Message protobuf schema

message Message {
    oneof content {
	    … 
    }
}

message PrePrepare {
    uint64 view = 1;
    uint64 seq = 2;
    bytes payload = 3;
    bytes header = 4;
    bytes metadata = 5;	
}

message Prepare {
    uint64 view = 1;
    uint64 seq = 2;
    bytes digest = 3;
}

message Commit {
    uint64 view = 1;
    uint64 seq = 2;
    bytes digest = 3;
    uint64 signer_id = 4;
    bytes signature = 5; 
}

message Error {
    uint64 view = 1;
    uint64 seq = 2;
    bytes digest = 3;
    string reason = 4;
}

message ViewChange {
    uint64 next_view = 1;
    string reason = 2;
}

message ViewData {
    uint64 next_view = 1;
    bytes signature = 2; 
    repeated PrePrepare last_proposals = 3;
    repeated Commit last_proposal_proofs = 4;
}

message NewView {
    uint64 next_view = 1;
}

message HeartBeat {
    int64 view = 1;
    uint64 seq = 2;
}