fix: separate golang license caches from mod dir (#2852)

Signed-off-by: Keith Zantow <kzantow@gmail.com>

internal/cache/filesystem.go

@@ -0,0 +1,120 @@
+package cache
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net/url"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/spf13/afero"
+
+	"github.com/anchore/syft/internal/log"
+)
+
+// NewFromDir creates a new cache manager which returns caches stored on disk, rooted at the given directory
+func NewFromDir(dir string, ttl time.Duration) (Manager, error) {
+	dir = filepath.Clean(dir)
+	fsys, err := subFs(afero.NewOsFs(), dir)
+	if err != nil {
+		return nil, err
+	}
+	return &filesystemCache{
+		dir: dir,
+		fs:  fsys,
+		ttl: ttl,
+	}, nil
+}
+
+const filePermissions = 0700
+const dirPermissions = os.ModeDir | filePermissions
+
+type filesystemCache struct {
+	dir string
+	fs  afero.Fs
+	ttl time.Duration
+}
+
+func (d *filesystemCache) GetCache(name, version string) Cache {
+	fsys, err := subFs(d.fs, name, version)
+	if err != nil {
+		log.Warnf("error getting cache for: %s/%s: %v", name, version, err)
+		return &bypassedCache{}
+	}
+	return &filesystemCache{
+		dir: filepath.Join(d.dir, name, version),
+		fs:  fsys,
+		ttl: d.ttl,
+	}
+}
+
+func (d *filesystemCache) RootDirs() []string {
+	if d.dir == "" {
+		return nil
+	}
+	return []string{d.dir}
+}
+
+func (d *filesystemCache) Read(key string) (ReaderAtCloser, error) {
+	path := makeDiskKey(key)
+	f, err := d.fs.Open(path)
+	if err != nil {
+		log.Tracef("no cache entry for %s %s: %v", d.dir, key, err)
+		return nil, errNotFound
+	} else if stat, err := f.Stat(); err != nil || stat == nil || time.Since(stat.ModTime()) > d.ttl {
+		log.Tracef("cache entry is too old for %s %s", d.dir, key)
+		return nil, errExpired
+	}
+	log.Tracef("using cache for %s %s", d.dir, key)
+	return f, nil
+}
+
+func (d *filesystemCache) Write(key string, contents io.Reader) error {
+	path := makeDiskKey(key)
+	return afero.WriteReader(d.fs, path, contents)
+}
+
+// subFs returns a writable directory with the given name under the root cache directory returned from findRoot,
+// the directory will be created if it does not exist
+func subFs(fsys afero.Fs, subDirs ...string) (afero.Fs, error) {
+	dir := filepath.Join(subDirs...)
+	dir = filepath.Clean(dir)
+	stat, err := fsys.Stat(dir)
+	if errors.Is(err, afero.ErrFileNotFound) {
+		err = fsys.MkdirAll(dir, dirPermissions)
+		if err != nil {
+			return nil, fmt.Errorf("unable to create directory at '%s/%s': %v", dir, strings.Join(subDirs, "/"), err)
+		}
+		stat, err = fsys.Stat(dir)
+		if err != nil {
+			return nil, err
+		}
+	}
+	if err != nil || stat == nil || !stat.IsDir() {
+		return nil, fmt.Errorf("unable to verify directory '%s': %v", dir, err)
+	}
+	fsys = afero.NewBasePathFs(fsys, dir)
+	return fsys, err
+}
+
+var keyReplacer = regexp.MustCompile("[^-._/a-zA-Z0-9]")
+
+// makeDiskKey makes a safe sub-path but not escape forward slashes, this allows for logical partitioning on disk
+func makeDiskKey(key string) string {
+	// encode single dot directory
+	if key == "." {
+		return "%2E"
+	}
+	// replace any disallowed chars with encoded form
+	key = keyReplacer.ReplaceAllStringFunc(key, url.QueryEscape)
+	// allow . in names but not ..
+	key = strings.ReplaceAll(key, "..", "%2E%2E")
+	return key
+}
+
+var errNotFound = fmt.Errorf("not found")
+var errExpired = fmt.Errorf("expired")