fix(backupbackingimage): encode URL for NFS backup target with options

And add an unit test case for config.go

ref: longhorn/longhorn 9702

Signed-off-by: James Lu <james.lu@suse.com>

backupbackingimage/config.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/url"
 	"path/filepath"
+	"strings"
 
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
@@ -117,7 +118,11 @@ func getBackingImageBlockPath() string {
 func EncodeBackupBackingImageURL(backingImageName, destURL string) string {
 	v := url.Values{}
 	v.Add("backingImage", backingImageName)
-	return destURL + "?" + v.Encode()
+	prefixChar := "?"
+	if strings.Contains(destURL, "?") {
+		prefixChar = "&"
+	}
+	return destURL + prefixChar + v.Encode()
 }
 
 func DecodeBackupBackingImageURL(backupURL string) (string, string, error) {

backupbackingimage/config_test.go

@@ -0,0 +1,85 @@
+package backupbackingimage
+
+import (
+	"net/url"
+	"testing"
+)
+
+func TestEncodeBackupBackingImageURL(t *testing.T) {
+	tests := []struct {
+		backingImageName string
+		destURL          string
+		expectedURL      string
+	}{
+		{
+			backingImageName: "test-image",
+			destURL:          "http://example.com",
+			expectedURL:      "http://example.com?backingImage=test-image",
+		},
+		{
+			backingImageName: "test-image",
+			destURL:          "http://example.com?param=value",
+			expectedURL:      "http://example.com?param=value&backingImage=test-image",
+		},
+		{
+			backingImageName: "another-image",
+			destURL:          "https://example.org/path",
+			expectedURL:      "https://example.org/path?backingImage=another-image",
+		},
+		{
+			backingImageName: "another-image",
+			destURL:          "https://example.org/path?existing=param",
+			expectedURL:      "https://example.org/path?existing=param&backingImage=another-image",
+		},
+		{
+			backingImageName: "test-image",
+			destURL:          "nfs://longhorn-test-nfs-svc.default:/opt/backupstore",
+			expectedURL:      "nfs://longhorn-test-nfs-svc.default:/opt/backupstore?backingImage=test-image",
+		},
+		{
+			backingImageName: "test-image",
+			destURL:          "nfs://longhorn-test-nfs-svc.default:/opt/backupstore?nfsOptions=soft,timeo=330,retrans=3",
+			expectedURL:      "nfs://longhorn-test-nfs-svc.default:/opt/backupstore?nfsOptions=soft,timeo=330,retrans=3&backingImage=test-image",
+		},
+		{
+			backingImageName: "test image with spaces",
+			destURL:          "nfs://longhorn-test-nfs-svc.default:/opt/backup store",
+			expectedURL:      "nfs://longhorn-test-nfs-svc.default:/opt/backup%20store?backingImage=test%20image%20with%20spaces",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.backingImageName, func(t *testing.T) {
+			result := EncodeBackupBackingImageURL(tt.backingImageName, tt.destURL)
+			// Validate the result is a well-formed URL
+			if _, err := url.Parse(result); err != nil {
+				t.Errorf("Generated URL is not valid: %v", err)
+			}
+			if result != tt.expectedURL {
+				t.Errorf("EncodeBackupBackingImageURL(%s, %s) = %s; want %s", tt.backingImageName, tt.destURL, result, tt.expectedURL)
+			}
+		})
+	}
+}
+
+// Add negative test cases
+func TestEncodeBackupBackingImageURLInvalid(t *testing.T) {
+	tests := []struct {
+		name             string
+		backingImageName string
+		destURL          string
+	}{
+		{"empty backing image", "", "nfs://valid.host:/path"},
+		{"empty dest URL", "image", ""},
+		{"invalid URL", "image", "not-a-url"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := EncodeBackupBackingImageURL(tt.backingImageName, tt.destURL)
+			if result != "" {
+				t.Errorf("Expected empty result for invalid input, got %s", result)
+			}
+		})
+	}
+}