add romCache file

main.go

@@ -31,14 +31,15 @@ type HTTPResponseJSON struct {
 
 // Caches data about available ROMs in memory so we don't need to reference the filesystem for each request
 type ROMCache struct {
-	ROMs       []LineageOSROM
-	Cached     map[string]bool // to quickly lookup if a file is already cached
-	sync.Mutex                 // We have multiple goroutines that may be accessing this data simultaneously, so we much lock / unlock it to prevent race conditions
+	ROMs       []LineageOSROM  `json:"roms"`
+	Cached     map[string]bool `json:"-"` // to quickly lookup if a file is already cached
+	sync.Mutex `json:"-"`      // We have multiple goroutines that may be accessing this data simultaneously, so we much lock / unlock it to prevent race conditions
 }
 
 const (
 	romDirectory      = "public" // directory where ROMs are available for download
 	buildOutDirectory = "out"    // directory from build system containing artifacts which we can move to romDirectory
+	cacheFile         = "public/romcache.json"
 )
 
 var ( // evil global variable
@@ -46,8 +47,25 @@ var ( // evil global variable
 )
 
 func init() {
+	// intialize and load ROMCache from file - so we don't have to rehash all the big files again
 	romCache = ROMCache{}
 	romCache.Cached = make(map[string]bool)
+	romCacheJson, err := os.ReadFile(cacheFile)
+	if err != nil {
+		if err != os.ErrNotExist { // don't care if it doesn't exist, just skip it
+			log.Printf("failed to read romCache file : %v", err)
+		}
+	} else { // if opening the file's successful, then load the contents
+		err = json.Unmarshal(romCacheJson, &romCache)
+		if err != nil {
+			log.Printf("failed to unmarshal romCacheJson to romCache struct: %v", err)
+		}
+	}
+
+	for _, rom := range romCache.ROMs {
+		romCache.Cached[rom.ID] = true
+		log.Printf("loaded cached file: %s", rom.Filename)
+	}
 
 	// Check if any new build artifacts and preload the romCache
 	moveBuildArtifacts()
@@ -132,6 +150,26 @@ func updateROMCache() {
 			romCache.Unlock()
 		}(files[i])
 	}
+
+	// save file to disk for next startup so we don't have to rehash all the files again
+	romCache.Lock()
+	romCacheJson, err := json.Marshal(romCache)
+	romCache.Unlock()
+	if err != nil {
+		log.Printf("failed to marshal romCache to json: %v", err)
+		return
+	}
+
+	err = os.WriteFile(cacheFile, romCacheJson, 0644)
+	if err != nil {
+		log.Printf("failed to write '%s' file: %v", cacheFile, err)
+		log.Printf("attempting to remove '%s' to ensure integrity during next program startup...", cacheFile)
+		err = os.Remove(cacheFile)
+		if err != nil {
+			log.Printf("failed to remove file '%s': %v", cacheFile, err)
+		}
+		return
+	}
 }
 
 // returns true if new builds were moved