# Tendermint Socket Protocol (TMSP)

Blockchains are a system for creating shared multi-master application state. 
**TMSP** is a socket protocol enabling a blockchain consensus engine, running in one process,
to manage a blockchain application state, running in another.

For more information on TMSP, motivations, and tutorials, please visit [our blog post](http://tendermint.com/posts/tendermint-socket-protocol/).

## Message types

TMSP requests/responses are simple Protobuf messages.  Check out the [schema file](https://github.com/tendermint/tmsp/blob/master/types/types.proto).

#### AppendTx
  * __Arguments__:
    * `Data ([]byte)`: The request transaction bytes
  * __Returns__:
    * `Code (uint)`: Response code
    * `Data ([]byte)`: Result bytes, if any
    * `Log (string)`: Debug or error message
  * __Usage__:<br/>
    Append and run a transaction.  If the transaction is valid, returns CodeType.OK

#### CheckTx
  * __Arguments__:
    * `Data ([]byte)`: The request transaction bytes
  * __Returns__:
    * `Code (uint)`: Response code
    * `Data ([]byte)`: Result bytes, if any
    * `Log (string)`: Debug or error message
  * __Usage__:<br/>
    Validate a transaction.  This message should not mutate the state.
    Transactions are first run through CheckTx before broadcast to peers in the mempool layer.
    You can make CheckTx semi-stateful and clear the state upon `Commit`, to ensure that all txs in the blockchain are valid.

#### Commit 
  * __Returns__:
    * `Data ([]byte)`: The Merkle root hash
    * `Log (string)`: Debug or error message
  * __Usage__:<br/>
    Return a Merkle root hash of the application state.

#### Query
  * __Arguments__:
    * `Data ([]byte)`: The query request bytes
  * __Returns__:
    * `Code (uint)`: Response code
    * `Data ([]byte)`: The query response bytes
    * `Log (string)`: Debug or error message

#### Flush
  * __Usage__:<br/>
    Flush the response queue.  Applications that implement `types.Application` need not implement this message -- it's handled by the project.

#### Info
  * __Returns__:
    * `Data ([]byte)`: The info bytes
  * __Usage__:<br/>
    Return information about the application state.  Application specific.

#### SetOption
  * __Arguments__:
    * `Key (string)`: Key to set
    * `Value (string)`: Value to set for key
  * __Returns__:
    * `Log (string)`: Debug or error message
  * __Usage__:<br/>
    Set application options.  E.g. Key="mode", Value="mempool" for a mempool connection, or Key="mode", Value="consensus" for a consensus connection.
    Other options are application specific.

## Changelog

### Feb 14th, 2016

* s/GetHash/Commit/g
* Document Protobuf request/response fields

### Jan 23th, 2016

* Added CheckTx/Query TMSP message types
* Added Result/Log fields to AppendTx/CheckTx/SetOption
* Removed Listener messages
* Removed Code from ResponseSetOption and ResponseGetHash
* Made examples BigEndian

### Jan 12th, 2016

* Added "RetCodeBadNonce = 0x06" return code

### Jan 8th, 2016

Tendermint/TMSP now comes to consensus on the order first before AppendTx.
This means that we no longer need the Commit/Rollback TMSP messages.
Instead, there’s a “CheckTx” message for mempool to check the validity of a message.
One consequence is that txs in blocks now may include invalid txs that are ignored.
In the future, we can include a bitarray or merkle structure in the block so anyone can see which txs were valid.
To prevent spam, applications can implement their “CheckTx” messages to deduct some balance, so at least spam txs will cost something.  This isn’t any more work that what we already needed to do, so it’s not any worse.
You can see the new changes in the tendermint/tendermint “order_first” branch, and tendermint/tmsp “order_first” branch.  If you your TMSP apps to me I can help with the transition.
Please take a look at how the examples in TMSP changed, e.g. how AppContext was removed, CheckTx was added, how the TMSP msg bytes changed, and how commit/rollback messages were removed.