Copyright © 2013 Jirka Kosek and John Lumley, published by the

This specification was published by the

This proposal provides an API for XPath 2.0 to handle binary data. It defines extension functions to process data from binary files, including extracting subparts, searching, basic binary operations and conversion between binary and structured forms. It has been designed to be compatible with XQuery 1.0 and XSLT 2.0, as well as any other XPath 2.0 usage.

The module homepage, with more information, is on the EXPath website at

revisiondesc

This document is a final specification.

The module defined by this document defines several functions, all contained in the
namespace `http://expath.org/ns/binary`

. In this document, the `bin`

prefix, when used, is bound to this namespace URI.

Error codes are defined in the same namespace (`http://expath.org/ns/binary`

),
and in this document are displayed with the same prefix, `bin`

.

Binary file I/O uses facilities defined in `http://expath.org/ns/file`

. In this document, the
`file`

prefix, when used, is bound to this namespace URI.

Error conditions are identified by a code (a `QName`

.) When such an error
condition is reached in the evaluation of an expression, a dynamic error is thrown, with
the corresponding error code (as if the standard XPath function `error()`

had
been called.)

The principal binary type within this module is `xs:base64Binary`

.

Conversion to and from `xs:hexBinary`

can be performed by casting with

As these types are normally implemented as wrappers around byte array structures containing the data, and differ only when being serialized to or parsed from text, such casting in-process should not involve data copying.

An item of type `xs:base64Binary`

can be `xs:string`

can contain no
characters.) Where 'data' arguments to functions that return binary data are optional
(i.e.

) and any of those optional arguments is set
to the empty sequence, in general an empty sequence is returned, rather than an empty item
of type `xs:base64Binary`

.

A suite of test-cases for all the functions defined in this module, in

Development of this specification was driven by requirements which some XML developers regularly encounter in examining or generating data which is presented in binary, or other non-textual forms. Some typical use cases include:

Getting the dimensions of an image file.

Extracting image metadata.

Processing images embedded as base64 encodings within a SOAP message.

Processing legacy text files which use different encodings in separate sections.

Generating PDF files from SVG graphical data.

As an example, the following code reads the binary form of a JPEG image file, searches for the 'Start of Frame/DCT' segment, and unpacks the relevant binary sections to integers of height and width:

(The `'most-significant-first'()`

argument ensures the numeric conversion is
'big-endian', which is the format in JPEG.)

Type – 1 octet – in this case the value `0x02`

Length – >=1 octet – the number of octets in the integer value. The length field itself can be variable in length – to accomodate VERY large integers (requiring more than 127 octets to represent, e.g. 2048-bit crypto keys.)

Payload – >=0 octets – the octets of the integer value in most-significant-first order.

To generate such a representation for an integer from XSLT/XPath, the following code might be used:

The function `bin:int-octets()`

returns a sequence of all the 'significant'
octets of the integer (i.e. eliminating leading 'zeroes') in most-significant order.
Examples of the encoding are:

The first example requires no octets to encode zero, hence its octets are
`2,0`

. Both the second and third examples can be represented in less than 128
octets (2 and 15 respectively), so length is encoded as a single octet. The first three
octets of the result for the last example, which encodes a 900-digit integer, are:
`2,130,1`

indicating that the data is represented by (130-128) * 256 + 1 =
513 octets and the length required two octets to encode.

Decoding is a matter of compound use of the integer decoding function:

(all numbers in ASN are 'big-endian') and the examples from above reverse:

This module defines no specific functions for reading and writing binary data from files.
The EXPath File Module

Users of the package may need to define binary 'constants' within their code or examine the basic octets. The following functions support these:

Returns the binary form of the set of octets written as a sequence of (ASCII) hex digits ([0-9A-Fa-f]).

`$in`

will be effectively zero-padded from the left to generate an integral
number of octets, i.e. an even number of hexadecimal digits. If `$in`

is an empty
string, then the result will be a `xs:base64Binary`

with no embedded data.

Byte order in the result follows (per-octet) character order in the string.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$in`

cannot be parsed as a
hexadecimal number.

When the input string has an even number of characters, this function behaves similarly to
the double cast `xs:base64Binary(xs:hexBinary(`

.*$string*))

Returns the binary form of the set of octets written as a sequence of (8-wise) (ASCII) binary digits ([01]).

`$in`

will be effectively zero-padded from the left to generate an integral
number of octets. If `$in`

is an empty string, then the result will be a
`xs:base64Binary`

with no embedded data.

Byte order in the result follows (per-octet) character order in the string.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$in`

cannot be parsed as a
binary number.

Returns the binary form of the set of octets written as a sequence of (ASCII) octal digits ([0-7]).

`$in`

will be effectively zero-padded from the left to generate an integral
number of octets. If `$in`

is an empty string, then the result will be a
`xs:base64Binary`

with no embedded data.

Byte order in the result follows (per-octet) character order in the string.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$in`

cannot be parsed as an
octal number.

Returns binary data as a sequence of octets.

If `$in`

is a zero length binary data then the empty sequence is returned.

Octets are returned as integers from 0 to 255.

Converts a sequence of octets into binary data.

Octets are integers from 0 to 255.

If the value of `$in`

is the empty sequence, the function returns zero-sized
binary data.

The `bin:length`

function returns the size of binary data in octets.

Returns the size of binary data in octets.

The `bin:part`

function returns a specified part of binary data.

Returns a section of binary data starting at the `$offset`

octet. If
`$size`

is defined, the size of the returned binary data is `$size`

octets. If `$size`

is absent, all remaining data from `$offset`

is
returned.

The `$offset`

is zero based.

The values of `$offset`

and `$size`

It is a dynamic error if `$offset`

+ `$size`

is larger than the size
of the binary data in `$in`

.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$offset`

is negative or
`$offset + $size`

is larger than the size of the binary data of
`$in`

.

`$size`

is negative.

Note that `fn:subsequence()`

and `fn:substring()`

`xs:double`

for offset and size – this is a legacy
from XPath 1.0.

Testing whether `$data`

variable starts with binary content consistent with a
PDF file:

`25504446`

is the magic number for PDF files: it is the US-ASCII encoded
hexadecimal value for `%PDF`

.

Returns the binary data created by concatenating the binary data items in a sequence.

The function returns an `xs:base64Binary`

created by concatenating the items in
the sequence `$in`

, in order.

If the value of `$in`

is the empty sequence, the function returns a binary item
containing no data bytes.

The `bin:insert-before`

function inserts additional binary data at a given point
in other binary data.

Returns binary data consisting sequentially of the data from `$in`

upto and
including the `$offset - 1`

octet, followed by all the data from
`$extra`

, and then the remaining data from `$in`

.

The `$offset`

is zero based.

The value of `$offset`

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

If the value of `$extra`

is the empty sequence, the function returns
`$in`

.

If `$offset eq 0`

the result is the binary concatenation of `$extra`

and `$in`

, i.e. equivalent to `bin:join(($extra,$in))`

.

`$offset`

is negative or
`$offset`

is larger than the size of the binary data of `$in`

.

Note that when `$offset gt 0 and $offset lt bin:size($in)`

the function is
equivalent to:

Returns the binary data created by padding `$in`

with `$size`

octets
from the left. The padding octet values are `$octet`

or zero if omitted.

The function returns an `xs:base64Binary`

created by padding the input with
`$size`

octets *in front of* the input. If `$octet`

is
specified, the padding octets each have that value, otherwise they are initialized to 0.

`$size`

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$size`

is negative.

`$octet`

lies outside the range 0
– 255.

Padding with a non-zero octet value can also be accomplished by the XPath expressions:

Returns the binary data created by padding `$in`

with `$size`

blank
octets from the right. The padding octet values are `$octet`

or zero if
omitted.

The function returns an `xs:base64Binary`

created by padding the input with
`$size`

blank octets *after* the input. If `$octet`

is
specified, the padding octets each have that value, otherwise they are initialized to 0.

`$size`

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$size`

is negative.

`$octet`

lies outside the range 0
– 255.

Padding with a non-zero octet value can also be accomplished by the XPath expressions:

Returns the first location in `$in`

of `$search`

, starting at the
`$offset`

octet.

The function returns the first location of the binary search sequence in the input, or if not found, the empty sequence.

If `$search`

is empty `$offset`

is returned.

The value of `$offset`

The `$offset`

is zero based.

The returned location is zero based.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$offset`

is negative or
`$offset`

is larger than the size of the binary data of `$in`

.

Finding all the matches can be accomplished with simple recursive application:

Decodes binary data as a string in a given encoding.

If `$offset`

and `$size`

are provided, the `$size`

octets
from `$offset`

are decoded. If `$offset`

alone is provided, octets
from `$offset`

to the end are decoded, otherwise the entire octet sequence is
used.

The `$encoding`

argument is the name of an encoding. The values for this
attribute follow the same rules as for the `encoding`

attribute in an XML
declaration. The only values which every implementation is `utf-8`

and `utf-16`

.

If `$encoding`

is ommitted, `utf-8`

encoding is assumed.

The values of `$offset`

and `$size`

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$offset`

is zero based.

`$offset`

is negative or
`$offset + $size`

is larger than the size of the binary data of
`$in`

.

`$size`

is negative.

`$encoding`

is invalid or not
supported by the implementation.

Testing whether `$data`

variable starts with binary content consistent with a
PDF file:

The first four characters of a PDF file are `'%PDF'`

.

Encodes a string into binary data using a given encoding.

The `$encoding`

argument is the name of an encoding. The values for this
attribute follow the same rules as for the `encoding`

attribute in an XML
declaration. The only values which every implementation is `utf-8`

and `utf-16`

.

If `$encoding`

is ommitted, `utf-8`

encoding is assumed.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

`$encoding`

is invalid or not
supported by the implementation.

Packing and unpacking numeric values can be performed in 'most-significant-first'
('big-endian') or 'least-significant-first' ('little-endian') octet order. The default is
`$octet-order`

whose string value controls the order. Least-significant-first
order is indicated by any of the values `least-significant-first`

,
`little-endian`

or `LE`

. Most-significant-first order is indicated
by any of the values `most-significant-first`

, `big-endian`

or
`BE`

.

Integers within binary data are represented, or assumed to be represented, as an integral
number of octets. Integers where `$length`

is greater than 8 octets (and thus
not representable as a `long`

) might be expected in some situations, e.g.
encryption. Whether the range of integers is limited to `±2^63`

may be
implementation-dependant.

Care should be taken with the packing and unpacking of floating point numbers
(`xs:float`

and `xs:double`

). The binary representations are
expected to correspond with those of the IEEE single/double-precision 32/64-bit floating
point types

Positive and negative infinities are supported. `INF`

maps to ```
0x7f80
0000
```

(float), `0x7ff0 0000 0000 0000`

(double). `-INF`

maps
to `0xff80 0000`

(float), `0xfff0 0000 0000 0000`

(double).

Negative zero (`0x8000 0000 0000 0000`

double, `0x8000 0000`

float)
encountered during unpacking will yield negative zero forms (e.g.
`-xs:double(0.0)`

) and negative zeros will be written as a result of
packing.

`0x7fc0 0000`

(float), `0x7ff8 0000 0000 0000`

(double). These are the bit forms that will be
packed. 'Signalling' NaN values (`0x7f80 0001`

-> `0x7fbf ffff`

or `0xff80 0001`

-> `0xffbf ffff`

, ```
0x7ff0 0000 0000
0001
```

-> `0x7ff7 ffff ffff ffff`

or ```
0xfff0 0000 0000
0001
```

-> `0xfff7 ffff ffff ffff`

) encountered during unpacking will
be replaced by 'quiet' NaN. Any low-order payload in a unpacked quiet NaN is also zeroed.

Returns the 8-octet binary representation of a

Most-significant-octet-first number representation is assumed unless the
`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

The binary representation will correspond with that of the IEEE double-precision 64-bit
floating point type

`$octet-order`

is
unrecognized.

Returns the 4-octet binary representation of a

Most-significant-octet-first number representation is assumed unless the
`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

The binary representation will correspond with that of the IEEE single-precision 32-bit
floating point type

`$octet-order`

is
unrecognized.

Returns the *twos-complement* binary representation of an integer value treated as
`$size`

octets long. Any 'excess' high-order bits are discarded.

Most-significant-octet-first number representation is assumed unless the
`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

Specifying a `$size`

of zero yields an empty binary data.

`$octet-order`

is
unrecognized.

`$size`

is negative.

If the integer being packed has a maximum precision of `$size`

octets, then
signed/unsigned versions are not necessary. If the data is considered unsigned, then the
most significant bit of the bottom `$size`

octets has a normal positive
(`2^(8 *$size - 1)`

) meaning. If it is considered to be a signed value, then
the MSB and all the higher order, discarded bits will be '1' for a negative value and '0'
for a positive or zero. If this function were to check the 'sizing' of the supplied integer
against the packing size, then any values of MSB and the discarded higher order bits other
than 'all 1' or 'all 0' would constitute an error. *This function does not perfom such
checking.*

Extract

Extract the `$offset`

octet of the binary data of
`$in`

.

`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

The value of `$offset`

The `$offset`

is zero based.

The binary representation is expected to correspond with that of the IEEE double-precision
64-bit floating point type

`$offset`

is negative or
`$offset + 8`

(octet-length of `$in`

.

`$octet-order`

is
unrecognized.

Extract

Extract the `$offset`

octet of the binary data of
`$in`

.

`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

The value of `$offset`

The `$offset`

is zero based.

The binary representation is expected to correspond with that of the IEEE single-precision
32-bit floating point type

`$offset`

is negative or
`$offset + 4`

(octet-length of `$in`

.

`$octet-order`

is
unrecognized.

Returns a signed integer value represented by the `$size`

octets starting from
`$offset`

in the input binary representation. Necessary sign extension is
performed (i.e. the result is negative if the high order bit is '1').

`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

The values of `$offset`

and `$size`

`$offset`

is zero based.

Specifying a `$size`

of zero yields the integer `0`

.

`$offset`

is negative or
`$offset + $size`

is larger than the size of the binary data of
`$in`

.

`$size`

is negative.

`$octet-order`

is
unrecognized.

For discussion on integer range see

Returns an unsigned integer value represented by the `$size`

octets starting
from `$offset`

in the input binary representation.

`$octet-order`

parameter is specified. Acceptable values for
`$octet-order`

are described in

The values of `$offset`

and `$size`

The `$offset`

is zero based.

Specifying a `$size`

of zero yields the integer `0`

.

`$offset`

is negative or
`$offset + $size`

is larger than the size of the binary data of
`$in`

.

`$size`

is negative.

`$octet-order`

is
unrecognized.

For discussion on integer range see

Returns the "bitwise or" of two binary arguments.

Returns "bitwise or" applied between `$a`

and `$b`

.

If either argument is the empty sequence, an empty sequence is returned.

Returns the "bitwise xor" of two binary arguments.

Returns "bitwise exclusive or" applied between `$a`

and `$b`

.

If either argument is the empty sequence, an empty sequence is returned.

Returns the "bitwise and" of two binary arguments.

Returns "bitwise and" applied between `$a`

and `$b`

.

If either argument is the empty sequence, an empty sequence is returned.

Returns the "bitwise not" of a binary argument.

Returns "bitwise not" applied to `$in`

.

If the argument is the empty sequence, an empty sequence is returned.

Shift bits in binary data.

If `$by`

is positive then bits are shifted `$by`

times to the
left.

If `$by`

is negative then bits are shifted `-$by`

times to the
right.

If `$by`

is zero, the result is identical to `$in`

.

If `|$by|`

is greater than the bit-length of `$in`

then an all-zeros
result, of the same length as `$in`

, is returned.

`|$by|`

can be greater than 8, implying multi-byte shifts.

The result always has the same size as `$in`

.

The shifting is logical: zeros are placed into discarded bits.

If the value of `$in`

is the empty sequence, the function returns an empty
sequence.

Bit shifting across byte boundaries implies 'big-endian' treatment, i.e. the leftmost (high-order) bit when shifted left becomes the low-order bit of the preceding byte.