prepare/prepareok

server/src/versioning.rs

diff --git a/server/src/versioning.rs b/server/src/versioning.rs
index edb07f5..8394fe0 100644
--- a/server/src/versioning.rs
+++ b/server/src/versioning.rs
@@ -4,7 +4,7 @@
 
 const VERSION: &str = env!("CARGO_PKG_VERSION");
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Copy)]
 pub struct SemanticVersion {
     pub major: u32,
     pub minor: u32,

server/src/vsr/header.rs

diff --git a/server/src/vsr/header.rs b/server/src/vsr/header.rs
index 613c29b..e56fa8b 100644
--- a/server/src/vsr/header.rs
+++ b/server/src/vsr/header.rs
@@ -1,12 +1,67 @@
+use crate::versioning::SemanticVersion;
+use super::{Operation, ProtocolVersion};
+
 pub enum Header {
+    // TODO: Add Request header, for now let's just use the `Command` enum
+    // and ignore the request_number and all of the client side data required by VSR.
     Prepare(Prepare),
     PrepareOk(PrepareOk),
 }
 
+#[derive(Debug, Clone)]
 pub struct Prepare {
-
+    pub checksum: u128,
+    pub checksum_body: u128,
+    // Reserved for further usage, for encryption.
+    pub nonce_reserved: u128,
+    pub cluster: u128,
+    pub size: u32,
+    // Reserved for further usage.
+    pub epoch: u32,
+    pub view_number: u32,
+    pub release: SemanticVersion,
+    // Version of VSR protocol.
+    pub protocol_version: ProtocolVersion,
+    // Currently not used, since our body has that information in it's payload.
+    pub command: u32,
+    pub replica: u8,
+    // Reserved for further usage.
+    pub parent: u128,
+    pub request_checksum: u128,
+    pub checkpoint_id: u128,
+    pub session_id: u64,
+    pub op_number: u64,
+    pub commit_number: u64,
+    pub timestamp: u64,
+    pub request_number: u32,
+    pub operation: Operation,
 }
 
+#[derive(Debug, Clone)]
 pub struct PrepareOk {
-
+    pub checksum: u128,
+    pub checksum_body: u128,
+    // Reserved for further usage, for encryption.
+    pub nonce_reserved: u128,
+    pub cluster: u128,
+    pub size: u32,
+    // Reserved for further usage.
+    pub epoch: u32,
+    pub view: u32,
+    pub release: SemanticVersion,
+    // Version of VSR Protocol
+    pub protocol_version: ProtocolVersion,
+    // Currently not used, since our body has that information in it's payload.
+    pub command: u32,
+    pub replica: u8,
+    // Reserved for further usage.
+    pub parent: u128,
+    pub prepare_checksum: u128,
+    pub checkpoint_id: u128,
+    pub session_id: u64,
+    pub op_number: u64,
+    pub commit_number: u64,
+    pub timestamp: u64,
+    pub request_number: u32,
+    pub operation: Operation,
 }

server/src/vsr/message.rs

diff --git a/server/src/vsr/message.rs b/server/src/vsr/message.rs
index e5317ff..c198573 100644
--- a/server/src/vsr/message.rs
+++ b/server/src/vsr/message.rs
@@ -1,6 +1,7 @@
+use bytes::Bytes;
 use super::header::Header;
 
 pub struct IggyMessage {
     header: Header,
-    body: ()
+    body: Bytes,
 }

server/src/vsr/mod.rs

diff --git a/server/src/vsr/mod.rs b/server/src/vsr/mod.rs
index 450c170..97d9fb0 100644
--- a/server/src/vsr/mod.rs
+++ b/server/src/vsr/mod.rs
@@ -9,6 +9,18 @@
 pub(crate) type CommitNumber = u64;
 pub(crate) type ViewNumber = u32;
 pub(crate) type Version = usize;
+pub(crate) type ProtocolVersion = u16;
+
+
+#[derive(Debug, Clone)]
+pub(crate) enum Operation {
+    /// Authorization
+    Auth,
+    /// Metadata such as CRUD on streams / topics / partitions
+    Metadata,
+    /// Messages(User data) persisted by our storage.
+    Messages,
+}
 
 // TODO: const generics ?
 pub(crate) struct QuorumCounter<T> {

server/src/vsr/replica.rs

diff --git a/server/src/vsr/replica.rs b/server/src/vsr/replica.rs
index c820d08..3e38955 100644
--- a/server/src/vsr/replica.rs
+++ b/server/src/vsr/replica.rs
@@ -1,5 +1,5 @@
 use super::*;
-use crate::versioning::SemanticVersion;
+use crate::{command::ServerCommand, versioning::SemanticVersion};
 use client_table::ClientTable;
 use status::Status;
 use std::marker::PhantomData;
@@ -45,8 +45,66 @@
 }
 
 impl<S,B> Replica<S,B> {
+    fn on_command(&self, command: ServerCommand) {
+        match command {
+            ServerCommand::CreateStream(command) => {
 
-    fn on_command(&self) {
+            },
+            ServerCommand::UpdateStream(command) => {
 
+            }
+            ServerCommand::DeleteStream(command) => {
+
+            }
+            ServerCommand::PurgeStream(command) => {
+
+            }
+            ServerCommand::CreateTopic(command) => {
+
+            }
+            ServerCommand::UpdateTopic(command) => {
+
+            }
+            ServerCommand::DeleteTopic(command) => {
+
+            }
+            ServerCommand::PurgeTopic(command) => {
+
+            }
+            ServerCommand::CreatePartitions(command) => {
+
+            }
+            ServerCommand::DeletePartitions(command) => {
+
+            }
+            ServerCommand::CreateConsumerGroup(command) => {
+
+            }
+            ServerCommand::DeleteConsumerGroup(command) => {
+
+            }
+            ServerCommand::CreateUser(command) => {
+
+            }
+            ServerCommand::UpdateUser(command) => {
+
+            }
+            ServerCommand::DeleteUser(command) => {
+
+            }
+            ServerCommand::ChangePassword(command) => {
+
+            }
+            ServerCommand::UpdatePermissions(command) => {
+
+            }
+            ServerCommand::CreatePersonalAccessToken(command) => {
+
+            }
+            ServerCommand::DeletePersonalAccessToken(command) => {
+
+            }
+            _ => { unreachable!();}
+        }
     }
 }