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diff --git a/src/gnunet/service/dht/blocks/handlers.go b/src/gnunet/service/dht/blocks/handlers.go
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+++ b/src/gnunet/service/dht/blocks/handlers.go
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+// This file is part of gnunet-go, a GNUnet-implementation in Golang.
+// Copyright (C) 2019-2022 Bernd Fix  >Y<
+//
+// gnunet-go is free software: you can redistribute it and/or modify it
+// under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, either version 3 of the License,
+// or (at your option) any later version.
+//
+// gnunet-go is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+// Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// SPDX-License-Identifier: AGPL3.0-or-later
+
+package blocks
+
+import (
+        "gnunet/crypto"
+        "gnunet/enums"
+)
+
+// BlockHandler interface defines methods specific to block types.
+type BlockHandler interface {
+
+        // Parse a block instance from binary data
+        ParseBlock(buf []byte) (Block, error)
+
+        // ValidateBlockQuery is used to evaluate the request for a block as part of
+        // DHT-P2P-GET processing. Here, the block payload is unknown, but if possible
+        // the XQuery and Key SHOULD be verified.
+        ValidateBlockQuery(key *crypto.HashCode, xquery []byte) bool
+
+        // ValidateBlockKey returns true if the block key is the same as the
+        // query key used to access the block.
+        ValidateBlockKey(b Block, key *crypto.HashCode) bool
+
+        // ValidateBlockStoreRequest is used to evaluate a block payload as part of
+        // PutMessage and ResultMessage processing.
+        ValidateBlockStoreRequest(b Block) bool
+
+        // SetupResultFilter is used to setup an empty result filter. The arguments
+        // are the set of results that must be filtered at the initiator, and a
+        // MUTATOR value which MAY be used to deterministically re-randomize
+        // probabilistic data structures.
+        SetupResultFilter(filterSize int, mutator uint32) ResultFilter
+
+        // ParseResultFilter from binary data
+        ParseResultFilter(data []byte) ResultFilter
+
+        // FilterResult is used to filter results against specific queries. This
+        // function does not check the validity of the block itself or that it
+        // matches the given key, as this must have been checked earlier. Thus,
+        // locally stored blocks from previously observed ResultMessages and
+        // PutMessages use this function to perform filtering based on the request
+        // parameters of a particular GET operation. Possible values for the
+        // FilterEvaluationResult are defined above. If the main evaluation result
+        // is RF_MORE, the function also returns and updated result filter where
+        // the block is added to the set of filtered replies. An implementation is
+        // not expected to actually differentiate between the RF_DUPLICATE and
+        // RF_IRRELEVANT return values: in both cases the block is ignored for
+        // this query.
+        FilterResult(b Block, key *crypto.HashCode, rf ResultFilter, xQuery []byte) int
+}
+
+// BlockHandlers is a map of block query validation implementations
+// for supported block types.
+var BlockHandlers map[enums.BlockType]BlockHandler
+
+// initializer function
+func init() {
+        // create map instance
+        BlockHandlers = make(map[enums.BlockType]BlockHandler)
+
+        // add validation functions
+        BlockHandlers[enums.BLOCK_TYPE_DHT_URL_HELLO] = new(HelloBlockHandler)
+}