tools: websocket: Add connection set up / tear down

This was validated by sniffing the communication with Wireshark. The
following is executed:

- TCP initial handshake
- GET /rpc from tool
- HTTP 101 Switching Protocols (to Websocket) from Shelly
- ACK by tool
- TCP connection close initiated by tool

This shows that the tool is able to make Websocket connections.

1 files changed, 40 insertions, 2 deletions

diff --git a/tools/websocket.go b/tools/websocket.go
index e429a6d..575bcd5 100644
--- a/tools/websocket.go
+++ b/tools/websocket.go
@@ -1,9 +1,47 @@
+// Websocket debug tool
+//
+// Usage: ./websocket-linux-amd64 ws://<shelly-ip>/rpc
+//
+// This tools is intended to support development of the Websocket-based
+// application programming interface (API) of the Shelly Internet of Things
+// (IoT) devices.
+
 package main
 
 import (
-	"fmt"
+	"log"
+	"net/url"
+	"os"
+	"os/signal"
+
+	"github.com/gorilla/websocket"
 )
 
 func main() {
-	fmt.Println("Websockets are cool.")
+	log.SetFlags(0)
+
+	interrupt := make(chan os.Signal, 1)
+	signal.Notify(interrupt, os.Interrupt)
+
+	var u url.URL = getURL()
+	log.Printf("connecting to %s", u.String())
+
+	c, _, err := websocket.DefaultDialer.Dial(u.String(), nil)
+	if (err != nil) {
+		log.Fatal(err)
+	}
+	defer c.Close()
+}
+
+func getURL() url.URL {
+	if (len(os.Args) != 2) {
+		log.Fatalf("Exactly one argument expected but got %d.", len(os.Args) - 1)
+	}
+
+	maybeURL, err := url.Parse(os.Args[1])
+	if (err != nil) {
+		log.Fatalf("Cannot parse given URL: %s", os.Args[1])
+	}
+
+	return *maybeURL
 }