implement "starting key" feature for list keys

closes #9

src/datastore/berkeleydb_datastore.cc

@@ -219,15 +219,25 @@ std::vector<ds_bulk_t> BerkeleyDBDataStore::list_keys(const ds_bulk_t &start, si
     std::vector<ds_bulk_t> keys;
     Dbc * cursorp;
     Dbt key, data;
+    int ret;
     _dbm->cursor(NULL, &cursorp, 0);
-    for (size_t i=0; i< count; i++) {
-        int ret = cursorp->get(&key, &data, DB_NEXT);
-        if (ret !=0 ) break;
 
-        ds_bulk_t k(key.get_size() );
-        memcpy(k.data(), key.get_data(), key.get_size() );
-        /* I hope this is a deep copy! */
-        keys.push_back(std::move(k));
+    if (start.size()) {
+	key.set_size(start.size());
+	key.set_data((void *)start.data());
+	ret = cursorp->get(&key, &data, DB_SET);
+	if (ret != 0) {
+	    cursorp->close();
+	    return keys;
+	}
+    }
+    while (keys.size() < count) {
+	ret = cursorp->get(&key, &data, DB_NEXT);
+	if (ret !=0 ) break;
+
+	ds_bulk_t k(key.get_size() );
+	memcpy(k.data(), key.get_data(), key.get_size() );
+	keys.push_back(std::move(k));
     }
     cursorp->close();
     return keys;

src/datastore/leveldb_datastore.cc

@@ -132,8 +132,16 @@ std::vector<ds_bulk_t> LevelDBDataStore::list_keys(const ds_bulk_t &start, size_
     std::vector<ds_bulk_t> keys;
 
     leveldb::Iterator *it = _dbm->NewIterator(leveldb::ReadOptions());
+    leveldb::Slice start_slice(start.data(), start.size());
     size_t i=0;
-    for (it->SeekToFirst(); it->Valid(); it->Next() ) {
+
+    if (start.size() > 0) {
+	it->Seek(start_slice);
+    } else {
+	it->SeekToFirst();
+    }
+    /* note: iterator initialized above, not in for loop */
+    for (; it->Valid(); it->Next() ) {
         ds_bulk_t k(it->key().size());
         memcpy(k.data(), it->key().data(), it->key().size() );
         keys.push_back(k);

src/kv-server.cc

@@ -357,8 +357,9 @@ static hg_return_t list_handler(hg_handle_t handle)
     list_in_t list_in;
     list_out_t list_out;
 
-    std::vector<char> start{};
     margo_get_input(handle, &list_in);
+    ds_bulk_t start(list_in.list_in.start_key,
+	    list_in.list_in.start_key + list_in.list_in.start_ksize);
 
     auto keys = datastore->list_keys(start, list_in.list_in.max_keys);