FemtoDB

A simple key/value datastore for Ethereum smart contracts.

Disclaimer

This library has NOT been security reviewed, pentested, production-hardened, or used in anger. Do not use for any contract intended to control more than, like, $10. There are definitely bugs, and it WILL lose your money.

NPM

FemtoDB is available on npm as femto-db, and is compatible with Truffle's beta NPM integration.

Basic Usage

The core functions are:

• put(address target, uint256 key, uint256 value)

which adds data to the database, and:

• get(address owner, address target, uint256 key) constant returns(uint256 value)

which retrieves it. To explain each variable:

• owner is automatically set to the address that sends the put call. You must provide it for a get.
• target is the address the data is "about". In case you want to store data about yourself, you can simply provide your own address.
• key is a unsigned integer representing the key.
• value is an unsigned integer representing the value.

This API is designed to be as minimal as possible. We recommend using a more convenient interface built on top of this basic API, especially for handling other datatypes. Ownage's interface will be released shortly.

Synchronization

If you would like to synchronize a FemtoDB with an off-chain database, you can watch the following event:

LogPut(uint256 indexed revisionID, address indexed owner, address indexed target, uint256 key, uint256 value);

revisionID is a simple counter, which increments on each put. It can be used to notice lost messages, or check if your data is stale. There is also a function for accessing the latest revisionID directly:

revisionID() constant returns(uint256)

Compatibility with EtherRouter

FemtoDB is fully compatible with EtherRouter, Ownage's solution for contract upgrades. Simply follow the directions in the EtherRouter repo.