< draft-wildgrube-sdxf-07.txt		draft-wildgrube-sdxf-08.txt >
	Network Working Group M. Wildgrube		A new Request for Comments is now available in online RFC libraries.
	INTERNET-DRAFT
	Category: Informational
	Document: draft-wildgrube-sdxf-07.txt Oktober 2000
	Expiration Date: April 2001
	STRUCTURED DATA EXCHANGE FORMAT (SDXF)
	This document is an Internet-Draft and is in full conformance with
	all provisions of Section 10 of RFC2026.
	Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that
	other groups may also distribute working documents as
	Internet-Drafts.
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	The list of current Internet-Drafts can be accessed at
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	Please send your comments to the author: max@wildgrube.com
	Abstract:
	This specification describes an all-purpose interchange format for
	use as a file format or for net-working. Data is organized in chunks
	which can be ordered in hierarchical structures. This format is
	self-describing and CPU-independent.
	Table of Contents
	1. Introduction
	2. Description of the SDXF data format.
	3. Introduction to the SDXF functions
	3.1 General remarks
	3.2 Writing a SDXF buffer
	3.3 Reading a SDXF buffer
	3.4 Example
	4. Platform independence
	5. Compression
	6. Encryption
	7. Arrays
	8. Description of the SDXF functions
	8.1 Introduction
	8.2 Basic definitions
	8.3 Definitions for C++
	8.4 Common Definitions
	8.5 Special functions
	9. 'Support' of UTF-8
	10. Security Considerations
	11. Some general hints
	12. IANA considerations
	13. Discussion
	13.1 SDXF vs. ASN.1
	13.2 SDXF vs. XML
	14. Author's Address
	15. Acknowledgements
	16. References
	1. Introduction
	The purpose of the Structured Data eXchange Format (SDXF) is to
	permit the interchange of an arbitrary structured data block with
	different kinds of data (numerical, text, bitstrings).
	Because data is normalized to an abstract computer architecture
	independent "network format", SDXF is usable as a network
	interchange data format.
	This data format is not limited to any application, the demand for
	this format is that it is usable as a text format for
	word-processing, as a picture format, a sound format, for remote
	procedure calls with complex parameters, suitable for document
	formats, for interchanging business data, etc.
	SDXF is self-describing, every program can unpack every SDXF-data
	without knowing the meaning of the individual data elements.
	Together with the description of the data format a set of functions
	will be introduced. With the help of these functions one can create
	and access the data elements of SDXF. The idea is that a programmer
	should only use these functions instead of maintaining the structure
	by himself on the level of bits and bytes. (In the speech of
	object-oriented programming these functions are methods of an object
	which works as a handle for a given SDXF data block.)
	SDXF is not limited on a specific platform, along with a correct
	preparation of the SDXF functions the SDXF data can be interchanged
	(via network or data carrier) across the boundaries of different
	architectures (specified by the character code like ASCII, ANSI or
	EBCDIC and the byte order for binary data)
	SDXF is also prepared to compress and encrypt parts or the whole
	block of SDXF data.
	2. Description of SDXF data format.
	2.1 First we introduce the term "chunk". A chunk is a data structure
	with a fixed set of components. A chunk may be "elementary" or
	"structured". The latter one contains itself one or more other
	chunks.
	A chunk consists of a header and the data body (content):
	+----------+-----+-------+-----------------------------------+
	| Name | Pos.| Length| Description |
	+----------+-----+-------+-----------------------------------+
	| chunk-ID | 1 | 2 | ID of the chunk (unsigned short) |
	| flags | 3 | 1 | type and properties of this chunk |
	| length | 4 | 3 | length of the following data |
	| content | 7 | *) | net data or a list of of chunks |
	+----------+-----+-------+-----------------------------------+
	(* as stated in "length". total length of chunk is length+6.
	The chunk ID is a non-zero positive number.
	or more visually:
	+----+----+----+----+----+----+----+----+----+-...
	| chunkID | fl | length | content
	+----+----+----+----+----+----+----+----+----+-...
	or in ASN.1 syntax:
	chunk ::= SEQUENCE
	{
	chunkID INTEGER (1..65535),
	flags BIT STRING,
	length OCTET STRING SIZE 3, -- or: INTEGER (0..16777215)
	content OCTET STRING
	}
	2.2 Structured chunk.
	A structured chunk is marked as such by the flag byte (see 2.5).
	Opposed to an elementary chunk its content consists of a list of
	chunks (elementary or structured):
	+----+-+---+-------+-------+-------+-----+-------+
	| id |f|len| chunk | chunk | chunk | ... | chunk |
	+----+-+---+-------+-------+-------+-----+-------+
	With the help of this concept you can reproduce every hierarchically
	structured data into a SDXF chunk.
	2.3 Some Remarks about the internal representation of the chunk's
	elements:
	Binary values are always in high-order-first (big endian) format,
	like the binary values in the IP header (network format). A length
	of 300 (=256 + 32 + 12) is stored as
	+----+----+----+----+----+----+----+----+----+--
	| | | 00 01 2C | content
	+----+----+----+----+----+----+----+----+----+--
	in hexadecimal notation.
	This is also valid for the chunk-ID.
	2.4 Character values in the content portion are also an object of
	adaptation: see chapter 4.
	2.5 Meaning of the flag-bits: Let us represent the flag byte in this
	manner:
	+-+-+-+-+-+-+-+-+
	|0|1|2|3|4|5|6|7|
	+-+-+-+-+-+-+-+-+
	| | | | | | | |
	| | | | | | | +-- reserved
	| | | | | | +---- array
	| | | | | +------ short chunk
	| | | | +-------- encrypted chunk
	| | | +---------- compressed chunk
	| | |
	+-+-+------------ data type (0..7)
	data types are:
	0 -- pending structure (chunk is inconsistent, see also 11.1)
	1 -- structure
	2 -- bit string
	3 -- numeric
	4 -- character
	5 -- float (ANSI/IEEE 754-1985)
	6 -- UTF-8
	7 -- reserved
	2.6 A short chunk has no data body. The 3 byte Length field is used
	as data bytes instead. This is used in order to save space when
	there are many small chunks.
	2.7 Compressed and encrypted chunks are explained in chapter 5 and 6.
	2.8 Arrays are explained in chapter 7.
	2.9 Handling of UTF-8 is explained in chapter 9.
	2.10 Not all combinations of bits are allowed or reasonable:
	- the flags 'array' and 'short' are mutually exclusive.
	- 'short' is not applicable for data type 'structure' and 'float'.
	- 'array' is not applicable for data type 'structure'.
	3. Introduction to the SDXF functions
	3.1 General remarks
	The functionality of the SDXF concept is not bounded to any
	programming language, but of course the functions themselves must be
	coded in a particular language. I discuss these functions in C and
	C++, because in the meanwhile these languages are available on
	almost all platforms.
	All these functions for reading and writing SDXF chunks uses only
	one parameter, a parameter structure.
	In C++ this parameter structure is part of the "SDXF class" and the
	SDXF functions are methods of this class.
	An exact description of the interface is given in chapter 8.
	3.2 Writing a SDXF buffer
	For to write SDXF chunks, there are following functions:
	init -- initialize the parameter structure
	create -- create a new chunk
	leave -- "close" a structured chunk
	3.3 Reading a SDXF buffer
	For to read SDXF chunks, there are following functions:
	init -- initialize the parameter structure
	enter -- "go into" a structured chunk
	next -- "go to" the next chunk inside a structured chunk
	extract -- extract the content of an elementary chunk into
	user's data area
	leave -- "go out" off a structured chunk
	3.4 Example:
	3.4.1 Writing:
	(For demonstration we use a reduced (outlined) C++ Form of these
	functions with polymorph definitions:
	void create (short chunkID); // opens a new structure,
	void create (short chunkID, char *string);
	// creates a new chunk with dataType character, etc.)
	The sequence:
	SDXF x(new); // create the SDXF object "x" for a new chunk
	// includes the "init"
	x.create (3301); // opens a new structure
	x.create (3302, "first chunk");
	x.create (3303, "second chunk");
	x.create (3304); // opens a new structure
	x.create (3305, "chunk in a structure");
	x.create (3306, "next chunk in a structure");
	x.leave (); // closes the inner structure
	x.create (3307, "third chunk");
	x.leave (); // closes the outer structure
	creates a chunk which we can show graphically like:
	3301
	|
	+--- 3302 = "first chunk"
	|
	+--- 3303 = "second chunk"
	|
	+--- 3304
	| |
	| +--- 3305 = "chunk in a structure"
	| |
	| +--- 3306 = "next chunk in a structure"
	|
	+--- 3307 = "last chunk"
	3.4.2 Reading
	A typically access to a structured SDXF chunk is a selection inside
	a loop:
	SDXF x(old); // defines a SDXF object "x" for an old chunk
	x.enter (); // enters the structure
	while (x.rc == 0) // 0 == ok, rc will set by the SDXF functions
	{
	switch (x.chunkID)
	{
	case 3302:
	x.extract (data1, maxLength1);
	// extr. 1st chunk into data1
	break;
	case 3303:
	x.extract (data2, maxLength2);
	// extr. 2nd chunk into data2
	break;
	case 3304: // we know this is a structure
	x.enter (); // enters the inner structure
	while (x.rc == 0) // inner loop
	{
	switch (x.chunkID)
	{
	case 3305:
	x.extract (data3, maxLength3);
	// extr. the chunk inside struct.
	break;
	case 3306:
	x.extract (data4, maxLength4);
	// extr. 2nd chunk inside struct.
	break;
	}
	x.next (); // returns x.rc == 1 at end of structure
	} // end-while
	break;
	case 3307:
	x.extract (data5, maxLength5);
	// extract last chunk into data
	break;
	// default: none - ignore unknown chunks !!!
	} // end-switch
	x.next (); // returns x.rc = 1 at end of structure
	} // end-while
	4. Platform independence
	The very most of the computer platforms today have a
	8-Bits-in-a-Byte architecture, which enables data exchange between
	these platforms. But there are two significant points in which
	platforms may be different:
	a) The representation of binary numerical (the short and long int
	and floats).
	b) The representation of characters (ASCII/ANSI vs. EBCDIC)
	Point (a) is the phenomenon of "byte swapping": How is a short int
	value 259 = 0x0103 = X'0103' be stored at address 4402?
	The two flavours are:
	4402 4403
	01 03 the big-endian, and
	03 01 the little-endian.
	Point (b) is represented by a table of the assignment of the 256
	possible values of a Byte to printable or control characters. (In
	ASCII the letter "A" is assigned to value (or position) 0x41 = 65,
	in EBCDIC it is 0xC1 = 193.)
	The solution of these problems is to normalize the data:
	We fix:
	(a) The internal representation of binary numerals are 2-complements
	in big-endian order.
	(b) The internal representation of characters is ISO 8859-1 (also
	known as Latin 1).
	The fixing of point (b) should be regarded as a first strike. In
	some environment 8859-1 seems not to be the best choice, in a greek
	or russian environment 8859-5 or 8859-7 are appropriate.
	Nevertheless, in a specific group (or world) of applications, that
	is to say all the applications which wants to interchange data with
	a defined protocol (via networking or diskette or something else),
	this internal character table must be unique.
	So a possibility to define a translation table (and his inversion)
	should be given.
	Important: You construct a SDXF chunk not for a specific addressee,
	but you adapt your data into a normalized format (or network format).
	This adaption is not done by the programmer, it will be done by the
	create and extract function. An administrator has take care of
	defining the correct translation tables.
	5. Compression
	As stated in 2.5 there is a flag bit which declares that the
	following data (elementary or structured) are compressed. This data
	is not further interpretable until it is decompressed. Compression
	is transparently done by the SDXF functions: "create" does the
	compression for elementary chunks, "leave" for structured chunks,
	"extract" does the decompression for elementary chunks, "enter" for
	structured chunks.
	Transparently means that the programmer has only to tell the SDXF
	functions that he want compress the following chunk(s).
	For choosing between different compression methods and for
	controlling the decompressed (original) length, there is an
	additional definition:
	After the chunk header for a compressed chunk, a compression header
	is following:
	+-----------------------+---------------+---------------->
	| chunk header | compr. header | compressed data
	+---+---+---+---+---+---+---+---+---+---+---------------->
	|chunkID|flg| length |md | orglength |
	+---+---+---+---+---+---+---+---+---+---+---------------->
	- 'orglength' is the original (decompressed) length of the data.
	- 'md' is the "compression method": Two methods are described here:
	# method 01 for a simple (fast but not very effective)
	"Run Length 1" or "Byte Run 1" algorithm. (More then two
	consecutive identical characters are replaced by the number of
	these characters and the character itself.)
	more precisely:
	The compressed data consists of several sections of various
	length. Every section starts with a "counter" byte, a signed
	"tiny" (8 bit) integer, which contains a length information.
	If this byte contains the value "n",
	with n >= 0 (and n <128), the next n+1 bytes will be taken
	unchanged;
	with n < 0 (and n > -128), the next byte will be replicated
	-n+1 times;
	n = -128 will be ignored.
	Appending blanks will be cutted in general. If these are
	necessary, they can be reconstructed while "extract"ing with
	the parameter field "filler" (see 8.2.1) set to space
	character.
	# method 02 for the wonderful "deflate" algorithm which comes
	from the "zip"-people.
	The authors are:
	Jean-loup Gailly (deflate routine),
	Mark Adler (inflate routine), and others.
	The deflate format is described in [DEFLATE]. For more
	information: see http://www.info-zip.org/pub/infozip
	The values for the compression method number are maintained by
	IANA, see chap. 12.1.
	6. Encryption
	As stated in 2.5 there is a flag bit which declares that the
	following data (elementary or structured) is encrypted. This data is
	not interpretable until it is decrypted. En/Decryption is
	transparently done by the SDXF functions, "create" does the
	encryption for elementary chunks, "leave" for structured chunks,
	"extract" does the decryption for elementary chunks, "enter" for
	structured chunks. (Yes it sounds very similar to chapter 5.)
	More then one encryption method for a given range of applications is
	not very reasonable. We specify that the length of the data will not
	be changed by encryption. So a special encryption header (similar as
	the compression header) is not necessary.
	If an application (or network connect handshaking protocol) needs to
	negotiate an encryption method it should be used a method number
	maintained by IANA, see chap. 12.2.
	Even the en/decryption is done transparently, an encryption key
	(password) must be given to the SDXF functions.
	Encryption is done after translating character data into, decryption
	is done before translation from the internal ("network-") format.
	If both, encryption and compression are applied on the same chunk,
	compression is done first - compression on good encrypted data (same
	strings appears as different after encryption) tends to zero
	compression rates.
	7. Arrays
	An array is a sequence of chunks with identical chunk-ID, length and
	data type.
	At first a hint: in principle a special definition in SDXF for such
	an array is not really necessary:
	It is not forbidden that there are more than one chunk with equal
	chunk-ID within the same structured chunk.
	Therefore with a sequence of SDX_next / SDX_extract calls one can
	fill the destination array step by step.
	If there are many occurences of chunks with the same chunk-ID (and a
	comparative small length), the overhead of the chunk-packages may be
	significant.
	Therefore the array flag is introduced. An array chunk has only one
	chunk header for the complete sequence of elementary chunks. After
	the chunk header for an array chunk, an array header is following:
	This is a short integer (big endian!) which contains the number of
	the array elements (CT) . Every element has a fixed length (EL), so
	the chunklength (CL) is CL = EL * CT + 2.
	The data elements follows immediately after the array header.
	The complete array will be constructed by SDX_create, the complete
	array will be read by SDX_extract.
	The parameter fields (see 8.2.1) 'dataLength' and 'count' are used
	for the SDXF functions 'extract' and 'create':
	Field 'dataLength' is the common length of the array elements,
	'count' is the actual dimension of the array for 'create' (input).
	For the 'extract' function 'count' acts both as an input and output
	parameter:
	Input : the maximum dimension
	output: the actual array dimension.
	(If output count is greater than input count, the 'data cutted'
	warning will be responded and the destination array is filled up to
	the maximum dimension.)
	8. Description of the SDXF functions
	8.1 Introduction
	Following the principles of Object Oriented Programming, not only
	the description of the data is necessary, but also the functions
	which manipulate data - the "methods".
	For the programmer knowing the methods is more important than
	knowing the data structure, the methods has to know the exact
	specifications of the data and guarantees the consistence of the
	data while creating them.
	A SDXF object is an instance of a parameter structure which acts as
	a programming interface. Especially it points to an actual SDXF data
	chunk, and, while processing on this data, there is a pointer to the
	actual inner chunk which will be the focus for the next operation.
	The benefit of an exact interface description is the same as using
	for example the standard C library functions: By using standard
	interfaces your code remains platform independent.
	8.2 Basic definitions
	8.2.1 The SDXF Parameter structure
	All SDXF access functions need only one parameter, a pointer to the
	SDXF parameter structure:
	First 3 prerequisite definitions:
	typedef short int ChunkID;
	typedef unsigned char Byte;
	typedef struct Chunk
	{
	ChunkID chunkID;
	Byte flags;
	char length [3];
	Byte data;
	} Chunk;
	And now the parameter structure:
	typedef struct
	{
	ChunkID chunkID; // name (ID) of Chunk
	Byte *container; // pointer to the whole Chunk
	long bufferSize; // size of container
	Chunk *currChunk; // pointer to actual Chunk
	long dataLength; // length of data in Chunk
	long maxLength; // max. length of Chunk for SDX_extract
	long remainingSize; // rem. size in cont. after SDX_create
	long value; // for data type numeric / init option
	double fvalue; // for data type float
	char *function; // name of the executed SDX function
	Byte *data; // pointer to Data
	Byte *cryptkey; // pointer to Crypt Key
	short count; // (max.) number of elements in an array
	short dataType; // Chunk data type / init open type
	short ec; // extended return-code
	short rc; // return-code
	short level; // level of hierarchy
	char filler; // filler char for SDX_extract
	Byte encrypt; // Indication if data to encrypt (0 / 1)
	Byte compression; // compression method
	// (00=none, 01=RL1, 02=zip/deflate)
	} SDX_obj, *SDX_handle;
	Only the "public" fields of the parameter structure which acts as
	input and output for the SDXF functions is described here.
	A given implementation may add some "private" fields to this
	structure.
	8.2.2 Basic Functions
	All these functions works with a SDX_handle as the only formal
	parameter. Every function returns as output ec and rc as a report of
	success. For the values for ec, rc and dataType see chap. 8.4.
	1. SDX_init : Initialize the parameter structure.
	input : container, dataType, bufferSize (for dataType =
	SDX_NEW only)
	output: currChunk, dataLength (for dataType = SDX_OLD only),
	ec, rc,
	the other fields of the parameter structure will be
	initialized.
	2. SDX_enter : Enter a structured chunk.
	You can access the first chunk inside this structured chunk.
	input : none
	output: currChunk, chunkID, dataLength, level, dataType,
	ec, rc
	3. SDX_leave : Leave the actual entered structured chunk.
	input : none
	output: currChunk, chunkID, dataLength, level, dataType,
	ec, rc
	4. SDX_next : Go to the next chunk inside a structured chunk.
	input : none
	output: currChunk, chunkID, dataLength, dataType, count,
	ec, rc
	At the end of a structured chunk SDX_next returns rc =
	SDX_RC_failed and ec = SDX_EC_eoc (end of chunk)
	The actual structured chunk is SDX_leave'd automatically.
	5. SDX_extract : Extract data of the actual chunk.
	(If actual chunk is structured, only a copy is done, elsewhere
	the data is converted to host format.)
	input / output depends on the dataType:
	if dataType is structured, binary or char:
	input : data, maxLength, count, filler
	output: dataLength, count, ec, rc
	if dataType is numeric (float resp.):
	input : none
	output: value (fvalue resp.), ec, rc
	6. SDX_select : Go to the (next) chunk with a given chunkID.
	input : chunkID
	output: currChunk, dataLength, dataType, ec, rc
	7. SDX_create : Creating a new chunk (at the end of the actual
	structured chunk).
	input : chunkID, dataLength, data, (f)value, dataType,
	compression, encrypt, count
	update: remainingSize, level
	output: currChunk, dataLength, ec, rc
	8. SDX_append : Append a complete chunk at the end of the actual
	structured chunk).
	input : data, maxLength, currChunk
	update: remainingSize, level
	output: chunkID, chunkLength, maxLength, dataType, ec, rc
	8.3 Definitions for C++
	This is the specification of the SDXF class in C++: (The type 'Byte'
	is defined as "unsigned char" for bitstrings, opposed to "signed
	char" for character strings)
	class C_SDXF
	{
	public:
	// constructors and destructor:
	C_SDXF (); // dummy
	C_SDXF (Byte *cont); // old container
	C_SDXF (Byte *cont, long size); // new container
	C_SDXF (long size); // new container
	~C_SDXF ();
	// methods:
	void init (void); // old container
	void init (Byte *cont); // old container
	void init (Byte *cont, long size); // new container
	void init (long size); // new container
	void enter (void);
	void leave (void);
	void next (void);
	long extract (Byte *data, long length); // chars, bits
	long extract (void); // numeric data
	void create (ChunkID); // structured
	void create (ChunkID, long value); // numeric
	void create (ChunkID, double fvalue); // float
	void create (ChunkID, Byte *data, long length);// binary
	void create (ChunkID, char *data); // chars
	void set_compression (Byte compression_method);
	void set_encryption (Byte *encryption_key);
	// interface:
	ChunkID id; // see 8.4.1
	short dataType; // see 8.4.2
	long length; // length of data or chunk
	long value;
	double fvalue;
	short rc; // the raw return code see 8.4.3
	short ec; // the extended return code see 8.4.4
	protected:
	// implementation dependent ...
	};
	8.4 Common Definitions:
	8.4.1 Definition of ChunkID:
	typedef short ChunkID;
	8.4.2 Values for dataType:
	SDX_DT_inconsistent = 0
	SDX_DT_structured = 1
	SDX_DT_binary = 2
	SDX_DT_numeric = 3
	SDX_DT_char = 4
	SDX_DT_float = 5
	data types for SDX_init:
	SDX_OLD = 1
	SDX_NEW = 2
	8.4.3 Values for rc:
	SDX_RC_ok = 0
	SDX_RC_failed = 1
	SDX_RC_warning = 1
	SDX_RC_illegalOperation = 2
	SDX_RC_dataError = 3
	SDX_RC_parameterError = 4
	SDX_RC_programError = 5
	SDX_RC_noMemory = 6
	8.4.4 Values for ec:
	SDX_EC_ok = 0
	SDX_EC_eoc = 1 // end of chunk
	SDX_EC_notFound = 2
	SDX_EC_dataCutted = 3
	SDX_EC_overflow = 4
	SDX_EC_wrongInitType = 5
	SDX_EC_comprerr = 6 // compression error
	SDX_EC_forbidden = 7
	SDX_EC_unknown = 8
	SDX_EC_levelOvflw = 9
	SDX_EC_paramMissing = 10
	SDX_EC_magicError = 11
	SDX_EC_not_consistent = 12
	SDX_EC_wrongDataType = 13
	SDX_EC_noMemory = 14
	SDX_EC_error = 99 // rc is sufficiently
	8.5 Special functions
	Besides the basic definitions there is a global function
	(SDX_getOptions) which returns a pointer to a global table of
	options.
	With the help of these options you can adapt the behaviour of SDXF.
	Especially you can define an alternative pair of translation tables
	or an alternative function which reads these tables from an external
	resource (p.e. from disk).
	Within this table of options there is also a pointer to the function
	which is used for encryption / decryption: You can install your own
	encryption algorithm by setting this pointer.
	The options pointer is received by:
	SDX_TOptions opt = SDX_getOptions ();
	With:
	typedef struct
	{
	Byte *toHost; // Trans tab net -> host
	Byte *toNet; // Trans tab host -> net
	int maxlevel; // highest possible level
	int translation; // translation net <-> host
	// is in effect=1 or not=0
	TEncryptProc *encryptProc; // alternate encryption routine
	TGetTablesProc *getTablesProc; // alternate routine defining
	// translation Tables
	TcvtUTF8Proc *convertUTF8; // routine to convert to/from UTF-8
	} SDX_TOptions;
	typedef int TEncryptProc
	( int mode, // 1 = to encrypt, 2 = to decrypt
	Byte *buffer, // data to en/decrypt
	long len, // len: length of buffer
	char *passw); // Password
	// returns success: 1 = ok, 0 = error
	typedef int TGetTablesProc (Byte **toNet, Byte **toHost);
	// toNet, toHost: pointer to output params. Both params
	// points to translation tables of 256 Bytes.
	// returns success: 1 = ok, 0 = error.
	typedef int TcvtUTF8Proc
	( int mode, // 1 = to UTF-8, 2 = from UTF-8
	Byte *target, int *targetlength, // output
	Byte *source, int sourcelength); // input
	// targetlength contains maximal size as input param.
	// returns success: 1 = ok, 0 = no conversion
	9. 'Support' of UTF-8.
	Many systems supports [UTF-8] as a character format for transferred
	data. The benefit is that no fixing of a specific character set for
	an application is needed because the set of 'all' characters is
	used, represented by the 'Universal Character Set' UCS-2 [UCS], a
	double byte coding for characters.
	SDXF does not really deal with UTF-8 by itself, there are many
	possibilities to interprete an UTF-8 sequence:
	The application may:
	- reconstruct the UCS-2 sequence,
	- accepts only the pure ASCII character and maps non-ASCII to a
	special 'non-printable' character.
	- target is pure ASCII, non-ASCII is replaced in a senseful manner
	(French accented vowels replaced by vowels without accents, etc.).
	- target is a specific ANSI character set, the non-ASCII chars are
	mapped as possible, other replaced to a 'non-printable'.
	- etc.
	But SDXF offers an interface for the 'extract' and 'create'
	functions:
	A function pointer may be specified in the options table to maintain
	this possibility (see 8.5).
	Default for this pointer is NULL: No further conversions are done by
	SDXF, the data are copied 'as is', it is treated as a bit string as
	for data type 'binary'.
	If this function is specified, it is used by the 'create' function
	with the 'toUTF8' mode, and by the 'extract' function with the
	'fromUTF8' mode. The invoking of these functions is done by SDXF
	transparently.
	If the function returns zero (no conversion) SDXF copies the data
	without conversion.
	10. Security Considerations
	Any corruption of data in the chunk headers denounce the complete
	SDXF structure.
	Any corruption of data in a encrypted or compressed SDXF structure
	makes this chunk unusable. An integrity check after decryption or
	decompression should be done by the "enter" function.
	While using TCP/IP (more precisely: IP) as a transmission medium we
	can trust on his CRC check on the transport layer.
	11. Some general hints
	1. A consistent construction of a SDXF structure is done if every
	"create" to a structured chunk is closed by a paired "leave".
	While a structured chunk is under construction, his data type is
	set to zero - that means: this chunk is inconsistent. The
	SDX_leave function sets the datatype to "structured".
	2. While creating an elementary chunk a platform dependent
	transformation to a platform independent format of the data is
	performed - at the end of construction the content of the buffer
	is ready to transport to another site, without any further
	translation.
	3. As you see no data definition in your programming language is
	needed for to construct a specific SDXF structure. The data is
	created dynamically by function calls.
	4. With SDXF as a base you can define protocols for client / server
	applications. With following two rules these protocols may be
	extended in downward compatibility manner:
	Rule 1: Ignore unknown chunkIDs.
	Rule 2: The sequence of chunks should not be significant.
	12. IANA considerations
	The compression and encryption algorithms for SDXF is not fixed,
	SDXF is open for various algorithms. Therefore an agreement is
	necessary to interprete the compression and encryption algorithm
	method numbers.
	(encryption methods are not a semantic part of SDXF, but may be used
	for a connection protocol to negotiate the encryption method to use)
	Following two items are registered by IANA:
	12.1 COMPRESSION METHODS FOR SDXF
	The compressed SDXF chunk starts with a "compression header". This
	header contains the compression method as an unsigned 1-Byte integer
	(1-255). These numbers are assigned by IANA and listed here:
	compression
	method Description Hints
	--------- ------------------------------- -------------
	01 RUN-LENGTH algorithm see chap. 5
	02 DEFLATE (ZIP) see [DEFLATE]
	03-239 IANA to assign
	240-255 private or application specific
	12.2 ENCRYPTION METHODS FOR SDXF
	An unique encryption method is fixed or negotiated by handshaking.
	For the latter one a number for each encryption method is necessary.
	These numbers are unsigned 1-Byte integers (1-255). These numbers
	are assigned by IANA and listed here:
	encryption
	method Description
	--------- ------------------------------
	01-239 IANA to assign
	240-255 private or application specific
	12.3 Hints for assigning a number:
	Developers which want to register a compression or encrypt method
	for SDXF should contact IANA for a method number. The ASSIGNED
	NUMBERS document should be referred to for a current list of METHOD
	numbers and their corresponding protocols, see [IANA].
	The new method SHOULD be a standard published as a RFC or by a
	established standardization organization (as OSI).
	13. Discussion
	There are already some standards for Internet data exchanging, IETF
	prefers ASN.1 and XML therefore. So the reasons for establish a new
	data format should be discussed.
	13.1 SDXF vs. ASN.1
	The demand of ASN.1 (see [ASN.1]) is to serve program language
	independent means to define data structures. The real data format
	which is used to send the data is not defined by ASN.1 but usually
	BER or PER (or some derivates of them like CER and DER) are used in
	this context, see [BER] and [PER].
	The idea behind ASN.1 is: On every platform on which a given
	application is to develop descriptions of the used data structures
	are available in ASN.1 notation. Out off these notations the real
	language dependent definitions are generated with the help of an
	ASN.1-compiler.
	This compiler generates also transform functions for these data
	structures for to pack and unpack to and from the BER (or other)
	format.
	A direct comparison between ASN.1 and SDXF is somehow inappropriate:
	The data format of SDXF is related rather to BER (and relatives).
	The use of ASN.1 to define data structures is no contradiction to
	SDXF, but: SDXF does not require a complete data structure to build
	the message to send, nor a complete data structure will be generated
	out off the received message.
	The main difference lies in the concept of building and
	interpretation of the message, I want to name it the "static" and
	"dynamic" concept:
	o ASN.1 uses a "static" approach: The whole data structure must
	exists before the message can be created.
	o SDXF constructs and interpretes the message in a "dynamic" way,
	the message will be packed and unpacked step by step by the SDXF
	functions.
	The use of static structures may be appropriate for a series of
	applications, but for complex tasks it is often impossible to define
	the message as a whole.
	As an example try to define an ASN.1 description for a complex
	structured text document which is presented in XML:
	There are sections and paragraphs and text elements which may
	recursively consist of sections with specific text attributes.
	13.2 SDXF vs. XML
	On the one hand SDXF and XML are similar as they can handle any
	recursive complex data stream. The main difference is the kind of
	data which are to be maintained:
	o XML works with pure text data (though it should be noted that the
	character representation is not standardized by XML). And: a XML
	document with all his tags is readable by human. Binary data as
	graphic is not included directly but may be referenced by an
	external link as in HTML.
	In XML there is no strong separation between informational and
	control data, escape characters (like "<" and "&") and the
	[data[...]] construction are used to distinguish between these
	two types of data.
	o SDXF maintains machine-readable data, it is not designed to be
	readable by human nor to edit SDXF data with a text editor (even
	more if compression and encryption is used). With the help of the
	SDXF functions you have a quick and easy access to every data
	element. The standard parser for a SDXF data structure follows
	always a simple template, the "while - switch -case ID -
	enter/extract" pattern as outlined in chap. 3.4.2.
	Because of the complete different philosophy behind XML and SDXF
	(and even ASN.1) a direct comparison may not be very senseful, as
	XML has its own right to exist next to ASN.1 (and even SDXF).
	Nevertheless there is a chance to convert a XML data stream into a
	SDXF structure:
	As a first strike, every XML tag becomes a SDXF chunk ID. An
	elementary sequence <tag>pure text</tag> can be transformed into an
	elementary (non-structured) chunk with data type "character". Tags
	with attributes and sequences with nested tags are transformed into
	structured chunks.
	Because XML allows a tag sequence everywhere in a text stream, an
	artifically "elementary text" tag must be introduced:
	If <t> is the tag for text elements, the sequence:
	<t>this is a text <attr value='bold'>with</attr> attributes</t>
	is to be "in thought" replaced by:
	<t><et>this is a text </et><attr value='bold'><et>with</et></attr>
	<et> attributes</et></t>
	(With "et" as the "elementary text" tag)
	This results in following SDXF structure:
	ID_t
	|
	+-- ID_et = " this is a text "
	|
	+-- ID_attr
	| |
	| +-- ID_value = "bold"
	| |
	| +-- ID_et = "with"
	|
	+-- ID_et = " attributes"
	ID_t and ID_et may be represented by the same chunk ID, only
	distinguished by the data type ("structured" for <t> and "character"
	for <et>)
	Binary data as pictures can be directly imbedded into a SDXF
	structure instead referencing them as an external link like in HTML.
	14. Author's Address
	Max Wildgrube
	Schlossstrasse 120
	60486 Frankfurt
	Germany
	EMail: max@wildgrube.com		RFC 3072
	15. Acknowledgements		Title: Structured Data Exchange Format (SDXF)
			Author(s): M. Wildgrube
			Status: Informational
			Date: March 2001
			Mailbox: max@wildgrube.com
			Pages: 25
			Characters: 48481
			Updates/Obsoletes/SeeAlso: None
	I would like to thank Michael J. Slifcak (mslifcak@iss.net) for the		I-D Tag: draft-wildgrube-sdxf-08.txt
	supporting discussions.
	16. References		URL: ftp://ftp.rfc-editor.org/in-notes/rfc3072.txt
	[ASN.1] Information processing systems - Open Systems		This specification describes an all-purpose interchange format for
	Interconnection, "Specification of Abstract Syntax		use as a file format or for net-working. Data is organized in chunks
	Notation One (ASN.1)", International Organization for		which can be ordered in hierarchical structures. This format is
	Standardization, International Standard 8824, December		self-describing and CPU-independent.
	1987.
	[BER] Information Processing Systems - Open Systems		This memo provides information for the Internet community. It does
	Interconnection - "Specification of Basic Encoding Rules		not specify an Internet standard of any kind. Distribution of this
	for Abstract Notation One (ASN.1)", International		memo is unlimited.
	Organization for Standardization, International Standard
	8825-1, December 1987.
	[DEFLATE] L. Peter Deutsch 1996 (and Jean-Loup Gailly, Mark Adler):		This announcement is sent to the IETF list and the RFC-DIST list.
	DEFLATE Compressed Data Format Specification version 1.3		Requests to be added to or deleted from the IETF distribution list
			should be sent to IETF-REQUEST@IETF.ORG. Requests to be
			added to or deleted from the RFC-DIST distribution list should
			be sent to RFC-DIST-REQUEST@RFC-EDITOR.ORG.
	[IANA] Internet Assigned Numbers Authority,		Details on obtaining RFCs via FTP or EMAIL may be obtained by sending
	http://www.iana.org/numbers.htm		an EMAIL message to rfc-info@RFC-EDITOR.ORG with the message body
			help: ways_to_get_rfcs. For example:
	[PER] Information Processing Systems - Open Systems		To: rfc-info@RFC-EDITOR.ORG
	Interconnection -"Specification of Packed Encoding Rules		Subject: getting rfcs
	for Abstract Syntax Notation One (ASN.1)", International
	Organization for Standardization, International Standard
	8825-2.
	[UCS] ISO/IEC 10646-1:1993. International Standard --		help: ways_to_get_rfcs
	Information technology --Universal Multiple-Octet Coded
	Character Set (UCS)
	[UTF8] RFC 2279: UTF-8, a transformation format of ISO 10646, F.		Requests for special distribution should be addressed to either the
	Yergeau, January 1998		author of the RFC in question, or to RFC-Manager@RFC-EDITOR.ORG. Unless
			specifically noted otherwise on the RFC itself, all RFCs are for
			unlimited distribution.echo
			Submissions for Requests for Comments should be sent to
			RFC-EDITOR@RFC-EDITOR.ORG. Please consult RFC 2223, Instructions to RFC
			Authors, for further information.
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