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The Hessian home page contains the latest information about Hessian.

Unlike older binary protocols, Hessian is both self-describing, compact, and portable across languages. The wire protocol for web services should be invisible to application writers, it should not require external schema or IDL.

The Hessian protocol has the following design goals:

- It must not require external IDL or schema definitions, i.e. the protocol should be invisible to application code.
- It must have sufficient power to serialize Java, including circular references.
- It must be language-independent. In particular, it must allow non-Java clients to use web services.
- It must be simple so it can be effectively tested and implemented.
- It must be as fast as possible.
- It must be as compact as possible.
- It must support unicode strings.
- It must support 8-bit binary data (i.e. without encoding or using attachments.)
- It must allow web services to deployed as a Servlet.
- It must have sufficient power to support EJB.
- It must support encryption, compression, signature, and transaction context envelopes.
- Hessian 2.0 must be backwards compatible with Hessian 1.0. Hessian 2.0 parsers must be read Hessian 1.0 messages.

# starting production top ::= object # 8-bit binary data split into 64k chunks binary ::= 'b' b1 b0 <binary-data> binary # non-final chunk ::= 'B' b1 b0 <binary-data> # final chunk ::= [x20-x2f] <binary-data> # binary data of length 0-15 # boolean true/false boolean ::= 'T' ::= 'F' # time in UTC encoded as 64-bit long milliseconds since epoch date ::= 'd' b7 b6 b5 b4 b3 b2 b1 b0 # 64-bit IEEE double double ::= 'D' b7 b6 b5 b4 b3 b2 b1 b0 ::= x67 # 0.0 ::= x68 # 1.0 ::= x69 b0 # byte cast to double (-128.0 to 127.0) ::= x6a b1 b0 # short cast to double ::= x6b b3 b2 b1 b0 # 32-bit float cast to double # 32-bit signed integer int ::= 'I' b3 b2 b1 b0 ::= [x80-xbf] # -x10 to x3f ::= [xc0-xcf] b0 # -x800 to x7ff ::= [xd0-xd7] b1 b0 # -x40000 to x3ffff # list/vector length length ::= 'l' b3 b2 b1 b0 ::= x6e int # list/vector list ::= 'V' type? length? object* 'z' ::= 'v' int int object* # type-ref, length # 64-bit signed long integer long ::= 'L' b7 b6 b5 b4 b3 b2 b1 b0 ::= [xd8-xef] # -x08 to x0f ::= [xf0-xff] b0 # -x800 to x7ff ::= [x38-x3f] b1 b0 # -x40000 to x3ffff ::= x77 b3 b2 b1 b0 # 32-bit integer cast to long # map/object map ::= 'M' type? (object object)* 'z' # key, value map pairs ::= 'o' int object* # Object instance - type-ref # null value null ::= 'N' # main production for object serialization object ::= null ::= binary ::= boolean ::= date ::= double ::= int ::= list ::= long ::= map ::= object-def object ::= remote ::= ref ::= string ::= xml # definition for an object (compact map) object-def ::= 'O' type int string* # Object reference (e.g. circular trees and graphs) ref ::= 'R' b3 b2 b1 b0 # reference to nth map/list in stream ::= x4a b0 # reference to 1-255th map/list ::= x4b b1 b0 # reference to 1-65535th map/list # UTF-8 encoded character string split into 64k chunks string ::= 's' b1 b0 <string-data> string # non-final chunk ::= 'S' b1 b0 <string-data> # string of length 0-65535 ::= [x00-x1f] <string-data> # string of length 0-31 # map/list types for OO languages type ::= 't' b1 b0 <type-string> # type name ::= x75 int # type reference # UTF-8 encoded XML data xml ::= 'x' b1 b0 <xml-data> xml ::= 'X' b1 b0 <xml-data> top ::= call ::= envelope ::= message ::= reply # RPC-style call call ::= 'c' x02 x00 method object* 'z' # Envelope for encryption/headers envelope ::= 'E' x02 x00 env-chunk* 'z' # header, body, footer env-chunk ::= int (string object)* binary int (string object)* fault ::= 'f' (object object)* 'z' # message/streaming message message ::= 'p' x02 x00 object* 'z' ::= 'P' x02 x00 object* 'z' # RPC method name (possibly mangled for overloading) method ::= 'm' b1 b0 <method-string> # RPC reply reply ::= 'r' x02 x00 object 'z' # successful message/reply ::= 'r' x02 x00 fault 'z' # exception/fault reply

Hessian's object serialization has 9 primitive types:

1. boolean
2. 32-bit int
3. 64-bit long
4. 64-bit double
5. 64-bit date
6. UTF8-encoded string
7. UTF8-encoded xml
8. raw binary data
9. remote objects

It has 2 combining constructs:

1. list for lists and arrays
2. map for objects and hash tables.

Finally, it has 2 special contructs:

1. null for null values
2. ref for shared and circular object references.

Hessian 2.0 has 3 reference maps:

1. An object/list reference map.
2. A type (class) reference map.
3. An object definition reference map.

binary ::= b b1 b0 <binary-data> binary ::= B b1 b0 <binary-data> ::= [x20-x2f] <binary-data>

Binary data is encoded in chunks. 'B' represents the final chunk and 'b' represents any non-final chunk. Each chunk has a 16-bit length value.

Binary data with length less than 15 may be encoded with a single length byte [x20-x2f].

x20 # zero-length binary data x23 x01 x02 x03 # 3 byte data B x10 x00 .... # 4k final chunk of data b x04 x00 .... # 1k non-final chunk of data boolean ::= T ::= F

The byte 'F' represents false and the byte 'T' represents true.

T # true F # false <def> date ::= d b7 b6 b5 b4 b3 b2 b1 b0

Date represented by a 64-bit long of milliseconds since the epoch, GMT.

d x00 x00 x00 xd0 x4b x92 x84 xb8 double ::= D b7 b6 b5 b4 b3 b2 b1 b0 ::= x67 ::= x68 ::= x69 b0 ::= x6a b1 b0 ::= x6b b3 b2 b1 b0

A 64-bit IEEE floating pointer number.

The double 0.0 can be represented by the byte `x67`

The double 1.0 can be represented by the byte `x68`

Doubles between -128.0 and 127.0 with no fractional component can be represented in two bytes by casting the byte value to a double.

Doubles between -32768.0 and 32767.0 with no fractional component can be represented in three bytes by casting the short value to a double.

Doubles which are equivalent to their 32-bit float representation can be represented as the 4-byte float and then cast to double.

x67 # 0.0 x68 # 1.0 x69 x00 # 0.0 x69 x80 # -128.0 x69 xff # 127.0 x70 x00 x00 # 0.0 x70 x80 x00 # -32768.0 x70 xff xff # 32767.0 D x40 x28 x80 x00 x00 x00 x00 x00 # 12.25 int ::= 'I' b3 b2 b1 b0 ::= [x80-xbf] ::= [xc0-xcf] b0 ::= [xd0-xd7] b1 b0

A 32-bit signed integer. An integer is represented by the byte 'I' followed by the 4-bytes of the integer in big-endian order

Integers between -16 and 47 can be encoded by a single byte in the range `x80` to `xbf`. The value of the integer is `code - x90`.

Integers between -2048 and 2047 can be encoded in two bytes with the leading byte in the range `xc0` to `xcf`. The value of the integer is `256 * (code - xc8) + b0`.

Integers between -262144 and 262143 can be encoded in three bytes with the leading byte in the range `xd0` to `xd7`. The value of the integer is `65536 * (code - xd4) + 256 * b1 + b0`.

x90 # 0 x80 # -16 xbf # 47 xc8 x00 # 0 xc0 x00 # -2048 xc7 x00 # -256 xcf xff # 2047 xd4 x00 x00 # 0 xd0 x00 x00 # -262144 xd7 xff xff # 262143 I x00 x00 x00 x00 # 0 I x00 x00 x01 x2c # 300 list ::= V type? length? object* z ::= v int int object*

An ordered list, like an array. All lists have a type string, a length, a list of objects, and a trailing 'z'. The type string may be an arbitrary UTF-8 string understood by the service (often a Java class name, but this isn't required.) The length may be -1 to indicate that the list is variable length.

Each list item is added to the reference list to handle shared and circular elements. See the ref element.

Any parser expecting a list must also accept a null or a shared ref.

<note>The valid values of type are not specified in this document and may depend on the specific application. For example, a Java EJB server which exposes an Hessian interface can use the type information to instantiate the specific array type. On the other hand, a Perl server would likely ignore the contents of type entirely and create a generic array. </note>

Hessian 2.0 allows a compact form of the list for successive lists of the same type where the length is known beforehand. The type and length are encoded by integers, where the type is a reference to an earlier specified type.

V t x00 x04 [int # encoding of int[] type x6e x02 # length = 2 x90 # integer 0 x91 # integer 1 z V x90 # integer 0 x06 foobar # "foobar" z V t x00 x04 [int # type for int[] (save as type #1) x63 x02 # length 2 x90 # integer 0 x91 # integer 1 z v x91 # type reference to int[] (integer #1) x92 # length 2 x92 # integer 2 x93 # integer 3 <def> long ::= L b7 b6 b5 b4 b3 b2 b1 b0 ::= [xd8-xef] ::= [xf0-xff] b0 ::= [x38-x3f] b1 b0 ::= x77 b3 b2 b1 b0

A 64-bit signed integer. An long is represented by the byte 'L' followed by the 8-bytes of the integer in big-endian order

Longs between -8 and 15 are represented by a single byte in the range `xd8` to `xef`. The value of the long is `code - xe0`.

Longs between -2048 and 2047 are encoded in two bytes with the leading byte in the range `xf0` to `xff`. The value of the long is `256 * (code - xf8) + b0`.

Longs between -262144 and 262143 are encoded in three bytes with the leading byte in the range `x38` to `x3f`. The value of the long is `65536 * (code - x3c) + 256 * b1 + b0`.

Longs between which fit into 32-bits are encoded in five bytes with the leading byte `x77`.

xe0 # 0 xd8 # -8 xef # 15 xf8 x00 # 0 xf0 x00 # -2048 xf7 x00 # -256 xff xff # 2047 x3c x00 x00 # 0 x38 x00 x00 # -262144 x3f xff xff # 262143 x77 x00 x00 x00 x00 # 0 x77 x00 x00 x01 x2c # 300 L x00 x00 x00 x00 x00 x00 x01 x2c # 300 <def> map ::= M type? (object object)* z ::= 'o' int object* object-def ::= 'O' type int string*

Represents serialized objects and Maps. The type element describes the type of the map. Objects are represented by a map from field names to their values and type is the class of the object itself.

The type may be empty, i.e. a zero length. The parser is responsible for choosing a type if one is not specified. For objects, unrecognized keys will be ignored.

Each map is added to the reference list. Any time the parser expects a map, it must also be able to support a null or a ref.

<note>The type is chosen by the service. Often it may be the Java classname describing the service.</note>

Hessian 2.0 has a compact object form where the field names are only serialized once. Following objects only need to serialize their values

The object definition includes a mandatory type string, the number of fields, and the field names. The object definition is stored in the object definition map and will be referenced by object instances with an integer reference.

Hessian 2.0 has a compact object form where the field names are only serialized once. Following objects only need to serialize their values

The object instantiation creates a new object based on a previous definition. The integer value refers to the object definition.

map = new HashMap(); map.put(new Integer(1), "fee"); map.put(new Integer(16), "fie"); map.put(new Integer(256), "foe"); --- M x91 # 1 x03 fee # "fee" xa0 # 16 x03 fie # "fie" xb9 x00 # 256 x03 foe # "foe" z public class Car implements Serializable { String color = "aquamarine"; String model = "Beetle"; int mileage = 65536; } --- M t x00 x13 com.caucho.test.Car # type x05 color # color field x0a aquamarine x05 model # model field x06 Beetle x07 mileage # mileage field I x00 x01 x00 x00 z class Car { String color; String model; } out.writeObject(new Car("red", "corvette")); out.writeObject(new Car("green", "civic")); --- O # object definition (#0) t x00 x0b example.Car # type is example.Car x92 # two fields x05 color # color field name x05 model # model field name o x90 # object definition #0 x03 red # color field value x08 corvette # model field value o x90 # object definition #0 x05 green # color field value x05 civic # model field value enum Color { RED, GREEN, BLUE, } out.writeObject(Color.RED); out.writeObject(Color.GREEN); out.writeObject(Color.BLUE); out.writeObject(Color.GREEN); --- O # object definition #0 t x00 x0b example.Color # type is example.Color x91 # one field x04 name # enumeration field is "name" o # object #0 x90 # object definition ref #0 x03 RED # RED value o # object #1 x90 # object definition ref #0 x05 GREEN # GREEN value o # object #2 x90 # object definition ref #0 x04 BLUE # BLUE value x4a x01 # object ref #1, i.e. Color.GREEN null ::= N

Null represents a null pointer.

The byte 'N' represents the null pointer.

null values are allowed in place of any string, xml, binary, list, map, or remote.

An integer referring to a previous list or map instance. As each list or map is read from the input stream, it is assigned the integer position in the stream, i.e. the first list or map is '0', the next is '1', etc. A later ref can then use the previous object. Writers are not required to generate refs, but parsers must be able to recognize them.

<def> ref ::= R b3 b2 b1 b0

ref can refer to incompletely-read items. For example, a circular linked-list will refer to the first link before the entire list has been read.

A possible implementation would add each map and list to an array as it's read. The ref will return the corresponding object from the array. To support circular structures, the implementation would store the map or list immediately, before filling in the object's contents.

Each <list> or <array> is stored into an array as it is parsed. <ref> selects one of the stored objects. The first object is numbered '0'.

list = new LinkedList(); list.head = 1; list.tail = list; <results> M t x00 x0a LinkedList S x00 x04 head I x00 x00 x00 x01 S x00 x04 tail R x00 x00 x00 x00 z <note>ref only refers to list and map elements. string and binary, in particular, will only share references if they're wrapped in a list or map.</note>

A reference to a remote object. The remote has a type and a utf-8 string representing the object's URL.

<def> remote ::= r t b1 b0 <type-name> string r t x00 x0c test.TestObj S x00 x24 http://slytherin/ejbhome?id=69Xm8-zW string ::= s b1 b0 <utf-8-data> string ::= S b1 b0 <utf-8-data> ::= [x00-x1f] <utf-8-data>

A 16-bit unicode character string encoded in UTF-8. Strings are encoded in chunks. 'S' represents the final chunk and 's' represents any non-final chunk. Each chunk has a 16-bit length value.

The length is the number of characters, which may be different than the number of bytes.

String chunks may not split surrogate pairs.

Strings with length less than 32 may be encoded with a single byte length [x00-x1f].

x00 # "", empty string x05 hello # "hello" x01 xc3 x83 # "\u00c3" S x00 x05 hello # "hello" xml ::= x b1 b0 <utf-8-data> xml ::= X b1 b0 utf-8-data

An XML document encoded as a 16-bit unicode character string encoded in UTF-8. XML data is encoded in chunks. 'X' represents the final chunk and 'x' represents any initial chunk.

Each chunk has a 16-bit length value. The length is the number of characters, which may be different than the number of bytes.

X x00 x10 <top>hello</top> <note>Because this document does not define the language mapping, implementations are free to return a string when reading an xml entity.</note>

Hessian message syntax organizes serialized data for messaging and RPC applications. The envelope syntax enables compression, encryption, signatures, and any routing or context headers to wrap a Hessian message.

- Call ('c'): contains a Hessian RPC call, with a method name and arguments.
- Envelope ('E'): wraps a Hessian message for compression, encryption, etc. Envelopes can be nested.
- Message ('p'): contains a sequence of serialized Hessian objects.
- Reply ('r'): contains a reply to a Hessian RPC call.

<def> call ::= c x02 x00 m b1 b0 <method-string> object* z

A Hessian call invokes a method on an object with an argument list. The object is specified by the container, e.g. for a HTTP request, it's the HTTP URL. The arguments are specified by Hessian serialization.

Method names must be unique. Two styles of overloading are supported: overloading by number of argumetns and overloading by argument types. Overloading is permitted by encoding the argument types in the method names. The types of the actual arguments must not be used to select the methods.

Method names beginning with _hessian_ are reserved.

Servers should accept calls with either the mangled method name or the unmangled method name. Clients should send the mangled method name.

<note>See the Java binding for a possible overloading scheme.</note> <example>add(int a, int b) <results>add_int_int <example>add(double a, double b) <results>add_double_double <example>add(shopping.Cart cart, shopping.Item item) <results>add_shopping.Cart_shopping.Item

Arguments immediately follow the method in positional order. Argument values use Hessian's serialization.

All arguments share references, i.e. the reference list starts with the first argument and continues for all other arguments. This lets two arguments share values.

bean = new qa.Bean("foo", 13); System.out.println(remote.eq(bean, bean)); <results> c x02 x00 m x00 x02 eq M t x00 x07 qa.Bean S x00 x03 foo I x00 x00 x00 x0d z R x00 x00 x00 x00 z

The number and type of arguments are fixed by the remote method. Variable length arguments are forbidden. Implementations may take advantage of the expected type to improve performance.

c x02 x00 # call for Hessian 2.0 m x00 x04 add2 # method "add2" x92 # 2 - argument 1 x93 # 3 - argument 2 z # end of argument marker r x02 x00 x95 z <def> envelope ::= E x02 x00 m b1 b0 <method-string> env-chunk* z env-chunk ::= int (string object)* binary int (string object)*

A Hessian envelope wraps a Hessian message, adding headers and footers and possibly compressing or encrypting the wrapped message. The envelope type is identified by a method string, e.g. "com.caucho.hessian.io.Deflation" or "com.caucho.hessian.security.X509Encryption".

Some envelopes may chunk the data, providing multiple header/footer chunks. For example, a signature envelope might chunk a large streaming message to reduce the amount of buffering required to validate the signatures.

E x02 x00 m x00 x08 Identity # "Identity" envelope does nothing to the body x90 # no headers B x00 x0a # binary wrapped body (12 bytes) p x02 x00 # wrapped message x05 hello # "hello" z # end of wrapped message x90 # no footers z # end of envelope E x02 x00 m x00 x08 Identity # "Identity" envelope does nothing to the body x90 # no headers B x00 x0c # binary header for wrapped body (10 bytes) p x02 x00 # wrapped message x07 hello, # "hello, " z # end of wrapped message x90 # no footers x90 # no headers B x00 x08 # binary wrapped body (10 bytes) p x02 x00 # wrapped message x05 world # world z x90 # no footers z # end of envelope E x02 x00 m x00 x09 Deflation # "Deflation" envelope compresses the body x90 # no headers B x00 x0a # binary wrapped body (32 bytes) x78 x9c x4b... # compressed message x90 # no footers z # end of envelope <def> message ::= p x02 x00 object* z

A Hessian message contains a sequence of Hessian serialized objects. Messages can be used for multihop data transfer or simply for storing serialized data.

<def> valid-reply ::= r x02 x00 header* object z fault-reply ::= r x02 x00 header* fault z

A successful reply returns a single value and possibly some header information.

r x01 x00 I x00 x00 x00 x05 z

Failed calls return a fault.

Each fault has a number of informative fields, expressed like <map> entries. The defined fields are code, message, and detail. code is one of a short list of strings defined below. message is a user-readable message. detail is an object representing the exception. In Java, detail will be a serialized exception.

r x01 x00 f S x00 x04 code S x00 x10 ServiceException S x00 x07 message S x00 x0e File Not Found S x00 x06 detail M t x00 x1d java.io.FileNotFoundException z z <deftable>
ProtocolException The Hessian request has some sort of syntactic error.
NoSuchObjectException The requested object does not exist.
NoSuchMethodException The requested method does not exist.
RequireHeaderException A required header was not understood by the server.
ServiceException The called method threw an exception.
</deftable>

The call and response tags include a major and minor byte. The current version is 2.0.

Hessian services are identified by URLs. Typically, these will be HTTP URLs, although protocols would be possible as well.

URLs are flexible enough to encode object instances as well as simple static service locations. The URL uniquely identifies the Hessian object. Thus, Hessian can support object-oriented services, e.g. naming services, entity beans, or session beans, specified by the URL without requiring extra method parameters or headers.

Object naming may use the query string convention that "?id=XXX" names the object "XXX" in the given service. This convention is recommented, but not required.

For example, a stock quote service might have a factory interface like http://foo.com/stock and object instances like http://foo.com?id=PEET. The factory interface would return valid object references through the factory methods.

As an example, the following format is used for EJB:

<def> http://hostname/hessian/ejb-name?id=object-id

http://hostname/hessian identifies the EJB container. In Resin-EJB, this will refer to the EJB Servlet. "/hessian" is the servlet prefix (url-pattern.) HTTP is just used as an example; Hessian does not require the use of HTTP.

/ejb-name, the path info of the request, identifies the EJB name, specifically the home interface. EJB containers can contain several entity and session beans, each with its own EJB home. The ejb-name corresponds to the ejb-name in the deployment descriptor.

object-id identifies the specific object. For entity beans, the object-id encodes the primary key. For session beans, the object-id encodes a unique session identifier. Home interfaces have no ";ejbid=..." portion.

http://localhost/hessian/my-entity-bean http://localhost/hessian/my-entity-bean?ejbid=slytherin http://localhost/hessian/my-session-bean http://localhost/hessian/my-session-bean?ejbid=M9Zs1Zm

Hessian is organized as a bytecode protocol. A Hessian implementation is essentially a big switch statement on the initial bytecode.

x00 - x1f # utf-8 string length 0-32 x20 - x2f # binary data length 0-16 x30 - x37 # reserved x38 - x3f # long from -x40000 to x3ffff x40 - x41 # reserved x42 # 8-bit binary data final chunk ('B') x43 # reserved ('C' streaming call) x44 # 64-bit IEEE encoded double ('D') x45 # reserved ('E' envelope) x46 # boolean false ('F') x47 # reserved x48 # reserved ('H' header) x49 # 32-bit signed integer ('I') x4a # reference to 1-256th map/list x4b # reference to 1-65536th map/list x4c # 64-bit signed long integer ('L') x4d # map with optional type ('M') x4e # null ('N') x4f # object definition ('O') x50 # reserved ('P' streaming message/post) x51 # reserved x52 # reference to map/list - integer ('R') x53 # utf-8 string final chunk ('S') x54 # boolean true ('T') x55 # reserved x56 # list/vector ('V') x57 # reserved x58 # utf-8 xml final chunk ('X') x59 - x62 # reserved x62 # 8-bit binary data non-final chunk ('b') x63 # reserved ('c' call for RPC) x64 # UTC time encoded as 64-bit long milliseconds since epoch ('d') x65 # reserved x66 # reserved ('f' for fault for RPC) x67 # double 0.0 x68 # double 1.0 x69 # double represented as byte (-128.0 to 127.0) x6a # double represented as short (-32768.0 to 327676.0) x6b # double represented as float x6c # list/vector length ('l') x6d # reserved ('m' method for RPC call) x6e # list/vector compact length x6f # object instance ('o') x70 # reserved ('p' - message/post) x71 # reserved x72 # reserved ('r' reply for message/RPC) x73 # utf-8 string non-final chunk ('s') x74 # map/list type ('t') x75 # type-ref x76 # compact vector ('v') x77 # long encoded as 32-bit int x78 # utf-8 XML non-final chunk ('x') x79 # reserved x7a # list/map terminator ('z') x7b - x7f # reserved x80 - xbf # one-byte compact int (-x10 to x3f, x90 is 0) xc0 - xcf # two-byte compact int (-x800 to x3ff) xd0 - xd7 # three-byte compact int (-x40000 to x3ffff)

Copyright 2000-2007 Caucho Technology, Inc. All Rights Reserved.

Any party may implement this protocol for any purpose without royalty or license fee, provided that the implementation conforms to this specification. Caucho Technology reserves the right to create a test suite, freely available without royalty or license fee, to validate implementation conformance. The limited permissions granted herein are perpetual and may not be revoked by Caucho Technology or its successors or assigns.

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and these paragraphs are included on all such copies and derivative works.

This document and the information contained herein is provided on an "AS IS" basis and CAUCHO TECHNOLOGY DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

- Added envelope ('E') syntax.
- Added post/message ('p') syntax.
- Changed encoding to avoid name conflicts.
- Split object definition/instance.
- Expanded int and string single-byte range.

- Added compact encoding.

- Clarified that length of XML and strings is in characters (Petr Gladkikh)

- Removed unidirectional messages.

- Added unidirectional messages
- Removed 'v' from reply
- changed length code to 'l'
- made type and length optional

- EJB naming: clarified examples especially for session beans (John Mitchell)
- Formal definitions: clarified grammar and added missing object (John Mitchell)
- Formal definitions: initial binary should use 'b' (John Mitchell)

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