From d7a6bd635ce60d0fc6a6a40dc3027cee308701f6 Mon Sep 17 00:00:00 2001
From: Brad Anderson <brad@cloudant.com>
Date: Tue, 8 Jun 2010 12:00:59 -0400
Subject: fabric attachments

---
 src/fabric.erl                 |   6 ++-
 src/fabric_doc_attachments.erl | 103 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100644 src/fabric_doc_attachments.erl

(limited to 'src')

diff --git a/src/fabric.erl b/src/fabric.erl
index 983cd818..80bc6d4c 100644
--- a/src/fabric.erl
+++ b/src/fabric.erl
@@ -6,7 +6,7 @@
 
 % Documents
 -export([open_doc/3, open_revs/4, get_missing_revs/2, update_doc/3,
-    update_docs/3]).
+    update_docs/3, att_receiver/2]).
 
 % Views
 -export([all_docs/4, query_view/5]).
@@ -42,7 +42,7 @@ delete_db(DbName, Options) ->
     fabric_db_delete:delete_db(dbname(DbName), opts(Options)).
 
 
-
+% doc operations
 open_doc(DbName, Id, Options) ->
     fabric_doc_open:go(dbname(DbName), docid(Id), opts(Options)).
 
@@ -60,6 +60,8 @@ update_doc(DbName, Doc, Options) ->
 update_docs(DbName, Docs, Options) ->
     fabric_doc_update:go(dbname(DbName), docs(Docs), opts(Options)).
 
+att_receiver(Req, Length) ->
+    fabric_doc_attachments:receiver(Req, Length).
 
 all_docs(DbName, #view_query_args{} = QueryArgs, Callback, Acc0) when
         is_function(Callback, 2) ->
diff --git a/src/fabric_doc_attachments.erl b/src/fabric_doc_attachments.erl
new file mode 100644
index 00000000..6230a444
--- /dev/null
+++ b/src/fabric_doc_attachments.erl
@@ -0,0 +1,103 @@
+-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) ->
+    % ?LOG_INFO("generating chunked attachment processes", []),
+    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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