some major improvements to the (server-side) cache middleware and an example of a client-side responsibility cache

Former-commit-id: 93d3a7a6f163c6d49f315f86d10e63f7b1b1d93a

cache/entry/entry.go

@@ -13,6 +13,11 @@ type Entry struct {
 	// ExpiresAt is the time which this cache will not be available
 	expiresAt time.Time
 
+	// when `Reset` this value is reseting to time.Now(),
+	// it's used to send the "Last-Modified" header,
+	// some clients may need it.
+	LastModified time.Time
+
 	// Response the response should be served to the client
 	response *Response
 	// but we need the key to invalidate manually...xmm
@@ -78,10 +83,23 @@ func (e *Entry) ChangeLifetime(fdur LifeChanger) {
 	}
 }
 
+// CopyHeaders clones headers "src" to "dst" .
+func CopyHeaders(dst map[string][]string, src map[string][]string) {
+	if dst == nil || src == nil {
+		return
+	}
+
+	for k, vv := range src {
+		v := make([]string, len(vv))
+		copy(v, vv)
+		dst[k] = v
+	}
+}
+
 // Reset called each time the entry is expired
 // and the handler calls this after the original handler executed
 // to re-set the response with the new handler's content result
-func (e *Entry) Reset(statusCode int, contentType string,
+func (e *Entry) Reset(statusCode int, headers map[string][]string,
 	body []byte, lifeChanger LifeChanger) {
 
 	if e.response == nil {
@@ -91,8 +109,10 @@ func (e *Entry) Reset(statusCode int, contentType string,
 		e.response.statusCode = statusCode
 	}
 
-	if contentType != "" {
-		e.response.contentType = contentType
+	if len(headers) > 0 {
+		newHeaders := make(map[string][]string, len(headers))
+		CopyHeaders(newHeaders, headers)
+		e.response.headers = newHeaders
 	}
 
 	e.response.body = body
@@ -101,5 +121,8 @@ func (e *Entry) Reset(statusCode int, contentType string,
 	if lifeChanger != nil {
 		e.ChangeLifetime(lifeChanger)
 	}
-	e.expiresAt = time.Now().Add(e.life)
+
+	now := time.Now()
+	e.expiresAt = now.Add(e.life)
+	e.LastModified = now
 }

cache/entry/response.go

@@ -1,19 +1,21 @@
 package entry
 
+import "net/http"
+
 // Response is the cached response will be send to the clients
 // its fields setted at runtime on each of the non-cached executions
 // non-cached executions = first execution, and each time after
-// cache expiration datetime passed
+// cache expiration datetime passed.
 type Response struct {
-	// statusCode for the response cache handler
+	// statusCode for the response cache handler.
 	statusCode int
-	// contentType for the response cache handler
-	contentType string
-	// body is the contents will be served by the cache handler
+	// body is the contents will be served by the cache handler.
 	body []byte
+	// the total headers of the response, including content type.
+	headers http.Header
 }
 
-// StatusCode returns a valid status code
+// StatusCode returns a valid status code.
 func (r *Response) StatusCode() int {
 	if r.statusCode <= 0 {
 		r.statusCode = 200
@@ -22,14 +24,19 @@ func (r *Response) StatusCode() int {
 }
 
 // ContentType returns a valid content type
-func (r *Response) ContentType() string {
-	if r.contentType == "" {
-		r.contentType = "text/html; charset=utf-8"
-	}
-	return r.contentType
+// func (r *Response) ContentType() string {
+// 	if r.headers == "" {
+// 		r.contentType = "text/html; charset=utf-8"
+// 	}
+// 	return r.contentType
+// }
+
+// Headers returns the total headers of the cached response.
+func (r *Response) Headers() http.Header {
+	return r.headers
 }
 
-// Body returns contents will be served by the cache handler
+// Body returns contents will be served by the cache handler.
 func (r *Response) Body() []byte {
 	return r.body
 }