vinegar/vinegarUtil/webLRU.go

package vinegarUtil

import (
	"errors"
	"fmt"
	"log"
	"strings"
	"time"
)

const (
	DefaultCacheTimeInMinutes = 15
)

type (
	lru map[string]*LruEntry
	Lru struct {
		entries     *lru
		limit       int64
		currentSize int64
	}

	LruEntry struct {
		path              string
		Content           []byte
		CompressedContent []byte
		created           time.Time
		expires           time.Time
		mostRecentAccess  time.Time
		totalSize         int64
		MimeType          string
	}

	SingleFileCache struct {
		path  string
		entry *LruEntry
	}

	Cache interface {
		Get(key string) (*LruEntry, bool)
		GetFresh(key string) (*LruEntry, bool)
		Put(key string, pathlike string) error
		Remove(key string)
	}
)

func NewLRU(size int64) *Lru {
	cLru := make(lru)
	return &Lru{&cLru, size, 0}
}

func NewSingleFileCache(pathlike string) *SingleFileCache {
	entry := newLRUEntry(pathlike)
	sfc := SingleFileCache{path: pathlike, entry: entry}
	return &sfc
}

func (l *Lru) Get(key string) (*LruEntry, bool) {
	entry, exists := (*l.entries)[key]
	if exists && entry.expires.Before(time.Now()) {
		fmt.Println("Cache miss due to expired content")
		entry.Reload()
		return entry, true
	} else {
		if exists {
			entry.mostRecentAccess = time.Now()
		}
		return entry, exists
	}
}

func (l *Lru) GetFresh(key string) (*LruEntry, bool) {
	entry, exists := l.Get(key)
	if exists {
		entry.Reload()
	}
	return l.Get(key)
}

func (l *Lru) Put(key string, pathlike string) error {
	entry, exists := (*l.entries)[key]

	var size int64

	if exists {
		content, fExists := GetDiskContent(pathlike)
		if !fExists {
			return errors.New("attempted to refresh cache with file that no longer exists on disk")
		}
		zippedContent := *GZipBytes(content)
		size = int64(len(*content)) + int64(len(zippedContent))
		l.ensureVacancy(size)

		entry.Content = *content
		entry.CompressedContent = zippedContent
		entry.created = time.Now()
		entry.expires = time.Now().Add(DefaultCacheTimeInMinutes * time.Minute)
		entry.mostRecentAccess = time.Now()
		entry.totalSize = size
	} else {
		entry = newLRUEntry(pathlike)

	}

	(*l.entries)[key] = entry

	l.recalcSize()
	return nil
}

func (l *Lru) Remove(key string) {
	entry, exists := (*l.entries)[key]
	if exists {
		size := entry.totalSize
		delete(*l.entries, key)
		l.currentSize = l.currentSize - size
	}
}

func (l *Lru) ensureVacancy(required int64) {
	if l.currentSize == 0 {
		return
	}
	for l.currentSize+required > l.limit {
		leastKey := l.getLeastRecentlyUsedKey()
		l.Remove(leastKey)
	}
}

func (l *Lru) getLeastRecentlyUsedKey() string {
	started := false
	var benchmark *LruEntry
	leastUsedKey := ""
	for key, entry := range *l.entries {
		if !started {
			started = true
			benchmark = entry
			leastUsedKey = key
			continue
		}
		if benchmark.mostRecentAccess.After(entry.mostRecentAccess) {
			benchmark = entry
		}
	}
	if leastUsedKey == "" {
		panic("Invalid key for LRU: [" + leastUsedKey + "]")
	}
	return leastUsedKey
}

func (l *Lru) recalcSize() {
	var total int64
	for _, entry := range *l.entries {
		total += entry.totalSize
	}
	l.currentSize = total
}

func (le *LruEntry) Reload() {
	content, _ := GetDiskContent(le.path)
	le.Content = *content
	le.CompressedContent = *GZipBytes(content)
	le.created = time.Now()
	le.mostRecentAccess = le.created
	le.expires = le.created.Add(time.Minute * DefaultCacheTimeInMinutes)
}

func (sfc *SingleFileCache) Get(key string) (*LruEntry, bool) {
	return sfc.entry, true
}

func (sfc *SingleFileCache) GetFresh(key string) (*LruEntry, bool) {
	sfc.entry.Reload()
	return sfc.entry, true
}

// Put THIS WILL DELETE ANYTHING YOU HAVE STORED IN THIS CACHE.
func (sfc *SingleFileCache) Put(key string, pathlike string) error {
	//there's a bug in this. we don't return an error from newLRUEntry, so if the file disappears, the server will die
	entry := newLRUEntry(pathlike)
	sfc.entry = entry
	return nil
}

func (sfc *SingleFileCache) Remove(key string) {
	//i'm actually not sure what to do here. why would you ever remove from a single-file cache?
}

func newLRUEntry(pathlike string) *LruEntry {
	bits, exists := GetDiskContent(pathlike)
	if !exists {
		panic("Could not load single file for single file path: " + pathlike)
	}

	compressedBits := GZipBytes(bits)

	size := int64(len(*bits)) + int64(len(*compressedBits))

	entry := LruEntry{
		path:              pathlike,
		Content:           *bits,
		CompressedContent: *compressedBits,
		created:           time.Now(),
		expires:           time.Now().Add(DefaultCacheTimeInMinutes * time.Minute),
		mostRecentAccess:  time.Now(),
		totalSize:         size,
		MimeType:          GuessMimetype(pathlike),
	}
	return &entry
}

func GuessMimetype(filePath string) string {
	dotIndex := strings.LastIndex(filePath, ".")
	ext := filePath[dotIndex+1:]
	switch ext {
	case "css":
		return "text/css"
	case "htm":
	case "html":
		return "text/html"
	case "ico":
		return "image/vnd.microsoft.icon"
	case "jpg":
		fallthrough
	case "jpeg":
		return "image/jpeg"
	case "js":
		return "text/javascript"
	case "json":
		return "application/json"
	case "png":
		return "image/png"
	case "svg":
		return "image/svg+xml"
	case "webp":
		return "image/webp"
	default:
		log.Default().Printf("[WARN] '%s' is unrecognized MimeType. Returning as [application/octet-stream]. Please use VinegarServlet.AddMimeType() to define the appropriate response for this file extension.", ext)
		return "application/octet-stream"
	}
	return "application/octet-stream"
}