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Diffstat (limited to 'shared-mime-info-spec.xml')
| -rw-r--r-- | shared-mime-info-spec.xml | 217 |
1 files changed, 70 insertions, 147 deletions
diff --git a/shared-mime-info-spec.xml b/shared-mime-info-spec.xml index 97acfbd1..17f28647 100644 --- a/shared-mime-info-spec.xml +++ b/shared-mime-info-spec.xml @@ -23,17 +23,24 @@ <address><email>david@mandrakesoft.com</email></address> </affiliation> </author> + <author> + <firstname>Alex</firstname> + <surname>Larsson</surname> + <affiliation> + <address><email>alexl@devserv.devel.redhat.com</email></address> + </affiliation> + </author> </authorgroup> <title>Shared MIME-info Database</title> - <date>26 April 2002</date> + <date>03 May 2002</date> </articleinfo> <sect1> <title>Introduction</title> <sect2> <title>Version</title> <para> -This is version 0.6 of the Shared MIME-info Database spec, last updated 26 April 2002. +This is version 0.7 of the Shared MIME-info Database spec, last updated 03 May 2002. </para> </sect2> <sect2> @@ -289,7 +296,7 @@ Comment=HTML document Comment[af]=... [... etc. other translations ] Patterns=*.htm;*.html -Contents=(strcmp-at 0 "<HTML") +Contents=50:(string 0:64 "<HTML") Hidden=false ]]></programlisting> </para> @@ -410,164 +417,80 @@ about its own types, conflicts should be rare. <sect2> <title>Contents matching</title> <para> -The value of the Contents attribute is a scheme-like expression. If the -expression evaluates to a true value then the file is assumed to be of this -type. Since scanning a file's contents can be very slow, applications may -choose to do pattern matching first and only fall back to content matching, or -not perform it at all. +The value of the Contents attribute contains a priority and an expression. +If several expressions match for one file, the one with the highest priority is used. +As a guide, priorities should be between 1 and 100, with 50 being the normal case. +Generic types (such as XML or GZip-compressed files) should have lower priorities. + </para><para> +Since scanning a file's contents can be very slow, applications may choose to +do pattern matching first and only fall back to content matching, or not +perform it at all. </para> <para> -An expression is a list of space-separated items surrounded by parenthesis, eg: +The basic building blocks of expressions are bracketed lists containing a type, +an offset (or range of offsets), the data to match and, optionally, a mask. For +example: <programlisting><![CDATA[ -(strcmp-at 0 "<?xml ") +(string 0 "%PDF-") +(string 0 "\177ELF") +(string 0:64 "<svg") +(string 0 "BMxxxx\000\000" 0xffff00000000ffff) ]]></programlisting> -The first element of the list (<userinput>strcmp-at</userinput> in this -example) is the name of a function. The remaining elements are its arguments. -The result of evaluating the expression is the result of applying the function -to the arguments. Each argument may be: - <variablelist> - <varlistentry><term>An integer</term> - <listitem><para> -A 64-bit signed integer, such as <userinput>32</userinput>. - </para></listitem> - </varlistentry> - <varlistentry><term>A string</term> - <listitem><para> -A string of characters with C-style escaping. This string contains the -sequence of bytes <0, 8, 9, 10>: <userinput>"\0\010\t\xa"</userinput>. - </para></listitem> - </varlistentry> - <varlistentry><term>A symbol</term> - <listitem><para> -A symbol is a constant for the file being tested. For example, -<userinput>size</userinput> evaluates to the file's size. - </para></listitem> - </varlistentry> - <varlistentry><term>A list</term> - <listitem><para> -Lists may be nested. Each sub-list is evaluated in the same way as the top-level -list, eg <userinput>(+ (* 3 2) (* 4 3))</userinput> is 18. - </para></listitem> - </varlistentry> - </variablelist> -Functions may return integers or strings. 'True' is represented by the integer -1, and False by 0. The following functions and symbols are provided: +The first element of the list is the type of the data (see the table below), the +second is the range of offsets to check, the third is the value to match and +the last, if present, is the mask. + </para> + <para> +Integers have the usual C-style prefixes (0 for octal numbers, 0x for hexadecimal). +Strings have C-style escaping. This string contains the sequence of bytes +<0, 8, 9, 10>: <userinput>"\0\010\t\xa"</userinput>. + </para> + <para> +A range gives the range of valid starting offsets. If the end of the range is omitted then +it is assumed to be the same as the start (that is, the match is only checked at one point +in the file). + </para> + <para> +The possible types of match are listed below: + </para> <informaltable> <tgroup cols="3"> <thead> <row> -<entry>Function example</entry><entry>Result</entry><entry>Description</entry> +<entry>Type</entry><entry>Description</entry> </row> </thead> <tbody> - <row> -<entry>(+ 1 2 3)</entry><entry>6</entry> -<entry>The sum of the arguments</entry> - </row> - <row> -<entry>(- 10 6 6)</entry><entry>-2</entry> -<entry>The first argument minus the sum of the remaining arguments</entry> - </row> - <row> -<entry>(* 2 2 3)</entry><entry>12</entry> -<entry>The product of the arguments</entry> - </row> - <row> -<entry>(/ 20 2 2)</entry><entry>5</entry> -<entry>The first argument divided by the -product of the remaining arguments</entry> - </row> - <row> -<entry>(> 1 2)</entry><entry>0</entry> -<entry>True iff the first argument is greater than the second</entry> - </row> - <row> -<entry>(< 1 2)</entry><entry>1</entry> -<entry>True iff the first argument is less than the second</entry> - </row> - <row> -<entry>(= 1 2)</entry><entry>0</entry> -<entry>True iff the first argument is equal to the second</entry> - </row> - <row> -<entry>(not size)</entry><entry>1</entry> -<entry>True iff argument is false (0 or "")</entry> - </row> - <row> -<entry>(and "one" 2 3)</entry><entry>3</entry> -<entry>The first false argument, or the last argument if none are false</entry> - </row> - <row> -<entry>(or 0 "" 2 0)</entry><entry>2</entry> -<entry>The first true argument, or the last argument if none are true</entry> - </row> - <row> -<entry>(& 3 6)</entry><entry>2</entry> -<entry>Bit-wise AND of the arguments</entry> - </row> - <row> -<entry>(| 3 6)</entry><entry>7</entry> -<entry>Bit-wise OR of the arguments</entry> - </row> - <row> -<entry>(^ 3 6)</entry><entry>5</entry> -<entry>Bit-wise XOR of the arguments</entry> - </row> - <row> -<entry>size</entry><entry>10</entry> -<entry>The size of the file in bytes</entry> - </row> - <row> -<entry>(strcmp-at 0 "Hello")</entry> -<entry>1</entry><entry>True iff the string starting at the file offset given by the -first argument matches the second argument</entry> - </row> - <row> -<entry>(byte-at 0)</entry> -<entry>72</entry><entry>The signed byte at the given file offset</entry> - </row> - <row> -<entry>(big-16 4)</entry> -<entry>28503</entry><entry>The big-endian 16-bit signed integer starting -at the given file offset.</entry> - </row> - <row> -<entry>(little-16 4)</entry> -<entry>22383</entry><entry>The little-endian 16-bit signed integer starting -at the given file offset.</entry> - </row> - <row> -<entry>(big-32 0)</entry> -<entry>1214606444</entry> -<entry>As above, but for a 32-bit big-endian integer</entry> - </row> - <row> -<entry>(little-32 0)</entry> -<entry>1819043144</entry> -<entry>As above, but for a 32-bit little-endian integer</entry> - </row> - <row> -<entry>(big-64 0)</entry> -<entry>5216694956358856562</entry> -<entry>As above, but for a 64-bit big-endian integer</entry> - </row> - <row> -<entry>(little-64 0)</entry> -<entry>8245905578810697032</entry> -<entry>As above, but for a 64-bit little-endian integer</entry> - </row> - <row> -<entry>(string-at 4 6)</entry> -<entry>"oWorld"</entry><entry>The string of bytes starting at the offset -given by the first argument and of length given by the second argument -</entry> - </row> +<row><entry>string</entry><entry>String of bytes</entry></row> +<row><entry>byte</entry><entry>Single byte</entry></row> +<row><entry>big16</entry><entry>16-bit big-endian integer</entry></row> +<row><entry>big32</entry><entry>32-bit big-endian integer</entry></row> +<row><entry>little16</entry><entry>16-bit little-endian integer</entry></row> +<row><entry>little32</entry><entry>32-bit little-endian integer</entry></row> +<row><entry>host16</entry><entry>16-bit integer in host-order</entry></row> +<row><entry>host32</entry><entry>32-bit integer in host-order</entry></row> </tbody> </tgroup> </informaltable> -The <userinput>and</userinput> and <userinput>or</userinput> functions should only evaluate -as many arguments as are necessary to determine the result. - </para> + <para> +These basic expressions may be combined using the <userinput>and</userinput> and +<userinput>or</userinput> syntax, eg: + <programlisting><![CDATA[ +(and (string 0 "\037\213") (string 10 "KOffice") (string 18 "application/x-kchart\004\006")) +]]></programlisting> +The <userinput>and</userinput> keyword corresponds to a more-deeply indented continuation +line in the original <citerefentry><refentrytitle>file</refentrytitle> +<manvolnum>1</manvolnum></citerefentry> syntax, while <userinput>or</userinput> corresponds +to elements at the same indentation. They may be nested in the obvious (scheme-like) +fashion. + </para> + <para> +Since many formats have sub-formats (for example, KOffice stores its files in +GZip format, with a generic KOffice marker and a specific application marker), +it may be a useful optimisation to spot the same subexpression (eg +<userinput>(string 10 "KOffice")</userinput>) being used in several types and +only check it once. + </para> </sect2> <sect2> <title>Security implications</title> |