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<A NAME="9"><!-- Empty --></A>
<H2>9 CORBA_Environment C Structure</H2>
<A NAME="corbaenv"><!-- Empty --></A>
<P>This chapter describes the CORBA_Environment C structure.


<A NAME="9.1"><!-- Empty --></A>
<H3>9.1 C Structure</H3>

<P> Here is the complete definition of the CORBA_Environment 
C structure, defined in file &#34;ic.h&#34; : 

<PRE>
/* Environment definition */
typedef struct {

  /*----- CORBA compatibility part ------------------------*/
  /* Exception tag, initially set to CORBA_NO_EXCEPTION ---*/
  CORBA_exception_type   _major;          

  /*----- External Implementation part - initiated by the user ---*/
  /* File descriptor                                              */
  int                    _fd;             
  /* Size of input buffer                                         */
  int                    _inbufsz;        
  /* Pointer to always dynamically allocated buffer for input     */
  char                  *_inbuf;         
  /* Size of output buffer                                        */
  int                    _outbufsz;       
  /* Pointer to always dynamically allocated buffer for output    */ 
  char                  *_outbuf;        
 /* Size of memory chunks in bytes, used for increasing the outpuy
    buffer, set to &#62;= 32, should be around &#62;= 1024 for performance
    reasons                                                       */ 
 int                    _memchunk;       
 /* Pointer for registered name                                   */
  char                   _regname[256];   
 /* Process identity for caller                                   */
  erlang_pid            *_to_pid;         
  /* Process identity for callee                                  */ 
  erlang_pid            *_from_pid;      

  /*- Internal Implementation part - used by the server/client ---*/
  /* Index for input buffer                                       */
  int                    _iin;            
  /* Index for output buffer                                      */
  int                    _iout;          
  /* Pointer for operation name                                   */
  char                   _operation[256];
   /* Used to count parameters                                    */
  int                    _received;      
  /* Used to identify the caller                                  */
  erlang_pid             _caller;        
 /* Used to identify the call                                     */
  erlang_ref             _unique;         
  /* Exception id field                                           */
  CORBA_char            *_exc_id;        
  /* Exception value field                                        */
   void                  *_exc_value;           

  
} CORBA_Environment; 
      
    
</PRE>

<P> The structure is divided into three parts:

<P>
<UL>

<LI>
                 The CORBA Compatibility part, demanded by the standard OMG
         IDL mapping v2.0.
        <BR>


</LI>


<LI>
                 The external implementation part used for generated
         client/server code.
        <BR>


</LI>


<LI>
                 The internal part useful for those who wish to define their
         own functions.
        <BR>


</LI>


</UL>
<A NAME="9.2"><!-- Empty --></A>
<H3>9.2 The CORBA Compatibility Part</H3>

<P> Contains only one field <CODE>_major</CODE> defined as a
CORBA_Exception_type. The CORBA_Exception type is an integer
which can be one of:

<P>
<UL>

<LI>
                 <STRONG>CORBA_NO_EXCEPTION</STRONG>, by default equal to 0, can be
         set by the application programmer to another value.
        <BR>


</LI>


<LI>
                 <STRONG>CORBA_SYSTEM_EXCEPTION</STRONG>, by default equal to -1, can
         be set by the application programmer to another value.
        <BR>


</LI>


</UL>

<P> The current definition of these values are:

<PRE>
      #define CORBA_NO_EXCEPTION      0
      #define CORBA_SYSTEM_EXCEPTION -1
    
</PRE>
<A NAME="9.3"><!-- Empty --></A>
<H3>9.3 The External Part</H3>

<P> This part contains the following fields:

<P>
<UL>

<LI>
                 int <STRONG>_fd</STRONG> - a file descriptor returned from
         erl_connect. Used for connection setting.
        <BR>


</LI>


<LI>
                 char* <STRONG>_inbuf</STRONG> - pointer to a buffer used for
         input. Buffer size checks are done under runtime that
         prevent buffer overflows. This is done by expanding the
         buffer to fit the input message. In order to allow buffer
         reallocation, the output buffer must always be dynamically
         allocated. The pointer value can change under runtime in
         case of buffer reallocation.
        <BR>


</LI>


<LI>
                 int <STRONG>_inbufsz</STRONG> - start size of input buffer. Used
         for setting the input buffer size under initialization of
         the Erl_Interface function ei_receive_encoded/5. The value
         of this field can change under runtime in case of input
         buffer expansion to fit larger messages
        <BR>


</LI>


<LI>
                 int <STRONG>_outbufsz</STRONG> - start size of output buffer. The
         value of this field can change under runtime in case of
         input buffer expansion to fit larger messages
        <BR>


</LI>


<LI>
                 char* <STRONG>_outbuf</STRONG> - pointer to a buffer used for
         output. Buffer size checks prevent buffer overflows under
         runtime, by expanding the buffer to fit the output message
         in cases of lack of space in buffer. In order to allow
         buffer reallocation, the output buffer must always be
         dynamically allocated. The pointer value can change under
         runtime in case of buffer reallocation.
        <BR>


</LI>


<LI>
                 int <STRONG>_memchunk</STRONG> - expansion unit size for the output
         buffer. This is the size of memory chunks in bytes used for
         increasing the output in case of buffer expansion. The value
         of this field must be allways set to &#62;= 32, should be at
         least 1024 for performance reasons.
        <BR>


</LI>


<LI>
                 char <STRONG>regname[256]</STRONG> - a registered name for a process. 
        <BR>


</LI>


<LI>
                 erlang_pid* <STRONG>_to_pid</STRONG> - an Erlang process identifier,
         is only used if the registered_name parameter is the empty
         string.
        <BR>


</LI>


<LI>
                 erlang_pid* <STRONG>_from_pid</STRONG> - your own process id so the
         answer can be returned.
        <BR>


</LI>


</UL>
<A NAME="9.4"><!-- Empty --></A>
<H3>9.4 The Internal Part</H3>

<P> This part contains the following fields:

<P>
<UL>

<LI>
                 int <STRONG>_iin</STRONG> - Index for input buffer. Initially set
         to zero. Updated to agree with the length of the received
         encoded message.
        <BR>


</LI>


<LI>
                 int <STRONG>_iout</STRONG> - Index for output buffer Initially set
         to zero. Updated to agree with the length of the message
         encoded to the communication counterpart.
        <BR>


</LI>


<LI>
                 char <STRONG>_operation[256]</STRONG> - Pointer for operation name.
         Set to the operation to be called.
        <BR>


</LI>


<LI>
                 int <STRONG>_received</STRONG> - Used to count parameters.
         Initially set to zero.
        <BR>


</LI>


<LI>
                 erlang_pid <STRONG>_caller</STRONG> - Used to identify the caller.
         Initiated to a value that identifies the caller.
        <BR>


</LI>


<LI>
                 erlang_ref <STRONG>_unique</STRONG> - Used to identify the call.
         Set to a default value in the case of generated functions.
        <BR>


</LI>


<LI>
                 CORBA_char* <STRONG>_exc_id</STRONG> - Exception id field.
         Initially set to NULL to agree with the initial value of
         _major (CORBA_NO_EXCEPTION).
        <BR>


</LI>


<LI>
                 void* <STRONG>_exc_value</STRONG> - Exception value field Initially
         set to <STRONG>NULL</STRONG> to agree with the initial value of
         _major (CORBA_NO_EXCEPTION).
        <BR>


</LI>


</UL>

<P> The advanced user who defines his own functions has to
update/support these values in a way similar to how they are
updated in the generated code.
<A NAME="9.5"><!-- Empty --></A>
<H3>9.5 Creating and Initiating the CORBA_Environment Structure</H3>

<P> There are two ways to set the CORBA_Environment structure:

<P>
<UL>

<LI>
                 Manually
        <BR>

        The following default values must be set to the
         CORBA_Environment *<STRONG>ev</STRONG> fields, when buffers for
         input/output should have the size <STRONG>inbufsz</STRONG>/
         <STRONG>outbufsz</STRONG>:<BR>


        
<UL>

<LI>
                 <STRONG>ev-&#62;_inbufsz</STRONG> = <STRONG>inbufsz</STRONG>;
         <BR>

                 The value for this field can be between 0 and maximum
         size of a signed integer.
         <BR>

         
</LI>


<LI>
                 <STRONG>ev-&#62;_inbuf</STRONG> = malloc(<STRONG>inbufsz</STRONG>);
         <BR>

                 The size of the allocated buffer must be equal to the
         value of its corresponding index, _inbufsz.
         <BR>

         
</LI>


<LI>
                 <STRONG>ev-&#62;_outbufsz</STRONG> = <STRONG>outbufsz</STRONG>;
         <BR>

                 The value for this field can be between 0 and maximum
         size of a signed integer.
         <BR>

         
</LI>


<LI>
                 <STRONG>ev-&#62;_outbuf</STRONG> = malloc(<STRONG>outbufsz</STRONG>);
         <BR>

                 The size of the allocated buffer must be equal to the
         value of its corresponding index, _outbufsz.
         <BR>

         
</LI>


<LI>
                 <STRONG>ev-&#62;_memchunk</STRONG> = <STRONG>__OE_MEMCHUNK__</STRONG>;
         <BR>

                 Please note that __OE_MEMCHUNK__ is equal to
         <STRONG>1024</STRONG>, you can set this value to a value bigger
         than 32 yourself.
         <BR>

</LI>


<LI>
                 <STRONG>ev-&#62;_to_pid</STRONG> = <STRONG>NULL</STRONG>;
         <BR>

         
</LI>


<LI>
                 <STRONG>ev-&#62;_from_pid</STRONG> = <STRONG>NULL</STRONG>;
         <BR>

         
</LI>


</UL>


        <BR>


</LI>


<LI>
                 By using the <STRONG>CORBA_Environment_alloc</STRONG>/2 function. 
        <BR>

                 The CORBA_Environment_alloc function is defined as:
         <BR>

        
<PRE>
          CORBA_Environment *CORBA_Environment_alloc(int inbufsz, 
                                                     int outbufsz);
        
</PRE>

        where:<BR>


        
<UL>

<LI>
         <STRONG>inbufsz</STRONG> is the desired size of input buffer<BR>

         
</LI>


<LI>
         <STRONG>outbufsz</STRONG> is the desired size of output
         buffer<BR>

         
</LI>


<LI>
         return value is a <STRONG>pointer</STRONG> to an allocated and
         initialized <STRONG>CORBA_Environment</STRONG> structure.<BR>
         <BR>

</LI>


</UL>


        This function will set all needed default values and
         allocate buffers equal to the values passed, but will not
         allocate space for the _to_pid and _from_pid fields.<BR>


        To free the space allocated by CORBA_Environment_alloc/2:<BR>


         
<UL>

<LI>
                                 First call CORBA_free for the input and output buffers.
                <BR>

         
</LI>


<LI>
                                 After freeing the buffer space, call CORBA_free for
                 the CORBA_Environment space.
                <BR>

         
</LI>


</UL>


</LI>


</UL>

<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Note!" SRC="note.gif"></TD>
    <TD>

<P>     Remember to set the fields <STRONG>_fd</STRONG>, <STRONG>_regname</STRONG>,
        <STRONG>*_to_pid</STRONG> and/or <STRONG>*_from_pid</STRONG> to the
        appropriate application values. These are not automatically
        set by the stubs.
    </TD>
  </TR>
</TABLE>

<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Warning!" SRC="warning.gif"></TD>
    <TD>

<P>Never assign static buffers to the buffer pointers. Never set
the <STRONG>_memchunk</STRONG> field to a value less than
<STRONG>32</STRONG>.    </TD>
  </TR>
</TABLE>
<A NAME="9.6"><!-- Empty --></A>
<H3>9.6 Setting System Exceptions</H3>

<P> If the user wishes to set own system exceptions at critical
positions on the code, it is strongly recommended to use one of
the current values:

<P>
<UL>

<LI>
                 CORBA_NO_EXCEPTION upon success. The value of the _exc_id
         field should be then set to NULL. The value of the
         _exc_value field should be then set to NULL.
        <BR>


</LI>


<LI>
                 CORBA_SYSTEM_EXCEPTION upon system failure. The value of
         the _exc_id field should be then set to one of the values
         defined in &#34;ic.h&#34; :
        <BR>


        
<PRE>
  #define UNKNOWN          &#34;UNKNOWN&#34;
  #define BAD_PARAM        &#34;BAD_PARAM&#34;
  #define NO_MEMORY        &#34;NO_MEMORY&#34;
  #define IMPL_LIMIT       &#34;IMP_LIMIT&#34;
  #define COMM_FAILURE     &#34;COMM_FAILURE&#34;
  #define INV_OBJREF       &#34;INV_OBJREF&#34;
  #define NO_PERMISSION    &#34;NO_PERMISSION&#34;
  #define INTERNAL         &#34;INTERNAL&#34;
  #define MARSHAL          &#34;MARSHAL&#34;
  #define INITIALIZE       &#34;INITIALIZE&#34;
  #define NO_IMPLEMENT     &#34;NO_IMPLEMENT&#34;
  #define BAD_TYPECODE     &#34;BAD_TYPECODE&#34;
  #define BAD_OPERATION    &#34;BAD_OPERATION&#34;
  #define NO_RESOURCES     &#34;NO_RESOURCES&#34;
  #define NO_RESPONSE      &#34;NO_RESPONSE&#34;
  #define PERSIST_STORE    &#34;PERSIST_STORE&#34;
  #define BAD_INV_ORDER    &#34;BAD_INV_ORDER&#34;
  #define TRANSIENT        &#34;TRANSIENT&#34;
  #define FREE_MEM         &#34;FREE_MEM&#34;
  #define INV_IDENT        &#34;INV_IDENT&#34;
  #define INV_FLAG         &#34;INV_FLAG&#34;
  #define INTF_REPOS       &#34;INTF_REPOS&#34;
  #define BAD_CONTEXT      &#34;BAD_CONTEXT&#34;
  #define OBJ_ADAPTER      &#34;OBJ_ADAPTER&#34;
  #define DATA_CONVERSION  &#34;DATA_CONVERSION&#34;
  #define OBJ_NOT_EXIST    &#34;OBJECT_NOT_EXIST&#34;
        
</PRE>


</LI>


</UL>

<P> The value of the _exc_value field should be then set to a string
that explains the problem in an informative way. The user
should use the functions CORBA_exc_set/4 and
CORBA_exception_free/1 to free the exception.

The user has to use CORBA_exception_id/1 and
CORBA_exception_value/1 to access exception information.
Prototypes for these functions are declared in &#34;ic.h&#34;
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