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97 lines
4.3 KiB
Plaintext
97 lines
4.3 KiB
Plaintext
License Mixing with apps, libcurl and Third Party Libraries
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===========================================================
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libcurl can be built to use a fair amount of various third party libraries,
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libraries that are written and provided by other parties that are distributed
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using their own licenses. Even libcurl itself contains code that may cause
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problems to some. This document attempts to describe what licenses libcurl and
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the other libraries use and what possible dilemmas linking and mixing them all
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can lead to for end users.
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I am not a lawyer and this is not legal advice!
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One common dilemma is that GPL[1]-licensed code is not allowed to be linked
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with code licensed under the Original BSD license (with the announcement
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clause, unless there's a specified exception in the GPL-licensed module). You
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may still build your own copies that use them all, but distributing them as
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binaries would be to violate the GPL license - unless you accompany your
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license with an exception[2]. This particular problem was addressed when the
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Modified BSD license was created, which does not have the annoncement clause
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that collides with GPL.
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libcurl http://curl.haxx.se/docs/copyright.html
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Uses an MIT (or Modified BSD)-style license that is as liberal as
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possible. Some of the source files that deal with KRB4 have Original
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BSD-style announce-clause licenses. You may not distribute binaries
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with krb4-enabled libcurl that also link with GPL-licensed code!
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OpenSSL http://www.openssl.org/source/license.html
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Uses an Original BSD-style license with an announement clause that
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makes it "incompatible" with GPL. You are not allowed to ship binaries
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that link with OpenSSL that includes GPL code (unless that specific
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GPL code includes an exception for OpenSSL - a habit that is growing
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more and more common). If OpenSSL's licensing is a problem for you,
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consider using GnuTLS instead.
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GnuTLS http://www.gnutls.org/
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Uses the LGPL[3] license. If this is a problem for you, consider using
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OpenSSL instead. Also note that GnuTLS itself depends on and uses
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other libs (libgcrypt and libgpg-error) and they too are LGPL- or
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GPL-licensed.
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c-ares http://daniel.haxx.se/projects/c-ares/license.html
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Uses an MIT license that is very liberal and imposes no restrictions
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on any other library or part you may link with.
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zlib http://www.gzip.org/zlib/zlib_license.html
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Uses an MIT-style license that shouldn't collide with any other
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library.
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krb4
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While nothing in particular says that a Kerberos4 library must use any
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particular license, the one I've tried and used successfully so far
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(kth-krb4) is Original BSD-licensed with the announcement clause. Some
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of the code in libcurl that is written to deal with Kerberos4 likewise
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have such a license.
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GSSAPI
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While nothing in particular says that a GSS/Kerberos5 library must use
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any particular license, the one I've used (Heimdal) is Original BSD-
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licensed with the announcement clause.
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fbopenssl
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Unclear license. Based on its name, I assume that it uses the OpenSSL
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license and thus shares the same issues as described for OpenSSL
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above.
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libidn http://www.gnu.org/licenses/lgpl.html
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Uses the GNU Lesser General Public License. LGPL is a variation of GPL
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with slightly less aggressive "copyleft". This license requires more
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requirements to be met when distributing binaries, see the license for
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details. Also note that if you distribute a binary that includes this
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library, you must also include the full LGPL license text. Please
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properly point out what parts of the distributed package that the
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license addresses.
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OpenLDAP http://www.openldap.org/software/release/license.html
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Uses a Modified BSD-style license. Since libcurl uses OpenLDAP as a
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shared library only, I have not heard of anyone that ships OpenLDAP
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linked with libcurl in an app.
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[1] = GPL - GNU General Public License: http://www.gnu.org/licenses/gpl.html
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[2] = http://www.fsf.org/licenses/gpl-faq.html#GPLIncompatibleLibs details on
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how to write such an exception to the GPL
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[3] = LGPL - GNU Lesser General Public License:
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http://www.gnu.org/licenses/lgpl.html
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