues
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.
+ your system has such. Note that you must never share the same handle in
+ multiple threads.
+
+ libcurl's implementation of timeouts might use signals (depending on what it
+ was built to use for name resolving), and signal handling is generally not
+ thread-safe. Multi-threaded Applicationss that call libcurl from different
+ threads (on different handles) might want to use CURLOPT_NOSIGNAL, e.g.:
+
+ curl_easy_setopt(handle, CURLOPT_NOSIGNAL, true);
If you use a OpenSSL-powered libcurl in a multi-threaded environment, you
need to provide one or two locking functions:
libcurl will reuse connections for all transfers that are made using the
same libcurl handle.
+ When you use the easy interface, the connection cache is kept within the
+ easy handle. If you instead use the multi interface, the connection cache
+ will be kept within the multi handle and will be shared among all the easy
+ handles that are used within the same multi handle.
+
5.7 Link errors when building libcurl on Windows!
You need to make sure that your project, and all the libraries (both static
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 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:
+ dynamic import symbols. If you're using Visual Studio, you need to instead
+ add CURL_STATICLIB in the "Preprocessor Definitions" section.
- 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
+ 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.3: open failed: No such file or directory
+ 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.3.
+ 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.3. You can do that
+ 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:
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
+ - 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
+ 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 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.
+ Using this offers asynchronous name resolves.
- - The Windows threaded resolver. It use:
+ - The threaded resolver (default option on Windows). It uses:
- A - gethostbyname() on plain ipv4 windows hosts
- B - getaddrinfo() on ipv6-enabled windows hosts
+ 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.
5.12 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!
+ No. libcurl operates on a higher level. Besides, faking IP address would
+ imply sending IP packet with a made-up source address, and then you normally
+ get a problem with receiving the packet 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.
+ remote server will see you coming from. You may also consider using
+ http://www.torproject.org .
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.
+ With the easy interface you make sure to return the correct error code from
+ one of the callbacks, 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 returns 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.
- 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.
+ If you're using the multi interface, you can also stop a transfer by
+ removing the particular easy handle from the multi stack at any moment you
+ think the transfer is done or when you wish to abort the transfer.
5.14 Using C++ non-static functions for callbacks?
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)
+ static YourClass::func(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_WRITEFUNCTION, YourClass:func);
curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this);
- 5.15 How do I get an FTP directory listing?
+ 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
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
+ 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.
+
+ 5.16 I want a different time-out!
+
+ Time and time again users realize that CURLOPT_TIMEOUT and
+ CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all
+ the various use cases and scenarios applications end up with.
+
+ libcurl offers many more ways to time-out operations. A common alternative
+ is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to
+ specify the lowest possible speed to accept before to consider the transfer
+ timed out.
+
+ The most flexible way is by writing your own time-out logic and using
+ CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and
+ use that to figure out exactly when the right condition is met when the
+ transfer should get stopped.
+
+ 5.17 Can I write a server with libcurl?
+ No. libcurl offers no functions or building blocks to build any kind of
+ internet protocol server. libcurl is only a client-side library. For server
+ libraries, you need to continue your search elsewhere but there exist many
+ good open source ones out there for most protocols you could possibly want a
+ server for. And there are really good stand-alone ones that have been tested
+ and proven for many years. There's no need for you to reinvent them!
+
+ 5.18 Does libcurl use threads?
+
+ Put simply: no, libcurl will execute in the same thread you call it in. All
+ callbacks will be called in the same thread as the one you call libcurl in.
+
+ If you want to avoid your thread to be blocked by the libcurl call, you make
+ sure you use the non-blocking API which will do transfers asynchronously -
+ but still in the same single thread.
+
+ libcurl will potentially internally use threads for name resolving, if it
+ was built to work like that, but in those cases it'll create the child
+ threads by itself and they will only be used and then killed internally by
+ libcurl and never exposed to the outside.
6. License Issues
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.
+ one if you want true and accurate legal insights without our prejudice. Note
+ especially that this section concerns the libcurl license only; compiling in
+ features of libcurl that depend on other libraries (e.g. OpenSSL) may affect
+ the licensing obligations of your application.
6.1 I have a GPL program, can I use the libcurl library?
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
+ You do not have to broadcast to the world 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.
+ All we ask is that you disclose "the copyright notice and this permission
+ notice" somewhere. Most probably like in the documentation or in the section
+ where other third party dependencies already are mentioned and acknowledged.
+
+ 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
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?
+ 7.2 Who wrote 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
projects / platform / upstream / curl.git / blobdiff