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docs: rst-ify the intro

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Introduction
============
Welcome to the Tendermint guide! This is the best place to start if you're new
to Tendermint. If you're already familiar with the basics of Tendermint and
ABCI, find more details in the [documentation](/docs).
Welcome to the Tendermint guide! This is the best place to start if you are new
to Tendermint.
What is Tendermint?
-------------------
@ -32,7 +31,7 @@ or a quirky scripting language), developers can use Tendermint for BFT state mac
whatever programming language and development environment is right for them.
Tendermint is designed to be easy-to-use, simple-to-understand, highly performant, and useful
for a wide variety of distributed applications. [Get started with Tendermint](/download) today!
for a wide variety of distributed applications.
Tendermint vs. X
----------------
@ -68,7 +67,7 @@ it focuses on arbitrary state machine replication, so developers can build the a
that's right for them, from key-value store to cryptocurrency to e-voting platform and beyond.
The layout of this Tendermint website content is also ripped directly and without shame from
[consul.io](https://www.consul.io/) and the other [Hashicorp sites](https://www.hashicorp.com/#tools).
`consul.io <https://www.consul.io/>`__ and the other `Hashicorp sites <https://www.hashicorp.com/#tools>`__.
Bitcoin, Ethereum, etc.
~~~~~~~~~~~~~~~~~~~~~~~
@ -82,34 +81,35 @@ this is what made Tendermint a Proof-of-Stake algorithm.
Since then, Tendermint has evolved to be a general purpose blockchain consensus engine that can host arbitrary application states.
That means it can be used as a plug-and-play replacement for the consensus engines of other blockchain software.
So one can take the current Ethereum code base, whether in Rust, or Go, or Haskell, and run it as a ABCI application
using Tendermint consensus. Indeed, [we did that](https://github.com/tendermint/ethermint).
using Tendermint consensus. Indeed, `we did that with Ethereum <https://github.com/tendermint/ethermint>`__.
And we plan to do the same for Bitcoin, ZCash, and various other deterministic applications as well.
Another example of a cryptocurrency application built on Tendermint is [Cosmos](http://cosmos.network)
Another example of a cryptocurrency application built on Tendermint is `the Cosmos network <http://cosmos.network>`__.
## Fabric, Burrow
Fabric, Burrow
~~~~~~~~~~~~~~
[Fabric](https://github.com/hyperledger/fabric), takes a similar approach to Tendermint, but is more opinionated about how the state is managed,
`Fabric <https://github.com/hyperledger/fabric>`__, takes a similar approach to Tendermint, but is more opinionated about how the state is managed,
and requires that all application behaviour runs in potentially many docker containers, modules it calls "chaincode".
It uses an implementation of [PBFT](http://pmg.csail.mit.edu/papers/osdi99.pdf)
It uses an implementation of `PBFT <http://pmg.csail.mit.edu/papers/osdi99.pdf>`__.
from a team at IBM that is
[augmented to handle potentially non-deterministic chaincode](https://www.zurich.ibm.com/~cca/papers/sieve.pdf)
`augmented to handle potentially non-deterministic chaincode <https://www.zurich.ibm.com/~cca/papers/sieve.pdf>`__
It is possible to implement this docker-based behaviour as a ABCI app in Tendermint,
though extending Tendermint to handle non-determinism remains for future work.
[Burrow](https://github.com/hyperledger/burrow) is an implementation of the Ethereum Virtual Machine and Ethereum transaction mechanics,
`Burrow <https://github.com/hyperledger/burrow>`__ is an implementation of the Ethereum Virtual Machine and Ethereum transaction mechanics,
with additional features for a name-registry, permissions, and native contracts, and an alternative blockchain API.
It uses Tendermint as its consensus engine, and provides a particular application state.
ABCI Overview
-------------
The Application BlockChain Interface (ABCI) allows for Byzantine Fault Tolerant replication of applications written in any programming language.
The `Application BlockChain Interface (ABCI) <https://github.com/tendermint/abci>`__ allows for Byzantine Fault Tolerant replication of applications written in any programming language.
Motivation
~~~~~~~~~~
Thus far, all blockchains "stacks" (such as [Bitcoin](https://github.com/bitcoin/bitcoin)) have had a monolithic design. That is, each blockchain stack is a single program that handles all the concerns of a decentralized ledger; this includes P2P connectivity, the "mempool" broadcasting of transactions, consensus on the most recent block, account balances, Turing-complete contracts, user-level permissions, etc.
Thus far, all blockchains "stacks" (such as `Bitcoin <https://github.com/bitcoin/bitcoin>`__) have had a monolithic design. That is, each blockchain stack is a single program that handles all the concerns of a decentralized ledger; this includes P2P connectivity, the "mempool" broadcasting of transactions, consensus on the most recent block, account balances, Turing-complete contracts, user-level permissions, etc.
Using a monolithic architecture is typically bad practice in computer science.
It makes it difficult to reuse components of the code, and attempts to do so result in complex maintanence procedures for forks of the codebase.
@ -125,10 +125,10 @@ Thus we have an interface, the Application BlockChain Interface (ABCI), and its
Intro to ABCI
~~~~~~~~~~~~~
[Tendermint Core](https://github.com/tendermint/tendermint) (the "consensus engine") communicates with the application via a socket protocol that
satisfies the [ABCI](https://github.com/tendermint/abci).
`Tendermint Core <https://github.com/tendermint/tendermint>`__ (the "consensus engine") communicates with the application via a socket protocol that
satisfies the `ABCI <https://github.com/tendermint/abci>`__.
To draw an analogy, lets talk about a well-known cryptocurrency, Bitcoin. Bitcoin is a cryptocurrency blockchain where each node maintains a fully audited Unspent Transaction Output (UTXO) database. If one wanted to create a Bitcoin-like system on top of ABCI, Tendermint Core would be responsible for
To draw an analogy, lets talk about a well-known cryptocurrency, Bitcoin. Bitcoin is a cryptocurrency blockchain where each node maintains a fully audited Unspent Transaction Output (UTXO) database. If one wanted to create a Bitcoin-like system on top of ABCI, Tendermint Core would be responsible for
- Sharing blocks and transactions between nodes
- Establishing a canonical/immutable order of transactions (the blockchain)
@ -142,9 +142,9 @@ The application will be responsible for
Tendermint is able to decompose the blockchain design by offering a very simple API (ie. the ABCI) between the application process and consensus process.
The ABCI consists of 3 primary message types that get delivered from the core to the application. The application replies with corresponding response messages.
The ABCI consists of 3 primary message types that get delivered from the core to the application. The application replies with corresponding response messages.
The messages are specified here: [ABCI Message Types](https://github.com/tendermint/abci#message-types)
The messages are specified here: `ABCI Message Types <https://github.com/tendermint/abci#message-types>`__.
The `DeliverTx` message is the work horse of the application. Each transaction in the blockchain is delivered with this message. The application needs to validate each transaction received with the `DeliverTx` message against the current state, application protocol, and the cryptographic credentials of the transaction. A validated transaction then needs to update the application state — by binding a value into a key values store, or by updating the UTXO database, for instance.
@ -152,7 +152,7 @@ The `CheckTx` message is similar to `DeliverTx`, but it's only for validating tr
The `Commit` message is used to compute a cryptographic commitment to the current application state, to be placed into the next block header. This has some handy properties. Inconsistencies in updating that state will now appear as blockchain forks which catches a whole class of programming errors. This also simplifies the development of secure lightweight clients, as Merkle-hash proofs can be verified by checking against the block hash, and that the block hash is signed by a quorum.
There can be multiple ABCI socket connections to an application. Tendermint Core creates three ABCI connections to the application; one for the validation of transactions when broadcasting in the mempool, one for the consensus engine to run block proposals, and one more for querying the application state.
There can be multiple ABCI socket connections to an application. Tendermint Core creates three ABCI connections to the application; one for the validation of transactions when broadcasting in the mempool, one for the consensus engine to run block proposals, and one more for querying the application state.
It's probably evident that applications designers need to very carefully design their message handlers to create a blockchain that does anything useful but this architecture provides a place to start. The diagram below illustrates the flow of messages via ABCI.
@ -161,15 +161,15 @@ It's probably evident that applications designers need to very carefully design
A Note on Determinism
~~~~~~~~~~~~~~~~~~~~~
The logic for blockchain transaction processing must be deterministic. If the application logic weren't deterministic, consensus would not be reached among the Tendermint Core replica nodes.
The logic for blockchain transaction processing must be deterministic. If the application logic weren't deterministic, consensus would not be reached among the Tendermint Core replica nodes.
Solidity on Ethereum is a great language of choice for blockchain applications because, among other reasons, it is a completely deterministic programming language. However, it's also possible to create deterministic applications using existing popular languages like Java, C++, Python, or Go. Game programmers and blockchain developers are already familiar with creating deterministic programs by avoiding sources of non-determinism such as:
Solidity on Ethereum is a great language of choice for blockchain applications because, among other reasons, it is a completely deterministic programming language. However, it's also possible to create deterministic applications using existing popular languages like Java, C++, Python, or Go. Game programmers and blockchain developers are already familiar with creating deterministic programs by avoiding sources of non-determinism such as:
* random number generators (without deterministic seeding)
* race conditions on threads (or avoiding threads altogether)
* the system clock
* uninitialized memory (in unsafe programming languages like C or C++)
* [floating point arithmetic](http://gafferongames.com/networking-for-game-programmers/floating-point-determinism/)
* `floating point arithmetic <http://gafferongames.com/networking-for-game-programmers/floating-point-determinism/>`__.
* language features that are random (e.g. map iteration in Go)
While programmers can avoid non-determinism by being careful, it is also possible to create a special linter or static analyzer for each language to check for determinism. In the future we may work with partners to create such tools.
@ -224,11 +224,9 @@ Validators can be forced, by logic in the application,
to "bond" their currency holdings in a security deposit that can be destroyed if they're found to misbehave in the consensus protocol.
This adds an economic element to the security of the protocol, allowing one to quantify the cost of violating the assumption that less than one-third of voting power is Byzantine.
The [Cosmos Network](http://cosmos.network) is designed to use this Proof-of-Stake mechanism across an array of cryptocurrencies implemented as ABCI applications.
The `Cosmos Network <http://cosmos.network>`__ is designed to use this Proof-of-Stake mechanism across an array of cryptocurrencies implemented as ABCI applications.
- Inspect the following diagram for [Tendermint in a (technical) nutshell](https://github.com/mobfoundry/hackatom/blob/master/tminfo.pdf)
- View the following diagram for [Tendermint in a (technical) nutshell](https://github.com/mobfoundry/hackatom/blob/master/tminfo.pdf)
<img src="../assets/images/tm-transaction-flow.png">