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There are a few steps that need to be followed when connecting a client to server running the protobuf interface.

Binary Negotiation

After connecting to the server (and doing any socket level security negotiation such as SSL), the client will need to send a single byte to identify the protocol they are using.  For the protobuf protocol this byte should be 110.  Additionally once the client has identified that they'll be communicating via protobuf, they'll need to send one more byte describing the major version of the protobuf protocol they'll be speaking.  This will provide the server with enough information to exchange a protobuf handshake message with the client.

Handshake

The handshake message is used to fully establish the major and minor version of the protocol in use on the connection. The first message sent from a client to a server must be a handshake. Once the server accepts the client's handshake, it will guarantee that its response messages match the client's protocol version, regardless of the version of protobuf being run on the server.

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