ESP32: remove use of luaM_free in file module (#2631)

* file: remove use of luaM_free

* added safe pushlstring function

components/base_nodemcu/include/lnodeaux.h

@@ -65,4 +65,9 @@ inline bool luaX_valid_ref(lua_ref_t ref) {
     return ref > 0;
 }
 
+// luaX_pushlstring is the same as lua_pushlstring except it will return nonzero in case of error
+// (instead of throwing an exception and never returning) and will put the error message on the top of the stack.
+int luaX_pushlstring(lua_State* L, const char* s, size_t l);
+
+
 #endif

components/base_nodemcu/lnodeaux.c

@@ -111,7 +111,30 @@ void luaX_unset_ref(lua_State* L, lua_ref_t* ref) {
 // luaX_set_ref pins a reference to a lua object, provided a registry
 // or stack position
 void luaX_set_ref(lua_State* L, int idx, lua_ref_t* ref) {
-    luaX_unset_ref(L, ref);                      // make sure we free previous reference
+    luaX_unset_ref(L, ref);                 // make sure we free previous reference
     lua_pushvalue(L, idx);                  // push on the stack the referenced index
     *ref = luaL_ref(L, LUA_REGISTRYINDEX);  // set the reference (pops 1 value)
 }
+
+// pushlstring_t is a helper struct to provide a protected lua_pushlstring call
+typedef struct {
+    const char* s;
+    size_t l;
+} pushlstring_t;
+
+// safe_pushlstring is a private function meant to be called in protected mode.
+static int safe_pushlstring(lua_State* L) {
+     pushlstring_t *ps = (pushlstring_t*)lua_touserdata(L,-1);
+     lua_pushlstring(L, ps->s, ps->l);
+     return 1;
+}
+
+// luaX_pushlstring is the same as lua_pushlstring except it will return nonzero in case of error
+// (instead of throwing an exception and never returning) and will put the error message on the top of the stack.
+int luaX_pushlstring(lua_State* L, const char* s, size_t l) {
+    lua_pushcfunction(L, &safe_pushlstring);
+    pushlstring_t* ps =(pushlstring_t*) lua_newuserdata(L, sizeof(pushlstring_t));
+    ps->s = s;
+    ps->l = l;
+    return lua_pcall(L, 1, 1, 0);
+}

components/modules/file.c

@@ -2,6 +2,7 @@
 
 #include "module.h"
 #include "lauxlib.h"
+#include "lnodeaux.h"
 #include "lmem.h"
 #include "platform.h"
 
@@ -140,7 +141,6 @@ static int file_obj_free( lua_State *L )
   if (ud->fd) {
     // close file if it's still open
     vfs_close(ud->fd);
-    ud->fd = 0;
   }
 
   return 0;
@@ -383,32 +383,27 @@ static int file_stat( lua_State* L )
 // g_read()
 static int file_g_read( lua_State* L, int n, int16_t end_char, int fd )
 {
-  static char *heap_mem = NULL;
-  // free leftover memory
-  if (heap_mem) {
-    luaM_free(L, heap_mem);
-    heap_mem = NULL;
-  }
+  char *heap_mem = NULL;
 
   if(n <= 0)
     n = FILE_READ_CHUNK;
 
   if(end_char < 0 || end_char >255)
     end_char = EOF;
 
-
   if(!fd)
     return luaL_error(L, "open a file first");
 
   char *p;
   int i;
+  size_t bufsize = n;
 
   if (n > LUAL_BUFFERSIZE) {
     // get buffer from heap
-    p = heap_mem = luaM_malloc(L, n);
+    p = heap_mem = luaM_malloc(L, bufsize);
   } else {
     // small chunks go onto the stack
-    p = alloca(n);
+    p = alloca(bufsize);
   }
 
   n = vfs_read(fd, p, n);
@@ -424,21 +419,24 @@ static int file_g_read( lua_State* L, int n, int16_t end_char, int fd )
     i = n;
   }
 
+  int err = 0;
+
   if (i == 0 || n == VFS_RES_ERR) {
-    if (heap_mem) {
-      luaM_free(L, heap_mem);
-      heap_mem = NULL;
-    }
     lua_pushnil(L);
-    return 1;
+  } else {
+    vfs_lseek(fd, -(n - i), VFS_SEEK_CUR);
+    err = luaX_pushlstring(L, p, i); // On error it will return nonzero and leave a message on top of the stack.
   }
 
-  vfs_lseek(fd, -(n - i), VFS_SEEK_CUR);
-  lua_pushlstring(L, p, i);
   if (heap_mem) {
-    luaM_free(L, heap_mem);
-    heap_mem = NULL;
+    luaM_freearray(L, heap_mem, bufsize, char);
   }
+
+  if (err){
+    lua_error(L); // luaX_pushlstring failed and the error message is on top of the stack. Throw it.
+    // never returns
+  }
+
   return 1;
 }