69 lines
2.4 KiB
Markdown
69 lines
2.4 KiB
Markdown
<!--
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Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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-->
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ABI - Application Binary Interface
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==================================
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"ABI" describes the low-level interface between an application program and a
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library. Calling conventions, function arguments, return values, struct
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sizes/defines and more.
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[Wikipedia has a longer description](https://en.wikipedia.org/wiki/Application_binary_interface)
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## Upgrades
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A libcurl upgrade does not break the ABI or change established and documented
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behavior. Your application can remain using libcurl just as before, only with
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fewer bugs and possibly with added new features.
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## Version Numbers
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In libcurl land, you cannot tell by the libcurl version number if that
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libcurl is binary compatible or not with another libcurl version. As a rule,
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we do not break the ABI so you can *always* upgrade to a later version without
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any loss or change in functionality.
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## SONAME Bumps
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Whenever there are changes done to the library that causes an ABI breakage,
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that may require your application to get attention or possibly be changed to
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adhere to new things, we bump the SONAME. Then the library gets a different
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output name and thus can in fact be installed in parallel with an older
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installed lib (on most systems). Thus, old applications built against the
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previous ABI version remains working and using the older lib, while newer
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applications build and use the newer one.
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During the first seven years of libcurl releases, there have only been four
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ABI breakages.
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We are determined to bump the SONAME as rarely as possible. Ideally, we never
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do it again.
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## Downgrades
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Going to an older libcurl version from one you are currently using can be a
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tricky thing. Mostly we add features and options to newer libcurls as that
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does not break ABI or hamper existing applications. This has the implication
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that going backwards may get you in a situation where you pick a libcurl that
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does not support the options your application needs. Or possibly you even
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downgrade so far so you cross an ABI break border and thus a different
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SONAME, and then your application may need to adapt to the modified ABI.
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## History
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The previous major library SONAME number bumps (breaking backwards
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compatibility) happened the following times:
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0 - libcurl 7.1, August 2000
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1 - libcurl 7.5 December 2000
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2 - libcurl 7.7 March 2001
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3 - libcurl 7.12.0 June 2004
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4 - libcurl 7.16.0 October 2006
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