Added file.exists() method to save the need to use file.list() for checking file existence

app/modules/file.c

@@ -114,6 +114,22 @@ static int file_seek (lua_State *L)
   return 1;
 }
 
+// Lua: exists(filename)
+static int file_exists( lua_State* L )
+{
+  size_t len;
+  const char *fname = luaL_checklstring( L, 1, &len );
+  if( len > FS_NAME_MAX_LENGTH )
+    return luaL_error(L, "filename too long");
+
+  spiffs_stat stat;
+  int rc = SPIFFS_stat(&fs, (char *)fname, &stat);
+
+  lua_pushboolean(L, (rc == SPIFFS_OK ? 1 : 0));
+
+  return 1;
+}
+
 // Lua: remove(filename)
 static int file_remove( lua_State* L )
 {
@@ -312,6 +328,7 @@ static const LUA_REG_TYPE file_map[] = {
 //{ LSTRKEY( "check" ),     LFUNCVAL( file_check ) },
   { LSTRKEY( "rename" ),    LFUNCVAL( file_rename ) },
   { LSTRKEY( "fsinfo" ),    LFUNCVAL( file_fsinfo ) },
+  { LSTRKEY( "exists" ),    LFUNCVAL( file_exists ) },  
 #endif
   { LNILKEY, LNILVAL }
 };

docs/en/modules/file.md

@@ -28,6 +28,34 @@ file.close()
 #### See also
 [`file.open()`](#fileopen)
 
+## file.exists()
+
+Determines whether the specified file exists.
+
+#### Syntax
+`file.exists(filename)`
+
+#### Parameters
+- `filename` file to check
+
+#### Returns
+true of the file exists (even if 0 bytes in size), and false if it does not exist
+
+#### Example
+
+```lua
+files = file.list()
+if files["device.config"] then
+    print("Config file exists")
+end
+
+if file.exists("device.config") then
+    print("Config file exists")
+end
+```
+#### See also
+[`file.list()`](#filelist)
+
 ## file.flush()
 
 Flushes any pending writes to the file system, ensuring no data is lost on a restart. Closing the open file using [`file.close()`](#fileclose) performs an implicit flush as well.