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MessageWriter, MessageReader logic is depends on a remote IgniteProductVersion.
Message#writeTo, Message#readFrom is auto-generated and stored separately from Message classes.
Add Message#writeObject - for serializing Objects (java functions, and user objects) :
1. MessageWriter for communication protocol use BinaryMarshaller
2. MessageWriter for discovery protocol use JdkMarshaller
with BinaryMarshaller.
Message fields may containMessage fields contain:
1. primitive classes.
2. known collections.
3. POJO - that are other others Message.
4. Users classes and java functions (e.g. ComputeJob).
5. byte[] fields (objects serialized externally) must be avoided as much as possible, because their compatibility can't be guaranteed.
Order of fields in Message is fixed with @Order annotation.
Adding and removing fields must be go along with @Since, @Until annotations for Message classes and fields.

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Data - set of declared Message classes, including ser/des algorithm.
Transport - algorithm of transport the Messages to remote node.

Data compatibility

Message - is base class for all messages transported between nodes. Proposed changes:

Deprecate Message#writeTo and Message#readFrom in favor generated MessageSerializer.
MessageSerializer#writeTo Message#writeTo consumes MessageWriter that stores IgniteProductVersion of a receiver node and use it for serializing data for this version (mostly, for ignoring some fields).

Message#readFrom MessageSerializer#readFrom consumes MessageReader that stores IgniteProductVersion of source node and use it for deserializing data (mostly, for setting default values of new fields).

Code Block

language	java
title	Message

public interface MessageSerializer {
    public boolean writeTo(Message msg, ByteBuffer buf, MessageWriter writer);

    public boolean readFrom(Message msg, ByteBuffer buf, MessageReader reader);
}

public interface MessageWriter {
     public IgniteProductVersion receiverVersion();
}

public interface MessageReader {
     public IgniteProductVersion senderVersion();
}

Introduce annotations @Since and @Until for Message classes and Message fields, to use it for generating code for Message#writeTo and Message#readFrom:

Code Block

language	java
title	MyMessage

// Package where the Message is defined.
package org.apache.ignite.internal.my.message;

@Since(version = "2.19.0")
public class MyMessage implements Message {
    @Order(0)
    private int id;
    
 	/** Remove field. */
    @Until(version = "2.20.0")
    @Order(1)
    private String rmFld;

    /** New field. */
    @Since(version = "2.20.0")
 	@Order(2)
    private String newFld;

	// Message must have setters/getters for all @Ordered fields. Methods names are equal to a corresponding field name. 
	public void id(int id) {
		this.id = id;
	}

  	public int id() {
		return id;
	}

  	public void newFld(String newFld) {
		this.newFld = newFld;
	}
 
 	public String newFld() {
		return newFld;
	}

    // Delegates #writeTo method call to generated serializer.
    @Override public boolean writeTo(ByteBuffer buf, MessageWriter writer) {
        return MyMessageSerializer.writeTo(this, buf, writer);
    }

 	// Delegates #readFrom method call to generated serializer.
    @Override public boolean readFrom(ByteBuffer buf, MessageReader reader) {
         return MyMessageSerializer.readFrom(this, buf, reader);
    }
}

// Generated code from the message ^ for Ignite version 2.20.0.
// Use the same package as corresponding message.
package org.apache.ignite.internal.my.message;

class MyMessageSerializer {
    public static boolean writeTo(MyMessageMessage msgm, MByteBufferByteBuffer buf, MessageWriter writer) {
		MyMessage msg       = (MyMessage)m;

		IgniteProductVersion rcvVer = writer.receiverVersion();

        writer.writeString(msg.id());

        if (rcvVer.lessThan(2, 20, 0))
            writer.writeString(msg.rmFld());

        if (rcvVer.greaterThanEqual(2, 20, 0))
            writer.writeString(msg.newFld());
    
        return true;
    }

    public static boolean readFrom(MyMessageMessage msgm, ByteBuffer buf, MessageReader reader) {
 		MyMessage msg = (MyMessage)m;
 
        IgniteProductVersion srcVer = reader.senderVersion();

        msg.id(reader.readString());

		if (srcVer.lessThan(2, 20, 0))
			msg.rmFld(reader.readString());

        if (srcVer.greaterThanEqual(2, 20, 0))
            msg.newFld(reader.readString());

        return true;
    }
}

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Data compatibility