Architecture Overview

mmap-guard is intentionally thin. The entire crate consists of four source files.

Module Structure

graph TD
    A[lib.rs] -->|re-exports| B[file_data.rs]
    A -->|re-exports| C[map.rs]
    A -->|re-exports| D[load.rs]
    C -->|uses| B
    D -->|delegates to| C
    D -->|uses| B
    C -->|unsafe| E[memmap2::Mmap]

lib.rs

Crate root. Sets #![deny(clippy::undocumented_unsafe_blocks)] and re-exports the public API:

• FileData
• map_file
• load, load_stdin

file_data.rs

Defines the FileData enum — the unified type returned by all public functions. Both variants (Mapped and Loaded) deref to &[u8].

map.rs

Contains map_file() and the single unsafe block in the crate. Acquires a shared advisory lock (via fs4) before mapping, which mitigates SIGBUS from concurrent truncation when cooperating processes also use advisory locks. Performs pre-flight checks (file exists, non-empty) before creating the memory mapping.

load.rs

Convenience layer. load() routes "-" to load_stdin(Some(1 GiB)) for stdin, and delegates all other paths to map_file(). load_stdin(max_bytes) reads stdin in bounded chunks into a heap buffer and returns FileData::Loaded; passing None removes the cap.

Dependency Graph

graph LR
    A[mmap-guard] -->|runtime| B[memmap2]
    A -->|runtime| E[fs4]
    A -->|dev| C[tempfile]
    B --> D[libc]

The crate has two runtime dependencies (memmap2 and fs4) and one dev-dependency (tempfile).