19-EVMFILE: Filesystem Library on Ethereum Virtual Machine

This RFC provides a filesystem specification that can be built on top of the Ethereum Virtual Machine.


The filesystem is built using EVM’s account storage. Pathes of files are hashed to get the storage key, and the contents of files are stored as the storage value.

Filesystem Prefix

The implementation library should have a pre-set prefix string that avoids conflicts with other libraries that also use account storage. This prefix string is implementation-specific.

Storing Files

When storing a file, keccak256("{prefix}:{path}:{len}") is used to store the length of the file. If the length of the file is 0, the file does not exist.

If the length of the file is greater than 0, keccak256("{prefix}:{path}:{index}") is used as the key to store contents of the file of every 32 bytes.


Folders are normal files with contents of the list of files stored inside. The list of files are a list of UTF-8 strings ended with \0 and padded in 32 bytes.

File Metadata

File metadata are normal files stored with path {file_path}#metadata. The format of metadata is implementation-specific.