change(cache): use cache-specific http headers for their lifetime

This uses the 'Age', 'Cache-Control' and 'Expires' HTTP headers to more
accurately set up the cache lifetime, falling back to a static 1-week
time if they're not present in the response.

Signed-off-by: flow <flowlnlnln@gmail.com>

launcher/net/HttpMetaCache.h

@@ -64,6 +64,14 @@ class MetaEntry {
     auto getMD5Sum() -> QString { return md5sum; }
     void setMD5Sum(QString md5sum) { this->md5sum = md5sum; }
 
+    auto getCurrentAge() -> qint64 { return current_age; }
+    void setCurrentAge(qint64 age) { current_age = age; }
+
+    auto getMaximumAge() -> qint64 { return max_age; }
+    void setMaximumAge(qint64 age) { max_age = age; }
+
+    bool isExpired(qint64 offset) { return current_age >= max_age - offset; };
+
    protected:
     QString baseId;
     QString basePath;
@@ -72,6 +80,8 @@ class MetaEntry {
     QString etag;
     qint64 local_changed_timestamp = 0;
     QString remote_changed_timestamp;  // QString for now, RFC 2822 encoded time
+    qint64 current_age = 0;
+    qint64 max_age = 0;
     bool stale = true;
 };