Send requests to different servers using round-robin

.gitignore

@@ -1,3 +1,4 @@
 result
 vrnp
+main
 *.swp

main.go

@@ -8,7 +8,9 @@ import "net/http"
 import "net/url"
 import "os"
 import "slices"
+import "strings"
 import "strconv"
+import "sync/atomic"
 import "time"
 
 // JSON unmarshaling types for departure monitor API
@@ -43,11 +45,23 @@ type DMDateTime struct {
 	Minute string `json:"minute"`
 }
 
-func FetchDepartures(stopId string) (DMResponse, error) {
+type EFAClient interface {
+	GetName() string
+	BuildRequest(string) (*http.Request, error)
+}
+
+type VRNEFAClient struct {
+}
+
+func (c VRNEFAClient) GetName() string {
+	return "VRN"
+}
+
+func (c VRNEFAClient) BuildRequest(stopId string) (*http.Request, error) {
 	// Create request object
 	req, err := http.NewRequest("GET", "https://www.vrn.de/mngvrn/XML_DM_REQUEST", nil)
 	if err != nil {
-		return DMResponse{}, err
+		return nil, err
 	}
 
 	// Configure our request
@@ -65,6 +79,44 @@ func FetchDepartures(stopId string) (DMResponse, error) {
 	query.Set("useRealtime", "1")
 	req.URL.RawQuery = query.Encode()
 
+	return req, nil
+}
+
+type KVVEFAClient struct {
+}
+
+func (c KVVEFAClient) GetName() string {
+	return "KVV"
+}
+
+func (c KVVEFAClient) BuildRequest(stopId string) (*http.Request, error) {
+	form := url.Values{}
+	form.Set("action", "XSLT_DM_REQUEST")
+	form.Set("name_dm", stopId)
+	form.Set("type_dm", "stop")
+	form.Set("useRealtime", "1")
+	form.Set("limit", "10")
+	form.Set("mode", "direct")
+	form.Set("outputFormat", "json")
+	body := strings.NewReader(form.Encode())
+
+	req, err := http.NewRequest("POST", "https://www.kvv.de/tunnelEfaDirect.php", body)
+	if err != nil {
+		return nil, err
+	}
+
+	req.Header.Set("User-Agent", "coolio/1.0")
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	return req, nil
+}
+
+func FetchDepartures(c EFAClient, stopId string) (DMResponse, error) {
+	req, err := c.BuildRequest(stopId)
+	if err != nil {
+		return DMResponse{}, err
+	}
+
 	// Send the request, wait max 10 seconds
 	client := http.Client{
 		Timeout: 10 * time.Second,
@@ -151,6 +203,13 @@ func main() {
 		panic("Required environment variable VRNP_PASSWORD is not set")
 	}
 
+	// Use round-robin to send incoming requests to different servers
+	var efaClient atomic.Uint64
+	efaClients := []EFAClient{
+		VRNEFAClient{},
+		KVVEFAClient{},
+	}
+
 	http.HandleFunc("/departures", func(w http.ResponseWriter, r *http.Request) {
 		user, pass, ok := r.BasicAuth()
 		if !(ok && user == "admin" && pass == password) {
@@ -172,7 +231,8 @@ func main() {
 			platform = &query["platform"][0]
 		}
 
-		ds, err := FetchDepartures(stopId)
+		c := efaClients[(efaClient.Add(1) - 1) % uint64(len(efaClients))]
+		ds, err := FetchDepartures(c, stopId)
 		if err != nil {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return