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All peers hold predefined messages schemas.
Messages follow schema in strict way - no fields are skipped and order of fields is guaranteed.
Peers send messages as byte stream serializing fields one by one, no delimiters are used between fields and messages.
For serializing POJO fields different techniques are used:
- External marshaller Message consumes already serialized byte array (e.g. JdkMarshaller for IgniteDiagnosticMessage, SchemaOperationStatusMessage... BinaryMarshaller for GridJobExecuteRequest#jobBytes) - sender consumes serialized byte array to message.
- User's BinaryObjects, Binarylizable are marshalled to byte array prior to serializing a message (the array is stored in cache structures).
- Some messages contain POJO field annotated with GridDirectTransient, and additional byte array field fill with GridCacheMessage#prepareMarshal (e.g. BinaryMarshaller for GridChangeGlobalStateMessageResponse).

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Code Block

language	java
title	MyMessage

package org.apache.ignite.internal.messages;

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

    /** New field. */
    @Since(version = "2.20.0")
    private String newFld;
}
    
// Generated code from the schema ^. 
package org.apache.ignite.internal.messages.codegen;

public class MyMessage {
    private int id;
    
	/**
     * Remove field. 
     * @deprecated since 2.20.0. 
     */
    @Deprecated
    private String rmFld;

    /** 
     * New field.
     * @since 2.20.0
     */
    private String newFld;

    @Override public boolean writeTo(ByteBuffer buf, MessageWriter writer, IgniteProductVersion destVer) {
        if (destVer.lessThan(2, 19, 0))
            throw new IgniteException("Must not send the message to destination node");

        if (!writer.writeString(id))
            return false;

        if (destVer.lessThan(2, 20, 0)) {
            if (!writer.writeString(rmFld))
                return false;
        }

        if (destVer.greaterThanEqual(2, 20, 0)) {
            if (!writer.writeString(newFld))
                return false;
        }

        return true;
    }

    @Override public boolean readFrom(ByteBuffer buf, MessageReader reader, IgniteProductVersion srcVer) {
        id = reader.readString();

        if (srcVer.greaterThanEqual(2, 20, 0))
            newFld = reader.readString();
        else
            newFld = null;

        return true;
    }
}

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