add FastGetCountry func

decoder.go

@@ -895,3 +895,12 @@ func (d *decoder) nextValueOffset(offset, numberToSkip uint) (uint, error) {
 	}
 	return d.nextValueOffset(offset, numberToSkip-1)
 }
+
+// getBuffer for faster way to search data
+func (d *decoder) getBuffer() []byte {
+	return d.buffer
+}
+
+func (d *decoder) DecodeKey(offset uint) ([]byte, uint, error) {
+	return d.decodeKey(offset)
+}

reader.go

@@ -308,3 +308,57 @@ func (r *Reader) resolveDataPointer(pointer uint) (uintptr, error) {
 	}
 	return resolved, nil
 }
+
+// readToLeaf read the tree till leaf node
+func (r *Reader) readToLeaf(offset uint, paths []string) ([]byte, uint, error) {
+	typeNum, size, newOffset, err := r.decoder.decodeCtrlData(offset)
+	if err != nil {
+		return nil, offset, err
+	}
+	if typeNum == _String {
+		newOffset = newOffset + size
+		buf := r.decoder.getBuffer()
+		s := buf[offset+1 : newOffset]
+		return s, newOffset, nil
+	}
+	offset = newOffset
+	if typeNum != _Map {
+		return nil, offset, fmt.Errorf("support map only")
+	}
+	for i := uint(0); i < size; i++ {
+		var key []byte
+		var err error
+		key, offset, err = r.decoder.DecodeKey(offset)
+		if err != nil {
+			return nil, offset, err
+		}
+		if string(key) == paths[0] {
+			return r.readToLeaf(offset, paths[1:])
+		}
+		offset, err = r.decoder.nextValueOffset(offset, 1)
+		if err != nil {
+			return nil, offset, err
+		}
+	}
+	return nil, offset, nil
+}
+
+var countryPaths = []string{"country", "iso_code"}
+
+// FastGetCountry when we need country only, this func is 2.91 times faster than Lookup
+func (r *Reader) FastGetCountry(ip net.IP) ([]byte, error) {
+	if r.buffer == nil {
+		return nil, errors.New("cannot call Lookup on a closed database")
+	}
+	pointer, _, _, err := r.lookupPointer(ip)
+	if pointer == 0 || err != nil {
+		return nil, err
+	}
+	offset, err := r.resolveDataPointer(pointer)
+	if err != nil {
+		return nil, err
+	}
+	var result []byte
+	result, _, err = r.readToLeaf(uint(offset), countryPaths)
+	return result, err
+}

reader_test.go

@@ -875,3 +875,26 @@ func randomIPv4Address(r *rand.Rand, ip []byte) {
 func testFile(file string) string {
 	return filepath.Join("test-data/test-data", file)
 }
+
+func TestGetCountry(t *testing.T) {
+	db := "test-data/test-data"
+	mmdb, err := Open(db)
+	if err != nil {
+		t.Error(err.Error())
+		return
+	}
+	defer mmdb.Close()
+	// 220.255.1.166 singapore
+	// 116.179.33.17  cn
+	ip := net.ParseIP("220.255.1.166")
+	result, err := mmdb.FastGetCountry(ip)
+	if err != nil {
+		t.Error(err.Error())
+		return
+	}
+	if result == nil {
+		t.Error("not found")
+		return
+	}
+	t.Logf("%+v", string(result))
+}