disk cache: add a path based API

This allows maintaining only a single cache entry per path when the
path's contents change.

tools/disk_cache/api.go

@@ -17,6 +17,7 @@ type Entry struct {
 
 type Metadata struct {
 	TotalSize     int64
+	PathMap       map[string]string
 	SortedEntries []*Entry
 }
 
@@ -29,29 +30,45 @@ type DiskCache struct {
 	entries          Metadata
 	entry_map        map[string]*Entry
 	entries_mod_time time.Time
+	entries_dirty    bool
 	get_dir          string
+	read_count       int
 }
 
 func NewDiskCache(path string, max_size int64) (dc *DiskCache, err error) {
 	return new_disk_cache(path, max_size)
 }
 
-func KeyForPath(path string) (key string, err error) {
-	return key_for_path(path)
-}
-
-func (dc *DiskCache) Get(key string, items ...string) map[string]string {
+func (dc *DiskCache) Get(key string, items ...string) (map[string]string, error) {
 	dc.lock()
 	defer dc.unlock()
 	return dc.get(key, items)
 }
 
+func (dc *DiskCache) GetPath(path string, items ...string) (string, map[string]string, error) {
+	dc.lock()
+	defer dc.unlock()
+	key, err := key_for_path(path)
+	if err != nil {
+		return "", nil, err
+	}
+	ans, err := dc.get(key, items)
+	return key, ans, err
+}
+
 func (dc *DiskCache) Remove(key string) (err error) {
 	dc.lock()
 	defer dc.unlock()
 	return dc.remove(key)
 }
 
+func (dc *DiskCache) AddPath(path, key string, items map[string][]byte) (ans map[string]string, err error) {
+	dc.lock()
+	defer dc.unlock()
+	ans, err = dc.add_path(path, key, items)
+	return
+}
+
 func (dc *DiskCache) Add(key string, items map[string][]byte) (ans map[string]string, err error) {
 	dc.lock()
 	defer dc.unlock()