chore: simplify and cleanup

Signed-off-by: Keith Zantow <keith.zantow@anchore.com>

internal/archive/exclusions.go

@@ -0,0 +1,38 @@
+package archive
+
+import (
+	"strings"
+
+	"github.com/bmatcuk/doublestar/v4"
+)
+
+// Exclusions are the scan's exclusion patterns that apply inside archives.
+//
+// A scan accepts three pattern shapes: `./x` anchored at the scan root, `*/x` exactly one level below
+// it, and `**/x` at any depth. Only the last means the same thing when re-rooted at an archive, so
+// only it reaches inside one.
+type Exclusions []string
+
+func NewExclusions(scanPatterns []string) Exclusions {
+	var out Exclusions
+	for _, pattern := range scanPatterns {
+		if strings.HasPrefix(pattern, "**/") {
+			// a trailing slash reads as "a directory" but makes doublestar match nothing (issue #4839)
+			out = append(out, strings.TrimSuffix(pattern, "/"))
+		}
+	}
+	return out
+}
+
+// Excludes reports whether an archive-relative path, or any directory above it, matches a pattern.
+// Directories are checked because an archive need not list a directory before the files in it.
+func (e Exclusions) Excludes(entryPath string) bool {
+	for _, pattern := range e {
+		for end := len(entryPath); end > 0; end = strings.LastIndexByte(entryPath[:end], '/') {
+			if matched, _ := doublestar.Match(pattern, entryPath[:end]); matched {
+				return true
+			}
+		}
+	}
+	return false
+}