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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. |