1. Justin Sheehy
  2. riak

Source

riak / src / merkerl.erl

justin 1c37b76 























Bryan Fink c89564c 
justin 1c37b76 
















Bryan Fink c89564c 


justin 1c37b76 






















































































































































































































































































Bryan Fink c89564c 
justin 1c37b76 


Bryan Fink c89564c 




justin 1c37b76 





Bryan Fink c89564c 
justin 1c37b76 

Bryan Fink c89564c 
justin 1c37b76 
Bryan Fink c89564c 
justin 1c37b76 
Bryan Fink c89564c 

justin 1c37b76 

Bryan Fink c89564c 
justin 1c37b76 
Bryan Fink c89564c 

justin 1c37b76 

Bryan Fink c89564c 
justin 1c37b76 
%% @copyright 2007-2008 Basho Technologies

%% @reference Ralph C. Merkle, A Digital Signature Based on a Conventional Encryption Function, A Conference on the Theory and Applications of Cryptographic Techniques on Advances in Cryptology, p.369-378, August 16-20, 1987 

% @author Justin Sheehy <justin@basho.com>

% @doc An implementation of Merkle Trees for anti-entropy.
%
% Intended use is for synchronizing two key/value stores with
% similar but potentially-divergent content.
%
% Typical usage is when a pair (or more) of nodes or systems have
% views of a set of key/value objects which can change independently.
% Whenever a new object is created or an existing one is modified
% (there is no difference from the merkle point of view) the node
% seeing the change performs an insert/2 to record the change.  At any
% time, one node can send a representation of its tree to another
% node.  The receiving node can diff/2 the trees to see which objects
% differ on the two systems.  From this information, a system knows
% exactly which objects to send or request in order to converge toward
% a common view of the world.  Of course, if the objects contain
% versioning information it will be much easier to resolve which
% node's view for any given object is newer.
%
% See the code of merkle_test/0 for trivial example usage.
%
% Application usage note: the 'crypto' OTP application must be started
% before any of this module's functions will work.
%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%
%% http://www.apache.org/licenses/LICENSE-2.0
%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.

-module(merkerl).
-export([insert/2,delete/2,build_tree/1,diff/2,allkeys/1]).

-include_lib("eunit/include/eunit.hrl").

% TODO: fix doc, userdata is the ONLY user-exposed key
-record(merk, {nodetype,           % atom: expected values are 'leaf' or 'inner'
               key=undefined,      % if nodetype=leaf, then this is binary/160
                                   % (keys are 160b binaries)
               userdata=undefined, % (if user specified a non-binary key)
	       hashval,            % hash of value if leaf, of children if inner
	       offset=undefined,   % if inner, then offset to reach here
	       children=undefined  % if nodetype=inner, then this is orddict
	       }).

% TODO in doc: note that these are an internal-only form
-record(merkitem, {userdata=undefined, % for non-binary "keys"
                   hkey,               % SHA-1 of userdata
                   hval                % SHA-1 of value (user-supplied)
                  }).

% @type tree() = treeleaf() | treeinner() | undefined.
% The tree() type here is used as the internal representation of
% a Merkle tree.  It can be used locally with insert/2 or pickled
% via term_to_binary and inverse for use remotely in diff/2.

% @type treeleaf() = term().
% Not externally useful, this is one of two record types making up tree().

% @type treeinner() = term().
% Not externally useful, this is one of two record types making up tree().

% (NEED TO EDOC THE RECORD TYPES)
% The merkitem records...
% These make up the "real" leaves in the Merkle tree.
%
% This is the input that most clients of the library will need to provide.

% @type key() = binary().
% This is the key, or "name" for an object tracked by a Merkle tree.
% It should remain constant through changes to the object it references.
% It is expected to be a 160b binary, as produced by
% crypto:sha/1 -- if the natural names of objects are not such values,
% then simply crypto:sha(term_to_binary(the-name>).

% @type hash() = binary().
% This is a hash representing a unique content value for an object
% tracked by a Merkle tree.
% It should change if the object it references changes in value.
% It is expected to be a 160b binary, as produced by
% crypto:sha/1 -- crypto:sha(term_to_binary(value)) is the canonical
% way to produce a hash().

% %spec build_tree([kh()]) -> tree()
% @doc Build a Merkle tree from a list of KH's of objects.
build_tree([]) ->
    undefined;
build_tree([{K,H}|KHL]) ->
    insert({K,H},build_tree(KHL)).

delete(Key, Tree) when is_record(Tree, merk) ->
    mi_delete({0, #merkitem{userdata=Key,hkey=sha(Key),hval=undefined}}, Tree).
mi_delete({Offset, MI}, Tree) ->
    HKey = MI#merkitem.hkey,
    case Tree#merk.nodetype of
	leaf ->
	    case Tree#merk.key of
		HKey ->
		    undefined;
		_ ->
		    Tree
	    end;
	inner ->
            Kids = Tree#merk.children,
            OKey = offset_key(Offset,HKey),
            NewKids = case orddict:is_key(OKey,Kids) of
                          false ->
                              Kids;
                          true ->
                              SubTree = orddict:fetch(OKey,Kids),
                              orddict:store(OKey,
                                      mi_delete({Offset+8,MI},SubTree),Kids)
                      end,
            mkinner(Offset,NewKids)
    end.
    
% TODO: fix @spec to be merkitems instead of kh's
% spec insert(KH :: kh(),T :: tree()) -> tree()
% @doc Insert the KH for a new or changed object into T.
%
% This is used much like a typical tree-insert function.
% To create a new tree, this can be called with T set to the atom 'undefined'.
insert({Userdata, Hashval}, T) ->
    mi_insert(#merkitem{userdata=Userdata,hkey=sha(Userdata),hval=Hashval}, T).
mi_insert(MI,T) when is_record(MI, merkitem) ->
    mi_insert({0,MI},T);
mi_insert({_Offset,MI},undefined) ->
    mkleaf(MI);
mi_insert({160,MI},_Tree) ->
    % we're all the way deep!  replace.
    mkleaf(MI);
mi_insert({Offset,MI},Tree) ->
    Key = MI#merkitem.hkey,
    case Tree#merk.nodetype of
	leaf ->
	    case Tree#merk.key of
		Key -> % replacing!
		    mkleaf(MI);
		_ -> % turning a leaf into an inner
		    K0 = orddict:new(),
		    K1 = orddict:store(offset_key(Offset,Key),
				       mkleaf(MI),K0),
		    TKey = Tree#merk.key,
		    Kids = orddict:store(offset_key(Offset,TKey),Tree,K1),
		    mkinner(Offset,Kids)
	    end;
	inner ->
	    mi_insert1({Offset,MI},Tree)
    end.
mi_insert1({Offset,MI},Tree) ->
    Kids = Tree#merk.children,
    OKey = offset_key(Offset,MI#merkitem.hkey),
    NewKids = case orddict:is_key(OKey,Kids) of
		  false ->
		      orddict:store(OKey,mkleaf(MI),Kids);
		  true ->
		      SubTree = orddict:fetch(OKey,Kids),
		      orddict:store(OKey,
				   mi_insert({Offset+8,MI},SubTree),Kids)
	      end,
    mkinner(Offset,NewKids).

mkleaf(MI) ->
    #merk{nodetype=leaf,
          key=MI#merkitem.hkey,
          userdata=MI#merkitem.userdata,
          hashval=MI#merkitem.hval}.

mkinner(Offset,Kids) ->
    #merk{nodetype=inner,hashval=sha(Kids),offset=Offset,
          children=[{K,V} || {K,V} <- Kids, V =/= undefined]}.

offset_key(Offset,Key) ->
    % offset is a 8b-divisible integer from 0 to 152, inclusive
    % Key is a 160b binary
    <<_L:Offset/integer,RightKey/binary>> = Key,
    <<OKey:8/integer,_R/binary>> = RightKey,
    OKey.

% TODO FIX TO NOTE THAT WE RETURN USERDATA INSTEAD
% @spec diff(tree(), tree()) -> [key()]
% @doc Find the keys of objects which differ between the two trees.
%
% For this purpose, "differ" means that an object either exists in
% only one of the two trees or it exists in both but with different
% hash() values.
%
% No information about the differing objects is provided except the keys.
% (Objects with vector-clock versioning are helpful here)
diff(undefined, X) -> allkeys(X);
diff(X, undefined) -> allkeys(X);
diff(TreeA,TreeB) when is_record(TreeA,merk),is_record(TreeB,merk) ->
    % return the list of 'userdata' fields from inner nodes that differ
    lists:usort(diff1(TreeA,TreeB)).
diff1(TreeA,TreeB) ->
    % precondition: TreeA and TreeB are both merks at same offset
    case TreeA#merk.hashval == TreeB#merk.hashval of
 	true ->
 	    [];
 	false ->
	    diff2(TreeA,TreeB)
    end.
diff2(TreeA,TreeB) ->
    % precondition: TreeA and TreeB are both merks at same offset
    % precondition: TreeA and TreeB have different hashval
    case TreeA#merk.nodetype == TreeB#merk.nodetype andalso
	TreeA#merk.nodetype == leaf of
	true ->
	    [TreeA#merk.userdata,TreeB#merk.userdata];
	false ->
	    diff3(TreeA,TreeB)
    end.
diff3(TreeA,TreeB) ->
    % precondition: TreeA and TreeB are both merks at same offset
    % precondition: TreeA and TreeB have different hashval
    % precondition: at least one of TreeA and TreeB is not a leaf
    case TreeA#merk.nodetype == leaf of
	true ->
	    allbutmaybe(TreeB,TreeA);
	false ->
	    case TreeB#merk.nodetype == leaf of
		true ->
		    allbutmaybe(TreeA,TreeB);
		false ->
		    diff4(TreeA,TreeB)
	    end
    end.
diff4(TreeA,TreeB) ->
    % precondition: TreeA and TreeB are both merks at same offset
    % precondition: TreeA and TreeB have different hashval
    % precondition: TreeA and TreeB are both inner nodes
    diff4a(TreeA#merk.children,TreeB#merk.children,0,[]).
diff4a(KidsA,KidsB,Idx,Acc) ->
    % this is the ugly bit.
    case Idx > 255 of
	true ->
	    Acc;
	false ->
	    case KidsA of
		[] ->
		    lists:append(Acc,lists:flatten([allkeys(X) ||
                                                       {_Okey, X} <- KidsB]));
		_ ->
		    case KidsB of
			[] ->
			    lists:append(Acc,lists:append(
					       [allkeys(X) ||
                                                   {_Okey, X} <- KidsA]));
			_ ->
			    diff4b(KidsA,KidsB,Idx,Acc)
		    end
	    end
    end.
diff4b(KidsA,KidsB,Idx,Acc) ->
    % precondition: neither KidsA nor KidsB is empty
    [{OkeyA,NodeA}|RestA] = KidsA,
    [{OkeyB,NodeB}|RestB] = KidsB,
    case OkeyA == Idx of
	true ->
	    case OkeyB == Idx of
		true ->
		    diff4a(RestA,RestB,Idx+1,
			   lists:append(Acc,diff1(
					      NodeA,NodeB)));
		false ->
		    diff4a(RestA,KidsB,Idx+1,
			   lists:append(Acc,allkeys(
					      NodeA)))
	    end;
	false ->
	    case OkeyB == Idx of
		true ->
		    diff4a(KidsA,RestB,Idx+1,
			   lists:append(Acc,allkeys(
					      NodeB)));
		false ->
		    diff4a(KidsA,KidsB,Idx+1,Acc)
	    end
    end.

allkeys(undefined) -> [];
allkeys(Tree) when is_record(Tree, merk) ->
    case Tree#merk.nodetype of
	leaf ->
	    [Tree#merk.userdata];
	_ ->
	    lists:append([allkeys(Kid) || Kid <- getkids(Tree)])
    end.
	    
allbutmaybe(Tree,Leaf) when is_record(Tree, merk),is_record(Leaf,merk) ->
    % return all keys in Tree, maybe the one for Leaf
    % (depending on whether it is present&identical in Tree)
    case contains_node(Tree,Leaf) of
	true ->
	    lists:delete(Leaf#merk.userdata,allkeys(Tree));
	false ->
	    lists:append([Leaf#merk.userdata],allkeys(Tree))
    end.

contains_node(Tree,Node) ->
    case Tree#merk.nodetype of
	leaf ->
	    Tree#merk.hashval == Node#merk.hashval;
	_ ->
	    lists:any(fun(T) -> contains_node(T,Node) end, getkids(Tree))
    end.
	    
getkids(Tree) ->
    [V || {_K,V} <- orddict:to_list(Tree#merk.children)].

sha(X) ->
    crypto:sha(term_to_binary(X)).

% @spec merkle_test() -> bool()
% @doc A test function and example code.
%
% This should be changed into a proper unit test suite.
merkle_test() ->
    case lists:keymember(crypto, 1, application:loaded_applications()) of
        true  -> ok;
        false -> ok = application:start(crypto)
    end,
    A = [{one,"one data"},{two,"two data"},{three,"three data"},
	 {four,"four data"},{five,"five data"}],
    B = [{one,"one data"},{two,"other two"},{three,"three data"},
	 {four,"other four"},{five,"five data"}],
    A2 = build_tree(A),
    B2 = build_tree(B),
    ?assertEqual(lists:usort([two, four]), diff(A2,B2)),
    C = [{one,"one data"}],
    C2 = build_tree(C),
    ?assertEqual(lists:usort([two, three, four, five]), diff(A2,C2)),
    D = insert({four, sha("changed!")}, A2),
    ?assertEqual([four], diff(A2,D)),
    E = insert({five, sha("changed more!")}, D),
    ?assertEqual([five], diff(D,E)),
    ?assertEqual(lists:usort([four, five]), diff(A2,E)),
    F = delete(five,D),
    G = delete(five,E),
    ?assertEqual([], diff(F,G)),
    H = delete(two,A2),
    ?assertEqual([two], diff(A2,H)),
    ?assertEqual([one], diff(C2,undefined)),
    STree1 = build_tree([{"hello", "hi"},{"and", "what"}]),
    STree2 = build_tree([{"hello", "hi"},{"goodbye", "bye"}]),
    ?assertEqual(lists:usort(["and", "goodbye"]), diff(STree1, STree2)).