LICENSE-MIXING.md: switched to markdown

1 files changed, 124 insertions, 0 deletions

diff --git a/docs/LICENSE-MIXING.md b/docs/LICENSE-MIXING.md
new file mode 100644
index 000000000..0bff73e6d
--- /dev/null
+++ b/docs/LICENSE-MIXING.md
@@ -0,0 +1,124 @@
+License Mixing
+==============
+
+libcurl can be built to use a fair amount of various third party libraries,
+libraries that are written and provided by other parties that are distributed
+using their own licenses. Even libcurl itself contains code that may cause
+problems to some. This document attempts to describe what licenses libcurl and
+the other libraries use and what possible dilemmas linking and mixing them all
+can lead to for end users.
+
+I am not a lawyer and this is not legal advice!
+
+One common dilemma is that [GPL](https://www.gnu.org/licenses/gpl.html)
+licensed code is not allowed to be linked with code licensed under the
+[Original BSD license](https://spdx.org/licenses/BSD-4-Clause.html) (with the
+announcement clause). You may still build your own copies that use them all,
+but distributing them as binaries would be to violate the GPL license - unless
+you accompany your license with an
+[exception](https://www.gnu.org/licenses/gpl-faq.html#GPLIncompatibleLibs). This
+particular problem was addressed when the [Modified BSD
+license](https://opensource.org/licenses/BSD-3-Clause) was created, which does
+not have the announcement clause that collides with GPL.
+
+## libcurl
+
+ Uses an [MIT style license](https://curl.haxx.se/docs/copyright.html) that is
+ very liberal.
+
+## OpenSSL
+
+ (May be used for SSL/TLS support) Uses an Original BSD-style license with an
+ announcement clause that makes it "incompatible" with GPL. You are not
+ allowed to ship binaries that link with OpenSSL that includes GPL code
+ (unless that specific GPL code includes an exception for OpenSSL - a habit
+ that is growing more and more common). If OpenSSL's licensing is a problem
+ for you, consider using another TLS library.
+
+## GnuTLS
+
+ (May be used for SSL/TLS support) Uses the
+ [LGPL](https://www.gnu.org/licenses/lgpl.html) license. If this is a problem
+ for you, consider using another TLS library. Also note that GnuTLS itself
+ depends on and uses other libs (libgcrypt and libgpg-error) and they too are
+ LGPL- or GPL-licensed.
+
+## WolfSSL
+
+ (May be used for SSL/TLS support) Uses the GPL license or a propietary
+ license. If this is a problem for you, consider using another TLS library.
+
+## NSS
+
+ (May be used for SSL/TLS support) Is covered by the
+ [MPL](https://www.mozilla.org/MPL/) license, the GPL license and the LGPL
+ license. You may choose to license the code under MPL terms, GPL terms, or
+ LGPL terms. These licenses grant you different permissions and impose
+ different obligations. You should select the license that best meets your
+ needs.
+
+## axTLS
+
+ (May be used for SSL/TLS support) Uses a Modified BSD-style license.
+
+## mbedTLS
+
+ (May be used for SSL/TLS support) Uses the GPL license or a propietary
+ license. If this is a problem for you, consider using another TLS library.
+
+## BoringSSL
+
+ (May be used for SSL/TLS support) As an OpenSSL fork, it has the same
+ license as that.
+
+## libressl
+
+ (May be used for SSL/TLS support) As an OpenSSL fork, it has the same
+ license as that.
+
+## c-ares
+
+ (Used for asynchronous name resolves) Uses an MIT license that is very
+ liberal and imposes no restrictions on any other library or part you may link
+ with.
+
+## zlib
+
+ (Used for compressed Transfer-Encoding support) Uses an MIT-style license
+ that shouldn't collide with any other library.
+
+## MIT Kerberos
+
+ (May be used for GSS support) MIT licensed, that shouldn't collide with any
+ other parts.
+
+## Heimdal
+
+ (May be used for GSS support) Heimdal is Original BSD licensed with the
+ announcement clause.
+
+## GNU GSS
+
+ (May be used for GSS support) GNU GSS is GPL licensed. Note that you may not
+ distribute binary curl packages that uses this if you build curl to also link
+ and use any Original BSD licensed libraries!
+
+## libidn
+
+ (Used for IDNA support) Uses the GNU Lesser General Public License [3]. LGPL
+ is a variation of GPL with slightly less aggressive "copyleft". This license
+ requires more requirements to be met when distributing binaries, see the
+ license for details. Also note that if you distribute a binary that includes
+ this library, you must also include the full LGPL license text. Please
+ properly point out what parts of the distributed package that the license
+ addresses.
+
+## OpenLDAP
+
+ (Used for LDAP support) Uses a Modified BSD-style license. Since libcurl uses
+ OpenLDAP as a shared library only, I have not heard of anyone that ships
+ OpenLDAP linked with libcurl in an app.
+
+## libssh2
+
+ (Used for scp and sftp support) libssh2 uses a Modified BSD-style license.