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authorKirill Volinsky <mataes2007@gmail.com>2013-11-10 18:02:01 +0000
committerKirill Volinsky <mataes2007@gmail.com>2013-11-10 18:02:01 +0000
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- _ _ ____ _
- ___| | | | _ \| |
- / __| | | | |_) | |
- | (__| |_| | _ <| |___
- \___|\___/|_| \_\_____|
-
-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 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?
- 3.9 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?
- 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.
- 4.2 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?
- 5.16 I want a different time-out!
- 5.17 Can I write a server with libcurl?
-
- 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 wrote 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.
-
- In May 2012 Daniel did a counting game and came up with a number that may
- be completely wrong or somewhat accurate. 300 million!
-
- 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.
-
- 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 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),
- schannel (native Windows) or qssl (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.
-
- 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 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 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 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 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 "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.
-
- 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/
-
- 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?
-
- 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/
-
- 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 (ie 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
-
- 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 fulfil 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, 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.
-
- 4.10 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.
-
- 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
- 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.
-
- - 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?
-
- 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.
-
- 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?
-
- 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::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:func);
- 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.
-
- 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!
-
-
-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. 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?
-
- 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 broadcast to the world that you are using libcurl within
- your app.
-
- 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
-
- 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 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
- 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.