| Updated: August 10, 2004 (http://curl.haxx.se/docs/faq.html) |
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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? |
| |
| 2. Install Related Problems |
| 2.1 configure doesn't find OpenSSL even when it is installed |
| 2.1.1 native linker doesn't find OpenSSL |
| 2.1.2 only the libssl lib is missing |
| 2.2 Does curl work/build with other SSL libraries? |
| 2.3 Where can I find a copy of LIBEAY32.DLL? |
| 2.4 Does cURL support Socks (RFC 1928) ? |
| |
| 3. Usage Problems |
| 3.1 curl: (1) SSL is disabled, https: not supported |
| 3.2 How do I tell curl to resume a transfer? |
| 3.3 Why doesn't my posting using -F work? |
| 3.4 How do I tell curl to run custom FTP commands? |
| 3.5 How can I disable the Pragma: nocache header? |
| 3.6 Does curl support ASP, XML, XHTML or HTML version Y? |
| 3.7 Can I use curl to delete/rename a file through FTP? |
| 3.8 How do I tell curl to follow HTTP redirects? |
| 3.9 How do I use curl in my favorite programming language? |
| 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? |
| 3.11 How do I POST with a different Content-Type? |
| 3.12 Why do FTP specific features over HTTP proxy fail? |
| 3.13 Why does my single/double quotes fail? |
| 3.14 Does curl support javascript or pac (automated proxy config)? |
| 3.15 Can I do recursive fetches with curl? |
| |
| 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" ? |
| |
| 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.3: open failed: No such file or directory |
| |
| 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? |
| |
| ============================================================================== |
| |
| 1. Philosophy |
| |
| 1.1 What is cURL? |
| |
| cURL (or simply just 'curl') is a command line tool for getting or sending |
| files using URL syntax. 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 |
| abbrivation for "Client URL Request Library" or why not the recursive |
| version: "Curl URL Request Library". |
| |
| Curl supports a range of common Internet protocols, currently including |
| HTTP, HTTPS, FTP, FTPS, GOPHER, LDAP, DICT, TELNET and FILE. |
| |
| We spell it cURL or just curl. We pronounce it with an initial k sound: |
| [kurl]. |
| |
| NOTE: 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. |
| |
| 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. |
| |
| 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. |
| |
| Curl is not a single-OS program. 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. Sure, Daniel |
| Stenberg writes the major parts, 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 list of contributors in the docs/THANKS file is only a small part of all |
| the people that every day provide us with bug reports, suggestions, ideas |
| and source code. |
| |
| 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 |
| curl. We do this voluntarily on our spare time. |
| |
| We get some help from companies. Contactor Data hosts the curl web site, |
| Haxx owns the curl web site's domain and sourceforge.net hosts project |
| services we take advantage from, like the bug tracker. |
| |
| If you want to support our project with a donation or similar, one way of |
| doing that would be to buy "gift certificates" at useful online shopping |
| sites, such as amazon.com or thinkgeek.com. Another way would be to sponsor |
| us through a banner-program or even better: by helping us coding, |
| documenting, testing etc. You're welcome to send us a buck using paypal, as |
| described here: http://curl.haxx.se/donation.html |
| |
| 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. |
| |
| |
| 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 |
| |
| Solution submitted by: Bob Allison <allisonb@users.sourceforge.net> |
| |
| 2.1.2 only the libssl lib is missing |
| |
| If all include files and the libcrypto lib is present, with only the |
| libssl being missing according to configure, this is mostly likely because |
| a few functions are left out from the libssl. |
| |
| If the function names missing include RSA or RSAREF you can be certain |
| that this is because libssl requires the RSA and RSAREF libs to build. |
| |
| See the INSTALL file section that explains how to add those libs to |
| configure. Make sure that you remove the config.cache file before you |
| rerun configure with the new flags. |
| |
| 2.2 Does curl work/build with other SSL libraries? |
| |
| Curl has been written to use OpenSSL, although there should not be much |
| problems using a different library. If anyone does "port" curl to use a |
| different SSL library, we are of course very interested in getting the |
| patch! |
| |
| 2.3 Where can I find a copy of LIBEAY32.DLL? |
| |
| That is an OpenSSL binary built for Windows. |
| |
| Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs |
| on a windows machine to do https://. Check out the curl web site to find |
| accurate and up-to-date pointers to recent OpenSSL DLLs and other binary |
| packages. |
| |
| 2.4 Does cURL support Socks (RFC 1928) ? |
| |
| Yes, SOCKS5 is supported. |
| |
| |
| 3. Usage problems |
| |
| 3.1 curl: (1) SSL is disabled, https: not supported |
| |
| If you get this output when trying to get anything from a https:// server, |
| it means that the configure script couldn't find all libs and include files |
| it requires for SSL to work. If the configure script fails to find them, |
| curl is simply built without SSL support. |
| |
| To get the https:// support into a curl that was previously built but that |
| reports that https:// is not supported, you should dig through the document |
| and logs and check out why the configure script doesn't find the SSL libs |
| and/or include files. |
| |
| Also, check out the other paragraph in this FAQ labeled "configure doesn't |
| find OpenSSL even when it is installed". |
| |
| 3.2 How do I tell curl to resume a transfer? |
| |
| Curl supports resumed transfers both ways on both FTP and HTTP. |
| |
| Try the -C option. |
| |
| 3.3 Why doesn't my posting using -F work? |
| |
| You can't simply use -F or -d at your choice. The web server that will |
| receive your post assumes one of the formats. If the form you're trying to |
| "fake" sets the type to 'multipart/form-data', then and only then you must |
| use the -F type. In all the most common cases, you should use -d which then |
| causes a posting with the type 'application/x-www-form-urlencoded'. |
| |
| This is described in some detail in the MANUAL and TheArtOfHttpScripting |
| documents, and if you don't understand it the first time, read it again |
| before you post questions about this to the mailing list. Also, try reading |
| through the mailing list archives for old postings and questions regarding |
| this. |
| |
| 3.4 How do I tell curl to run custom FTP commands? |
| |
| You can tell curl to perform optional commands both before and/or after a |
| file transfer. Study the -Q/--quote option. |
| |
| Since curl is used for file transfers, you don't use curl to just perform |
| FTP commands without transferring anything. Therefore you must always specify |
| a URL to transfer to/from even when doing custom FTP commands. |
| |
| 3.5 How can I disable the Pragma: nocache header? |
| |
| You can change all internally generated headers by adding a replacement with |
| the -H/--header option. By adding a header with empty contents you safely |
| disable that one. Use -H "Pragma:" to disable that specific header. |
| |
| 3.6 Does curl support ASP, XML, XHTML or HTML version Y? |
| |
| To curl, all contents are alike. It doesn't matter how the page was |
| generated. It may be ASP, PHP, Perl, shell-script, SSI or plain |
| HTML-files. There's no difference to curl and it doesn't even know what kind |
| of language that generated the page. |
| |
| See also item 3.14 regarding javascript. |
| |
| 3.7 Can I use curl to delete/rename a file through FTP? |
| |
| Yes. You specify custom FTP commands with -Q/--quote. |
| |
| One example would be to delete a file after you have downloaded it: |
| |
| curl -O ftp://download.com/coolfile -Q '-DELE coolfile' |
| |
| 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 |
| |
| 3.9 How do I use curl in my favorite programming language? |
| |
| There exist many language interfaces/bindings for curl that integrates it |
| better with various languages. If you are fluid in a script language, you |
| may very well opt to use such an interface instead of using the command line |
| tool. |
| |
| Find out more about which languages that support curl directly, and how to |
| install and use them, in the libcurl section of the curl web site: |
| |
| http://curl.haxx.se/libcurl/ |
| |
| In February 2003, there are interfaces available for the following |
| languages: Basic, C, C++, Cocoa, Dylan, Euphoria, Java, Lua, Object-Pascal, |
| Pascal, Perl, PHP, PostgreSQL, Python, Rexx, Ruby, Scheme and Tcl. 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 work-arounds 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. |
| |
| |
| 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 & letter is treated special 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. |
| |
| An example that would invoke a remote CGI that uses &-letters could be: |
| |
| curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl' |
| |
| In Windows, the standard DOS shell treats the %-letter specially and you |
| need to use TWO %-letters for each single one you want to use in the URL. |
| |
| Also note that if you want the literal %-letter 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 %-letter doubled on Windows machines). |
| |
| 4.3 How can I use {, }, [ or ] to specify multiple URLs? |
| |
| Because those letters have a special meaning to the shell, and to be used in |
| a URL specified to curl you must quote them. |
| |
| An example that downloads two URLs (sequentially) would do: |
| |
| curl '{curl,www}.haxx.se' |
| |
| To be able to use those letters as actual parts of the URL (without using |
| them for the curl URL "globbing" system), use the -g/--globoff option: |
| |
| curl -g 'www.site.com/weirdname[].html' |
| |
| 4.4 Why do I get downloaded data even though the web page doesn't exist? |
| |
| Curl asks remote servers for the page you specify. If the page doesn't exist |
| at the server, the HTTP protocol defines how the server should respond and |
| that means that headers and a "page" will be returned. That's simply how |
| HTTP works. |
| |
| By using the --fail option you can tell curl explicitly to not get any data |
| if the HTTP return code doesn't say success. |
| |
| 4.5 Why do I get return code XXX from a HTTP server? |
| |
| RFC2616 clearly explains the return codes. This is a short transcript. Go |
| read the RFC for exact details: |
| |
| 4.5.1 "400 Bad Request" |
| |
| The request could not be understood by the server due to malformed |
| syntax. The client SHOULD NOT repeat the request without modifications. |
| |
| 4.5.2 "401 Unauthorized" |
| |
| The request requires user authentication. |
| |
| 4.5.3 "403 Forbidden" |
| |
| The server understood the request, but is refusing to fulfill it. |
| Authorization will not help and the request SHOULD NOT be repeated. |
| |
| 4.5.4 "404 Not Found" |
| |
| The server has not found anything matching the Request-URI. No indication |
| is given of whether the condition is temporary or permanent. |
| |
| 4.5.5 "405 Method Not Allowed" |
| |
| The method specified in the Request-Line is not allowed for the resource |
| identified by the Request-URI. The response MUST include an Allow header |
| containing a list of valid methods for the requested resource. |
| |
| 4.5.6 "301 Moved Permanently" |
| |
| If you get this return code and an HTML output similar to this: |
| |
| <H1>Moved Permanently</H1> The document has moved <A |
| HREF="http://same_url_now_with_a_trailing_slash/">here</A>. |
| |
| it might be because you request a directory URL but without the trailing |
| slash. Try the same operation again _with_ the trailing URL, or use the |
| -L/--location option to follow the redirection. |
| |
| 4.6 Can you tell me what error code 142 means? |
| |
| All 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? |
| |
| This is supported in curl 7.10.6 or later. No earlier curl version knows |
| of this magic. |
| |
| 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 |
| |
| |
| 5. libcurl Issues |
| |
| 5.1 Is libcurl thread-safe? |
| |
| Yes. |
| |
| We have written the libcurl code specificly adjusted for multi-threaded |
| programs. libcurl will use thread-safe functions instead of non-safe ones if |
| your system has such. |
| |
| We would appreciate some kind of report or README file from those who have |
| used libcurl in a threaded environment. |
| |
| 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 |
| curl_easy_setopt(CURLOPT_FILE) function. 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. |
| |
| (Provided by Joel DeYoung and Bob Schader) |
| |
| 5.6 What about Keep-Alive or persistent connections? |
| |
| curl and libcurl have excellent support for persistent connections when |
| transferring several files from the same server. Curl will attempt to reuse |
| connections for all URLs specified on the same command line/config file, and |
| libcurl will reuse connections for all transfers that are made using the |
| same libcurl handle. |
| |
| 5.7 Link errors when building libcurl on Windows! |
| |
| You need to make sure that your project, and all the libraries (both static |
| and dynamic) that it links against, are compiled/linked against the same run |
| time library. |
| |
| This is determined by the /MD, /ML, /MT (and their corresponding /M?d) |
| options to the command line compiler. /MD (linking against MSVCRT dll) seems |
| to be the most commonly used option. |
| |
| (Provided by Andrew Francis) |
| |
| 5.8 libcurl.so.3: 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. |
| |
| You need to make sure that ld.so finds libcurl.so.3. 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 |
| |
| |
| 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.) |
| |
| 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. |