benbjohnson · June 13, 2014 12:04 · Jun 13, 2014
diff --git a/store.go b/store.go
@@ -0,0 +1,68 @@
+package store
+
+import (
+	"fmt"
+
+	"github.com/boltdb/bolt"
+)
+
+// reap removes sessions older than a given duration.
+// This function assumes that all session data is stored in a "sessions" bucket
+// and the data is organized so the key is the session id and the value is
+// laid out as:
+//
+//   -8 bytes-   --n bytes--
+//   timestamp + sessiondata
+//
+func reap(db *bolt.DB, duration time.Duration) error {
+	// The batch size represents how many sessions we'll check at
+	// a time for a given transaction. We don't want to check all the
+	// sessions every time because that would lock the database for
+	// too long if the sessions bucket gets too large.
+	batchsz := 1000
+
+	var prev []byte
+	for {
+		// Get the current timestamp.
+		now := time.Now()
+
+		// Iterate over a subset of keys at a time and delete old ones.
+		err := db.Update(func(tx *bolt.Tx) error {
+			c := tx.Bucket([]byte("sessions")).Cursor()
+
+			var i int
+			for k, v := c.Seek(prev); ; k, v = c.Next() {
+				// If we hit the end of our sessions then exit and start over next time.
+				if k == nil {
+					seek = nil
+					return nil
+				}
+
+				// If we have iterated over our batch size then save our place
+				// and we'll start from there next time. We need to copy over
+				// the bytes in "k" because it's not guarenteed to exist there
+				// after the transaction is over.
+				if i == batchsz {
+					seek = make([]byte, len(k))
+					copy(seek, k)
+					return nil
+				}
+
+				// If we've made it this far then we can check if a session's
+				// timestamp is older than our expiration "duration". If so
+				// then we can delete the item in-place in the cursor.
+				timestamp := time.Unix(int64(binary.BigEndian.Uint64(v)), 0)
+				if now.Since(timestamp) > duration {
+					if err := c.Delete(); err != nil {
+						return fmt.Errorf("delete: %s", err)
+					}
+				}
+			}
+		})
+		if err != nil {
+			return err
+		}
+
+		time.Sleep(1 * time.Second)
+	}
+}
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