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% Copyright 2010 Cloudant
%
% 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(fabric_doc_attachments).
-include("fabric.hrl").
%% couch api calls
-export([receiver/2]).
receiver(_Req, undefined) ->
<<"">>;
receiver(_Req, {unknown_transfer_encoding, Unknown}) ->
exit({unknown_transfer_encoding, Unknown});
receiver(Req, chunked) ->
MiddleMan = spawn(fun() -> middleman(Req, chunked) end),
fun(4096, ChunkFun, ok) ->
write_chunks(MiddleMan, ChunkFun)
end;
receiver(_Req, 0) ->
<<"">>;
receiver(Req, Length) when is_integer(Length) ->
Middleman = spawn(fun() -> middleman(Req, Length) end),
fun() ->
Middleman ! {self(), gimme_data},
receive {Middleman, Data} -> Data end
end;
receiver(_Req, Length) ->
exit({length_not_integer, Length}).
%%
%% internal
%%
write_chunks(MiddleMan, ChunkFun) ->
MiddleMan ! {self(), gimme_data},
receive
{MiddleMan, {0, _Footers}} ->
% MiddleMan ! {self(), done},
ok;
{MiddleMan, ChunkRecord} ->
ChunkFun(ChunkRecord, ok),
write_chunks(MiddleMan, ChunkFun)
end.
receive_unchunked_attachment(_Req, 0) ->
ok;
receive_unchunked_attachment(Req, Length) ->
receive {MiddleMan, go} ->
Data = couch_httpd:recv(Req, 0),
MiddleMan ! {self(), Data}
end,
receive_unchunked_attachment(Req, Length - size(Data)).
middleman(Req, chunked) ->
% spawn a process to actually receive the uploaded data
RcvFun = fun(ChunkRecord, ok) ->
receive {From, go} -> From ! {self(), ChunkRecord} end, ok
end,
Receiver = spawn(fun() -> couch_httpd:recv_chunked(Req,4096,RcvFun,ok) end),
% take requests from the DB writers and get data from the receiver
N = erlang:list_to_integer(couch_config:get("cluster","n")),
middleman_loop(Receiver, N, dict:new(), 0, []);
middleman(Req, Length) ->
Receiver = spawn(fun() -> receive_unchunked_attachment(Req, Length) end),
N = erlang:list_to_integer(couch_config:get("cluster","n")),
middleman_loop(Receiver, N, dict:new(), 0, []).
middleman_loop(Receiver, N, Counters, Offset, ChunkList) ->
receive {From, gimme_data} ->
% figure out how far along this writer (From) is in the list
{NewCounters, WhichChunk} = case dict:find(From, Counters) of
{ok, I} ->
{dict:update_counter(From, 1, Counters), I};
error ->
{dict:store(From, 2, Counters), 1}
end,
ListIndex = WhichChunk - Offset,
% talk to the receiver to get another chunk if necessary
ChunkList1 = if ListIndex > length(ChunkList) ->
Receiver ! {self(), go},
receive {Receiver, ChunkRecord} -> ChunkList ++ [ChunkRecord] end;
true -> ChunkList end,
% reply to the writer
From ! {self(), lists:nth(ListIndex, ChunkList1)},
% check if we can drop a chunk from the head of the list
SmallestIndex = dict:fold(fun(_, Val, Acc) -> lists:min([Val,Acc]) end,
WhichChunk+1, NewCounters),
Size = dict:size(NewCounters),
{NewChunkList, NewOffset} =
if Size == N andalso (SmallestIndex - Offset) == 2 ->
{tl(ChunkList1), Offset+1};
true ->
{ChunkList1, Offset}
end,
middleman_loop(Receiver, N, NewCounters, NewOffset, NewChunkList)
after 10000 ->
ok
end.
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