docs: update examples in README.md

pkg/tuf/example_registry.go

@@ -0,0 +1,43 @@
+package tuf
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/docker/attest/internal/embed"
+	"github.com/theupdateframework/go-tuf/v2/metadata"
+)
+
+func ExampleTufRegistryClient() {
+	// create a tuf client
+	home, err := os.UserHomeDir()
+	if err != nil {
+		panic(err)
+	}
+	tufOutputPath := filepath.Join(home, ".docker", "tuf")
+
+	// using oci tuf metadata and targets
+	metadataURI := "regsitry-1.docker.io/docker/tuf-metadata:latest"
+	targetsURI := "regsitry-1.docker.io/docker/tuf-targets"
+	registryClient, err := NewTufClient(embed.DefaultRoot, tufOutputPath, metadataURI, targetsURI)
+	if err != nil {
+		panic(err)
+	}
+
+	// get trusted tuf metadata
+	trustedMetadata := registryClient.GetMetadata()
+	if err != nil {
+		panic(err)
+	}
+
+	// top-level target files
+	targets := trustedMetadata.Targets[metadata.TARGETS].Signed.Targets
+
+	for _, t := range targets {
+		// download target files
+		_, _, err := registryClient.DownloadTarget(t.Path, filepath.Join(tufOutputPath, "download"))
+		if err != nil {
+			panic(err)
+		}
+	}
+}