research/remote_log/remote_log_spec.md

Remote log specification

Version: 0.0.6 (Draft)

Authors: Oskar Thorén oskar@status.im, Dean Eigenmann dean@status.im

Table of Contents

• Abstract
• Definitions
• Wire Protocol
  • Secure Transport, storage, and name system
  • Payloads
• Synchronization
  • Roles
  • Flow
  • More on the remote log
  • Interaction with MVDS
• Footnotes
• Acknowledgements

Abstract

A remote log is a replication of a local log. This means a node can read data from a node that is offline.

This specification is complemented by a proof of concept implementation ¹.

Definitions

Term	Definition
CAS	Content-addressed storage. Stores data that can be addressed by its hash.
NS	Name system. Associates mutable data to a name.
Remote log	Replication of a local log at a different location.

Wire Protocol

Secure Transport, storage, and name system

This specification does not define anything related to to: secure transport, content addressed storage, or the name system. It is assumed these capabilities are abstracted away in such a way that any such protocol can easily be implemented.

Payloads

Payloads are implemented using protocol buffers v3.

CAS service:

package vac.cas;

service CAS {
  rpc Add(Content) returns (Address) {}
  rpc Get(Address) returns (Content) {}
}

message Address {
  bytes id = 1;
}

message Content {
  bytes data = 1;
}

NS service:

service NS {
  rpc Update(NameUpdate) returns (Response) {}
  rpc Fetch(Query) returns (Content) {}
}

message NameUpdate {
  string name = 1;
  bytes content = 2;
}

message Query {
  string name = 1;
}

message Content {
  bytes data = 1;
}

message Response {
  bytes data = 1;
}

Remote log:

message RemoteLog {
  Body body = 1;
  bytes tail = 2;

  message Body {
    repeated Pair pair = 1;
  }

  message Pair {
    bytes remoteHash = 1;
    bytes localHash = 2;
  }
}

Synchronization

Roles

There are four fundamental roles:

1. Alice
2. Bob
3. Name system (NS)
4. Content-addressed storage (CAS)

The remote log protobuf is what is stored at the Name system.

"Bob" can represents anything from 0 to N participants. Unlike Alice, Bob only needs read-only access to NS and CAS.

Flow

Figure 1: Remote log data synchronization.

More on the remote log

The remote log lets receiving nodes know what data they are missing. Depending on the specific requirements and capabilities of the nodes and name system, the information can be referred to differently. We distinguish between three rough modes:

1. Fully replicated log
2. Normal sized page with CAS mapping
3. "Linked list" mode - minimally sized page with CAS mapping

Interaction with MVDS

Footnotes

1. https://github.com/vacp2p/research/tree/master/remote_log

Acknowledgements

TBD.