1 files changed, 16 insertions, 1 deletions

diff --git a/src/ltn12.lua b/src/ltn12.lua
index ed3449b..dac932b 100644
--- a/src/ltn12.lua
+++ b/src/ltn12.lua
@@ -34,8 +34,23 @@ end
 local function chain2(f1, f2)
     if type(f1) ~= 'function' then error('invalid filter', 2) end 
     if type(f2) ~= 'function' then error('invalid filter', 2) end 
+    local co = coroutine.create(function(chunk)
+        while true do
+            local filtered1 = f1(chunk)
+            local filtered2 = f2(filtered1)
+            local done2 = filtered1 and ""
+            while true do
+                if filtered2 == "" or filtered2 == nil then break end
+                coroutine.yield(filtered2)
+                filtered2 = f2(done2)
+            end
+            if filtered1 == "" then chunk = coroutine.yield(filtered1)
+            elseif filtered1 == nil then return nil
+            else chunk = chunk and "" end
+        end
+    end)
     return function(chunk)
-        return f2(f1(chunk))
+        return shift(coroutine.resume(co, chunk))
     end
 end