1 files changed, 118 insertions, 0 deletions
diff --git a/hs100.go b/hs100.go
new file mode 100644
index 0000000..c972f8a
--- /dev/null
+++ b/hs100.go
@@ -0,0 +1,118 @@
+// vim: shiftwidth=4 tabstop=4 noexpandtab
+
+package main
+
+import (
+	"context"
+	"encoding/binary"
+	"fmt"
+	"net"
+	"time"
+)
+
+const (
+	MAX_PAYLOAD = 4294967295 // TP-Link WiFi plug protocol: max. 2^32-1 bytes
+)
+
+// Hs100 bundles every data associated with one TP-Link HS100 smart plug.
+type Hs100 struct {
+	Config Hs100Conf
+}
+
+// Hs100Conf is the configuration of one TP-Link HS100 smart plug.
+type Hs100Conf struct {
+	Ip net.IP
+	Name string
+}
+
+// encrypt() encrypts data for a TP-Link WiFi plug.
+func encrypt(data []byte) ([]byte, error) {
+
+	// assert maximum payload size to cast data length safely
+	if len(data) > MAX_PAYLOAD {
+		return []byte{}, fmt.Errorf("Too many bytes to encrypt (%d > %d)!\n",
+			len(data), MAX_PAYLOAD)
+	}
+	length := uint32(len(data))
+
+	// encode payload length as header
+	out := make([]byte, 4) // header buffer
+	binary.BigEndian.PutUint32(out, length)
+
+	// encryption algorithm
+	key := byte(171)
+	for _, value := range data {
+		key = key ^ value
+		out = append(out, byte(key))
+	}
+
+	return out, nil
+}
+
+// decrypt() decrypts data coming from a TP-Link WiFi plug.
+func decrypt(data []byte) []byte {
+
+	// TODO check if length given in header is correct
+
+	// cut-off header
+	data = data[4:]
+
+	// decryption algorithm
+	key := byte(171)
+	for index, value := range data {
+		data[index] = key ^ value
+		key = value
+	}
+
+	return data
+}
+
+// send() sends data via TCP to an address (like "192.168.1.42:9999").
+func send(address string, data []byte) error {
+
+	// create a Dialer with context
+	var d net.Dialer
+	ctx, cancel := context.WithTimeout(context.Background(), 3 * time.Second)
+	defer cancel()
+
+	// establish connection
+	conn, err := d.DialContext(ctx, "tcp", address)
+	if err != nil {
+		return fmt.Errorf("Failed to dial: %v", err)
+	}
+	defer conn.Close()
+
+	// writing data
+	_, err = conn.Write(data)
+	if err != nil {
+		return fmt.Errorf("Could not write data: %v", err)
+	}
+
+	return nil
+
+}
+
+// set() sets the relay state of a TP-Link WiFi plug.
+func set(host string, state string) error {
+
+	cmd := ""
+
+	// modify command according to state
+	if state == "on" {
+		cmd = `{"system":{"set_relay_state":{"state":1}}}`
+	} else if state == "off" {
+		cmd = `{"system":{"set_relay_state":{"state":0}}}`
+	} else {
+		return fmt.Errorf("set() just accepts values 'on' and 'off'!")
+	}
+
+	// format address, encrypt data and send it
+	address := fmt.Sprintf("%s:9999", host)
+	data, err := encrypt([]byte(cmd))
+	if err != nil {
+		return err
+	}
+	err = send(address, data)
+	
+	return err
+}