Use tables to deal with huge responses.

Instead of accumulating the response in a string, use a table. This reduces the chances of "out of memory" errors when testing endpoints that produces huge amounts of data.

It also changes the call to `common.send_content` to match the way it is used in wsapi itself.

src/wsapi/mock.lua

@@ -55,20 +55,23 @@ end
 -- Override common's output handler to avoid writing headers
 -- in the reponse body.
 function common.send_output(out, status, headers, res_iter, write_method,res_line)
-   common.send_content(out, res_iter, out:write())
+   common.send_content(out, res_iter, "write")
 end
 
 -- Mock IO objects
 local function make_io_object(content)
-  local receiver = { buffer = content or "", bytes_read = 0 }
+  local receiver = { buffer = { content }, bytes_read = 0 }
 
   function receiver:write(content)
-    if content then
-      self.buffer = self.buffer .. content
-    end
+    self.buffer[#self.buffer + 1] = content
+    return true
   end
 
   function receiver:read(len)
+    -- first read will turn the buffer into a string
+    if type(self.buffer) == "table" then
+      self.buffer = table.concat(self.buffer)
+    end
     len = len or (#self.buffer - self.bytes_read)
     if self.bytes_read >= #self.buffer then return nil end
     local s = self.buffer:sub(self.bytes_read + 1, self.bytes_read + len)
@@ -78,7 +81,7 @@ local function make_io_object(content)
   end
 
   function receiver:clear()
-    self.buffer = ""
+    self.buffer = {}
     self.bytes_read = 0
   end