Code generation for variable-length data field

[donmendelson]

I generated Java code for a message schema with variable-length data. The generated code has functions set and get the length of the data but not a direct way to locate the data in the buffer or to populate it. Not sure how to use this. It seems to me that a method to set data into the field should also set its length.

The encoding is this:

The field is defined this way:

The generated code:

/* Generated SBE (Simple Binary Encoding) message codec */
package MarketData;

import java.nio.ByteOrder;
import java.util.;
import uk.co.real_logic.sbe.generation.java.;

public class DATA implements FixedFlyweight
{
private DirectBuffer buffer;
private int offset;

public DATA reset(final DirectBuffer buffer, final int offset)
{
    this.buffer = buffer;
    this.offset = offset;
    return this;
}

public int size()
{
    return -1;
}

public int length()
{
    return CodecUtil.uint16Get(buffer, offset + 0, ByteOrder.LITTLE_ENDIAN);
}

public DATA length(final int value)
{
    CodecUtil.uint16Put(buffer, offset + 0, value, ByteOrder.LITTLE_ENDIAN);
    return this;
}

}

[donmendelson]

Actually, the message flyweight class has has a method to set the data, which also writes the length. It doesn't seem to use the generated DATA class.

[tmontgomery]

Can you send the XML schema for this?

It looks like this is only the length field and no place for the variable length data to go.

Usually the type looks like:

    <composite name="varDataEncoding">
        <type name="length" primitiveType="uint8" semanticType="Length"/>
        <type name="varData" primitiveType="uint8" length="0" characterEncoding="UTF-8" semanticType="data"/>
    </composite>

and a field like:

    <data name="make" id="17" type="varDataEncoding" semanticType="Make"/>

This is my understanding of the spec unless I've missed something crucial. It could be that the XML isn't being checked far enough to catch something.

Just FYI on usage....

Normally, when elements are used, they generate a set of methods that have "get" and "put" prepended to them for various ways of accessing them. Per element as well as using byte[]s in a Java way.

While we are working on doc, etc. you might check out the examples dir to get a feel for how it is used.
With the Car schema and SbeExample.java file. It has examples of the Model and Make fields and how they can be set and retrieved.

For example, encoding looks like:

car.putMake(MAKE, srcOffset, MAKE.length);

Decoding looks like:

car.getMake(buffer, 0, buffer.length)

[mjpt777]

As Todd has described the var data fields should be set via the generated message encoder. All entry points to encoding or decoding of messages should be via the message type. See the following link for an example.

https://github.com/real-logic/simple-binary-encoding/blob/master/examples/java/uk/co/real_logic/sbe/examples/SbeExample.java

Note: The generated stub for the type you looked at does not have the field to set data because it is declared variable length, i.e. length = 0. This is generated for metadata purposes only because we need to know the the type of the field that contains the length of the var data value which can be different sized integers according to the spec.