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%%
%% Copyright (c) 2014 Kungliga Tekniska Högskolan
%% (KTH Royal Institute of Technology, Stockholm, Sweden).
%%
%% 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.
%%
%% Writes(add, truncate, addlast) need to be serialized.
%% TODO: Checksums
-module(index).
-export([get/2, add/3, addlast/2, truncate/2]).
-define(ENTRYSIZE, 32).
-define(ENTRYSIZEINFILE, (?ENTRYSIZE*2+1)).
-spec add(string(), integer() | last, binary()) -> ok.
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,
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),
ok = file:close(File),
util:fsync([Basepath, filename:dirname(Basepath)]);
{error, Error} ->
util:exit_with_error(Error, writefile,
"Error opening file for writing")
end.
-spec addlast(string(), integer()) -> ok.
addlast(Basepath, Entry) ->
add(Basepath, last, Entry).
%% From lib/stdlib/src/lists.erl. For supporting < R17.
-spec droplast(nonempty_list()) -> list().
droplast([_T]) -> [];
droplast([H|T]) -> [H|droplast(T)].
decodedata(EntryText) when length(EntryText) == ?ENTRYSIZEINFILE ->
case [lists:last(EntryText)] of
"\n" ->
hex:hexstr_to_bin(droplast(EntryText));
_ ->
util:exit_with_error(badformat, readindex,
"Index line not ending with linefeed")
end.
-spec get(string(), integer()) -> binary().
get(Basepath, Index) ->
case file:open(Basepath, [read, binary]) of
{ok, File} ->
{ok, Filesize} = file:position(File, eof),
if
Index * ?ENTRYSIZEINFILE + ?ENTRYSIZEINFILE =< Filesize ->
{ok, _Position} = file:position(File,
Index * ?ENTRYSIZEINFILE),
{ok, EntryText} = file:read(File, ?ENTRYSIZEINFILE),
Entry = decodedata(binary_to_list(EntryText)),
file:close(File),
Entry;
true ->
noentry
end;
{error, Error} ->
util:exit_with_error(Error, readfile,
"Error opening file for reading")
end.
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