# HG changeset patch
# User jbe
# Date 1452126188 -3600
# Node ID fd5880964d9956b114320dd9e42d1dc747d4bfee
# Parent  0e641ac7664754a8d99e436d72945376933ce1f2
Hack to avoid cumulating memory leaks in case of (caught) out-of-memory errors

diff -r 0e641ac76647 -r fd5880964d99 libraries/mondelefant/mondelefant_native.c
--- a/libraries/mondelefant/mondelefant_native.c	Wed Jan 06 22:59:39 2016 +0100
+++ b/libraries/mondelefant/mondelefant_native.c	Thu Jan 07 01:23:08 2016 +0100
@@ -28,10 +28,24 @@
 typedef struct {
   PGconn *pgconn;
   int server_encoding;
+  void *todo_PQfreemem;
+  PGresult *todo_PQclear;
 } mondelefant_conn_t;
 #define MONDELEFANT_SERVER_ENCODING_ASCII 0
 #define MONDELEFANT_SERVER_ENCODING_UTF8  1
 
+// hack to avoid cumulating memory leaks in case of out-of-memory errors
+static void mondelefant_cleanup(mondelefant_conn_t *conn) {
+  if (conn->todo_PQfreemem) {
+    PQfreemem(conn->todo_PQfreemem);
+    conn->todo_PQfreemem = NULL;
+  }
+  if (conn->todo_PQclear) {
+    PQclear(conn->todo_PQclear);
+    conn->todo_PQclear = NULL;
+  }
+}
+
 // transform codepoint-position to byte-position for a given UTF-8 string:
 static size_t utf8_position_to_byte(const char *str, size_t utf8pos) {
   size_t bytepos;
@@ -598,14 +612,23 @@
   conn = mondelefant_get_conn(L, 1);
   // get second argument, which must be a string:
   input = luaL_checklstring(L, 2, &input_len);
+  // avoid cumulating memory leaks in case of previous out-of-memory errors:
+  mondelefant_cleanup(conn);
   // call PQescapeByteaConn, which allocates memory itself:
   output = (char *)PQescapeByteaConn(
     conn->pgconn, (const unsigned char *)input, input_len, &output_len
   );
-  // if PQescapeByteaConn returned NULL, then throw error:
   if (!output) {
-    return luaL_error(L, "Could not allocate memory for binary quoting.");
+    lua_gc(L, LUA_GCCOLLECT, 0);
+    output = (char *)PQescapeByteaConn(
+      conn->pgconn, (const unsigned char *)input, input_len, &output_len
+    );
+    if (!output) {
+      return luaL_error(L, "Could not allocate memory for binary quoting.");
+    }
   }
+  // ensure call of PQfreemem in case of unexpected out-of-memory error:
+  conn->todo_PQfreemem = output;
   // create Lua string enclosed by single quotes:
   luaL_buffinit(L, &buf);
   luaL_addchar(&buf, '\'');
@@ -614,6 +637,8 @@
   luaL_pushresult(&buf);
   // free memory allocated by PQescapeByteaConn:
   PQfreemem(output);
+  // avoid double call of PQfreemem later:
+  conn->todo_PQfreemem = NULL;
   // return Lua string:
   return 1;
 }
@@ -783,6 +808,7 @@
             lua_remove(L, -2);
             // Lua stack contains: ..., <buffer>, raw-value
             // branch according to type of value:
+            // NOTE: Lua automatically converts numbers to strings
             if (lua_isnil(L, -1)) {  // value is nil
               // push string "NULL" to stack:
               lua_pushliteral(L, "NULL");
@@ -790,9 +816,8 @@
               // push strings "TRUE" or "FALSE" to stack:
               lua_pushstring(L, lua_toboolean(L, -1) ? "TRUE" : "FALSE");
             } else if (lua_isstring(L, -1)) {  // value is string or number
-              // NOTE: In this version of lua a number will be converted
-              // push output of "quote_string" method of database
-              // connection to stack:
+              // push output of "quote_string" method of database connection
+              // to stack:
               lua_tostring(L, -1);
               lua_pushcfunction(L, mondelefant_conn_quote_string);
               lua_pushvalue(L, 1);
@@ -908,6 +933,8 @@
     mode = modes[command_idx];
     // if PQsendQuery call was successful, then fetch result data:
     if (sent_success) {
+      // avoid cumulating memory leaks in case of previous out-of-memory errors:
+      mondelefant_cleanup(conn);
       // NOTE: PQgetResult called one extra time. Break only, if all
       // queries have been processed and PQgetResult returned NULL.
       res = PQgetResult(conn->pgconn);
@@ -916,6 +943,8 @@
         pgstatus = PQresultStatus(res);
         rows = PQntuples(res);
         cols = PQnfields(res);
+        // ensure eventual call of PQclear in case of unexpected Lua errors:
+        conn->todo_PQclear = res;
       }
     }
     // handle errors:
@@ -1041,6 +1070,8 @@
         if (res) {
           PQclear(res);
           while ((res = PQgetResult(conn->pgconn))) PQclear(res);
+          // avoid double call of PQclear later:
+          conn->todo_PQclear = NULL;
         }
       }
       if (lua_toboolean(L, 3)) {
@@ -1185,6 +1216,8 @@
     if (lua_gettop(L) != 4) abort();  // should not happen
     // free memory acquired by libpq:
     PQclear(res);
+    // avoid double call of PQclear later:
+    conn->todo_PQclear = NULL;
   }
   // trace callback at stack position 3
   // result at stack position 4 (top of stack)