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Diffstat (limited to 'src/index.erl')
-rw-r--r-- | src/index.erl | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/src/index.erl b/src/index.erl new file mode 100644 index 0000000..5fd468b --- /dev/null +++ b/src/index.erl @@ -0,0 +1,87 @@ +%% +%% 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). + +decodedata(EntryText) when length(EntryText) == ?ENTRYSIZEINFILE -> + case [lists:last(EntryText)] of + "\n" -> + hex:hexstr_to_bin(lists: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. |