🥡 Starbox - Unboxing the Potential of Starlark

Starbox is a pragmatic Go wrapper around the Starlark in Go project, making it easier to execute Starlark scripts, exchange data between Go and Starlark, and call functions across the Go-Starlark boundary. With a focus on simplicity and usability, Starbox aims to provide an enhanced experience for developers integrating Starlark scripting into their Go applications.

🚀 Key Features

A host of powerful features are provided to supercharge your Starlark scripting experience:

• Streamlined Script Execution: Simplifies setting up and running Starlark scripts, offering a seamless interface for both script execution and interactive REPL sessions.
• Efficient Data Interchange: Enables robust and smooth data exchange between Go and Starlark, enhancing the interoperability and simplifying the integration process.
• Versatile Module Management: Extends Starlark's capabilities with a suite of built-in functions and the ability to load custom and override existing modules, covering functionalities from data processing to HTTP handling and file manipulation.
• Cross-Language Function Calls: Leverage the power of both languages by calling Go functions from Starlark and vice versa, creating powerful integrations.
• Integrated HTTP Context: Facilitates handling HTTP requests and responses within Starlark scripts, catering to web application development and server-side scripting.
• Collective Memory Sharing: Introduces a shared memory concept, enabling data sharing across different script executions and instances, fostering a more connected and dynamic scripting environment.
• Advanced Scripting Tools: Utilize features like REPL for interactive exploration and debugging, along with script caching for improved performance.

📦 Installation

To include starbox in your Go project, use the following command:

go get github.com/1set/starbox

⚙️ Usage

Here's a quick example of how you can use Starbox:

import"github.com/1set/starbox"// Define your box with global variables and modulesbox:=starbox.New("quick")
box.AddKeyValue("greet", func(namestring) string {
returnfmt.Sprintf("Hello, %s!", name)
})
box.AddNamedModules("random")
// Run a Starlark scriptscript:=starbox.HereDoc(` target = random.choice(["World", "Starlark", "Starbox"]) text = greet(target) print("Starlark:", text) print(__modules__)`)
res, err:=box.Run(script)
// Check for errors and resultsiferr!=nil {
fmt.Println("Error executing script:", err)
return
}
fmt.Println("Go:", res["text"].(string))

This may output:

[⭐|quick](15:50:27.677) Starlark: Hello, Starbox!
[⭐|quick](15:50:27.677) ["random"]
Go: Hello, Starbox!

🔒 Security Model & Capability Gating

Starbox is a host runtime: the Go host decides what an untrusted script may reach, and the script cannot widen that grant. The control surface has two distinct layers — Starbox implements the first; the second lives at the layer that constructs the modules.

Load gate — which modules a script may load()

New selects modules through a four-tier module set (EmptyModuleSet, SafeModuleSet, NetworkModuleSet, FullModuleSet); SafeModuleSet is an explicit, hand-curated allowlist that can reach neither the network nor the filesystem.

For stricter, host-declared control, construct the box with a Policy — a Go-side, default-deny allowlist the script can neither read nor mutate:

// Only "math" and "json" are loadable, no matter what the module set requests.box:=starbox.NewWithPolicy("sandboxed", starbox.Policy{
Modules: starbox.ModuleAllow{Names: []string{"math", "json"}},
})
box.SetModuleSet(starbox.FullModuleSet) // requested set is INTERSECTED with the policy

• The zeroPolicy{} permits nothing — strict default-deny by construction.
• ModuleAllow.Capabilities is opt-in capability widening: a non-zero tier (e.g. starlet.CapNetwork) permits every builtin whose capability set is a subset of it.
• The gate covers every named-module path a script can load: builtin, custom (AddModule*), dynamic, and script modules (AddModuleScript, matched by their registered .star name).
• A withheld builtin surfaces a typed ModuleWithheldError (matchable via errors.As). A policy-denied non-builtin (custom/dynamic/script) module is simply absent — load() fails as "not found", so the sandbox is not told a host-private module exists but is forbidden.

SetFS is an explicit exception. A host-mounted fs.FS is a raw filesystem grant with no module-name registry to match against, so it is not governed by the load gate. Under a restrictive policy, curate the mounted filesystem (or do not call SetFS).

Exec gate — what a loaded module may do — is NOT in Starbox

Per-call filesystem / network / command / secret gating (what a loaded module is allowed to actually do) is out of scope for Starbox: it never imports the domain modules, which arrive as opaque loaders, so exec-gating belongs where those loaders are constructed (the host shell / CLI). Starbox ships the load gate only; it does not ship inert exec-grant fields that would be a fail-open footgun.

📏 Execution Budgets & Output Limits

box.SetMaxExecutionSteps(1_000_000) // bound runaway loops a wall-clock timeout cannot stopbox.SetMaxOutputEntries(100) // cap the number of top-level result entries

A run that exceeds the step budget fails with a starlet.MaxStepsExceededError; one that produces too many result entries is withheld with an OutputLimitExceededError. Both are reachable via errors.As, and both are enforced on every run path (Run, RunFile, RunTimeout, RunInspect*, and the RunnerConfig.Execute() builder).

🔎 Inspection without Execution

Learn what a script would see, and catch problems, without running it:

diags, _:=box.Check(script) // []Diagnostic: syntax + resolve errors as "file:line:col: msg"surface, _:=box.DescribeSurface() // Surface: modules (name/origin/members) + globals (name/type)

Both honor the active Policy — they report and accept exactly the modules a real Run would load, never a wider surface.

📤 Structured Results & Console Capture

box.AddResultBuiltin("output") // script calls output(v) once per run to set its resultres, _:=box.Run(`output({"ok": True})`)
val, ok:=box.GetResult() // the captured value; reset at the start of every runcon:=box.EnableConsoleCapture() // funnel console output into a drainable buffer instead of stderrbox.Run(`print("hi")`)
for_, e:=rangecon.Drain() { // []ConsoleEntry: Time, Level, Message, structured Fieldsfmt.Println(e.Level, e.Message, e.Fields)
}

print() becomes a LevelPrint entry; when the log module is loaded, log.* calls become leveled entries whose keyword arguments are preserved as structured Fields (never pre-rendered into the message). Drain returns the buffered entries and clears them, for a per-run drain.

🧩 Typed Errors

Run failures carry typed, errors.As-matchable causes, and ClassifyRunError maps any run failure to a RunError{Kind} (Syntax, Compile, ModuleWithheld, MaxSteps, OutputLimit, Eval) for uniform host handling.

👥 Contributing

We welcome contributions to the Starbox project. If you encounter any issues or have suggestions for improvements, please feel free to open an issue or submit a pull request. Before undertaking any significant changes, please let us know by filing an issue or claiming an existing one to ensure there is no duplication of effort.

📜 License

Starbox is licensed under the MIT License.

🙌 Credits

This project is inspired by and builds upon several open-source projects:

• Starlark in Go: The official Starlark interpreter in Go, created by Google.
• Starlight: A well-known Go wrapper and data conversion tool between Go and Starlark.
• Starlight Enhanced: A sophisticated fork of the original Starlight, with bug fixes and enhancement features.
• Starlib: A collection of third-party libraries for Starlark.
• Starlet: A Go wrapper that simplifies usage, offers data conversion, libraries and extensions for Starlark.

We thank the authors and contributors of these projects for their excellent works 🎉