rion

Record your Rust / C / C++ / Go program under rr and time-travel through every line it executed — hit counts, call stacks, watch values at every step, a flamechart, and a scrubbable timeline that streams in live while the recording is still running.

Created by replay.io — the time-travel debugging industry leaders.

npx @brett_lamy/rion record -- ./your-program

Your default browser pops open on the live trace the moment recording starts.

Requirements

• Docker — recording runs inside a sandboxed rr container (rion builds the image on first use: npx @brett_lamy/rion doctor --build)
• Node 18+
• A program built with debug info (-g -O0, cargo dev profile, or go build -gcflags='all=-N -l') — the binary must be a Linux build, since it runs inside the container

Getting started

# 1. Sign in (opens your browser to approve this CLI):
npx @brett_lamy/rion login

# 2. Check your setup (and build the recorder image on first run):
npx @brett_lamy/rion doctor --build

# 3. Record, from your project directory:
npx @brett_lamy/rion record -- ./target/debug/your-program

The trace uploads to rr-dash under your account and starts streaming immediately — you can watch execution arrive line by line while the program is still being recorded.

Commands

| Command | What it does | | --- | --- | | rion login [--server <url>] | Browser-approval sign-in; token cached at ~/.config/rion/auth.json | | rion logout | Forget the saved token | | rion doctor [--build] | Verify Docker, the recorder images, and connectivity | | rion record [opts] -- <cmd…> | Record <cmd> under rr and upload the trace |

record options

| Flag | Default | Description | | --- | --- | --- | | --lang rust\|c\|cpp\|go | auto-detected | Source language | | --src <dir> | cwd | Project directory (mounted into the sandbox) | | --title <string> | the command | Trace title in the dashboard | | --id <recordingId> | generated | Explicit recording id | | --server <url> | rr-dash prod | Dashboard host |

Environment variables

| Variable | Purpose | | --- | --- | | RION_API_KEY | Non-interactive auth (create one at /welcome) — the CI equivalent of rion login | | RION_HOST | Override the default dashboard host | | RION_NO_OPEN | Set to 1 to skip auto-opening the trace in a browser |

How it works

rion record runs your command under rr record (software-counters mode) in a Docker sandbox, replays the trace under gdb to extract per-line hit counts, an ordered linetrace, and sampled call stacks + locals at every step, then uploads everything through the dashboard's authenticated API. Nothing is uploaded anonymously; recordings are attributed to your account.

Prefer zero local setup? The Playground compiles and records small programs in a cloud sandbox instead.