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Daniel Stenberg
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docs/DISTRO-DILEMMA
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docs/DISTRO-DILEMMA
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Date: August 31, 2005
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Author: Daniel Stenberg <daniel@haxx.se>
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URL:
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Condition
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This document is written to describe the sitution as it is right now. libcurl
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7.14.0 is currently the latest version available. Things may (or perhaps
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will) of course change in the future.
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This document reflects my view and understanding of these things. Please tell
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me where and how you think I'm wrong, and I'll try to correct my mistakes.
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Background
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The Free Software Foundation has deemed the Original BSD license[1] to be
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"incompatible"[2] with GPL[3]. I'd rather say it is the other way around, but
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the point is the same: if you distribute a binary version of a GPL program,
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it MUST NOT be linked with any Original BSD-licenced parts or
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libraries. Doing so will violate the GPL license. For a long time, very many
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GPL licensed programs have avoided this license mess by adding an
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exception[8] to their license. And many others have just closed their eyes
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for this problem.
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libcurl is MIT-style[4] licensed - how on earth did this dilemma fall onto
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our plates?
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libcurl is only a little library. libcurl can be built to use OpenSSL for its
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SSL/TLS capabilities. OpenSSL is basically Original BSD licensed[5].
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If libcurl built to use OpenSSL is used by a GPL-licensed application and you
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decide to distribute a binary version of it (Linux distros - for example -
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tend to), you have a clash. GPL vs Original BSD.
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This dilemma is not libcurl-specific nor is it specific to any particular
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Linux distro.
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Part of the Operating System
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This would not be a problem if the used lib would be considered part of the
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uderlying operating system, as then the GPL license has an exception
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clause[6] that allows applications to use such libs without having to be
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allowed to distribute it or its sources. Possibly some distros will claim
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that OpenSSL is part of their operating system.
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Debian does however not take this stance and has officially(?) claimed that
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OpenSSL is not a required part of the Debian operating system
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Debian-legal
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In August 2004 I figured I should start pulling people's attention to this to
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see if anyone has any bright ideas or if they would dismiss my worries based
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on some elegant writing I had missed somewhere:
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My post to debian-legal on August 12 2004:
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http://lists.debian.org/debian-legal/2004/08/msg00279.html
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Several people agreed then that this is a known and rather big problem, but
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the following discussion didn't result in much.
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GnuTLS
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With the release of libcurl 7.14.0 (May 2005), it can now get built to use
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GnuTLS instead of OpenSSL. GnuTLS is a LGPL[7] licensed library that offers a
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matching set of features as OpenSSL does. Now, you can build and distribute
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an SSL capable libcurl without including any Original BSD licensed code.
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I believe Debian is the first distro to provide libcurl/GnutTLS packages.
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GnuTLS vs OpenSSL
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While these two libraries offer similar features, they are not equal. Both
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libraries have features the other one lacks. libcurl does not (yet) offer a
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standardized stable ABI if you decide to switch from using libcurl-openssl to
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libcurl-gnutls or vice versa. The GnuTLS support is very recent in libcurl
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and it has not been tested nor used very extensively, while the OpenSSL
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equivalent code has been used and thus matured for more than seven (7) years.
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In August 2005, the debian-devel mailing list discovered the license issue as
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a GPL licensed application wanted SSL capabilities from libcurl and thus was
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forced to use the GnuTLS powered libcurl. For a reason that is unknown to me,
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the application authors didn't want to or was unable to add an exception to
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their GPL license. Alas, the license problem hit the fan again.
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The Better License, Original BSD or LGPL?
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It isn't obvious or without debate to any objective interested party that
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either of these licenses are the "better" or even the "preferred" one in a
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generic situation. In the Debian camp they frawn upon OpenSSL's BSD license,
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but that seems to merely stem from the general FSF friendliness and GPL
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bigotry than based on a sane and proper analysis (assuming such a one is even
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possible within an area as filled with religion and personal preferences such
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as this). This is however not a subject suitable for this document.
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Instead, I think we should accept the fact that the SSL/TLS libraries and
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their different licenses will fit different applications and their authors
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differently depending on the applications' licenses and their general usage
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pattern (considering how LGPL libraries can be burdonsome for embedded
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systems usage).
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More SSL Libraries
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In libcurl, there's no stopping us here. There are at least a few more Open
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Source/Free SSL/TLS libraries and we would very much like to support them as
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well, to offer application authors an even wider scope of choice.
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Application Angle of this Problem
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libcurl is built to use one SSL/TLS library. It uses a single fixed name (by
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default), and applications are built/linked to use that single lib. Replacing
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one libcurl instance with another one that uses the other SSL/TLS library
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might break one or more applications (due to ABI differences and/or different
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feature set). You want your application to use the libcurl it was built for.
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Project cURL Angle of this Problem
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We distribute libcurl and everyone may build libcurl with either library. At
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their choice. This problem is not directly a problem of ours. It merely
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affects users - GPL application authors only - of our lib as it comes
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included and delivered on some distros.
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Distro Angle of this Problem
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A distro can provide separate libcurls built with different SSL/TLS libraries
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to work around this, but at least Debian seems to be very hostile against
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such an approach, probably since it makes things like devel packages for the
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different libs collide since they would provide the same include files and
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man pages etc.
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Fixing the Only Problem
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The only problem is thus for distributions that want to offer libcurl
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versions built with more than one SSL/TLS library.
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Since multiple libcurl binaries using different names are ruled out, we need
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to come up with a way to have one single libcurl that someone uses different
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underlying libraries. The best(?) approach currently suggested involves this:
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A new intermediate library (named lib2 so far in the discussions) with the
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single purpose of providing libcurl with SSL/TLS capabilities. It would have
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a unified API and ABI no matter what underlying library it would use.
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There would be one lib2 binary provided for each supported SSL/TLS library.
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For example: lib2-openssl, lib2-gnutls, lib2-yassl, lib2-matrixssl and
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lib2-nossl. Yes, take note of the last one that provides the lib2 ABI but
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that lacks the actual powers.
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When libcurl is built and linked, it will be linked against a lib2 with the
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set ABI.
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When you link an app against libcurl, it would also need to provide one of
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the (many) lib2 libs to decide what approach that fits the app. An app that
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doesn't want SSL at all would still need to link with the lib2-nossl lib.
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GPL apps can pick the lib2-gnutls, others may pick the lib2-openssl.
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This concept works equally well both for shared and static libraries.
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When Will This Happen
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Note again that this is not a problem in curl, it doesn't solve any actual
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technical problems in our project. Don't hold your breath for this to happen
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very soon (if at all) unless you step forward and contribute.
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The suggestion that is outlined above is still only a suggestion. Feel free
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to bring a better idea!
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Also, to keep in mind: I don't want this new concept to have too much of an
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impact on the existing code. Preferably it should be possible to build the
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code like today (without the use of lib2), should you decide to ignore the
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problems outlined in this document.
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Footnotes
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[1] = http://www.xfree86.org/3.3.6/COPYRIGHT2.html#6
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[2] = http://www.fsf.org/licensing/essays/bsd.html
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[3] = http://www.fsf.org/licensing/licenses/gpl.html
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[4] = http://curl.haxx.se/docs/copyright.html
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[5] = http://www.openssl.org/source/license.html
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[6] = http://www.fsf.org/licensing/licenses/gpl.html end of section 3
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[7] = http://www.fsf.org/licensing/licenses/lgpl.html
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[8] = http://en.wikipedia.org/wiki/OpenSSL_exception
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