VM Bridge protocol version 5.5

Requests are marked with "->", request arguments with -), responses
with "<-".  The server continues to process requests until EOF. Only
the first character is significant.

The communication must begin with ReferenceClass, CreateInstance,
Invoke or PropertyAccess. If the client waits for a response
(predicate==1) the server sends back a single ARG, as defined
below. Returned object id's ("CID") are 32 bit unsigned integer values
starting with 1, increased by 1.


Example:

     $o = new java("java.lang.Long", 6);
     $o->toString(); // discard result

->  <CreateInstance value="java.lang.Long" predicate="I"> 
      <Long value="6"/> 
    </CreateInstance>

<-  <Object value="1" predicate="O"/>

->  <Invoke value="1" method="toString" predicate="I">
    </Invoke>

<-  <Object value="2" predicate="O"/>

->  <Unref value="2" />

->  <Unref value="1" />

A second example which shows how to avoid round-trips. 

     $o = new java("java.lang.Long", 6);
     $o->toString(); // discard result

->  <K p="2" v="java.lang.Long" i="0"> 
      <L v="6" /> 
    </K

->  <Y p="3" v="1" m="toString" i="0"></Y>

->  <U value="1" /> # result from CreateInstance


Optional requests:

All acquired [O]bject handles may be destroyed by invoking U (destroy).
However, the server tracks all handles and automatically destroys them
after EOF. It is an error to further reference destroyed handles.

If [F]inish is called, the server closes or recycles the connection
and responds with F p=A, if the connection has been recycled, p=E
otherwise. Instead of sending <F p=E/> and waiting for the response,
it is also possible to simply close the connection.



Main requests:


->
CreateInstance:
<C v=name p=C|I> ...ARGS...
</C>
v: string
p: char (Reference[C]lass, Create[I]nstance)

->
Invoke:
<I v=object m=method p=P|I> ...ARGS...
</I>
v: unsigned long
m: string
p: char (examine[P]roperty, [I]nvoke method)

When v=0, the call is directed to the current request-handling
instance of the java bridge.

->
ReferenceClass (alternate form)
<H p=1|2|3 v=name> ...ARGS...
</H>
p: char 
v: string
Predicate 2 does not write a result, but stores a result proxy under ++CID.
Predicate 3 does not write a result and does not create a result proxy.

->
CreateInstance (alternate form)
<K p=1|2|3 v=name> ...ARGS...
</K>
p: char
v: string
Predicate 2 does not write a result, but stores a result proxy under ++CID.
Predicate 3 does not write a result and does not create a result proxy.

->
PropertyAccess (alternate form)
<G p=1|2|3 v=object m=method> ...ARGS...
</G>
p: char 
v: unsigned long
m: string
Predicate 2 does not write a result, but stores a result proxy under ++CID.
Predicate 3 does not write a result and does not create a result proxy.

->
Invoke (alternate form)
<Y p=1|2|3 v=object m=method> ...ARGS...
</Y>
p: char (examine[P]roperty, [I]nvoke method)
v: unsigned long
m: string
Predicate 2 does not write a result, but stores a result proxy under ++CID.
Predicate 3 does not write a result and does not create a result proxy.


When v=0, the call is directed to the current request-handling
instance of the java bridge.



ARGS or response:
<-)
String:
<S v=str/>
v: string

<-)
Boolean:
<B v=T|F/>
v: char ([T]rue, [F]alse)

-)
Boolean:(alternate form)
<T v=1]OTHER />
v: char [1]: true, everything else: false

<-)
Long: 
<L v=l p=[O|A]/>
v: unsigned long
p: char (p[O]sitive, neg[A]tive)

-)
Long: (alternate form)
<J v=l />
v: long (signed number)

<-)
Double:
<D v=d/>
v: double

-)
Object:
<O v=object />
v: unsigned long
NULL values can be sent as either v="" or v="0"

<-
Object:
<O v=object m=TYPE p=TYPE n=[T|F]/>
v: unsigned long
m: string
p: char ([A]rray/Map, [C]ollection, [O]bject, [E]xception)
n: char result can be cached (T) or not (F)

<-
Null:
<N/>

<-
Void:
<V m=[T|F]/>
n: char result can be cached (T) or not (F)

<-
Apply:
<A v=object p=cname m=fname n=param#> ...PAIRS...
</A>
v: unsigned long
p: string
m: string
n: unsigned long
Result can be used to send back the result of the current apply
call. If v is null, the function name p must be searched in the
"current" environment.

->
Result:
<R > ...ARG...
</R>

<-)
Exception:
<E v=object m=[T|F]/>
v: unsigned long
m: T signals an unchecked exception, F a checked exception. 
Unchecked exceptions (e.g.: RuntimeException or Error) should
terminate the script immediately

<-)
Composite:
<X t=A|H /> ...PAIRS...
</X>
t: char ([A]rray, [H]ashtable)

<-)
Pair:
<P [t=N|S v=key]> ...ARG...
</P>
t: char (key is [N]umeric, [S]tring or doesn't exist (if X=A))
v: unsigned long (if X=H and t=N)
v: string (if X=H and t=S)



OPTIONAL requests:
->
Destroy:
<U v=object />
v: unsigned long

<->
EndConnection:
<F p=A|E|a|e />
p: char (Keep [A]live, [E]nd connection).
Lower-case letters signal that an unchecked exception occured during
script execution.




NOTES:

If the first byte is 0177, the following byte has a special meaning:

Bit 1 0
-------
         return values  binary             comment
         as proxies(*)  data              
                                        
    0 0    yes          binary             default
    0 1    no           binary             if JAVA_PREFER_VALUES=1
    1 0    no           base64 encoded     if JAVA_PREFER_VALUES=1
    1 1    yes          base64 encoded     default

Bit 2,3,4: log level (from java.log_level)

Bit 5: always 0

Bit 6: set to 1 if bit[0,1] are used
Bit 7: set to 1 if bit[2,4] are used


If the header is missing, the following default values are used

         return values  binary             comment
         as proxies(*)  data              

           no           base64 encoded     default


(*) Primitive values like null, 1, false, etc. are proxied by
Request$PhpNull, Integer, Boolean, etc. by default.


Process communication
---------------------

  1) a simple client connects to a simple socket listener

  2) php connects to a simple socket or unix-domain socket listener

  3) php connects to a JEE server

  4) php is running within a JEE server


ad 1) 
  client opens socket connection
  client sends protocol requests
  client closes the socket connection

ad 2)
  php opens a socket connection
  php sends the bytes \0177 OPTIONS to initiate the communication
  php sends protocol requests
  php finishes the communication sending <F p="A"/>
   java sends back a <F p="A"/>
  ...
  php transparently re-uses the socket connection
  php sends the bytes \0177 OPTIONS
  php sends protocol requests
  php finishes the communication sending <F p="E"/>
   java sends back a <F p="E"/>
  php closes the socket connection

ad 3)
  php opens a HTTP socket connection to ${JAVA_HOSTS}[0] e.g.: localhost:8080
  php sends PUT ${JAVA_SERVLET}\r\rTransfer-Encoding: chunked\r\n\r\n
                      e.g.: PUT /JavaBridge/servlet.phpjavabridge\r\n\r\n
  php sends the bytes \0177 OPTIONS to initiate the communication
  php sends protocol requests
   java servlet responds with protocol responses
  php finishes the communication sending <F p="E"/>
   java servlet sends back a <F p="E"/>
  php sends final chunk: 0000\r\n\r\n
   java servlet sends final chunk: 0000\r\n\r\n
  php closes the socket connection

ad 4)
  php opens a socket connection
  php sends the bytes \0177 OPTIONS LEN_ID[1] LEN_ID[0] ID
   java thread sends \0 to avoid ack delay[1]
  php sends protocol requests
  php finishes the communication sending <F p="A"/> 
   java thread sends back a <F p="A"/>
  ...
  php transparently re-uses the socket connection
  php sends the bytes \0177 OPTIONS LEN_ID[1] LEN_ID[0] ID
   java thread sends \0 to avoid ack delay[1]
  php sends protocol requests
  php finishes the communication sending <F p="E"/> 
   java thread sends back a <F p="E"/>
  php closes the socket connection


[1] write/write/read delay is up to 500ms on free bsd operating
system.

NOTES  
-----
It is possible to "ping" the server by sending it the byte 0x0. If
alive it will send back a 0x0.