Persist compiled rules locally rather than in-memory

pkg/action/scan.go

@@ -307,7 +307,7 @@ func CachedRules(ctx context.Context, fss []fs.FS) (*yarax.Rules, error) {
 	var err error
 	compileOnce.Do(func() {
 		var yrs *yarax.Rules
-		yrs, err = compile.Recursive(ctx, fss)
+		yrs, err = compile.RecursiveCached(ctx, fss)
 		if err != nil {
 			err = fmt.Errorf("compile: %w", err)
 			return

pkg/compile/compile.go

@@ -7,10 +7,14 @@ import (
 	"context"
 	"fmt"
 	"io/fs"
+	"log/slog"
+	"os"
 	"path/filepath"
 	"regexp"
 	"strings"
 
+	"github.com/minio/sha256-simd"
+
 	"github.com/chainguard-dev/clog"
 	"github.com/chainguard-dev/malcontent/rules"
 
@@ -221,3 +225,129 @@ func Recursive(ctx context.Context, fss []fs.FS) (*yarax.Rules, error) {
 
 	return yxc.Build(), nil
 }
+
+// getCacheDir returns the directory for storing compiled rules.
+func getCacheDir() (string, error) {
+	var cacheDir string
+
+	if userCacheDir, err := os.UserCacheDir(); err == nil {
+		cacheDir = filepath.Join(userCacheDir, "malcontent")
+	} else {
+		cacheDir = filepath.Join(os.TempDir(), "malcontent-cache")
+	}
+
+	if err := os.MkdirAll(cacheDir, 0o755); err != nil {
+		return "", fmt.Errorf("create cache dir: %w", err)
+	}
+
+	return cacheDir, nil
+}
+
+// loadCachedRules attempts to load rules from the local, compiled rules.
+func loadCachedRules(cacheFile string) (*yarax.Rules, error) {
+	file, err := os.Open(cacheFile)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	compiledRules, err := yarax.ReadFrom(file)
+	if err != nil {
+		return nil, fmt.Errorf("read cached rules: %w", err)
+	}
+
+	return compiledRules, nil
+}
+
+// saveCachedRules saves rules to a local file.
+func saveCachedRules(compiledRules *yarax.Rules, cacheFile string) error {
+	tmpFile := cacheFile + ".tmp"
+	file, err := os.OpenFile(tmpFile, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0o644)
+	if err != nil {
+		return fmt.Errorf("create cache file: %w", err)
+	}
+	defer file.Close()
+
+	if _, err := compiledRules.WriteTo(file); err != nil {
+		os.Remove(tmpFile)
+		return fmt.Errorf("write rules to cache: %w", err)
+	}
+
+	if err := os.Rename(tmpFile, cacheFile); err != nil {
+		os.Remove(tmpFile)
+		return fmt.Errorf("rename cache file: %w", err)
+	}
+
+	return nil
+}
+
+// getRulesHash computes a hash of the rule sources for cache validation.
+func getRulesHash(ctx context.Context, fss []fs.FS) (string, error) {
+	if ctx.Err() != nil {
+		return "", ctx.Err()
+	}
+
+	hasher := sha256.New()
+
+	for _, fsys := range fss {
+		err := fs.WalkDir(fsys, ".", func(path string, d fs.DirEntry, err error) error {
+			if err != nil {
+				return err
+			}
+			if d.IsDir() {
+				return nil
+			}
+			if filepath.Ext(path) == ".yara" || filepath.Ext(path) == ".yar" {
+				hasher.Write([]byte(path))
+				content, err := fs.ReadFile(fsys, path)
+				if err != nil {
+					return err
+				}
+				hasher.Write(content)
+			}
+			return nil
+		})
+		if err != nil {
+			return "", err
+		}
+	}
+
+	return fmt.Sprintf("%x", hasher.Sum(nil)), nil
+}
+
+// RecursiveCached compiles rules with persistent disk caching to avoid penalizing successive executions with repeated rule compilations.
+func RecursiveCached(ctx context.Context, fss []fs.FS) (*yarax.Rules, error) {
+	if ctx.Err() != nil {
+		return nil, ctx.Err()
+	}
+
+	cacheDir, cacheErr := getCacheDir()
+	if cacheErr != nil {
+		return Recursive(ctx, fss)
+	}
+
+	hash, hashErr := getRulesHash(ctx, fss)
+	if hashErr != nil {
+		return Recursive(ctx, fss)
+	}
+
+	cacheFile := filepath.Join(cacheDir, fmt.Sprintf("rules-%s.cache", hash))
+	if cachedRules, loadErr := loadCachedRules(cacheFile); loadErr == nil {
+		slog.Debug("Loaded rules from cache", "file", cacheFile)
+		return cachedRules, nil
+	}
+
+	slog.Debug("Cache miss, compiling rules", "file", cacheFile)
+	compiledRules, err := Recursive(ctx, fss)
+	if err != nil {
+		return nil, fmt.Errorf("compile: %w", err)
+	}
+
+	if saveErr := saveCachedRules(compiledRules, cacheFile); saveErr != nil {
+		slog.Warn("Failed to save rules to cache", "error", saveErr)
+	} else {
+		slog.Debug("Saved rules to cache", "file", cacheFile)
+	}
+
+	return compiledRules, nil
+}