icinga2-matrix-notification/internal/matrix/message.go

// Copyright Jan Dittberner
// SPDX-License-Identifier: GPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package matrix

import (
	"bytes"
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
)

const transactionIDLength = 16

type Message struct {
	Type          string `json:"msgtype"`
	Body          string `json:"body"`
	FormattedBody string `json:"formatted_body"`
	Format        string `json:"format"`
}

func SendMessage(server *url.URL, room string, token string, message string) error {
	messageBytes, err := json.Marshal(Message{
		Type:          TextMessage,
		Body:          message,
		FormattedBody: message,
		Format:        HTMLFormat,
	})
	if err != nil {
		return fmt.Errorf("could not build JSON message: %w", err)
	}

	transaction, err := generateTransactionID()
	if err != nil {
		return err
	}

	postURL := server.JoinPath("/_matrix/client/r0/rooms/", room, "/send/m.room.message/", transaction)

	request, err := http.NewRequest(http.MethodPut, postURL.String(), bytes.NewBuffer(messageBytes))
	if err != nil {
		return fmt.Errorf("could not build request: %w", err)
	}

	request.Header.Set("Accept", "application/json")
	request.Header.Set("Content-Type", "application/json")
	request.Header.Set("Authorization", "Bearer "+token)

	response, err := http.DefaultClient.Do(request)
	if err != nil {
		return fmt.Errorf("could not send request: %w", err)
	}

	defer func() {
		_ = response.Body.Close()
	}()

	if response.StatusCode > http.StatusBadRequest {
		responseBody, err := io.ReadAll(response.Body)
		if err != nil {
			return fmt.Errorf("received an error: %s, could not read response body: %w", response.Status, err)
		}

		return fmt.Errorf("received an error: %s %s", response.Status, string(responseBody))
	}

	return nil
}

func generateTransactionID() (string, error) {
	IDBytes := make([]byte, transactionIDLength)

	_, err := rand.Read(IDBytes)
	if err != nil {
		return "", fmt.Errorf("could not generate transaction id: %w", err)
	}

	return base64.RawURLEncoding.EncodeToString(IDBytes), nil
}