[Minor] rspamd_text:byte() metamethod

contrib/lua-fun/fun.lua

     if state > #param then
         return nil
     end
-    local r = string.char(param:at(state))
+    local r = string.char(param:byte(state))
     return state, r
 end
 

lualib/lua_content/pdf.lua

           end
           -- Strip the first \n
           while first < last do
-            local chr = input:at(first)
+            local chr = input:byte(first)
             if chr ~= 13 and chr ~= 10 then break end
             first = first + 1
           end

lualib/lua_magic/heuristics.lua

   end
 
   local function process_dir_entry(offset)
-    local dtype = input:at(offset + 66)
+    local dtype = input:byte(offset + 66)
     lua_util.debugm(N, log_obj, "dtype: %s, offset: %s", dtype, offset)
 
     if dtype then

src/lua/lua_text.c

  * @return {rspamd_text} resulting text
  */
 LUA_FUNCTION_DEF (text, fromtable);
+/***
+ * @method rspamd_text:byte(pos[, pos2])
+ * Returns a byte at the position `pos` or bytes from `pos` to `pos2` if specified
+ * @param {integer} pos index
+ * @param {integer} pos2 index
+ * @return {integer} byte at the position `pos` or varargs of bytes
+ */
+LUA_FUNCTION_DEF (text, byte);
 /***
  * @method rspamd_text:len()
  * Returns length of a string
 		LUA_INTERFACE_DEF (text, split),
 		LUA_INTERFACE_DEF (text, at),
 		LUA_INTERFACE_DEF (text, memchr),
+		LUA_INTERFACE_DEF (text, byte),
 		LUA_INTERFACE_DEF (text, bytes),
 		LUA_INTERFACE_DEF (text, lower),
 		LUA_INTERFACE_DEF (text, exclude_chars),
 
 static gint
 lua_text_at (lua_State *L)
+{
+	return lua_text_byte(L);
+}
+
+static gint
+lua_text_byte (lua_State *L)
 {
 	LUA_TRACE_POINT;
 	struct rspamd_lua_text *t = lua_check_text (L, 1);
-	gint pos = lua_tointeger (L, 2);
-
-	if (t) {
-		if (pos > 0 && pos <= t->len) {
-			lua_pushinteger (L, t->start[pos - 1]);
-		}
-		else {
-			lua_pushnil (L);
-		}
-	}
-	else {
+	if (!t) {
 		return luaL_error (L, "invalid arguments");
 	}
 
-	return 1;
+	gsize start = relative_pos_start (luaL_optinteger (L, 2, 1), t->len);
+	gsize end = relative_pos_end (luaL_optinteger (L, 3, start), t->len);
+	start--;
+
+	if (start >= end) {
+		return 0;
+	}
+
+	for (gsize i = start; i < end; i++) {
+		lua_pushinteger (L, t->start[i]);
+	}
+	return end - start;
 }
 
 static gint

test/lua/unit/rspamd_text.lua

+context("Rspamd_text:byte() test", function()
+  local lua_util = require "lua_util"
+  local rspamd_text = require "rspamd_text"
+
+  local str = 'OMG'
+  local txt = rspamd_text.fromstring(str)
+  local fmt = 'case rspamd_text:byte(%s,%s)'
+  local cases = {
+    {'1', 'nil'},
+    {'nil', '1'},
+  }
+
+  for start = -4, 4 do
+    for stop = -4, 4 do
+      table.insert(cases, {tostring(start), tostring(stop)})
+    end
+  end
+
+  for _, case in ipairs(cases) do
+    local name = string.format(fmt, case[1], case[2])
+    test(name, function()
+      local txt_bytes = {txt:byte(tonumber(case[1]), tonumber(case[2]))}
+      local str_bytes = {str:byte(tonumber(case[1]), tonumber(case[2]))}
+      assert_rspamd_table_eq({
+        expect = str_bytes,
+        actual = txt_bytes
+      })
+    end)
+  end
+end)