3 files changed, 29 insertions, 13 deletions

diff --git a/src/ltn12.lua b/src/ltn12.lua
index 5216ff6..1a13a43 100644
--- a/src/ltn12.lua
+++ b/src/ltn12.lua
@@ -40,30 +40,27 @@ end
 function filter.chain(...) 
     local n = table.getn(arg)
     local top, index = 1, 1
+    local retry = ""
     return function(chunk)
+        retry = chunk and retry
         while true do 
             if index == top then
                 chunk = arg[index](chunk)
-                if chunk == "" or top == n then 
-                    return chunk
-                elseif chunk then 
-                    index = index + 1
+                if chunk == "" or top == n then return chunk
+                elseif chunk then index = index + 1
                 else 
                     top = top+1 
                     index = top
                 end
             else
-                local original = chunk
-                chunk = arg[index](original or "")
+                chunk = arg[index](chunk or "")
                 if chunk == "" then
                     index = index - 1
-                    chunk = original and chunk
+                    chunk = retry
                 elseif chunk then
                     if index == n then return chunk
                     else index = index + 1 end
-                else 
-                    base.error("filter returned inappropriate nil")
-                end
+                else base.error("filter returned inappropriate nil") end
             end
         end
     end
@@ -138,6 +135,8 @@ function source.rewind(src)
     end
 end
 
+local print = print
+
 -- chains a source with a filter
 function source.chain(src, f)
     base.assert(src and f)
@@ -151,13 +150,16 @@ function source.chain(src, f)
                 last_out = f(last_in)
                 if last_out ~= "" then return last_out end
                 if not last_in then 
-                    error('filter returned inappropriate ""') 
+                    base.error('filter returned inappropriate ""') 
                 end
             end
         elseif last_out then
             last_out = f(last_in and "")
             if last_in and not last_out then
-                error('filter returned inappropriate nil') 
+                base.error('filter returned inappropriate nil') 
+            end
+            if last_out == "" and not last_in then
+                base.error(base.tostring(f) .. ' returned inappropriate ""') 
             end
             return last_out
         else
diff --git a/src/mime.c b/src/mime.c
index 8bc20d3..bd48920 100644
--- a/src/mime.c
+++ b/src/mime.c
@@ -267,6 +267,7 @@ static int mime_global_b64(lua_State *L)
     if (!input) {
         asize = b64pad(atom, asize, &buffer);
         luaL_pushresult(&buffer);
+        if (!(*lua_tostring(L, -1))) lua_pushnil(L);
         lua_pushnil(L);
         return 2;
     }
@@ -306,6 +307,7 @@ static int mime_global_unb64(lua_State *L)
     /* if second is nil, we are done */
     if (!input) {
         luaL_pushresult(&buffer);
+        if (!(*lua_tostring(L, -1))) lua_pushnil(L);
         lua_pushnil(L);
         return 2;
     }
@@ -418,7 +420,7 @@ static size_t qppad(UC *input, size_t size, luaL_Buffer *buffer)
         if (qpclass[input[i]] == QP_PLAIN) luaL_putchar(buffer, input[i]);
         else qpquote(input[i], buffer);
     }
-    luaL_addstring(buffer, EQCRLF);
+    if (size > 0) luaL_addstring(buffer, EQCRLF);
     return 0;
 }
 
@@ -454,7 +456,9 @@ static int mime_global_qp(lua_State *L)
     if (!input) {
         asize = qppad(atom, asize, &buffer);
         luaL_pushresult(&buffer);
+        if (!(*lua_tostring(L, -1))) lua_pushnil(L);
         lua_pushnil(L);
+        return 2;
     }
     /* otherwise process rest of input */
     last = input + isize;
@@ -531,6 +535,7 @@ static int mime_global_unqp(lua_State *L)
     /* if second part is nil, we are done */
     if (!input) {
         luaL_pushresult(&buffer);
+        if (!(*lua_tostring(L, -1))) lua_pushnil(L);
         lua_pushnil(L);
         return 2;
     } 
diff --git a/src/mime.lua b/src/mime.lua
index 712600c..42d0b3c 100644
--- a/src/mime.lua
+++ b/src/mime.lua
@@ -49,6 +49,15 @@ mime.decodet['quoted-printable'] = function()
     return ltn12.filter.cycle(unqp, "")
 end
 
+local io, string = io, string
+
+local function format(chunk)
+    if chunk then
+        if chunk == "" then return "''"
+        else return string.len(chunk) end
+    else return "nil" end
+end 
+
 -- define the line-wrap filters
 mime.wrapt['text'] = function(length)
     length = length or 76