rsview — Rust proof-of-concept

A native port of react-obj-view's CLI core: memory-map a JSON file, parse on expand (subtrees are byte ranges, never materialized), flatten a level only as far as the viewport scrolls, and search on a background thread. Opening a multi-GB file stays near-constant memory.

This is a proof-of-concept, not the product: single JSON file argument only (no stdin/NDJSON streaming), no themes, no copy. Open / navigate / expand / search.

Build & run

cargo build --release
./target/release/rsview path/to/file.json
# or
cargo run --release -- path/to/file.json

Put it on your PATH (optional):

ln -sf "$PWD/target/release/rsview" ~/.local/bin/rsview
rsview big.json

Keys

Top line is filename <focus>/<rows>+ — the + means the row count is a lower bound: the level has only been flattened as far as you've scrolled. Matches render yellow; the current match is brighter.

Why it's fast (and stays small)

• mmap, not read. The file is mapped (memmap2), so opening it copies nothing — the kernel pages in 4 KB chunks only when a byte is actually touched. Browsing a 1 GB file sits around 2.6 MB RSS.
• Scan bytes, don't parse. scanner.rs walks raw &[u8] to find a container's child byte-ranges. Structural tokens ({ } [ ] " : ,) are ASCII; every byte of a multi-byte UTF-8 sequence is ≥ 0x80, so the scan never collides with them and never decodes. A value is decoded (from_utf8) only when it's drawn — and only that slice.
• Parse on expand, incrementally. A collapsed node costs O(1). Expanding uses a resumable Cursor that scans one more child per call, so a level with millions of keys only enumerates ~a screenful (flatten stops at a row budget). First paint is ~constant regardless of file size.
• Search on a real thread. search.rs scans the mmap on its own OS thread and streams match paths over an mpsc channel; an AtomicBool the thread polls is the cancel. Retyping drops the old search instantly. The UI never blocks because the scan isn't on the UI's loop. (A full scan does fault in the pages it reads — evictable, file-backed page cache — so search trades the near-zero-memory property for the bytes it must touch.)

Layout