feat(ssh): Support authless SSH health check (#956)

* Feature + Test +  Documentation: added no-auth ssh health cheack feature, changed documentation to fit new behavior, added ssh test cases.

* Refactor: refactored authenticate field to infer from username and password insted of specifying it inside config.

* Refactor: removed non used field.

* Refactor: changed error, removed spaces.

* Refactor: added comments.

README.md

@@ -2058,6 +2058,23 @@ endpoints:
       - "[STATUS] == 0"
 ```
 
+you can also use no authentication to monitor the endpoint by not specifying the username
+and password fields.
+
+```yaml
+endpoints:
+  - name: ssh-example
+    url: "ssh://example.com:22" # port is optional. Default is 22.
+    ssh:
+      username: ""
+      password: ""
+
+    interval: 1m
+    conditions:
+      - "[CONNECTED] == true"
+      - "[STATUS] == 0"
+```
+
 The following placeholders are supported for endpoints of type SSH:
 - `[CONNECTED]` resolves to `true` if the SSH connection was successful, `false` otherwise
 - `[STATUS]` resolves the exit code of the command executed on the remote server (e.g. `0` for success)

client/client.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"net"
 	"net/http"
 	"net/smtp"
@@ -197,6 +198,34 @@ func CanCreateSSHConnection(address, username, password string, config *Config)
 	return true, cli, nil
 }
 
+func CheckSSHBanner(address string, cfg *Config) (bool, int, error) {
+	var port string
+	if strings.Contains(address, ":") {
+		addressAndPort := strings.Split(address, ":")
+		if len(addressAndPort) != 2 {
+			return false, 1, errors.New("invalid address for ssh, format must be ssh://host:port")
+		}
+		address = addressAndPort[0]
+		port = addressAndPort[1]
+	} else {
+		port = "22"
+	}
+	dialer := net.Dialer{}
+	connStr := net.JoinHostPort(address, port)
+	conn, err := dialer.Dial("tcp", connStr)
+	if err != nil {
+		return false, 1, err
+	}
+	defer conn.Close()
+	conn.SetReadDeadline(time.Now().Add(time.Second))
+	buf := make([]byte, 256)
+	_, err = io.ReadAtLeast(conn, buf, 1)
+	if err != nil {
+		return false, 1, err
+	}
+	return true, 0, err
+}
+
 // ExecuteSSHCommand executes a command to an address using the SSH protocol.
 func ExecuteSSHCommand(sshClient *ssh.Client, body string, config *Config) (bool, int, error) {
 	type Body struct {

client/client_test.go

@@ -474,3 +474,38 @@ func TestQueryDNS(t *testing.T) {
 		time.Sleep(10 * time.Millisecond)
 	}
 }
+
+func TestCheckSSHBanner(t *testing.T) {
+	cfg := &Config{Timeout: 3}
+
+	t.Run("no-auth-ssh", func(t *testing.T) {
+		connected, status, err := CheckSSHBanner("tty.sdf.org", cfg)
+
+		if err != nil {
+			t.Errorf("Expected: error != nil, got: %v ", err)
+		}
+
+		if connected == false {
+			t.Errorf("Expected: connected == true, got: %v", connected)
+		}
+		if status != 0 {
+			t.Errorf("Expected: 0, got: %v", status)
+		}
+	})
+
+	t.Run("invalid-address", func(t *testing.T) {
+		connected, status, err := CheckSSHBanner("idontplaytheodds.com", cfg)
+
+		if err == nil {
+			t.Errorf("Expected: error, got: %v ", err)
+		}
+
+		if connected != false {
+			t.Errorf("Expected: connected == false, got: %v", connected)
+		}
+		if status != 1 {
+			t.Errorf("Expected: 1, got: %v", status)
+		}
+	})
+
+}

config/endpoint/endpoint.go

@@ -363,6 +363,18 @@ func (e *Endpoint) call(result *Result) {
 		}
 		result.Duration = time.Since(startTime)
 	} else if endpointType == TypeSSH {
+		// If there's no username/password specified, attempt to validate just the SSH banner
+		if len(e.SSHConfig.Username) == 0 && len(e.SSHConfig.Password) == 0 {
+			result.Connected, result.HTTPStatus, err =
+				client.CheckSSHBanner(strings.TrimPrefix(e.URL, "ssh://"), e.ClientConfig)
+			if err != nil {
+				result.AddError(err.Error())
+				return
+			}
+			result.Success = result.Connected
+			result.Duration = time.Since(startTime)
+			return
+		}
 		var cli *ssh.Client
 		result.Connected, cli, err = client.CanCreateSSHConnection(strings.TrimPrefix(e.URL, "ssh://"), e.SSHConfig.Username, e.SSHConfig.Password, e.ClientConfig)
 		if err != nil {

config/endpoint/ssh/ssh.go

@@ -19,6 +19,10 @@ type Config struct {
 
 // Validate the SSH configuration
 func (cfg *Config) Validate() error {
+	// If there's no username and password, this endpoint can still check the SSH banner, so the endpoint is still valid
+	if len(cfg.Username) == 0 && len(cfg.Password) == 0 {
+		return nil
+	}
 	if len(cfg.Username) == 0 {
 		return ErrEndpointWithoutSSHUsername
 	}

config/endpoint/ssh/ssh_test.go

@@ -7,10 +7,8 @@ import (
 
 func TestSSH_validate(t *testing.T) {
 	cfg := &Config{}
-	if err := cfg.Validate(); err == nil {
-		t.Error("expected an error")
-	} else if !errors.Is(err, ErrEndpointWithoutSSHUsername) {
-		t.Errorf("expected error to be '%v', got '%v'", ErrEndpointWithoutSSHUsername, err)
+	if err := cfg.Validate(); err != nil {
+		t.Error("didn't expect an error")
 	}
 	cfg.Username = "username"
 	if err := cfg.Validate(); err == nil {