From d7b7580b3913c17b404319cc4c153748d5e59194 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= <essen@ninenines.eu>
Date: Fri, 9 Nov 2018 17:42:37 +0100
Subject: Add sendfile support to cowboy_req:stream_body

It is now possible to stream one or more sendfile tuples.
A simple example of what can now be done would be for
example to build a tar file on the fly using the sendfile
syscall for sending the files, or to support Range requests
with more than one range with the sendfile syscall.

When using cowboy_compress_h unfortunately we have to read
the file in order to send it. More options will be added
at a later time to make sure users don't read too much
into memory. This is a new feature however so existing
code is not affected.

Also rework cowboy_http's data sending to be flatter.
---
 src/cowboy_compress_h.erl | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

(limited to 'src/cowboy_compress_h.erl')

diff --git a/src/cowboy_compress_h.erl b/src/cowboy_compress_h.erl
index 781cc0a..ed81db6 100644
--- a/src/cowboy_compress_h.erl
+++ b/src/cowboy_compress_h.erl
@@ -98,7 +98,7 @@ fold(Commands, State) ->
 
 fold([], State, Acc) ->
 	{lists:reverse(Acc), State};
-%% We do not compress sendfile bodies.
+%% We do not compress full sendfile bodies.
 fold([Response={response, _, _, {sendfile, _, _, _}}|Tail], State, Acc) ->
 	fold(Tail, State, [Response|Acc]);
 %% We compress full responses directly, unless they are lower than
@@ -171,6 +171,21 @@ gzip_headers({headers, Status, Headers0}, State) ->
 		<<"content-encoding">> => <<"gzip">>
 	}}, State#state{deflate=Z}}.
 
+%% It is not possible to combine zlib and the sendfile
+%% syscall as far as I can tell, because the zlib format
+%% includes a checksum at the end of the stream. We have
+%% to read the file in memory, making this not suitable for
+%% large files.
+gzip_data({data, nofin, Sendfile={sendfile, _, _, _}}, State=#state{deflate=Z}) ->
+	{ok, Data0} = read_file(Sendfile),
+	Data = zlib:deflate(Z, Data0),
+	{{data, nofin, Data}, State};
+gzip_data({data, fin, Sendfile={sendfile, _, _, _}}, State=#state{deflate=Z}) ->
+	{ok, Data0} = read_file(Sendfile),
+	Data = zlib:deflate(Z, Data0, finish),
+	zlib:deflateEnd(Z),
+	zlib:close(Z),
+	{{data, fin, Data}, State#state{deflate=undefined}};
 gzip_data({data, nofin, Data0}, State=#state{deflate=Z}) ->
 	Data = zlib:deflate(Z, Data0),
 	{{data, nofin, Data}, State};
@@ -179,3 +194,15 @@ gzip_data({data, fin, Data0}, State=#state{deflate=Z}) ->
 	zlib:deflateEnd(Z),
 	zlib:close(Z),
 	{{data, fin, Data}, State#state{deflate=undefined}}.
+
+read_file({sendfile, Offset, Bytes, Path}) ->
+	{ok, IoDevice} = file:open(Path, [read, raw, binary]),
+	try
+		_ = case Offset of
+			0 -> ok;
+			_ -> file:position(IoDevice, {bof, Offset})
+		end,
+		file:read(IoDevice, Bytes)
+	after
+		file:close(IoDevice)
+	end.
-- 
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