types

WASI filesystem is a filesystem API primarily intended to let users run WASI programs that access their files on their existing filesystems, without significant overhead.

Paths are passed as interface-type strings, meaning they must consist of a sequence of Unicode Scalar Values (USVs). Some filesystems may contain paths which are not accessible by this API.

The directory separator in WASI is always the forward-slash (/).

All paths in WASI are relative paths, and are interpreted relative to a descriptor referring to a base directory. If a path argument to any WASI function starts with /, or if any step of resolving a path, including .. and symbolic link steps, reaches a directory outside of the base directory, or reaches a symlink to an absolute or rooted path in the underlying filesystem, the function fails with error-code::not-permitted.

For more information about WASI path resolution and sandboxing, see WASI filesystem path resolution.

Though this package presents a portable interface modelled on POSIX, it prioritizes compatibility over portability: allowing users to access their files on their machine is more important than exposing a single semantics across all platforms. Notably, depending on the underlying operating system and file system:

• Paths may be case-folded or not.
• Deleting (unlinking) a file may fail if there are other file descriptors open.
• Durability and atomicity of changes to underlying files when there are concurrent writers.

Users that need well-defined, portable semantics should use a key-value store or a database instead.