Reimplement --cache-dir option (#114)

README.md

@@ -1020,6 +1020,12 @@ Total: 0 (UNKNOWN: 0, LOW: 0, MEDIUM: 0, HIGH: 0, CRITICAL: 0)
 
 </details>
 
+### Specify cache directory
+
+```
+$ trivy --cache-dir /tmp/trivy/ python:3.4-alpine3.9
+```
+
 ### Clear image caches
 
 The `--clear-cache` option removes image caches. This option is useful if the image which has the same tag is updated (such as when using `latest` tag).
@@ -1249,6 +1255,7 @@ OPTIONS:
   --auto-refresh              refresh DB automatically when updating version of trivy
   --debug, -d                 debug mode
   --vuln-type value           comma-separated list of vulnerability types (os,library)
+  --cache-dir value           cache directory (default: "/path/to/cache")
   --help, -h                  show help
   --version, -v               print the version
 ```

cmd/trivy/main.go

@@ -5,6 +5,8 @@ import (
 	"os"
 	"strings"
 
+	"github.com/knqyf263/trivy/pkg/utils"
+
 	"github.com/knqyf263/trivy/pkg/vulnsrc/vulnerability"
 
 	"github.com/urfave/cli"
@@ -106,6 +108,11 @@ OPTIONS:
 			Value: "os,library",
 			Usage: "comma-separated list of vulnerability types (os,library)",
 		},
+		cli.StringFlag{
+			Name:  "cache-dir",
+			Value: utils.DefaultCacheDir(),
+			Usage: "cache directory",
+		},
 	}
 
 	app.Action = pkg.Run

pkg/db/db.go

@@ -16,10 +16,11 @@ import (
 
 var (
 	db    *bolt.DB
-	dbDir = filepath.Join(utils.CacheDir(), "db")
+	dbDir string
 )
 
 func Init() (err error) {
+	dbDir = filepath.Join(utils.CacheDir(), "db")
 	if err = os.MkdirAll(dbDir, 0700); err != nil {
 		return xerrors.Errorf("failed to mkdir: %w", err)
 	}

pkg/run.go

@@ -27,6 +27,8 @@ func Run(c *cli.Context) (err error) {
 	if err = log.InitLogger(debug); err != nil {
 		l.Fatal(err)
 	}
+
+	utils.SetCacheDir(c.String("cache-dir"))
 	log.Logger.Debugf("cache dir:  %s", utils.CacheDir())
 
 	reset := c.Bool("reset")

pkg/utils/utils.go

@@ -12,13 +12,22 @@ import (
 	"golang.org/x/xerrors"
 )
 
-func CacheDir() string {
-	cacheDir, err := os.UserCacheDir()
+var cacheDir string
+
+func DefaultCacheDir() string {
+	tmpDir, err := os.UserCacheDir()
 	if err != nil {
-		cacheDir = os.TempDir()
+		tmpDir = os.TempDir()
 	}
-	dir := filepath.Join(cacheDir, "trivy")
-	return dir
+	return filepath.Join(tmpDir, "trivy")
+}
+
+func CacheDir() string {
+	return cacheDir
+}
+
+func SetCacheDir(dir string) {
+	cacheDir = dir
 }
 
 func FileWalk(root string, targetFiles map[string]struct{}, walkFn func(r io.Reader, path string) error) error {