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123 lines
5.5 KiB
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123 lines
5.5 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). You may still build your own copies that use them all, but
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distributing them as binaries would be to violate the GPL license - unless you
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accompany your license with an exception[2]. This particular problem was
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addressed when the Modified BSD license was created, which does not have the
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annoncement clause 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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(May be used for SSL/TLS support) Uses an Original BSD-style license
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with an announement clause that makes it "incompatible" with GPL. You
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are not allowed to ship binaries that link with OpenSSL that includes
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GPL code (unless that specific GPL code includes an exception for
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OpenSSL - a habit that is growing more and more common). If OpenSSL's
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licensing is a problem for you, consider using GnuTLS or yassl
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instead.
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GnuTLS http://www.gnutls.org/
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(May be used for SSL/TLS support) Uses the LGPL[3] license. If this is
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a problem for you, consider using OpenSSL instead. Also note that
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GnuTLS itself depends on and uses other libs (libgcrypt and
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libgpg-error) and they too are LGPL- or GPL-licensed.
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yassl http://www.yassl.com/
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(May be used for SSL/TLS support) Uses the GPL[1] license. If this is
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a problem for you, consider using OpenSSL or GnuTLS instead.
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NSS http://www.mozilla.org/projects/security/pki/nss/
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(May be used for SSL/TLS support) Is covered by the MPL[4] license,
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the GPL[1] license and the LGPL[3] license. You may choose to license
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the code under MPL terms, GPL terms, or LGPL terms. These licenses
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grant you different permissions and impose different obligations. You
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should select the license that best meets your needs.
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c-ares http://daniel.haxx.se/projects/c-ares/license.html
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(Used for asynchronous name resolves) Uses an MIT license that is very
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liberal and imposes no restrictions on any other library or part you
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may link with.
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zlib http://www.gzip.org/zlib/zlib_license.html
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(Used for compressed Transfer-Encoding support) Uses an MIT-style
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license that shouldn't collide with any other 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 partly Original BSD-licensed with the announcement
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clause. Some of the code in libcurl that is written to deal with
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Kerberos4 is Modified BSD-licensed.
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MIT Kerberos http://web.mit.edu/kerberos/www/dist/
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(May be used for GSS support) MIT licensed, that shouldn't collide
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with any other parts.
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Heimdal http://www.pdc.kth.se/heimdal/
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(May be used for GSS support) Heimdal is Original BSD licensed with
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the announcement clause.
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GNU GSS http://www.gnu.org/software/gss/
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(May be used for GSS support) GNU GSS is GPL licensed. Note that you
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may not distribute binary curl packages that uses this if you build
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curl to also link and use any Original BSD licensed libraries!
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fbopenssl
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(Used for SPNEGO support) Unclear license. Based on its name, I assume
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that it uses the OpenSSL license and thus shares the same issues as
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described for OpenSSL above.
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libidn http://www.gnu.org/licenses/lgpl.html
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(Used for IDNA support) Uses the GNU Lesser General Public
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License. LGPL is a variation of GPL with slightly less aggressive
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"copyleft". This license requires more requirements to be met when
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distributing binaries, see the license for details. Also note that if
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you distribute a binary that includes this library, you must also
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include the full LGPL license text. Please properly point out what
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parts of the distributed package that the license addresses.
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OpenLDAP http://www.openldap.org/software/release/license.html
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(Used for LDAP support) Uses a Modified BSD-style license. Since
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libcurl uses OpenLDAP as a shared library only, I have not heard of
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anyone that ships OpenLDAP 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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[4] = MPL - Mozilla Public License:
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http://www.mozilla.org/MPL/
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