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| <head> |
| <title>Protocol Buffers based data types for NN protocols</title> |
| </head> |
| <body> |
| <p> |
| The Protocol Buffers data types for NN protocols that use PB go in this package. |
| </p> |
| <h1>Steps to add a new protocol</h1> |
| <hr/> |
| <ol> |
| <li>Define the protobuf service for the protocol in <ProtocolName>.proto class. |
| <ul> |
| <li>This file should include both the protobuf service definition and the types |
| used for request and response. For example see - NamenodeProtocol.proto |
| <li>The naming convention for the protobuf service is <ProtocolName>Service. |
| Example: NamenodeProtocolService. |
| <li>Every RPC method takes a request and returns a response. The request |
| naming convention is <MethodName>RequestProto. The response naming convention |
| is <MethodName>ResponseProto. |
| </ul> |
| <li>Generate java files from the proto file using protoc tool. |
| <li>Define server side interface that extends BlockingInterface from the |
| generated files (Example: NamenodeProtocolService.BlockingInterface) |
| and VersionedProtocol. See NamenodePBProtocol.java for example. |
| <li>Define client side translator to translate the client protocol to |
| protobuf. See NamenodeProtocolTranslator. |
| <li>Define server side implementation that implements the server side interface. |
| This implementation receives the protobuf requests and delegates it to the |
| server side implementation. See NamenodePBProtocolImpl for example. |
| <li>Make changes to register this protocol at the server. See the other |
| protocols on how this is done. |
| </ol> |
| <h1>Steps to make changes to the existing protocol in a compatible way</h1> |
| <hr/> |
| <ol> |
| <li>Adding new methods is a compatible change.</li> |
| <li>When modifying an existing method, do not change the required parameters |
| to optional or optional parameters to required. Only add optional parameters |
| to the request and response.</li> |
| <li>When modifying an existing type, do not change the required parameters |
| to optional or optional parameters to require and optional parameters to |
| required. Only add optional parameters to the request and response.</li> |
| </ol> |
| |
