Introduce Webhook Channel

In its initial form, the webhook channel can be used to send
notifications against a HTTP/HTTPS web server with a dynamic
configurable URL and request body message.

Author: oxzi

cmd/channel/webhook/main.go

@@ -0,0 +1,170 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"github.com/icinga/icinga-notifications/internal"
+	"github.com/icinga/icinga-notifications/pkg/plugin"
+	"io"
+	"net/http"
+	"slices"
+	"strconv"
+	"strings"
+	"text/template"
+)
+
+type Webhook struct {
+	Method              string `json:"method"`
+	URLTemplate         string `json:"url_template"`
+	RequestBodyTemplate string `json:"request_body_template"`
+	ResponseStatusCodes string `json:"response_status_codes"`
+
+	tmplUrl         *template.Template
+	tmplRequestBody *template.Template
+
+	respStatusCodes []int
+}
+
+func (ch *Webhook) GetInfo() *plugin.Info {
+	elements := []*plugin.ConfigOption{
+		{
+			Name: "method",
+			Type: "string",
+			Label: map[string]string{
+				"en_US": "HTTP Method",
+				"de_DE": "HTTP-Methode",
+			},
+			Help: map[string]string{
+				"en_US": "HTTP request method used for the web request.",
+				"de_DE": "HTTP-Methode für die Anfrage.",
+			},
+			Default:  "POST",
+			Required: true,
+		},
+		{
+			Name: "url_template",
+			Type: "string",
+			Label: map[string]string{
+				"en_US": "URL Template",
+				"de_DE": "URL-Template",
+			},
+			Help: map[string]string{
+				"en_US": "URL, optionally as a Go template over the current plugin.NotificationRequest.",
+				"de_DE": "URL, optional als Go-Template über das zu verarbeitende plugin.NotificationRequest.",
+			},
+			Required: true,
+		},
+		{
+			Name: "request_body_template",
+			Type: "string",
+			Label: map[string]string{
+				"en_US": "Request Body Template",
+				"de_DE": "Anfragedaten-Template",
+			},
+			Help: map[string]string{
+				"en_US": "Go template applied to the current plugin.NotificationRequest to create an request body.",
+				"de_DE": "Go-Template über das zu verarbeitende plugin.NotificationRequest zum Erzeugen der mitgesendeten Anfragedaten.",
+			},
+			Default: `{{json .}}`,
+		},
+		{
+			Name: "response_status_codes",
+			Type: "string",
+			Label: map[string]string{
+				"en_US": "Response Status Codes",
+				"de_DE": "Antwort-Status-Codes",
+			},
+			Help: map[string]string{
+				"en_US": "Comma separated list of expected HTTP response status code, e.g., 200,201,202,208,418",
+				"de_DE": "Kommaseparierte Liste erwarteter Status-Code der HTTP-Antwort, z.B.: 200,201,202,208,418",
+			},
+			Default:  "200",
+			Required: true,
+		},
+	}
+
+	configAttrs, err := json.Marshal(elements)
+	if err != nil {
+		panic(err)
+	}
+
+	return &plugin.Info{
+		Name:             "Webhook",
+		Version:          internal.Version.Version,
+		Author:           "Icinga GmbH",
+		ConfigAttributes: configAttrs,
+	}
+}
+
+func (ch *Webhook) SetConfig(jsonStr json.RawMessage) error {
+	err := json.Unmarshal(jsonStr, ch)
+	if err != nil {
+		return err
+	}
+
+	tmplFuncs := template.FuncMap{
+		"json": func(a any) (string, error) {
+			data, err := json.Marshal(a)
+			if err != nil {
+				return "", err
+			}
+			return string(data), nil
+
+		},
+	}
+
+	ch.tmplUrl, err = template.New("url").Funcs(tmplFuncs).Parse(ch.URLTemplate)
+	if err != nil {
+		return fmt.Errorf("cannot parse URL template: %w", err)
+	}
+
+	ch.tmplRequestBody, err = template.New("request_body").Funcs(tmplFuncs).Parse(ch.RequestBodyTemplate)
+	if err != nil {
+		return fmt.Errorf("cannot parse Request Body template: %w", err)
+	}
+
+	respStatusCodes := strings.Split(ch.ResponseStatusCodes, ",")
+	ch.respStatusCodes = make([]int, len(respStatusCodes))
+	for i, respStatusCodeStr := range respStatusCodes {
+		respStatusCode, err := strconv.Atoi(respStatusCodeStr)
+		if err != nil {
+			return fmt.Errorf("cannot convert status code %q to int: %w", respStatusCodeStr, err)
+		}
+		ch.respStatusCodes[i] = respStatusCode
+	}
+
+	return nil
+}
+
+func (ch *Webhook) SendNotification(req *plugin.NotificationRequest) error {
+	var urlBuff, reqBodyBuff bytes.Buffer
+	if err := ch.tmplUrl.Execute(&urlBuff, req); err != nil {
+		return fmt.Errorf("cannot execute URL template: %w", err)
+	}
+	if err := ch.tmplRequestBody.Execute(&reqBodyBuff, req); err != nil {
+		return fmt.Errorf("cannot execute Request Body template: %w", err)
+	}
+
+	httpReq, err := http.NewRequest(ch.Method, urlBuff.String(), &reqBodyBuff)
+	if err != nil {
+		return err
+	}
+	httpResp, err := http.DefaultClient.Do(httpReq)
+	if err != nil {
+		return err
+	}
+	_, _ = io.Copy(io.Discard, httpResp.Body)
+	_ = httpResp.Body.Close()
+
+	if !slices.Contains(ch.respStatusCodes, httpResp.StatusCode) {
+		return fmt.Errorf("unaccepted HTTP response status code %d not in %v",
+			httpResp.StatusCode, ch.respStatusCodes)
+	}
+
+	return nil
+}
+
+func main() {
+	plugin.RunPlugin(&Webhook{})
+}