[datastore] Fix #3743

This change adds support for key == NULL to the datastore plugins
and replaces the offset argument with a next_uid and random arguments to
increase performance in the key == NULL case.

With the offset argument a datastore plugin would have to count all
matching keys before fetching the key at the right offset, which would
iterate over the entire database in the case of key == NULL.

The offset argument was used in two ways: to iterate over a set of
matching values and to start iteration at a random matching value. The new API
seperates these into two arguments: if random is true it will return a
random matching value, otherwise next_uid can be set to uid + 1 to return the
next matching value.

The random argument was not added to get_zero_anonymity. This function
is used to periodically insert zero anonymity values into the DHT. I
don't think it's necessary to randomize this.

1 files changed, 16 insertions, 6 deletions

diff --git a/src/datastore/datastore.h b/src/datastore/datastore.h
index 9de72f064..5fd360161 100644
--- a/src/datastore/datastore.h
+++ b/src/datastore/datastore.h
@@ -119,9 +119,14 @@ struct GetKeyMessage
   uint32_t type GNUNET_PACKED;
 
   /**
-   * Offset of the result.
+   * UID at which to start the search
    */
-  uint64_t offset GNUNET_PACKED;
+  uint64_t next_uid GNUNET_PACKED;
+
+  /**
+   * If true return a random result
+   */
+  uint32_t random GNUNET_PACKED;
 
   /**
    * Desired key.
@@ -148,9 +153,14 @@ struct GetMessage
   uint32_t type GNUNET_PACKED;
 
   /**
-   * Offset of the result.
+   * UID at which to start the search
+   */
+  uint64_t next_uid GNUNET_PACKED;
+
+  /**
+   * If true return a random result
    */
-  uint64_t offset GNUNET_PACKED;
+  uint32_t random GNUNET_PACKED;
 
 };
 
@@ -172,9 +182,9 @@ struct GetZeroAnonymityMessage
   uint32_t type GNUNET_PACKED;
 
   /**
-   * Offset of the result.
+   * UID at which to start the search
    */
-  uint64_t offset GNUNET_PACKED;
+  uint64_t next_uid GNUNET_PACKED;
 
 };