Imported libcurl source code.

2009-01-08 18:31:00 -05:00
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+         License Mixing with apps, libcurl and Third Party Libraries
+         ===========================================================
+
+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[1]-licensed code is not allowed to be linked
+with code licensed under the Original BSD license (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[2]. This particular problem was
+addressed when the Modified BSD license was created, which does not have the
+announcement clause that collides with GPL.
+
+libcurl http://curl.haxx.se/docs/copyright.html
+
+        Uses an MIT (or Modified BSD)-style license that is as liberal as
+        possible.  Some of the source files that deal with KRB4 have Original
+        BSD-style announce-clause licenses. You may not distribute binaries
+        with krb4-enabled libcurl that also link with GPL-licensed code!
+
+OpenSSL http://www.openssl.org/source/license.html
+
+        (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 GnuTLS or yassl
+        instead.
+
+GnuTLS  http://www.gnutls.org/
+
+        (May be used for SSL/TLS support) Uses the LGPL[3] license. If this is
+        a problem for you, consider using OpenSSL instead. Also note that
+        GnuTLS itself depends on and uses other libs (libgcrypt and
+        libgpg-error) and they too are LGPL- or GPL-licensed.
+
+yassl   http://www.yassl.com/
+
+        (May be used for SSL/TLS support) Uses the GPL[1] license. If this is
+        a problem for you, consider using OpenSSL or GnuTLS instead.
+
+NSS     http://www.mozilla.org/projects/security/pki/nss/
+
+        (May be used for SSL/TLS support) Is covered by the MPL[4] license,
+        the GPL[1] license and the LGPL[3] 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.
+
+c-ares  http://daniel.haxx.se/projects/c-ares/license.html
+
+        (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    http://www.gzip.org/zlib/zlib_license.html
+
+        (Used for compressed Transfer-Encoding support) Uses an MIT-style
+        license that shouldn't collide with any other library.
+
+krb4
+
+        While nothing in particular says that a Kerberos4 library must use any
+        particular license, the one I've tried and used successfully so far
+        (kth-krb4) is partly Original BSD-licensed with the announcement
+        clause. Some of the code in libcurl that is written to deal with
+        Kerberos4 is Modified BSD-licensed.
+
+MIT Kerberos http://web.mit.edu/kerberos/www/dist/
+
+        (May be used for GSS support) MIT licensed, that shouldn't collide
+        with any other parts.
+
+Heimdal http://www.pdc.kth.se/heimdal/
+
+        (May be used for GSS support) Heimdal is Original BSD licensed with
+        the announcement clause.
+
+GNU GSS http://www.gnu.org/software/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!
+
+fbopenssl
+
+        (Used for SPNEGO support) Unclear license. Based on its name, I assume
+        that it uses the OpenSSL license and thus shares the same issues as
+        described for OpenSSL above.
+
+libidn  http://josefsson.org/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 http://www.openldap.org/software/release/license.html
+
+        (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 http://www.libssh2.org/
+
+        (Used for scp and sftp support) libssh2 uses a Modified BSD-style
+        license.
+
+[1] = GPL - GNU General Public License: http://www.gnu.org/licenses/gpl.html
+[2] = http://www.fsf.org/licenses/gpl-faq.html#GPLIncompatibleLibs details on
+      how to write such an exception to the GPL
+[3] = LGPL - GNU Lesser General Public License:
+      http://www.gnu.org/licenses/lgpl.html
+[4] = MPL - Mozilla Public License:
+      http://www.mozilla.org/MPL/