Filestorage - smart contract, that controls decentralized file storage on SKALE chains.

Filestorage is a cost-effective storage layer within Ethereum capable of handling files up to 100MB. Filestorage uses UNIX-based filesystem of SKALE chains. Filestorage smart contract is a set of functions to interact with files on EVM. This contract may be predeployed on SKALE chains. It contains functions to work with Filestorage precompiled smart contracts.

Smart contract language - Solidity 0.8.9

To start using Filestorage (upload/delete files and create/remove directories) the space should be allocated for specific account, it could be done from account that is given ALLOCATOR_ROLE. Rules of occupying space in Filestorage:

1. For directory 4096 bytes is taken
2. File could be uploaded up to 100 MB (104857600 bytes)
3. Occupying space for file is rounded up to the nearest multiple of 4096 bytes
4. Empty file takes 4096 bytes of free space

After deleting file/directory's amount of space is freed according to the rules above

function reserveSpace(address userAddress, uint reservedSpace)

Reserves the Filestorage space for specific address. Could be called only with ALLOCATOR_ROLE

Parameters:

function setVersion(string newVersion)

Set the Filestorage version. Could be called only with DEFAULT_ADMIN_ROLE

Parameters:

function version()

Get the Filestorage version.

Parameters:

function getTotalStorageSpace()

Gets total space in Filestorage in bytes.

Returns:

function getTotalStorageSpace()

Gets total reserved space in Filestorage in bytes.

Returns:

function getReservedSpace(address owner)

Gets reserved space for account.

Parameters:

Returns:

function getOccupiedSpace(address owner)

Gets occupied space for account.

Parameters:

Returns:

To begin the uploading process, the file should be broken into chunks of 1MB (< 1MB for the last chunk) which are uploaded as separate transactions to FileStorage.sol. The pipeline of the uploading file is:

1. creating empty file of fixed size on EVM by calling startUpload,
2. uploading data chunk by chunk with uploadChunk,
3. checking the file validity and finishing process with finishUpload.

function startUpload(string memory filePath, uint256 fileSize)

Creates empty file on EVM with specific name and size. Owner of the file - message sender.

• Function is called by file owner
• Maximum amount of directories and files in one directory is 8196
• Maximum filesize is 100,000,000 bytes
• Owner should have enough free space

Parameters:

function uploadChunk(string memory filePath, uint position, bytes memory data)

Uploads 1MB chunk of data from specific position in specific file by file owner.

• Function is called by file owner.

Parameters:

function finishUpload(string memory filePath)

Finishes uploading of the file. Checks whether all chunks are uploaded correctly.

• Function is called by file owner.

Parameters:

function deleteFile(string memory filePath)

Deletes file from Filestorage.

• Function is called by file owner.

Parameters:

function readChunk(string memory storagePath, uint position, uint length)
        public
        view
        returns (bytes32[MAX_BLOCK_COUNT] memory out)

Reads chunk from file from specific position with specific length. Returns bytes32 array of fixed size with requested data.

• Maximum length of the chunk to read is 1Mb

Parameters:

Returns:

function getFileSize(string memory storagePath) 
        public 
        view 
        returns (uint fileSize)

Gets size of the requested file in bytes.

Parameters:

Returns:

function getFileStatus(string memory storagePath) 
        public 
        view 
        returns (int)

Returns status of the requested file:

• 0 - file does not exist
• 1 - file is created but has not finished uploading
• 2 - file is fully uploaded

Parameters:

Returns:

Filestorage is represented with UNIX-based filesystem that consisted of files and directories. Directories are stored in Directory structure that contains information about its content in ContentInfo structure. Maximum amount of content in separate directory is 8196.

function createDirectory(string memory directoryPath)

Creates directory in Filestorage. Owner of the directory - message sender.

• Function is called by directory owner
• Maximum amount of directories and files in one directory is 8196

Parameters:

function deleteDirectory(string memory directoryPath)

Deletes directory from Filestorage.

• Function is called by directory owner

Parameters:

function listDirectory(string memory storagePath) 
        public 
        view 
        returns (ContentInfo[])

List information about content of the specific directory.

Parameters:

Returns:

Object ContentInfo can be file or directory and contains:

Create an .env file with following data:

ENTRYPOINT='SKALE endpoint'
PRIVATEKEY='Private key for test account'

Compile FileStorage.sol:

truffle compile

Tests run only on SKALE chains. Create an .env file with following data:

ENTRYPOINT='SKALE endpoint'
SCHAIN_OWNER_PK='Private key of SKALE endpoint owner (or account with money)'
PRIVATEKEY='Private key for test account'

Run tests:

truffle test --network skaled