replace certificate path with tls.Config instance throughout the server

The example server now reads the certificate and key data itself. Tests
use the new testdata package, where the sample key & cert are stored.

Fixes #24

example/main.go

@@ -1,23 +1,36 @@
 package main
 
 import (
+	"crypto/tls"
+	"crypto/x509"
 	"flag"
+	"io/ioutil"
 	"net/http"
-	"os"
 
 	"github.com/lucas-clemente/quic-go/h2quic"
+	"github.com/lucas-clemente/quic-go/testdata"
 )
 
 func main() {
 	bindTo := flag.String("bind", "localhost", "bind to")
-	certPathDefault := os.Getenv("GOPATH") + "/src/github.com/lucas-clemente/quic-go/example/"
-	certPath := flag.String("certpath", certPathDefault, "certificate directory")
+	certPath := flag.String("certpath", "", "certificate directory")
 	www := flag.String("www", "/var/www", "www data")
 	flag.Parse()
 
+	var tlsConfig *tls.Config
+	if *certPath == "" {
+		tlsConfig = testdata.GetTLSConfig()
+	} else {
+		var err error
+		tlsConfig, err = tlsConfigFromCertpath(*certPath)
+		if err != nil {
+			panic(err)
+		}
+	}
+
 	http.Handle("/", http.FileServer(http.Dir(*www)))
 
-	server, err := h2quic.NewServer(*certPath)
+	server, err := h2quic.NewServer(tlsConfig)
 	if err != nil {
 		panic(err)
 	}
@@ -27,3 +40,26 @@ func main() {
 		panic(err)
 	}
 }
+
+func tlsConfigFromCertpath(certpath string) (*tls.Config, error) {
+	keyDer, err := ioutil.ReadFile(certpath + "/key.der")
+	if err != nil {
+		return nil, err
+	}
+	certDer, err := ioutil.ReadFile(certpath + "/cert.der")
+	if err != nil {
+		return nil, err
+	}
+	key, err := x509.ParsePKCS1PrivateKey(keyDer)
+	if err != nil {
+		return nil, err
+	}
+	return &tls.Config{
+		Certificates: []tls.Certificate{
+			tls.Certificate{
+				Certificate: [][]byte{certDer},
+				PrivateKey:  key,
+			},
+		},
+	}, nil
+}