1 License Mixing with apps, libcurl and Third Party Libraries 2 =========================================================== 3 4 libcurl can be built to use a fair amount of various third party libraries, 5 libraries that are written and provided by other parties that are distributed 6 using their own licenses. Even libcurl itself contains code that may cause 7 problems to some. This document attempts to describe what licenses libcurl and 8 the other libraries use and what possible dilemmas linking and mixing them all 9 can lead to for end users. 10 11 I am not a lawyer and this is not legal advice! 12 13 One common dilemma is that GPL[1]-licensed code is not allowed to be linked 14 with code licensed under the Original BSD license (with the announcement 15 clause). You may still build your own copies that use them all, but 16 distributing them as binaries would be to violate the GPL license - unless you 17 accompany your license with an exception[2]. This particular problem was 18 addressed when the Modified BSD license was created, which does not have the 19 announcement clause that collides with GPL. 20 21 libcurl https://curl.haxx.se/docs/copyright.html 22 23 Uses an MIT (or Modified BSD)-style license that is as liberal as 24 possible. 25 26 OpenSSL https://www.openssl.org/source/license.html 27 28 (May be used for SSL/TLS support) Uses an Original BSD-style license 29 with an announcement clause that makes it "incompatible" with GPL. You 30 are not allowed to ship binaries that link with OpenSSL that includes 31 GPL code (unless that specific GPL code includes an exception for 32 OpenSSL - a habit that is growing more and more common). If OpenSSL's 33 licensing is a problem for you, consider using another TLS library. 34 35 GnuTLS http://www.gnutls.org/ 36 37 (May be used for SSL/TLS support) Uses the LGPL[3] license. If this is 38 a problem for you, consider using another TLS library. Also note that 39 GnuTLS itself depends on and uses other libs (libgcrypt and 40 libgpg-error) and they too are LGPL- or GPL-licensed. 41 42 WolfSSL https://www.wolfssl.com/ 43 44 (May be used for SSL/TLS support) Uses the GPL[1] license or a 45 propietary license. If this is a problem for you, consider using 46 another TLS library. 47 48 NSS https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS 49 50 (May be used for SSL/TLS support) Is covered by the MPL[4] license, 51 the GPL[1] license and the LGPL[3] license. You may choose to license 52 the code under MPL terms, GPL terms, or LGPL terms. These licenses 53 grant you different permissions and impose different obligations. You 54 should select the license that best meets your needs. 55 56 axTLS http://axtls.sourceforge.net/ 57 58 (May be used for SSL/TLS support) Uses a Modified BSD-style license. 59 60 mbedTLS https://tls.mbed.org/ 61 62 (May be used for SSL/TLS support) Uses the GPL[1] license or a 63 propietary license. If this is a problem for you, consider using 64 another TLS library. 65 66 BoringSSL https://boringssl.googlesource.com/ 67 68 (May be used for SSL/TLS support) As an OpenSSL fork, it has the same 69 license as that. 70 71 libressl http://www.libressl.org/ 72 73 (May be used for SSL/TLS support) As an OpenSSL fork, it has the same 74 license as that. 75 76 c-ares https://daniel.haxx.se/projects/c-ares/license.html 77 78 (Used for asynchronous name resolves) Uses an MIT license that is very 79 liberal and imposes no restrictions on any other library or part you 80 may link with. 81 82 zlib http://www.zlib.net/zlib_license.html 83 84 (Used for compressed Transfer-Encoding support) Uses an MIT-style 85 license that shouldn't collide with any other library. 86 87 MIT Kerberos http://web.mit.edu/kerberos/www/dist/ 88 89 (May be used for GSS support) MIT licensed, that shouldn't collide 90 with any other parts. 91 92 Heimdal http://www.h5l.org 93 94 (May be used for GSS support) Heimdal is Original BSD licensed with 95 the announcement clause. 96 97 GNU GSS https://www.gnu.org/software/gss/ 98 99 (May be used for GSS support) GNU GSS is GPL licensed. Note that you 100 may not distribute binary curl packages that uses this if you build 101 curl to also link and use any Original BSD licensed libraries! 102 103 libidn http://josefsson.org/libidn/ 104 105 (Used for IDNA support) Uses the GNU Lesser General Public 106 License [3]. LGPL is a variation of GPL with slightly less aggressive 107 "copyleft". This license requires more requirements to be met when 108 distributing binaries, see the license for details. Also note that if 109 you distribute a binary that includes this library, you must also 110 include the full LGPL license text. Please properly point out what 111 parts of the distributed package that the license addresses. 112 113 OpenLDAP http://www.openldap.org/software/release/license.html 114 115 (Used for LDAP support) Uses a Modified BSD-style license. Since 116 libcurl uses OpenLDAP as a shared library only, I have not heard of 117 anyone that ships OpenLDAP linked with libcurl in an app. 118 119 libssh2 https://www.libssh2.org/ 120 121 (Used for scp and sftp support) libssh2 uses a Modified BSD-style 122 license. 123 124 [1] = GPL - GNU General Public License: https://www.gnu.org/licenses/gpl.html 125 [2] = https://www.gnu.org/licenses/gpl-faq.html#GPLIncompatibleLibs details on 126 how to write such an exception to the GPL 127 [3] = LGPL - GNU Lesser General Public License: 128 https://www.gnu.org/licenses/lgpl.html 129 [4] = MPL - Mozilla Public License: 130 https://www.mozilla.org/MPL/ 131
