Crate monty_fs 

Available on crate features code and embedded-python only.

Filesystem mounting system for sandboxed execution.

Provides MountTable, which maps virtual paths to real host directories with configurable access modes. When sandbox code calls filesystem methods like Path.read_text(), the mount table intercepts the operation, resolves the virtual path, and executes it according to the mount mode.

This crate is HOST-side code: it performs real std::fs I/O and is linked only by host/parent crates (monty-pool, the CLI, bindings). The monty interpreter crate deliberately does not depend on it — sandboxed code can only request filesystem operations by suspending with an OsFunctionCall, which a host holding a MountTable services via MountTable::handle_os_call.

Security

The monty runtime MUST NEVER read, write, or obtain any information about any file or directory outside the specific directory that is mounted.

Enforced by path_security::resolve_path via path canonicalization, boundary checks, and symlink escape detection. Each mount has an aggregate memory budget, defaulting to DEFAULT_MEMORY_USAGE_LIMIT, for retained overlay data and results.

Mount Modes

• MountMode::ReadWrite — full read/write access to the host directory
• MountMode::ReadOnly — reads work, writes raise PermissionError
• MountMode::OverlayMemory — reads fall through to host; writes stored in memory

Structs

Mount

A single mount point mapping a virtual path to a host directory.

MountTable

A collection of mount points mapping virtual paths to host directories.

OverlayState

In-memory overlay state for super::MountMode::OverlayMemory.

Enums

MountCallOutcome

Outcome of MountTable::handle_os_call.

MountError

Errors from mount configuration or filesystem operations.

MountMode

Access policy for a mount point.

Constants

DEFAULT_MEMORY_USAGE_LIMIT

Default aggregate memory budget for one mount: 100 MB in decimal bytes.