Use Cases

1. storing blocks (put)
2. retrieving blocks (get)
3. lookup of blocks (lookup). seems to be same as 2.
4. view the whole db asMap

Design Considerations

Interfaces  

System Interface

Hardware Interface

The LMDB instance needs to be able to read and write to a file.

Software Interface

trait BlockStore[F[_]] {
  def put(blockHash: BlockHash, blockMessage: BlockMessage): F[Unit]

  def get(blockHash: BlockHash): F[Option[BlockMessage]]

  def put(f: => (BlockHash, BlockMessage)): F[Unit]

  def asMap(): F[Map[BlockHash, BlockMessage]]
}

And instance:

class InMemBlockStore[F[_], E] private ()(implicit
                                          monadF: Monad[F],
                                          refF: Ref[F, Map[BlockHash, BlockMessage]],
                                          metricsF: Metrics[F])
    extends BlockStore[F] {

  def get(blockHash: BlockHash): F[Option[BlockMessage]] =
    for {
      _     <- metricsF.incrementCounter("block-store-get")
      state <- refF.get
    } yield state.get(blockHash)

  @deprecated(message = "to be removed when casper code no longer needs the whole DB in memmory",
              since = "0.5")
  def asMap(): F[Map[BlockHash, BlockMessage]] =
    for {
      _     <- metricsF.incrementCounter("block-store-as-map")
      state <- refF.get
    } yield state

  def put(f: => (BlockHash, BlockMessage)): F[Unit] =
    for {
      _ <- metricsF.incrementCounter("block-store-put")
      _ <- refF.update { state =>
            val (hash, message) = f
            state.updated(hash, message)
          }
    } yield ()
}

Usage example:

        BlockStore[F].put {
          awaitingJustificationToChild -= block.blockHash
          _blockDag.update(bd => {
            val hash = block.blockHash
            val newChildMap = parents(block).foldLeft(bd.childMap) {
              case (acc, p) =>
                val currChildren = acc.getOrElse(p, HashSet.empty[BlockHash])
                acc.updated(p, currChildren + hash)
            }

            val newSeqNum = bd.currentSeqNum.updated(block.sender, block.seqNum)
            bd.copy(
              childMap = newChildMap,
              currentSeqNum = newSeqNum
            )
          })
          (block.blockHash, block)
        }

User Interface

None. We are backend developers. We hail the matrix, and the matrix speaks to us.

Communications Interface

How will the software use any communications interfaces?

System Overview

Provide a description of the software system, including its functionality and matters relating to the overall system and design.  Feel free to split this up into subsections, or use data flow diagrams or process flow diagrams.  

Limitations

List any limitations or system constraints that have an impact on the design of the software.  These can be any of the following:

Hardware/software environment, End User Environment, Resource availability, Standards Compliance, Interop, Interface/Protocol requirements, Data requirements, Security, Performance, Networking, Verification & validation, means to address quality goals.

Assumptions and Dependencies

Could include software or hardware, Operating systems and platforms, User Personas, Changes in functionality. 

Architectural Strategies

Describe any design decisions and/or strategies that affect the overall organization of the system and its higher-level structures. These strategies should provide insight into the key abstractions and mechanisms used in the system architecture. Describe the reasoning employed for each decision and/or strategy (possibly referring to previously stated design goals and principles) and how any design goals or priorities were balanced or traded-off. Such decisions might concern (but are not limited to) things like the following:

• Use of a particular type of product (programming language, database, library, etc. ...)
• Reuse of existing software components to implement various parts/features of the system
• Future plans for extending or enhancing the software
• User interface paradigms (or system input and output models)
• Hardware and/or software interface paradigms
• Error detection and recovery
• Memory management policies
• External databases and/or data storage management and persistence
• Distributed data or control over a network
• Generalized approaches to control
• Concurrency and synchronization
• Communication mechanisms
• Management of other resources

System Architecture

This section should provide a high level overview of how the functionality and responsibilities of the the system were partitioned and then assigned to subsystems or components.  The main purpose here is to gain a general understanding of how and why the system was decomposed, and how the individual parts work together to provide the desired functionality.  If there are diagrams, models, flowcharts, or documented scenarios.  This applies only to the scope of the document, not the entire system.