github.com/zorawar87/trillian@v1.2.1/server/proof_fetcher.go (about)

     1  // Copyright 2016 Google Inc. All Rights Reserved.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package server
    16  
    17  import (
    18  	"context"
    19  	"fmt"
    20  
    21  	"github.com/google/trillian"
    22  	"github.com/google/trillian/merkle"
    23  	"github.com/google/trillian/merkle/hashers"
    24  	"github.com/google/trillian/storage"
    25  )
    26  
    27  // fetchNodesAndBuildProof is used by both inclusion and consistency proofs. It fetches the nodes
    28  // from storage and converts them into the proof proto that will be returned to the client.
    29  // This includes rehashing where necessary to serve proofs for tree sizes between stored tree
    30  // revisions. This code only relies on the NodeReader interface so can be tested without
    31  // a complete storage implementation.
    32  func fetchNodesAndBuildProof(ctx context.Context, tx storage.NodeReader, th hashers.LogHasher, treeRevision, leafIndex int64, proofNodeFetches []merkle.NodeFetch) (trillian.Proof, error) {
    33  	proofNodes, err := fetchNodes(ctx, tx, treeRevision, proofNodeFetches)
    34  	if err != nil {
    35  		return trillian.Proof{}, err
    36  	}
    37  
    38  	r := &rehasher{th: th}
    39  	for i, node := range proofNodes {
    40  		r.process(node, proofNodeFetches[i])
    41  	}
    42  
    43  	return r.rehashedProof(leafIndex)
    44  }
    45  
    46  // rehasher bundles the rehashing logic into a simple state machine
    47  type rehasher struct {
    48  	th         hashers.LogHasher
    49  	rehashing  bool
    50  	rehashNode storage.Node
    51  	proof      [][]byte
    52  	proofError error
    53  }
    54  
    55  func (r *rehasher) process(node storage.Node, fetch merkle.NodeFetch) {
    56  	switch {
    57  	case !r.rehashing && fetch.Rehash:
    58  		// Start of a rehashing chain
    59  		r.startRehashing(node)
    60  
    61  	case r.rehashing && !fetch.Rehash:
    62  		// End of a rehash chain, resulting in a rehashed proof node
    63  		r.endRehashing()
    64  		// And the current node needs to be added to the proof
    65  		r.emitNode(node)
    66  
    67  	case r.rehashing && fetch.Rehash:
    68  		// Continue with rehashing, update the node we're recomputing
    69  		r.rehashNode.Hash = r.th.HashChildren(node.Hash, r.rehashNode.Hash)
    70  
    71  	default:
    72  		// Not rehashing, just pass the node through
    73  		r.emitNode(node)
    74  	}
    75  }
    76  
    77  func (r *rehasher) emitNode(node storage.Node) {
    78  	r.proof = append(r.proof, node.Hash)
    79  }
    80  
    81  func (r *rehasher) startRehashing(node storage.Node) {
    82  	r.rehashNode = storage.Node{Hash: node.Hash}
    83  	r.rehashing = true
    84  }
    85  
    86  func (r *rehasher) endRehashing() {
    87  	if r.rehashing {
    88  		r.proof = append(r.proof, r.rehashNode.Hash)
    89  		r.rehashing = false
    90  	}
    91  }
    92  
    93  func (r *rehasher) rehashedProof(leafIndex int64) (trillian.Proof, error) {
    94  	r.endRehashing()
    95  	return trillian.Proof{
    96  		LeafIndex: leafIndex,
    97  		Hashes:    r.proof,
    98  	}, r.proofError
    99  }
   100  
   101  // fetchNodes extracts the NodeIDs from a list of NodeFetch structs and passes them
   102  // to storage, returning the result after some additional validation checks.
   103  func fetchNodes(ctx context.Context, tx storage.NodeReader, treeRevision int64, fetches []merkle.NodeFetch) ([]storage.Node, error) {
   104  	proofNodeIDs := make([]storage.NodeID, 0, len(fetches))
   105  
   106  	for _, fetch := range fetches {
   107  		proofNodeIDs = append(proofNodeIDs, fetch.NodeID)
   108  	}
   109  
   110  	proofNodes, err := tx.GetMerkleNodes(ctx, treeRevision, proofNodeIDs)
   111  	if err != nil {
   112  		return nil, err
   113  	}
   114  
   115  	if len(proofNodes) != len(proofNodeIDs) {
   116  		return nil, fmt.Errorf("expected %d nodes from storage but got %d", len(proofNodeIDs), len(proofNodes))
   117  	}
   118  
   119  	for i, node := range proofNodes {
   120  		// additional check that the correct node was returned
   121  		if !node.NodeID.Equivalent(fetches[i].NodeID) {
   122  			return []storage.Node{}, fmt.Errorf("expected node %v at proof pos %d but got %v", fetches[i], i, node.NodeID)
   123  		}
   124  	}
   125  
   126  	return proofNodes, nil
   127  }