fix(server): panic when passing empty string as ssh key (#736)

internal/e2etests/server/resource_test.go

@@ -916,6 +916,37 @@ func TestServerResource_Protection(t *testing.T) {
 	})
 }
 
+func TestServerResource_EmptySSHKey(t *testing.T) {
+	// Regression Test for https://github.com/hetznercloud/terraform-provider-hcloud/issues/727
+	var srv hcloud.Server
+
+	srvRes := &server.RData{
+		Name:    "server-empty-ssh-key",
+		Type:    e2etests.TestServerType,
+		Image:   e2etests.TestImage,
+		SSHKeys: []string{"\"\""},
+	}
+	srvRes.SetRName("server-empty-ssh-key")
+
+	tmplMan := testtemplate.Manager{}
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:          e2etests.PreCheck(t),
+		ProviderFactories: e2etests.ProviderFactories(),
+		CheckDestroy:      testsupport.CheckResourcesDestroyed(server.ResourceType, server.ByID(t, &srv)),
+		Steps: []resource.TestStep{
+			{
+				// Create a new Server using the required values
+				// only.
+				Config: tmplMan.Render(t,
+					"testdata/r/hcloud_server", srvRes,
+				),
+				ExpectError: regexp.MustCompile("Invalid ssh key passed"),
+			},
+		},
+	})
+}
+
 func isRecreated(new, old *hcloud.Server) func() error {
 	return func() error {
 		if new.ID == old.ID {

internal/server/resource.go

@@ -92,7 +92,15 @@ func Resource() *schema.Resource {
 			"ssh_keys": {
 				Type:     schema.TypeList,
 				Optional: true,
-				Elem:     &schema.Schema{Type: schema.TypeString},
+				Elem: &schema.Schema{Type: schema.TypeString,
+					ValidateDiagFunc: func(i interface{}, _ cty.Path) diag.Diagnostics {
+						s := i.(string)
+						if len(s) == 0 {
+							return diag.Errorf("Invalid ssh key passed. You need to pass a string with at least 1 character")
+						}
+
+						return nil
+					}},
 				ForceNew: true,
 			},
 			"keep_disk": {