feat: support monitoring WebSocket endpoints (#511)

* feat: support monitoring WebSocket endpoints

WebSocket endpoints are automatically identified by the URL protocol
specification: `wss://` or `ws://`. The request body is used as the
"message" written to the server, and the answer is stored in the
`[BODY]`.

Optionally, the user can set the `jsonrpc` flag to automatically wrap
the request body in a JSON RPC 2.0 method call.

* core:websocket: close connection after using it

* test: add tests related to WebSocket support

- test we can identify the endpoint type for WebSockets based on the URL
  supplied: `wss://` (with SSL/TLS) and `ws://` (plain text).
- test we can generate a JsonRPC 2.0 message via the new endpoint flag
  `JsonRPC`.

* core:endpoint: fix name of jsonrpc parameter

See https://en.wikipedia.org/wiki/JSON-RPC#Version_2.0

* core:websocket: fix dangling open connection on error

Move the `defer ws.Close()` to after opening the connection, so the
socket is closed also in case of errors.

* remove jsonrpc flag

* core:websocket: fix nil pointer dereference

The connection should only be closed if successfully opened.

* Move websocket function to client

* update go.mod

* Fix build errors

* Fix errors

* Update client/client.go

---------

Co-authored-by: TwiN <twin@linux.com>

core/endpoint.go

@@ -42,6 +42,7 @@ const (
 	EndpointTypeSTARTTLS EndpointType = "STARTTLS"
 	EndpointTypeTLS      EndpointType = "TLS"
 	EndpointTypeHTTP     EndpointType = "HTTP"
+	EndpointTypeWS       EndpointType = "WEBSOCKET"
 	EndpointTypeUNKNOWN  EndpointType = "UNKNOWN"
 )
 
@@ -149,6 +150,8 @@ func (endpoint Endpoint) Type() EndpointType {
 		return EndpointTypeTLS
 	case strings.HasPrefix(endpoint.URL, "http://") || strings.HasPrefix(endpoint.URL, "https://"):
 		return EndpointTypeHTTP
+	case strings.HasPrefix(endpoint.URL, "ws://") || strings.HasPrefix(endpoint.URL, "wss://"):
+		return EndpointTypeWS
 	default:
 		return EndpointTypeUNKNOWN
 	}
@@ -340,6 +343,9 @@ func (endpoint *Endpoint) call(result *Result) {
 		result.Duration = time.Since(startTime)
 	} else if endpointType == EndpointTypeICMP {
 		result.Connected, result.Duration = client.Ping(strings.TrimPrefix(endpoint.URL, "icmp://"), endpoint.ClientConfig)
+	} else if endpointType == EndpointTypeWS {
+		result.Connected, result.Body, err = client.QueryWebSocket(endpoint.URL, endpoint.ClientConfig, endpoint.Body)
+		result.Duration = time.Since(startTime)
 	} else {
 		response, err = client.GetHTTPClient(endpoint.ClientConfig).Do(request)
 		result.Duration = time.Since(startTime)

core/endpoint_test.go

@@ -313,6 +313,18 @@ func TestEndpoint_Type(t *testing.T) {
 			},
 			want: EndpointTypeHTTP,
 		},
+		{
+			args: args{
+				URL: "wss://example.com/",
+			},
+			want: EndpointTypeWS,
+		},
+		{
+			args: args{
+				URL: "ws://example.com/",
+			},
+			want: EndpointTypeWS,
+		},
 		{
 			args: args{
 				URL: "invalid://example.org",