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{{Infobox file format
| name = XAR
| icon =
| logo =
| screenshot =
| caption =
|_noextcode = on
| extensions = {{code|.xar}}, [[安裝程序_(macOS)|{{code|.pkg}}]], [[.XIP|{{code|.xip}}]]<ref name="x-xar" />
| mime = application/x-xar<ref name="x-xar">{{cite web|url=https://reposcope.com/mimetype/application/x-xar|language=en|title=application/x-xar|accessdate=2019-03-19|archive-date=2019-03-27|archive-url=https://web.archive.org/web/20190327090443/https://reposcope.com/mimetype/application/x-xar}}</ref>
| type code =
| uniform type = com.apple.xar-archive
| magic = xar!
| owner =
| released = 
| latest release version = 1.6.1
| latest release date = {{Start date and age|2012|09|17}}
| genre = [[归档文件]]
| container for =
| contained by =
| extended from = [[XML]], [[gzip]]
| extended to =
| standard =
| free =
| url = {{URL|https://mackyle.github.io/xar/}} {{URL|https://github.com/mackyle/xar}}
}}

'''XAR'''为'''可扩展归档格式'''（{{langx|en|''e'''X'''tensible '''AR'''chive format''}}）的缩写，是一种[[开源]][[文件归档器]]和其[[檔案格式|文件格式]]。它创建于[[OpenDarwin]]项目，并在[[Mac OS X 10.5]]及更高版本中用于软件安装例程，以及在[[Safari|Safari 5.0]]及更高版本中用于[[浏览器扩展]]安装。它取代了[[Gzip|gzip压缩]]的[[pax文件]]的使用。<ref name="xarLeopard">{{Cite web|url=http://www.nabble.com/xar-in-Mac-OS-X-t2081148.html|archiveurl=https://web.archive.org/web/20070207045420/http://www.nabble.com/xar-in-Mac-OS-X-t2081148.html|deadurl=yes|title=Nabble – xar in Mac OS X|archivedate=2007年2月7日|accessdate=2020年9月21日}}</ref>

[[RPM套件管理員|RPM]]的一个开发分支RPM5也使用xar。<ref name="xarRPM">{{Cite web|url=http://rpm5.org/roadmap.php|title=rpm package manager|website=rpm5.org|accessdate=2020-09-21|archive-date=2011-12-04|archive-url=https://web.archive.org/web/20111204224249/http://rpm5.org/roadmap.php|dead-url=no}}</ref>

== 文件结构 ==
[[File:XAR File Structure.svg|thumb]]
.xar文件包含三部分：文件头，目录表（Table of Contents, TOC）和堆。所有字段均按[[大端序|大端]]顺序存储。<ref name="project wiki">{{Cite web|url=https://github.com/mackyle/xar|title=mackyle/xar|website=GitHub|access-date=2020-09-21|archive-date=2021-05-06|archive-url=https://web.archive.org/web/20210506132946/https://github.com/mackyle/xar}}</ref>
=== 文件头 ===
{| class="wikitable"
! 偏移#
! 长度（字节）
! 描述
|-
| 0
| 4
| 文件特征签名，总是<code>xar!</code>
|-
| 4
| 2
| 文件头大小
|-
| 6
| 2
| 文件版本，目前只有版本1
|-
|8
|8
|TOC压缩后大小
|-
|16
|8
|TOC压缩前大小
|-
|24
|4
|[[校验和]]算法:{{plainlist}}
* 0 = 无
* 1 = [[SHA1]]
* 2 = [[MD5]]
* 3 = [[SHA-256]]<ref name="xar-man1">{{cite web|url=https://www.unix.com/man-page/mojave/1/xar|title=xar - eXtensible ARchiver mojave man page|accessdate=2019-03-26|last1=Braun|first1=Rob|last2=Fuller|first2=Landon|last3=Leimbach|first3=David|last4=Van Vechten|first4=Kevin|date=2015-06-04}}</ref>
* 4 = [[SHA-512]]
{{endplainlist}}
|-
|28
|0, 4 , 36
|填充字节或校验和算法名称
|}

=== 目录表（TOC） ===
与[[cpio]]，[[tar]]或[[Ar (Unix)|ar]]的不同，Xar将TOC（目录表）存储在文件的开头，这使得附加到归档文件变得更加复杂，但是好处是不必扫描整个归档文件来提取单个包含的文件。 TOC以[[UTF-8|UTF-8编码]]的[[XML|XML文档]]存储,[[zlib]]压缩。<ref>{{Cite web|url=https://code.google.com/archive/p/xar/wikis/xarformat.wiki|title=Google Code Archive - Long-term storage for Google Code Project Hosting.|website=code.google.com|access-date=2020-09-21|archive-date=2021-10-29|archive-url=https://web.archive.org/web/20211029012921/https://code.google.com/archive/p/xar/wikis/xarformat.wiki}}</ref><ref name="project wiki"/> 存储在Xar中的每个文件都经过独立压缩/编码，可以使用不同的压缩方法对不同文件进行编码。在某些系统上，文件还可以通过xz或lzma压缩方法进行编码。<ref name="xar-man1" />

'''TOC示例'''
<syntaxhighlight lang="xml">
<?xml version="1.0" encoding="UTF-8"?>
<xar>
<toc>
<checksum style="sha1">
<offset>0</offset>
<size>20</size>
</checksum>
<file id="1">
<group>staff</group>
<gid>20</gid>
<user>joe</user>
<uid>501</uid>
<mode>0755</mode>
<type>directory</type>
<name>com.foobar</name>
<file id="2">
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0775</mode>
<type>directory</type>
<name>Contents</name>
<file id="3">
<data>
<length>428</length>
<offset>20</offset>
<size>1005</size>
<encoding style="application/x-gzip"/>
<archived-checksum style="SHA1">a5f6f1461213a904f831d4ef6f214638342842ed</archived-checksum>
<extracted-checksum style="SHA1">21d21a0c90378248ce0dfb6f345376d1b00d65fc</extracted-checksum>
</data>
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0664</mode>
<type>file</type>
<name>Info.plist</name>
</file>
<file id="4">
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0775</mode>
<type>directory</type>
<name>Resources</name>
<file id="5">
<data>
<length>14868</length>
<offset>448</offset>
<size>274432</size>
<encoding style="application/x-gzip"/>
<archived-checksum style="SHA1">efe5c97921de7ccc5aebc158d158e9d4280d6814</archived-checksum>
<extracted-checksum style="SHA1">45c8be42d1d9afdb57ddd5e9311453010ec46161</extracted-checksum>
</data>
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0664</mode>
<type>file</type>
<name>foobar</name>
</file>
<file id="6">
<data>
<length>17635</length>
<offset>15316</offset>
<size>45056</size>
<encoding style="application/x-gzip"/>
<archived-checksum style="SHA1">3c761ffcc81ee6e232e4f4a1c4a81654c26c4e52</archived-checksum>
<extracted-checksum style="SHA1">0ea31f8ef0e5987a1838a64ab5c26ebf3ee4bc37</extracted-checksum>
</data>
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0664</mode>
<type>file</type>
<name>docSet.skidx</name>
</file>
<file id="7">
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0775</mode>
<type>directory</type>
<name>Documents</name>
<file id="8">
<data>
<length>35790</length>
<offset>32951</offset>
<size>209242</size>
<encoding style="application/x-gzip"/>
<archived-checksum style="SHA1">5242cd71585c34e722932f324706f8c00e1ae0c5</archived-checksum>
<extracted-checksum style="SHA1">c0e013e53d829511835e2b429abb5198731e9a3e</extracted-checksum>
</data>
<group></group>
<gid>20</gid>
<user></user>
<uid>501</uid>
<mode>0664</mode>
<type>file</type>
<name>foobar.html</name>
</file>
</file>
</file>
</file>
</file>
</toc>
</xar>
</syntaxhighlight>

==参考来源==
{{Reflist}}

==外部链接==
{{Portal|自由軟體}}
*[http://code.google.com/p/xar/ Xar homepage] {{Wayback|url=http://code.google.com/p/xar/ |date=20120406152702 }}
*[https://opensource.apple.com/source/xar/ Apple xar homepage] {{Wayback|url=https://opensource.apple.com/source/xar/ |date=20210727071500 }}

{{Archive formats}}

{{DEFAULTSORT:Xar (Archiver)}}

[[Category:归档格式]]

Xar - 版本历史

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imported>Zestbot：/* top */ bot:替換lang-x模板為langx