Added:

Updated: August 26, 2005 (http://curl.haxx.se/docs/faq.html)

zUpdated: November 2, 2005 (http://curl.haxx.se/docs/faq.html)

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  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?

 2. Install Related Problems

  2.1 configure doesn't find OpenSSL even when it is installed

  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 commerical apps?

 7. PHP/CURL Issues

  7.1 What is PHP/CURL?

  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

  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 the more than 400 contributors is found in the docs/THANKS

  The full list of the more than 450 contributors is found in the docs/THANKS

  file.

  curl is developed by a community, with Daniel at the wheel.

  flaw is announced to the world, thus lessen the impact the problem will have

  on existing users.

  1.9 Where do I buy commercial support for curl?

  curl is fully open source. It means you can hire any skilled engineer to fix

  your curl-related problems.

  We list available alternatives on the curl web site:

  http://curl.haxx.se/support.html

  1.10 How many are using curl?

  It is impossible to tell.

  We don't know how many users that knowingly have installed and use curl.

  We don't know how many users that use curl without knowing that they are in

  fact using it.

  We don't know how many users that downloaded or installed curl and then

  never use it.

  Some facts to use as input to the math:

  curl packages have been downloaded from the curl.haxx.se site well over a

  million times. curl is installed by default with most Linux

  distributions. curl is installed by default with Mac OS X. curl and libcurl

  as used by numerous applications that include libcurl binaries in their

  distribution packages (like Adobe Acrobat Reader and Google Earth).

  More than 40 known named companies use curl in commercial environments and

  products. More than 100 known named open source projects depend on

  (lib)curl.

  In a poll on the curl web site mid-2005, more than 50% of the 300+ answers

  estimated a user base of one million users or more.

  In March 2005, the "Linux Counter project" estimated a total Linux user base

  of some 29 millions, while Netcraft detected some 4 million "active" Linux

  based web servers. A guess is that a fair amount of these Linux

  installations have curl installed.

  http://curl.haxx.se/docs/companies.html

  http://curl.haxx.se/docs/programs.html

  http://curl.haxx.se/libcurl/using/apps.html

  http://counter.li.org/estimates.php

  http://news.netcraft.com/archives/2005/03/14/fedora_makes_rapid_progress.html

2. Install Related Problems

  - 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. 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.

    it.

  - Certificate Authority certificate ("CA cert"). You often have several CA

    certs in a CA cert bundle that can be used to verify a server certificate

    that was signed by one of the authorities in the bundle. curl comes with a

    default CA cert bundle. You can override the default.

    The server certificate verification process is made by using a Certificate

    Authority certificate ("CA cert") that was used to sign the server

    certificate. Server certificate verification is enabled by default in curl

    and libcurl and is often the reason for problems as explained in FAQ entry

    4.12 and the SSLCERTS document

    (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are

    "self-signed" or otherwise signed by a CA that you do not have a CA cert

    for, cannot be verified. If the verification during a connect fails, you

    are refused access. You then need to explicitly disable the verification

    to connect to the server.

  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

  No.

  But you could easily write your own program using libcurl to do such stunts.

4. Running Problems

  curl supports HTTP redirects fine (see item 3.8). Browsers generally support

  at least two other ways to perform directs that curl does not:

    1 - Meta tags. You can write a HTML tag that will cause the browser to

  - Meta tags. You can write a HTML tag that will cause the browser to

    redirect to another given URL after a certain time.

    2 - Javascript. You can write a javascript program embeded in a HTML page

  - Javascript. You can write a javascript program embeded 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

  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:

  CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback

  instead of a FILE * to a file:

        /* imaginary struct */

        struct MemoryStruct {

  5.9 How does libcurl resolve host names?

  libcurl includes a number of different name resolve functions:

  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):

  - The ipv6-resolver that uses getaddrinfo()

  - The c-ares based name resolver that uses the c-ares library for resolves.

    Using this offers asynchronous name resolves but it currently has no IPv6

    support.

  - The Windows threaded resolver. It use:

  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 a WRITEFUNCTION to receive the data, or possibly set

  WRITEDATA to a different FILE * handle.

  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?

  is just a brief summary for the cases we get the most questions. (Parts of

  this section was much enhanced by Bjorn Reese.)

  We are not lawyers and this is not legal advice. You should probably consult

  one if you want true and accurate legal insights without our prejudice.

  6.1 I have a GPL program, can I use the libcurl library?

  Yes!

  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 commerical apps?

  Next to none. All you need to adhere to is the MIT-style license (stated in

  the COPYING file) which basically says you have to include the copyright

  notice in "all copies" and that you may not use the copyright holder's name

  when promoting your software.

  You do not have to release any of your source code.

  You do not have to reveal or make public any changes to the libcurl source

  code.

  You do not have to reveal or make public that you are using libcurl within

  your app.

  As can be seen here: http://curl.haxx.se/docs/companies.html and

  elsewhere, more and more companies are dicovering the power

  of libcurl and take advantage of it even in commercial environments.

7. PHP/CURL Issues

  7.1 What is PHP/CURL?