Convert Structure into Byte Array for UDP transmission

Z

Zahid

Hi,

I have a number of structures that I want to send using
UDP protocol. How do I convert the structure into
bytes/array of bytes? Using UDP protocol is a MUST - a
Client Requirement for my PocketPC application.

Am I doing it all wrong? Should I create Classes instead
of these objects- if so how does that help?

In particular How would I send/Convert the array "data()"
into Bytes to send with the structure?

This code is part of an Interface specification that
communicates with a program written C/MFC code.

Thanks in advance
Here is my code:

Public Structure xvnetpkt_type
Public id As Byte
Public prid() As Byte
Public seqno As UInt16
Public length As UInt16 'Length of data
Public code As Char 'reply Code -
Public data() As srvrlogon_type 'Data

Public Sub Initialize()
ReDim prid(2)
ReDim data(MAXDATA)
End Sub

End Structure

Public Structure srvrlogon_type
Public Request As Char
Public ServerNo As UInt16
End Structure

Structure sell_type
Public Request As Char '10 = sell items
Public TableNo As UInt16
Public SplitNo As UInt16
Public nItems As UInt16 'No of ITEMINFO2(max 60)
Public Items() As iteminfo2_type
Public Sub Initialise()
ReDim Items(60)
End Sub
End Structure

Structure iteminfo2_type
Public PLU As UInt64
Public Flags As UInt16
Public quantity As UInt16
End Structure
 
P

Paul G. Tobey [eMVP]

There is no single right answer to 'convert this structure to a byte array',
so nothing can be done automatically. If you know what layout is correct
for the other end of your socket connection, add a method to each structure
or class called something like ToByteArray(), which returns a byte array,
and have that method pack things into the byte array the way your
communication partner wants them.

Paul T.
 
Z

Zahid

Hi,

Here is the code that the C/MFC program uses:

#define MAXDATA 500

typedef struct xvnetpkt_def {
unsigned char id
unsigned char prid[2];
unsigned short seqno;
unsigned short length;
unsigned char code;
char data[MAXDATA];
} XVNetPkt;

typedef struct srvrlogon_def {
unsigned char Request;
unsigned Short ServerNo;
} XV_SRVRLOGON;

Now that youve seen the actual data format what would you
suggest? How shall I go about solving this riddle?

Thanks in advance.
 
P

Paul G. Tobey [eMVP]

OK, there's still some missing information. What are the structure packing
settings on that program. The second structure, particularly, is going to
be sensitive to that. With a single character at the *beginning* of the
structure, it could be packed in several different ways:

offset field
0 Request
1 ServerNo

or

0 Request
2 ServerNo

or even

0 Request
4 ServerNo

Once you know that, you can start coding up something to do the conversion
for each structure in your managed code. You'd do something like this:

public class TestStruct

{

public byte Request;

public short ServerNo;



private const int offsetRequest = 0;

private const int sizeRequest = 1;

private const int offsetServerNo = 2;

private const int sizeServerNo = 2;

private const int arraySize = 4;



public byte[] ToByteArray()

{

byte[] ba = new byte[ arraySize ];

byte[] requestbytes = BitConverter.GetBytes( Request );

byte[] servernobytes = BitConverter.GetBytes( ServerNo );

Buffer.BlockCopy( ba, offsetRequest, requestbytes, 0,
requestbytes.Length );

Buffer.BlockCopy( ba, offsetServerNo, servernobytes, 0,
servernobytes.Length );

return ba;

}

};



Paul T.

Zahid said:
Hi,

Here is the code that the C/MFC program uses:

#define MAXDATA 500

typedef struct xvnetpkt_def {
unsigned char id
unsigned char prid[2];
unsigned short seqno;
unsigned short length;
unsigned char code;
char data[MAXDATA];
} XVNetPkt;

typedef struct srvrlogon_def {
unsigned char Request;
unsigned Short ServerNo;
} XV_SRVRLOGON;

Now that youve seen the actual data format what would you
suggest? How shall I go about solving this riddle?

Thanks in advance.
-----Original Message-----
There is no single right answer to 'convert this structure to a byte array',
so nothing can be done automatically. If you know what layout is correct
for the other end of your socket connection, add a method to each structure
or class called something like ToByteArray(), which returns a byte array,
and have that method pack things into the byte array the way your
communication partner wants them.

Paul T.




.
Click to expand...
Click to expand...
 
Z

Zahid

Hi,

Paul, what do you mean by structure packing settings? I
have been given a complete interface spec with lots of
structure declarations.

Also, Im trying to write a Test Emulator that will send
data back so I want to know how to interpret the recieved
data back into one of the structures and use it in my
program.

Thanks in advance.
-----Original Message-----
OK, there's still some missing information. What are the structure packing
settings on that program. The second structure, particularly, is going to
be sensitive to that. With a single character at the *beginning* of the
structure, it could be packed in several different ways:

offset field
0 Request
1 ServerNo

or

0 Request
2 ServerNo

or even

0 Request
4 ServerNo

Once you know that, you can start coding up something to do the conversion
for each structure in your managed code. You'd do something like this:

public class TestStruct

{

public byte Request;

public short ServerNo;



private const int offsetRequest = 0;

private const int sizeRequest = 1;

private const int offsetServerNo = 2;

private const int sizeServerNo = 2;

private const int arraySize = 4;



public byte[] ToByteArray()

{

byte[] ba = new byte[ arraySize ];

byte[] requestbytes = BitConverter.GetBytes( Request );

byte[] servernobytes = BitConverter.GetBytes( ServerNo );

Buffer.BlockCopy( ba, offsetRequest, requestbytes, 0,
requestbytes.Length );

Buffer.BlockCopy( ba, offsetServerNo, servernobytes, 0,
servernobytes.Length );

return ba;

}

};



Paul T.

Zahid said:
Hi,

Here is the code that the C/MFC program uses:

#define MAXDATA 500

typedef struct xvnetpkt_def {
unsigned char id
unsigned char prid[2];
unsigned short seqno;
unsigned short length;
unsigned char code;
char data[MAXDATA];
} XVNetPkt;

typedef struct srvrlogon_def {
unsigned char Request;
unsigned Short ServerNo;
} XV_SRVRLOGON;

Now that youve seen the actual data format what would you
suggest? How shall I go about solving this riddle?

Thanks in advance.
-----Original Message-----
There is no single right answer to 'convert this structure to a byte array',
so nothing can be done automatically. If you know
Click to expand...
what
layout is correct
for the other end of your socket connection, add a method to each structure
or class called something like ToByteArray(), which returns a byte array,
and have that method pack things into the byte array
Click to expand...
the
way your
communication partner wants them.

Paul T.

Hi,

I have a number of structures that I want to send using
UDP protocol. How do I convert the structure into
bytes/array of bytes? Using UDP protocol is a MUST - a
Client Requirement for my PocketPC application.

Am I doing it all wrong? Should I create Classes instead
of these objects- if so how does that help?

In particular How would I send/Convert the
Click to expand...
array "data
()"
into Bytes to send with the structure?

This code is part of an Interface specification that
communicates with a program written C/MFC code.

Thanks in advance
Here is my code:

Public Structure xvnetpkt_type
Public id As Byte
Public prid() As Byte
Public seqno As UInt16
Public length As UInt16 'Length of data
Public code As Char 'reply Code -
Public data() As srvrlogon_type 'Data

Public Sub Initialize()
ReDim prid(2)
ReDim data(MAXDATA)
End Sub

End Structure

Public Structure srvrlogon_type
Public Request As Char
Public ServerNo As UInt16
End Structure

Structure sell_type
Public Request As Char '10 = sell items
Public TableNo As UInt16
Public SplitNo As UInt16
Public nItems As UInt16 'No of ITEMINFO2
Click to expand...
(max
60)
Public Items() As iteminfo2_type
Public Sub Initialise()
ReDim Items(60)
End Sub
End Structure

Structure iteminfo2_type
Public PLU As UInt64
Public Flags As UInt16
Public quantity As UInt16
End Structure



.
Click to expand...
Click to expand...


.
Click to expand...
 
P

Paul G. Tobey [eMVP]

The compiler takes your standard C code and puts things in memory where it
wants to, usually to maximize performance of your code. For example, it's a
*lot* faster to read a 'long' from memory if the long is located at an
address which is divisible by four. When it's not, the memory bus must make
several accesses to the memory to get the value. When it is properly
aligned, a single access occurs. So, when you declare a structure with some
types of various sizes in it, the compiler *may* arrange it in a way so that
the first field *is not contiguous* with the second, etc., as I indicated in
my last message.

Network applications commonly assume that all 'structured types' will be
sent packed together as closely as possible (to conserve bandwidth). It is
*frequently* necessary to take your nice fast run-time structures and pack
them up for shipment across the network.

What you should do, if you are writing both ends of the communication
channel is *specify what goes across the network*. Then, you can write the
code on both ends to make sure that it happens that way.

Paul T.

Zahid said:
Hi,

Paul, what do you mean by structure packing settings? I
have been given a complete interface spec with lots of
structure declarations.

Also, Im trying to write a Test Emulator that will send
data back so I want to know how to interpret the recieved
data back into one of the structures and use it in my
program.

Thanks in advance.
-----Original Message-----
OK, there's still some missing information. What are the structure packing
settings on that program. The second structure, particularly, is going to
be sensitive to that. With a single character at the *beginning* of the
structure, it could be packed in several different ways:

offset field
0 Request
1 ServerNo

or

0 Request
2 ServerNo

or even

0 Request
4 ServerNo

Once you know that, you can start coding up something to do the conversion
for each structure in your managed code. You'd do something like this:

public class TestStruct

{

public byte Request;

public short ServerNo;



private const int offsetRequest = 0;

private const int sizeRequest = 1;

private const int offsetServerNo = 2;

private const int sizeServerNo = 2;

private const int arraySize = 4;



public byte[] ToByteArray()

{

byte[] ba = new byte[ arraySize ];

byte[] requestbytes = BitConverter.GetBytes( Request );

byte[] servernobytes = BitConverter.GetBytes( ServerNo );

Buffer.BlockCopy( ba, offsetRequest, requestbytes, 0,
requestbytes.Length );

Buffer.BlockCopy( ba, offsetServerNo, servernobytes, 0,
servernobytes.Length );

return ba;

}

};



Paul T.

Zahid said:
Hi,

Here is the code that the C/MFC program uses:

#define MAXDATA 500

typedef struct xvnetpkt_def {
unsigned char id
unsigned char prid[2];
unsigned short seqno;
unsigned short length;
unsigned char code;
char data[MAXDATA];
} XVNetPkt;

typedef struct srvrlogon_def {
unsigned char Request;
unsigned Short ServerNo;
} XV_SRVRLOGON;

Now that youve seen the actual data format what would you
suggest? How shall I go about solving this riddle?

Thanks in advance.
-----Original Message-----
There is no single right answer to 'convert this
structure to a byte array',
so nothing can be done automatically. If you know what
layout is correct
for the other end of your socket connection, add a
method to each structure
or class called something like ToByteArray(), which
returns a byte array,
and have that method pack things into the byte array the
way your
communication partner wants them.

Paul T.

Hi,

I have a number of structures that I want to send using
UDP protocol. How do I convert the structure into
bytes/array of bytes? Using UDP protocol is a MUST - a
Client Requirement for my PocketPC application.

Am I doing it all wrong? Should I create Classes
instead
of these objects- if so how does that help?

In particular How would I send/Convert the array "data
()"
into Bytes to send with the structure?

This code is part of an Interface specification that
communicates with a program written C/MFC code.

Thanks in advance
Here is my code:

Public Structure xvnetpkt_type
Public id As Byte
Public prid() As Byte
Public seqno As UInt16
Public length As UInt16 'Length of data
Public code As Char 'reply Code -
Public data() As srvrlogon_type 'Data

Public Sub Initialize()
ReDim prid(2)
ReDim data(MAXDATA)
End Sub

End Structure

Public Structure srvrlogon_type
Public Request As Char
Public ServerNo As UInt16
End Structure

Structure sell_type
Public Request As Char '10 = sell items
Public TableNo As UInt16
Public SplitNo As UInt16
Public nItems As UInt16 'No of ITEMINFO2 (max
60)
Public Items() As iteminfo2_type
Public Sub Initialise()
ReDim Items(60)
End Sub
End Structure

Structure iteminfo2_type
Public PLU As UInt64
Public Flags As UInt16
Public quantity As UInt16
End Structure



.
Click to expand...


.
Click to expand...
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