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

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

internal/cache/cache.go

@@ -0,0 +1,48 @@
+package cache
+
+import (
+	"io"
+)
+
+// Manager is responsible for managing cache data and instantiating all caches
+type Manager interface {
+	// GetCache returns a cache scoped to the given named, versioned data
+	GetCache(name, version string) Cache
+
+	// RootDirs returns any root directories this cache manager uses
+	RootDirs() []string
+}
+
+// ReaderAtCloser is an amalgamation of: io.Reader, io.ReaderAt, and io.Closer
+type ReaderAtCloser interface {
+	io.Reader
+	io.ReaderAt
+	io.Closer
+}
+
+// Cache is what the application interacts with to get and set cached data
+type Cache interface {
+	// Read returns a reader for the cache value, if found and not expired
+	// or errors when unable to find / expired
+	Read(key string) (ReaderAtCloser, error)
+
+	// Write writes the contents of the reader to the cache
+	// and closes it, if the reader implements io.Closer
+	Write(key string, contents io.Reader) error
+}
+
+// GetManager returns the global cache manager, which is used to instantiate all caches
+func GetManager() Manager {
+	return manager
+}
+
+// SetManager sets the global cache manager, which is used to instantiate all caches
+func SetManager(m Manager) {
+	if m == nil {
+		manager = &bypassedCache{}
+	} else {
+		manager = m
+	}
+}
+
+var manager Manager = &bypassedCache{}