Simplify SSE parsing

Every message ends with two newlines
Specs: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format

Author: johnd0e

openai/init.moon

@@ -95,27 +95,6 @@ parse_completion_chunk = types.partial {
   }
 }
 
--- lpeg pattern to read a json data block from the front of a string, returns
--- the json blob and the rest of the string if it could parse one
-consume_json_head = do
-  import C, S, P from require "lpeg"
-
-  -- this pattern reads from the front just enough characters to consume a
-  -- valid json object
-  consume_json = P (str, pos) ->
-    str_len = #str
-    for k=pos+1,str_len
-      candidate = str\sub pos, k
-      parsed = false
-      pcall -> parsed = cjson.decode candidate
-      if parsed
-        return k + 1
-
-    return nil -- fail
-
-  S("\t\n\r ")^0 * P("data: ") * C(consume_json) * C(P(1)^0)
-
-
 parse_error_message = types.partial {
   error: types.partial {
     message: types.string\tag "message"
@@ -245,13 +224,16 @@ class OpenAI
         accumulation_buffer ..= chunk
 
         while true
-          json_blob, rest = consume_json_head\match accumulation_buffer
-          unless json_blob
+          _, pos, line = accumulation_buffer\find "^(.-)\r?\n\r?\n"
+          unless line
             break
 
-          accumulation_buffer = rest
-          if chunk = parse_completion_chunk cjson.decode json_blob
-            chunk_callback chunk
+          accumulation_buffer = accumulation_buffer\sub pos+1
+
+          json_blob = line\match "^data:%s+(.-)%s*$"
+          if json_blob and json_blob~="[DONE]"
+            if chunk = parse_completion_chunk cjson.decode json_blob
+              chunk_callback chunk
 
       ...