Trait FsBackend 

pub trait FsBackend: Send + Sync {
    // Required methods
    fn read_text(
        &self,
        path: PathBuf,
        line: Option<u32>,
        limit: Option<u32>,
    ) -> BoxFuture<'_, Result<String, FsError>>;
    fn write_text(
        &self,
        path: PathBuf,
        content: String,
    ) -> BoxFuture<'_, Result<(), FsError>>;

    // Provided methods
    fn read_bytes(
        &self,
        path: PathBuf,
    ) -> BoxFuture<'_, Result<Vec<u8>, FsError>> { ... }
    fn fingerprint(
        &self,
        path: PathBuf,
    ) -> BoxFuture<'_, Result<Fingerprint, FsError>> { ... }
}

Fs backend trait.

Two verbs cover all low-level operations of the fs tool family:

• edit_file is composed at the tool layer (first read_text then write_text); the backend is unaware of patch semantics
• Delete / move / mkdir are not part of the fs tool family (ACP has no corresponding inverse methods); the LLM uses bash

Parameters use owned PathBuf / String to confine the future’s lifetime to &'_ self, avoiding explicit lifetime parameters; same trade-off as LlmProvider::complete.

Required Methods

fn read_text( &self, path: PathBuf, line: Option<u32>, limit: Option<u32>, ) -> BoxFuture<'_, Result<String, FsError>>

Reads the entire file as UTF-8 text.

line / limit have the same semantics as ACP ReadTextFileRequest:

• line = Some(n) starts reading from line n (1-based)
• limit = Some(k) reads at most k lines
• Both None reads the full file

fn write_text( &self, path: PathBuf, content: String, ) -> BoxFuture<'_, Result<(), FsError>>

Write a UTF-8 text file, overwriting any existing content.

The backend is responsible for ensuring the parent directory exists (mkdir -p semantics).

Line-ending / atomicity responsibilities are split as:

• Local backend performs line-ending normalization and atomic write via tmp + rename
• Delegated backend leaves the decision to the client

Provided Methods

fn read_bytes(&self, path: PathBuf) -> BoxFuture<'_, Result<Vec<u8>, FsError>>

Reads the raw bytes of an entire file. The read_file tool takes this path when it detects a binary type such as an image, passing the bytes to the caller for base64 encoding into a multimodal tool_result.

The default implementation returns FsError::NotPermitted — the delegated backend (AcpFsBackend) uses the ACP fs/read_text_file reverse channel, which is text-only and cannot obtain binary data. In ACP environments, reading images is discouraged by the system prompt (the # Environment section notes that the frontend is delegated). The local backend (LocalFsBackend) overrides this to read directly from disk.

fn fingerprint( &self, path: PathBuf, ) -> BoxFuture<'_, Result<Fingerprint, FsError>>

Returns a “content fingerprint” used by edit_file to detect concurrent write conflicts in the read–modify–write window.

The default implementation reads the full content via FsBackend::read_text and computes Fingerprint::of — this allows delegating backends (e.g. AcpFsBackend) to work without additional protocol methods. Local backends may override this method to use cheaper checks like mtime + size.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl FsBackend for NoopFsBackend