Running headless & in Docker

Spytial's default is to open one persistent browser viewer for dbg! captures; standalone diagram(&value) calls still open their own files. Both behaviors are wrong for CI, remote shells, containers, and test suites. Two environment variables cover the headless cases.

SPYTIAL_NO_OPEN — suppress the browser launch

Set to 1, true, or yes (case-insensitive) and spytial skips the platform browser-open command. For dbg!, it also skips the live loopback server while continuing to append captures to the session HTML on disk. The stable path is printed to stderr:

SPYTIAL_NO_OPEN=1 cargo run --example rbt

spytial: capture appended to /tmp/spytial-session-12345-0-987654321.html

dbg!'s pretty-printed output is unaffected, so cargo test capture behaves exactly as it does for std::dbg!.

SPYTIAL_OUTPUT_PATH — pin the output filename

The default dbg! session already uses one stable, unique temp path. To choose it — for serving with a static HTTP server, retaining it as an artifact, or round-tripping it off a remote machine — set SPYTIAL_OUTPUT_PATH:

SPYTIAL_OUTPUT_PATH=/var/www/diagram.html cargo run

The value is read when the session starts and used verbatim. Each capture atomically replaces it with the complete ordered session, the parent directory must already exist, and concurrent calls are serialized. The file persists after process exit. Operating-system cleanup policies eventually remove the default temp file; Spytial does not delete it because it is the post-mortem viewer once the in-process server has stopped.

diagram() retains its standalone behavior: with this variable set, each standalone call overwrites the path with one diagram rather than a session.

Persistent transport limits

The dbg! viewer transport is a synchronous, single-user debugging aid. It is not configurable to listen beyond 127.0.0.1, has no external-service or deployment mode, and stops with the captured program. This is separate from the repository's viz_server demo binary and deliberately does not turn that server into the async, authenticated deployment service discussed in issue #47.

Docker

The repository ships a Dockerfile and entrypoint that give you a one-command demo without a local Rust toolchain:

docker build -t spytial .
docker run --rm -p 8080:8080 spytial        # default: the rbt example
docker run --rm -p 8080:8080 spytial demo   # any example in examples/

The container builds and runs the example once, then serves the rendered HTML over a small HTTP server. Open http://localhost:8080/rust_viz_data.html on your host. The image sets both variables above — SPYTIAL_NO_OPEN=1 via the Dockerfile (no display in the container) and SPYTIAL_OUTPUT_PATH=/tmp/rust_viz_data.html via the entrypoint (the path the server serves). The server is single-threaded and for local viewing only.