feat: Add body to TCP, UDP, and TLS endpoints and templating (#1134)

* feat(endpoints): Add body to TCP, UDP, and TLS endpoints and templating

* Changed the template to be more consistent with the
rest of the application and added additional substritutions.

* Changed getModifiedBody to getParsedBody and fixed connected response

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Apply suggestion from @TwiN

* Update client/client.go

---------

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

README.md

@@ -288,6 +288,13 @@ You can then configure alerts to be triggered when an endpoint is unhealthy once
 | `endpoints[].ui.dont-resolve-failed-conditions` | Whether to resolve failed conditions for the UI.                                                                                            | `false`                    |
 | `endpoints[].ui.badge.response-time`            | List of response time thresholds. Each time a threshold is reached, the badge has a different color.                                        | `[50, 200, 300, 500, 750]` |
 
+You may use the following placeholders in the body (`endpoints[].body`):
+- `[ENDPOINT_NAME]` (resolved from `endpoints[].name`)
+- `[ENDPOINT_GROUP]` (resolved from `endpoints[].group`)
+- `[ENDPOINT_URL]` (resolved from `endpoints[].url`)
+- `[LOCAL_ADDRESS]` (resolves to the local IP and port like `192.0.2.1:25` or `[2001:db8::1]:80`)
+- `[RANDOM_STRING_N]` (resolves to a random string of numbers and letters of length N)
+
 
 ### External Endpoints
 Unlike regular endpoints, external endpoints are not monitored by Gatus, but they are instead pushed programmatically.
@@ -2125,8 +2132,9 @@ endpoints:
     conditions:
       - "[CONNECTED] == true"
 ```
+If `endpoints[].body` is set then it is sent and the first 1024 bytes of the response will be in `[BODY]`.
 
-Placeholders `[STATUS]` and `[BODY]` as well as the fields `endpoints[].body`, `endpoints[].headers`,
+Placeholder `[STATUS]` as well as the fields `endpoints[].headers`,
 `endpoints[].method` and `endpoints[].graphql` are not supported for TCP endpoints.
 
 This works for applications such as databases (Postgres, MySQL, etc.) and caches (Redis, Memcached, etc.).
@@ -2146,7 +2154,9 @@ endpoints:
       - "[CONNECTED] == true"
 ```
 
-Placeholders `[STATUS]` and `[BODY]` as well as the fields `endpoints[].body`, `endpoints[].headers`,
+If `endpoints[].body` is set then it is sent and the first 1024 bytes of the response will be in `[BODY]`.
+
+Placeholder `[STATUS]` as well as the fields `endpoints[].headers`,
 `endpoints[].method` and `endpoints[].graphql` are not supported for UDP endpoints.
 
 This works for UDP based application.
@@ -2181,7 +2191,8 @@ endpoints:
 ```
 
 The `[BODY]` placeholder contains the output of the query, and `[CONNECTED]`
-shows whether the connection was successfully established.
+shows whether the connection was successfully established. You can use Go template 
+syntax. The functions LocalAddr and RandomString with a length can be used.
 
 
 ### Monitoring an endpoint using ICMP
@@ -2293,6 +2304,11 @@ endpoints:
       - "[CERTIFICATE_EXPIRATION] > 48h"
 ```
 
+If `endpoints[].body` is set then it is sent and the first 1024 bytes of the response will be in `[BODY]`.
+
+Placeholder `[STATUS]` as well as the fields `endpoints[].headers`,
+`endpoints[].method` and `endpoints[].graphql` are not supported for TLS endpoints.
+
 
 ### Monitoring domain expiration
 You can monitor the expiration of a domain with all endpoint types except for DNS by using the `[DOMAIN_EXPIRATION]`

client/client.go

@@ -76,24 +76,37 @@ func GetDomainExpiration(hostname string) (domainExpiration time.Duration, err e
 	return domainExpiration, nil
 }
 
-// CanCreateTCPConnection checks whether a connection can be established with a TCP endpoint
+// parseLocalAddressPlaceholder returns a string with the local address replaced
-func CanCreateTCPConnection(address string, config *Config) bool {
+func parseLocalAddressPlaceholder(item string, localAddr net.Addr) string {
-	conn, err := net.DialTimeout("tcp", address, config.Timeout)
+	item = strings.ReplaceAll(item, "[LOCAL_ADDRESS]", localAddr.String())
-	if err != nil {
+	return item
-		return false
-	}
-	_ = conn.Close()
-	return true
 }
 
-// CanCreateUDPConnection checks whether a connection can be established with a UDP endpoint
+// CanCreateNetworkConnection checks whether a connection can be established with a TCP or UDP endpoint
-func CanCreateUDPConnection(address string, config *Config) bool {
+func CanCreateNetworkConnection(netType string, address string, body string, config *Config) (bool, []byte) {
-	conn, err := net.DialTimeout("udp", address, config.Timeout)
+	const (
+		MaximumMessageSize = 1024 // in bytes
+	)
+	connection, err := net.DialTimeout(netType, address, config.Timeout)
 	if err != nil {
-		return false
+		return false, nil
 	}
-	_ = conn.Close()
+	defer connection.Close()
-	return true
+	if body != "" {
+		body = parseLocalAddressPlaceholder(body, connection.LocalAddr())
+		connection.SetDeadline(time.Now().Add(config.Timeout))
+		_, err = connection.Write([]byte(body))
+		if err != nil {
+			return false, nil
+		}
+		buf := make([]byte, MaximumMessageSize)
+		n, err := connection.Read(buf)
+		if err != nil {
+			return false, nil
+		}
+		return true, buf[:n]
+	}
+	return true, nil
 }
 
 // CanCreateSCTPConnection checks whether a connection can be established with a SCTP endpoint
@@ -152,7 +165,10 @@ func CanPerformStartTLS(address string, config *Config) (connected bool, certifi
 }
 
 // CanPerformTLS checks whether a connection can be established to an address using the TLS protocol
-func CanPerformTLS(address string, config *Config) (connected bool, certificate *x509.Certificate, err error) {
+func CanPerformTLS(address string, body string, config *Config) (connected bool, response []byte, certificate *x509.Certificate, err error) {
+	const (
+		MaximumMessageSize = 1024 // in bytes
+	)
 	connection, err := tls.DialWithDialer(&net.Dialer{Timeout: config.Timeout}, "tcp", address, &tls.Config{
 		InsecureSkipVerify: config.Insecure,
 	})
@@ -166,9 +182,27 @@ func CanPerformTLS(address string, config *Config) (connected bool, certificate
 	// Reference: https://pkg.go.dev/crypto/tls#PeerCertificates
 	if len(verifiedChains) == 0 || len(verifiedChains[0]) == 0 {
 		peerCertificates := connection.ConnectionState().PeerCertificates
-		return true, peerCertificates[0], nil
+		certificate = peerCertificates[0]
+	} else {
+		certificate = verifiedChains[0][0]
 	}
-	return true, verifiedChains[0][0], nil
+	connected = true
+	if body != "" {
+		body = parseLocalAddressPlaceholder(body, connection.LocalAddr())
+		connection.SetDeadline(time.Now().Add(config.Timeout))
+		_, err = connection.Write([]byte(body))
+		if err != nil {
+			return
+		}
+		buf := make([]byte, MaximumMessageSize)
+		var n int
+		n, err = connection.Read(buf)
+		if err != nil {
+			return
+		}
+		response = buf[:n]
+	}
+	return
 }
 
 // CanCreateSSHConnection checks whether a connection can be established and a command can be executed to an address
@@ -234,6 +268,7 @@ func ExecuteSSHCommand(sshClient *ssh.Client, body string, config *Config) (bool
 	}
 	defer sshClient.Close()
 	var b Body
+	body = parseLocalAddressPlaceholder(body, sshClient.Conn.LocalAddr())
 	if err := json.Unmarshal([]byte(body), &b); err != nil {
 		return false, 0, err
 	}
@@ -304,6 +339,7 @@ func QueryWebSocket(address, body string, config *Config) (bool, []byte, error)
 		return false, nil, fmt.Errorf("error dialing websocket: %w", err)
 	}
 	defer ws.Close()
+	body = parseLocalAddressPlaceholder(body, ws.LocalAddr())
 	// Write message
 	if _, err := ws.Write([]byte(body)); err != nil {
 		return false, nil, fmt.Errorf("error writing websocket body: %w", err)

client/client_test.go

@@ -223,7 +223,7 @@ func TestCanPerformTLS(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
-			connected, _, err := CanPerformTLS(tt.args.address, &Config{Insecure: tt.args.insecure, Timeout: 5 * time.Second})
+			connected, _, _, err := CanPerformTLS(tt.args.address, "", &Config{Insecure: tt.args.insecure, Timeout: 5 * time.Second})
 			if (err != nil) != tt.wantErr {
 				t.Errorf("CanPerformTLS() err=%v, wantErr=%v", err, tt.wantErr)
 				return
@@ -235,11 +235,13 @@ func TestCanPerformTLS(t *testing.T) {
 	}
 }
 
-func TestCanCreateTCPConnection(t *testing.T) {
+func TestCanCreateConnection(t *testing.T) {
-	if CanCreateTCPConnection("127.0.0.1", &Config{Timeout: 5 * time.Second}) {
+	connected, _ := CanCreateNetworkConnection("tcp", "127.0.0.1", "", &Config{Timeout: 5 * time.Second})
+	if connected {
 		t.Error("should've failed, because there's no port in the address")
 	}
-	if !CanCreateTCPConnection("1.1.1.1:53", &Config{Timeout: 5 * time.Second}) {
+	connected, _ = CanCreateNetworkConnection("tcp", "1.1.1.1:53", "", &Config{Timeout: 5 * time.Second})
+	if !connected {
 		t.Error("should've succeeded, because that IP should always™ be up")
 	}
 }

config/connectivity/connectivity.go

@@ -42,7 +42,8 @@ type Checker struct {
 }
 
 func (c *Checker) Check() bool {
-	return client.CanCreateTCPConnection(c.Target, &client.Config{Timeout: 5 * time.Second})
+	connected, _ := client.CanCreateNetworkConnection("tcp", c.Target, "", &client.Config{Timeout: 5 * time.Second})
+	return connected
 }
 
 func (c *Checker) IsConnected() bool {

config/endpoint/endpoint.go

@@ -7,9 +7,12 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math/rand"
 	"net"
 	"net/http"
 	"net/url"
+	"regexp"
+	"strconv"
 	"strings"
 	"time"
 
@@ -229,7 +232,7 @@ func (e *Endpoint) ValidateAndSetDefaults() error {
 		}
 	}
 	// Make sure that the request can be created
-	_, err := http.NewRequest(e.Method, e.URL, bytes.NewBuffer([]byte(e.Body)))
+	_, err := http.NewRequest(e.Method, e.URL, bytes.NewBuffer([]byte(e.getParsedBody())))
 	if err != nil {
 		return err
 	}
@@ -326,6 +329,26 @@ func (e *Endpoint) EvaluateHealth() *Result {
 	return result
 }
 
+func (e *Endpoint) getParsedBody() string {
+	body := e.Body
+	body = strings.ReplaceAll(body, "[ENDPOINT_NAME]", e.Name)
+	body = strings.ReplaceAll(body, "[ENDPOINT_GROUP]", e.Group)
+	body = strings.ReplaceAll(body, "[ENDPOINT_URL]", e.URL)
+	randRegex, err := regexp.Compile(`\[RANDOM_STRING_\d+\]`)
+	if err == nil {
+		body = randRegex.ReplaceAllStringFunc(body, func(match string) string {
+			n, _ := strconv.Atoi(match[15 : len(match)-1])
+			const availableCharacterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+			b := make([]byte, n)
+			for i := range b {
+				b[i] = availableCharacterBytes[rand.Intn(len(availableCharacterBytes))]
+			}
+			return string(b)
+		})
+	}
+	return body
+}
+
 func (e *Endpoint) getIP(result *Result) {
 	if ips, err := net.LookupIP(result.Hostname); err != nil {
 		result.AddError(err.Error())
@@ -356,7 +379,7 @@ func (e *Endpoint) call(result *Result) {
 		if endpointType == TypeSTARTTLS {
 			result.Connected, certificate, err = client.CanPerformStartTLS(strings.TrimPrefix(e.URL, "starttls://"), e.ClientConfig)
 		} else {
-			result.Connected, certificate, err = client.CanPerformTLS(strings.TrimPrefix(e.URL, "tls://"), e.ClientConfig)
+			result.Connected, result.Body, certificate, err = client.CanPerformTLS(strings.TrimPrefix(e.URL, "tls://"), e.getParsedBody(), e.ClientConfig)
 		}
 		if err != nil {
 			result.AddError(err.Error())
@@ -365,10 +388,10 @@ func (e *Endpoint) call(result *Result) {
 		result.Duration = time.Since(startTime)
 		result.CertificateExpiration = time.Until(certificate.NotAfter)
 	} else if endpointType == TypeTCP {
-		result.Connected = client.CanCreateTCPConnection(strings.TrimPrefix(e.URL, "tcp://"), e.ClientConfig)
+		result.Connected, result.Body = client.CanCreateNetworkConnection("tcp", strings.TrimPrefix(e.URL, "tcp://"), e.getParsedBody(), e.ClientConfig)
 		result.Duration = time.Since(startTime)
 	} else if endpointType == TypeUDP {
-		result.Connected = client.CanCreateUDPConnection(strings.TrimPrefix(e.URL, "udp://"), e.ClientConfig)
+		result.Connected, result.Body = client.CanCreateNetworkConnection("udp", strings.TrimPrefix(e.URL, "udp://"), e.getParsedBody(), e.ClientConfig)
 		result.Duration = time.Since(startTime)
 	} else if endpointType == TypeSCTP {
 		result.Connected = client.CanCreateSCTPConnection(strings.TrimPrefix(e.URL, "sctp://"), e.ClientConfig)
@@ -376,7 +399,7 @@ func (e *Endpoint) call(result *Result) {
 	} else if endpointType == TypeICMP {
 		result.Connected, result.Duration = client.Ping(strings.TrimPrefix(e.URL, "icmp://"), e.ClientConfig)
 	} else if endpointType == TypeWS {
-		result.Connected, result.Body, err = client.QueryWebSocket(e.URL, e.Body, e.ClientConfig)
+		result.Connected, result.Body, err = client.QueryWebSocket(e.URL, e.getParsedBody(), e.ClientConfig)
 		if err != nil {
 			result.AddError(err.Error())
 			return
@@ -401,7 +424,7 @@ func (e *Endpoint) call(result *Result) {
 			result.AddError(err.Error())
 			return
 		}
-		result.Success, result.HTTPStatus, err = client.ExecuteSSHCommand(cli, e.Body, e.ClientConfig)
+		result.Success, result.HTTPStatus, err = client.ExecuteSSHCommand(cli, e.getParsedBody(), e.ClientConfig)
 		if err != nil {
 			result.AddError(err.Error())
 			return
@@ -435,12 +458,12 @@ func (e *Endpoint) buildHTTPRequest() *http.Request {
 	var bodyBuffer *bytes.Buffer
 	if e.GraphQL {
 		graphQlBody := map[string]string{
-			"query": e.Body,
+			"query": e.getParsedBody(),
 		}
 		body, _ := json.Marshal(graphQlBody)
 		bodyBuffer = bytes.NewBuffer(body)
 	} else {
-		bodyBuffer = bytes.NewBuffer([]byte(e.Body))
+		bodyBuffer = bytes.NewBuffer([]byte(e.getParsedBody()))
 	}
 	request, _ := http.NewRequest(e.Method, e.URL, bodyBuffer)
 	for k, v := range e.Headers {