Go SDK#

Use the Go SDK at a runtime boundary you own. This guide needs Go 1.22 or newer and the quickstart policy.

The package is github.com/backbay-labs/hush/packages/go/hushspec. Parse, resolution and compilation return (value, error). Guard.Check returns (GuardDecision, error); stop on error, then branch on Allowed(). There is no exception-based enforcement API.

Install and run the complete example#

Create an empty directory. Download these files, preserving the listed relative paths, and place policy.yaml at the top of that directory:

The module version is github.com/backbay-labs/hush/packages/go@v1.0.0. Signing uses Go's standard cryptography support. The guard is named Guard, not HushGuard.

Terminal

go mod tidy
go run . policy.yaml

Expected output: PASS: deny=0 dispatches; unconfirmed warn=0; confirmed warn=1; invalid policy refused. All effects are in a fresh temporary directory. No model API or credentials are required, and the program cleans up its own synthetic output.

Enforce before the effect#

The example parses and validates the policy, resolves it, and compiles it once. It then attaches a consistent actor and callback receipt sink to the guard. The synthetic handler creates one file only after enforcement permits dispatch.

main.goDownload

package main

import (
	"context"
	"fmt"
	hush "github.com/backbay-labs/hush/packages/go/hushspec"
	"os"
	"path/filepath"
)

func must(err error) {
	if err != nil {
		panic(err)
	}
}
func require(ok bool, message string) {
	if !ok {
		panic(message)
	}
}

func main() {
	policyPath := "policy.yaml"
	if len(os.Args) > 1 {
		policyPath = os.Args[1]
	}
	raw, err := os.ReadFile(policyPath)
	must(err)
	document, err := hush.Parse(string(raw))
	must(err)
	require(hush.Validate(document).IsValid(), "invalid document")
	resolution, err := hush.ResolveFileWithOptions(policyPath, hush.ResolveOptions{})
	must(err)
	compiled, err := hush.CompilePolicy(resolution.Spec)
	must(err)
	checkTrust(policyPath, resolution.Spec)
	require(compiled.Evaluate(&hush.EvaluationAction{Type: "tool_call", Target: "search"}).Decision == hush.DecisionAllow, "search denied")
	var receipts []*hush.DecisionReceipt
	options := hush.GuardOptions{
		Actor: &hush.Actor{AgentID: "docs-agent", SessionID: "docs-session", Principal: "docs-user", Runtime: "docs/1.0.0"},
		Sink:  hush.NewCallbackSink(func(receipt *hush.DecisionReceipt) error { receipts = append(receipts, receipt); return nil }),
	}
	guard, err := hush.NewGuard(resolution, options)
	must(err)
	directory, err := os.MkdirTemp("", "hush-doc-effect-")
	must(err)
	defer os.RemoveAll(directory)
	output := filepath.Join(directory, "effect.txt")
	dispatches := 0
	dispatch := func(g *hush.Guard, tool string) bool {
		outcome, err := g.Check(context.Background(), &hush.EvaluationAction{Type: "tool_call", Target: tool})
		must(err)
		if !outcome.Allowed() {
			return false
		}
		file, err := os.OpenFile(output, os.O_CREATE|os.O_EXCL|os.O_WRONLY, 0600)
		must(err)
		_, err = file.WriteString("confirmed once\n")
		must(err)
		must(file.Close())
		dispatches++
		return true
	}
	require(!dispatch(guard, "deploy"), "deploy dispatched")
	require(!dispatch(guard, "write_file"), "unconfirmed write dispatched")
	_, err = os.Stat(output)
	require(os.IsNotExist(err) && dispatches == 0, "blocked effect exists")
	options.OnWarn = func(hush.EvaluationResult, *hush.EvaluationAction) bool { return true }
	confirmed, err := hush.NewGuard(resolution, options)
	must(err)
	require(dispatch(confirmed, "write_file") && dispatches == 1, "confirmation did not dispatch exactly once")
	effect, err := os.ReadFile(output)
	must(err)
	require(string(effect) == "confirmed once\n", "effect mismatch")
	require(receipts[len(receipts)-1].Enforcement.Outcome == hush.EnforcementOutcomeConfirmed, "receipt not confirmed")
	require(receipts[len(receipts)-1].Actor.AgentID == "docs-agent", "actor mismatch")
	_, err = hush.Parse("hushspec: \"1.0.0\"\nunknown_rule: true\n")
	require(err != nil, "invalid policy accepted")
	fmt.Println("PASS: deny=0 dispatches; unconfirmed warn=0; confirmed warn=1; invalid policy refused")
}

The on_warn / onWarn callback in this demonstration approves one synthetic test action. A real integration must obtain approval from an authenticated channel and bind it to the pending action. Do not replace approval with unconditional true in a production agent.

Signing and keyrings#

The companion trust.go program is called by the main example. It creates an ephemeral test key, signs the resolved document, verifies with an explicit keyring, and rejects a different keyring. It prints no private key and does not persist one. Production signing identities belong to the operator.

Signing and verification must refer to the same resolved policy used for evaluation. See signing, bundles, and the exact signing APIs. A successful signature proves authenticity relative to your trust roots, not that a tool obeyed the policy.

Providers and reload#

NewGuardFromProvider loads the provider; use a PolicyWatcher/PolicyPoller with the documented lifecycle for ongoing reload. Check accepts a context. Confirmation, custom-sink and receipt-clock callbacks must not re-enter the same guard or wait on work that needs it. Observers run after the ordering gate releases.

Initial policy-load errors cannot fall back to a nonexistent policy. Ordinary guard reload preserves the last good policy on a rejected update and reports the error. It is not nonblocking: reload can wait for confirmation and receipt delivery. See hot reload for ordering and the distinct experimental coordinator refusal contract.

Receipts and failure handling#

The callback sink makes receipt contents visible to the test. It is not durable storage. Configure a chained file sink or another reviewed delivery path for operational evidence, and handle sink.error through an observer. A failed ordinary sink does not change the decision; if dispatch must require a durable permit, use the separately bounded experimental invocation workflow.

Receipts record actor fields, policy hash, decision, trace and enforcement outcome. They do not carry raw action content. The confirmed outcome distinguishes an approved warning from a plain allow.

API map and next steps#

The SDK API contract covers parse/validate, resolve/merge, compile/evaluate, actors, receipts, sinks, signing, keyrings, providers, panic mode and error conventions. For mapping effects, read MCP and runtime integration. Use conformance to understand what a test corpus establishes; this example is an integration regression, not an independent conformance certificate.