cache.go

package greenyfy

import (
    "bytes"
    "appengine"
    "appengine/memcache"
)

func getCached(c appengine.Context, key string, missing func(appengine.Context, string) (*bytes.Buffer, error)) (*memcache.Item, error) {

    item, err := memcache.Get(c, key)
    
    if err == memcache.ErrCacheMiss {
        c.Infof("item not in the cache: %v", key)
        
        result, err := missing(c, key)
        
        if err != nil {
            return nil, err
        }
        
        item = &memcache.Item{
            Key:   key,
            Value: result.Bytes(),
        }
        
        if err := memcache.Add(c, item); err == memcache.ErrNotStored {
            c.Warningf("item with key %q already exists", item.Key)
        } else if err != nil {
            return item, err
        }
    } else if err != nil {
        return item, err
    } else {
        c.Infof("Cache hit: %v", key)
    }
    
    return item, nil
}