add cache middleware

middleware/cache.go

@@ -0,0 +1,77 @@
+package middleware
+
+import (
+	"sync"
+
+	"github.com/n0x1m/gmifs/gemini"
+)
+
+type cache struct {
+	sync.RWMutex
+	documents map[string][]byte
+	mimeTypes map[string]string
+
+	tracker map[int]string
+	index   int
+	size    int
+}
+
+func (c *cache) Read(key string) ([]byte, string, bool) {
+	c.RLock()
+	doc, hitdoc := c.documents[key]
+	mt, hitmime := c.mimeTypes[key]
+	c.RUnlock()
+	return doc, mt, hitdoc && hitmime
+}
+
+func (c *cache) housekeeping(key string) {
+	// we enter locked and can modify
+	if len(c.tracker) >= c.size {
+		overflow := c.index
+		expired := c.tracker[overflow]
+		delete(c.documents, expired)
+		delete(c.mimeTypes, expired)
+		delete(c.tracker, overflow)
+	}
+	c.tracker[c.index] = key
+	c.index++
+	c.index = c.index % (c.size)
+}
+
+func (c *cache) Write(key string, mimeType string, doc []byte) {
+	c.Lock()
+	c.housekeeping(key)
+	c.documents[key] = doc
+	c.mimeTypes[key] = mimeType
+	c.Unlock()
+}
+
+func Cache(n int) func(next gemini.Handler) gemini.Handler {
+	return (&cache{
+		size:      n,
+		documents: make(map[string][]byte, n+1),
+		mimeTypes: make(map[string]string, n),
+		tracker:   make(map[int]string, n),
+	}).middleware
+}
+
+func (c *cache) middleware(next gemini.Handler) gemini.Handler {
+	fn := func(w gemini.ResponseWriter, r *gemini.Request) {
+		key := r.URL.Path
+		if body, mimeType, hit := c.Read(key); hit {
+			w.WriteHeader(gemini.StatusSuccess, mimeType)
+			w.Write(body)
+			return
+		}
+
+		ri := gemini.NewInterceptor(w)
+		next.ServeGemini(ri, r)
+
+		// only cache success responses
+		if ri.HasHeader() && ri.Code == gemini.StatusSuccess {
+			c.Write(key, ri.Meta, ri.Body.Bytes())
+		}
+		ri.Flush()
+	}
+	return gemini.HandlerFunc(fn)
+}