soft and hard ttl on cache

[Anders Aagaard]

Hi

I noticed the following code in CacheDispatcher:

                // If it is completely expired, just send it to the network.

                if (entry.isExpired()) {

                    request.addMarker("cache-hit-expired");

                    request.setCacheEntry(entry);

                    mNetworkQueue.put(request);

                    continue;

                }

                // We have a cache hit; parse its data for delivery back to the request.

                request.addMarker("cache-hit");

                Response<?> response = request.parseNetworkResponse(

                        new NetworkResponse(entry.data, entry.responseHeaders));

                request.addMarker("cache-hit-parsed");

                if (!entry.refreshNeeded()) {

                    // Completely unexpired cache hit. Just deliver the response.

                    mDelivery.postResponse(request, response);

                } else {

                    // Soft-expired cache hit. We can deliver the cached response,

                    // but we need to also send the request to the network for

                    // refreshing.

                    request.addMarker("cache-hit-refresh-needed");

But refreshNeeded and isExpired is exactly the same code. As ttl and softtl is set to the same value by HttpHeaderParser.

If I understand this right one can never get to cache-hit-refresh-needed without overriding something and writing to the cache ttl/softttl manually. How is this intended to be used?

Best regards

Anders

[Ficus Kirkpatrick]

refreshNeeded() and isExpired() are not exactly the same. One compares to the ttl value and the other to softTtl. This can be used to implement request semantics where you will return a response from cache even if it is "soft" expired, but will then go to the network and refresh, returning a new response if the data has changed.

I generally don't recommend using this unless you really, really know what you're doing because handling the second response can be pretty tricky to get right. And you need to implement a custom Request to use it anyhow.

Anders

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