Integrate consensus and network ledger to a trivial ledger.

The README describes the demo.

oddchain/LICENSE

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oddchain/NOTICE

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+Copyright 2019 IOHK
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oddchain/README.md

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+# About
+
+This project defines a simple ledger layer, and integrates it to the Cardano
+[consensus and network
+layers](https://github.com/input-output-hk/ouroboros-network) so that a node can
+be run. This project is intended to serve as a reference for those who want to
+integrate their own ledgers to the reusable parts of Cardano.
+
+We present next a high level description of the ledger logic that this project
+implements, how to run a demo, and how the code is organized.
+
+# The Oddchain
+
+We define a ledger layer for an _oddchain_: a chain that consists of odd numbers
+only. Blocks of the _oddchain_ consists of a sequence of odd numbers that are
+strictly increasing of decreasing, according to the current _phase_. The _phase_
+determines:
+
+- Whether the numbers inside a block should decrease or increase
+- A bound for the numbers in the block. If the phase is _decreasing_ then the
+  phase determines the upper bound, if the phase is increasing then the phase
+  determines the lower bound.
+
+For instance, if the current phase is decreasing and has a bound of 10, then a
+block produced in that phase must contain decreasing sequences of odd numbers
+smaller than 10.
+
+The bound of a phase changes after each block, and the sign of the phase
+(decreasing or increasing) is flipped after each epoch.
+
+## Running the demo
+
+The demo can run multiple nodes in a local machine. It shouldn't be too hard to
+modify this project to support running nodes in different machines, but for the
+sake of simplicity we do not implement this functionality.
+
+This project has been tested on Linux only at the moment. If you have access to
+a machine with a different OS feel free to try this out as well, and submit a PR
+with the changes needed to run this in different platforms :heart:.
+
+If you have [`stack`](https://docs.haskellstack.org/en/stable/README/) and
+[`tmux`](https://github.com/tmux/tmux/wiki) installed and use a Unix based
+operating system, we provide a simple script to start multiple nodes and
+clients.
+
+First make sure that you run:
+
+```sh
+stack build
+```
+
+After that, inside a `tmux` session run:
+
+```sh
+./oddchain/demo.hs --numNodes 3
+```
+
+The number of nodes can be between 1 and 3. If you have enough screen real state
+you could try modifying the script to allow a larger number of nodes.
+
+This will start `numNodes` nodes and `numNodes` clients (wallets). The nodes
+communicate to each other and issue blocks according to the Byzantine Fault
+Tolerant (BFT) consensus protocol, whereas the clients submit random
+transactions to their corresponding nodes.
+
+What you should see is a terminal split in `numNodes * 2` panes, where the top
+layer shows the nodes' output, and the bottom layer shows the clients' (simple
+wallet) output. At this bottom layer you should see the blocks produced being
+reported, and of course, all the clients should agree on the blocks they see
+:slightly_smiling_face:.
+
+### Running nodes individually
+
+If you wish to run nodes individually, this can be done as follows:
+
+```sh
+stack exec oddnode -- \
+--numberOfCoreNodes 3 \
+--nodeId 2 \
+--enableTracers Consensus \
+--startTimeString '2020-03-18 11:27:32.925865787 UTC'
+```
+
+here:
+
+- `numberOfCoreNodes` determines how many core nodes are in the network.
+- `nodeId` specifies the node id, which must be between 0 and `numberOfCoreNodes - 1`.
+- `enableTracers` allows to enable different tracers. See `OddNode.NodeTracer`
+  for available options.
+- `startTimeString` specifies the time at which the blockchain started. It is
+  **crucial** that all nodes in the network have the same start time.
+
+
+To run a client (wallet) that submits transaction to its corresponding node you
+can use:
+
+```sh
+stack run oddwallet -- --nodeId 2 --enabledTracers Rolls
+```
+
+where the `nodeId` and `enabledTracers` parameters have the same meaning above
+described. The data type `OddWallet.WalletTracer` defines the available tracers
+for the wallet.
+
+## Structure of the project
+
+Directory `app` contain the main files for the node and wallet.
+
+The entry point for running a node can be found in `src/OddNode.oddRun`. See the
+docstring in this function for some caveats that apply to this demo.
+
+Function `oddRun` requires several
+[`ouroboros-consensus`](https://github.com/input-output-hk/ouroboros-network/tree/master/ouroboros-consensus)
+instances, which are defined in `module OddChain`. The major instances one has to define are:
+
+- `BlockProtocol` type instance. This determines the protocol that the blocks
+  support.
+- `BlockSupportsProtocol` class instance. This determines how to obtain the data
+  required to validate the given header according to the consensus rules
+  (`ValidateView`) and how to obtain the data required to select among competing
+  chains (`SelectView`).
+- `LedgerSupportsProtocol` class instance. This links the ledger to the
+  protocol, by having the former giving the necessary information to the latter.
+  The consensus algorithm uses this information to determine if the node should
+  produce a block (`LedgerView`). For the BFT protocol, the ledger view is just
+  `()`, since leader election is based on a round-robin schedule. More
+  sophisticated consensus protocols, such as
+  [Praos](https://iohk.io/en/research/library/papers/ouroboros-praosan-adaptively-securesemi-synchronous-proof-of-stake-protocol/),
+  might require other information like some approximation of the stake
+  distribution.
+- `UpdateLedger` class instance. This defines how blocks can be applied to the
+  ledger state to update it. This is where the ledger logic lives.
+- `ApplyTx` class instance. Similar to `UpdateLedger`, this instance defines how
+  to different transactions affect the ledger state. This instance is used by
+  the mempool. Property `Test.OddChain.prop_mempool` defines the relation that
+  is expected to hold between the instances of these type classes. Be aware that
+  there might be other properties that aren't currently captured in the tests.
+- `RunNode` instance. This defines, among other things, functions to:
+  - forge blocks when the node is the leader (given, among other things, a
+    sequence of transactions)
+  - determine if the header matches the body
+  - serialize and deserialize data (blocks, headers, transactions, etc)
+
+In addition, the consensus layer does not prescribe which encoding to use. We
+use [`CBOR`](https://tools.ietf.org/html/rfc7049) for this purpose, and the
+`ToCBOR`/`FromCBOR` instances are defined in the `OddChain` module as well.
+
+The module `OddChain` defines `HasHeader` instances for both odd blocks and odd
+block headers. This is required since at certain stages the consensus layer
+would have either the whole block available or only the headers.
+
+Besides these instances, the `OddChain` module contains a definition of the
+block type for the odd chain, together with a definition of the ledger state.
+When defining the ledger state is **important** that that the ledger state can
+retrieve the header hash of the last applied block (see the instance of function
+`ledgerTipPoint`).
+
+The `OddWallet` module contains the implementation of a simple wallet that
+submits random transactions to the node it is connected to.
+
+Tests for the implementation are defined in the following modules:
+
+- `Test.ThreadNet.OddChain` which contains:
+  - a test to check that the consensus layer is behaving as expected for the odd
+    chain instance (see `prop_simple_oddchain_convergence`)
+
+- `Test.OddChain` which contains:
+  - roundtrip tests to make sure serialization and deserialization work as
+    expected.
+  - header encoding tests, to make sure that we correctly implement
+    `nodeEncodeBlockWithInfo`.
+  - ledger property tests (see next section).
+
+## Properties that the ledger layer should satisfy
+
+### Relation between `UpdateLedger` and `ApplyTx` instances
+
+Applying a sequence of transactions should result in the same state as applying
+those transactions as part of a block's payload. See
+`Test.OddChain.prop_mempool`.
+
+### Re-applying succeeds if applying does
+
+Function `reapplyLedgerBlock` should skip block payload validation but update
+the ledger state. So this means that if `applyLedgerBlock` succeeded, then
+`reapplyLedgerBlock` should succeed as well and they should end up in the same
+state.
+
+Functions `applyTx` and `reapplyTx` should also satisfy this property.
+
+### Lemmas
+
+The following lemmas are checked by consensus when assertions are enabled. See
+`flag asserts`. See also [this issue]().
+
+#### Relation between `anachronisticProtocolLedgerView` and  `applyChainTick`
+
+The anachronistic protocol ledger view returns the same view as the one obtained
+by applying chain tick with the given slot. Formally:
+
+```
+for all ledgerTipSlot st <= s <= L ,
+     anachronisticProtocolLedgerView cfg st s
+  == protocolLedgerView (applyChainTick cfg s st)
+```
+
+where `L` is the maximum number of slots the ledger can look ahead (for instance
+for Byron this is `2k`).
+
+#### Relation between block application and chain tick
+
+Applying a block and applying the chain tick result in the same protocol ledger
+view. Formally:
+
+
+```
+     protocolLedgerView (applyLedgerBlock cfg blk state)
+  == protocolLedgerView (applyChainTick cfg (blockSlot blk) state)
+```
+
+### Relation between applying a block, chain ticks, and applying transactions
+
+Applying a **valid** block `blk` on state `st` should result in the same state
+as ticking the ledger state by the block slot, and then applying the
+transactions inside the block. Note that here **validity** of block is crucial.
+If the block is invalid in the given state, then we can't say anything about the
+equality. Formally, for all valid blocks:
+
+```
+   applyLedgerBlock cfg blk st
+ == repeatedlyM (applyTx cfg) (extractTxs blk)
+                (applyChainTick cfg (blockSlot blk) st)
+```