From 80c8ef847d996af04ec677a79555d640733641f2 Mon Sep 17 00:00:00 2001
From: Magnus Ahltorp <map@kth.se>
Date: Sun, 19 Oct 2014 01:37:29 +0200
Subject: db:get_by_leaf_hash(): Return notfound instead of crashing when no
 entry could be found. db:get_by_entry_hash(): Don't fetch index, isn't used
 and might not exist. index:add(): Allow writes at exiting indicies.

---
 src/db.erl    | 25 +++++++++++++++++------
 src/index.erl | 64 +++++++++++++++++++++++++++++++++++------------------------
 2 files changed, 57 insertions(+), 32 deletions(-)

diff --git a/src/db.erl b/src/db.erl
index 6315ae5..6fce8a3 100644
--- a/src/db.erl
+++ b/src/db.erl
@@ -103,7 +103,12 @@ entry_for_leafhash(LeafHash) ->
     perm:readfile(entry_root_path(), LeafHash).
 
 index_for_leafhash(LeafHash) ->
-    binary_to_integer(perm:readfile(indexforhash_root_path(), LeafHash)).
+    case perm:readfile(indexforhash_root_path(), LeafHash) of
+        noentry ->
+            noentry;
+        Index ->
+            binary_to_integer(Index)
+    end.
 
 leafhash_for_index(Index) ->
     index:get(index_path(), Index).
@@ -148,9 +153,17 @@ handle_call({get_by_index, Index}, _From, State) ->
     {reply, R, State};
 
 handle_call({get_by_leaf_hash, LeafHash}, _From, State) ->
-    Entry = entry_for_leafhash(LeafHash),
-    Index = index_for_leafhash(LeafHash),
-    R = {Index, LeafHash, Entry},
+    R = case entry_for_leafhash(LeafHash) of
+            noentry ->
+                notfound;
+            Entry ->
+                case index_for_leafhash(LeafHash) of
+                    noentry ->
+                        notfound;
+                    Index ->
+                        {Index, LeafHash, Entry}
+                end
+        end,
     {reply, R, State};
 
 handle_call({get_by_entry_hash, EntryHash}, _From, State) ->
@@ -159,7 +172,7 @@ handle_call({get_by_entry_hash, EntryHash}, _From, State) ->
                 notfound;
             LeafHash ->
                 Entry = entry_for_leafhash(LeafHash),
-                Index = index_for_leafhash(LeafHash),
-                {Index, LeafHash, Entry}
+                %% Don't fetch index, isn't used and might not exist
+                {notfetched, LeafHash, Entry}
         end,
     {reply, R, State}.
diff --git a/src/index.erl b/src/index.erl
index 7871215..5169fbb 100644
--- a/src/index.erl
+++ b/src/index.erl
@@ -1,17 +1,18 @@
 %%% Copyright (c) 2014, NORDUnet A/S.
 %%% See LICENSE for licensing information.
 
-%% Implements an interface to a file pair (basename and basename.chksum)
-%% that stores an ordered list of fixed-size entries. Entries can be
-%% added at the end and are retrieved by index. The list can also be
-%% truncated.
+%% Implements an interface to a file pair (basename and
+%% basename.chksum) that stores an ordered list of fixed-size entries.
+%% Entries can be added at the end and are retrieved by index. Entries
+%% can also be added at already existing indices, but then the
+%% contents must be the same.
 %%
-%% Writes(add, truncate, addlast) need to be serialized.
+%% Writes(add, addlast) need to be serialized.
 
 %% TODO: Checksums
 
 -module(index).
--export([get/2, add/3, addlast/2, truncate/2]).
+-export([get/2, add/3, addlast/2]).
 
 -define(ENTRYSIZE, 32).
 -define(ENTRYSIZEINFILE, (?ENTRYSIZE*2+1)).
@@ -21,27 +22,38 @@ add(Basepath, Index, Entry) when is_binary(Entry), size(Entry) == ?ENTRYSIZE ->
     case file:open(Basepath, [read, write, binary]) of
         {ok, File} ->
             {ok, Position} = file:position(File, eof),
-            case Index of
-                last when Position rem ?ENTRYSIZEINFILE == 0 ->
-                    ok;
-                Index when is_integer(Index),
-                           Index * ?ENTRYSIZEINFILE == Position ->
-                    ok
-            end,
+            Mode = case Index of
+                       last when Position rem ?ENTRYSIZEINFILE == 0 ->
+                           write;
+                       Index when is_integer(Index),
+                                  Index * ?ENTRYSIZEINFILE == Position ->
+                           write;
+                       Index when is_integer(Index),
+                                  Index * ?ENTRYSIZEINFILE < Position ->
+                           read;
+                       _ ->
+                           util:exit_with_error(invalid, writefile,
+                                                "Index not valid")
+                   end,
             EntryText = hex:bin_to_hexstr(Entry) ++ "\n",
-            ok = file:write(File, EntryText),
-            ok = file:close(File),
-            util:fsync([Basepath, filename:dirname(Basepath)]);
-        {error, Error} ->
-            util:exit_with_error(Error, writefile,
-                                 "Error opening file for writing")
-    end.
-
-truncate(Basepath, Index) ->
-    case file:open(Basepath, [read, write, binary]) of
-        {ok, File} ->
-            {ok, _Position} = file:position(File, Index * ?ENTRYSIZEINFILE),
-            ok = file:truncate(File),
+            case Mode of
+                write ->
+                    ok = file:write(File, EntryText);
+                read ->
+                    {ok, _Position} =
+                        file:position(File, {bof, Index * ?ENTRYSIZEINFILE}),
+                    {ok, OldEntryText} = file:read(File, ?ENTRYSIZEINFILE),
+                    %% check that the written content is the same as
+                    %% the old content
+                    case binary_to_list(OldEntryText) of
+                        EntryText ->
+                            ok;
+                        _ ->
+                            util:exit_with_error(invalid, writefile,
+                                                 "Written content not the" ++
+                                                     " same as old content")
+                    end
+            end,
             ok = file:close(File),
             util:fsync([Basepath, filename:dirname(Basepath)]);
         {error, Error} ->
-- 
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