Added Slack webhook handling

Signed-off-by: Marcus Noble <github@marcusnoble.co.uk>

slack.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+
+	"github.com/gofiber/fiber/v2"
+	"github.com/slack-go/slack"
+	"maunium.net/go/mautrix"
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/format"
+	"maunium.net/go/mautrix/id"
+)
+
+func HandleSlackPayloadPost(c *fiber.Ctx) error {
+	payload := slack.WebhookMessage{}
+	if err := c.BodyParser(&payload); err != nil {
+		fmt.Println("Failed to parse payload", err)
+		return err
+	}
+
+	fmt.Println("Got slack payload")
+
+	s, _ := json.MarshalIndent(payload, "", "\t")
+	fmt.Println(string(s))
+
+	room := payload.Channel
+	if room == "" {
+		room = c.Query("room", *defaultRoom)
+	}
+
+	_, err := matrixClient.SendMessageEvent(
+		id.RoomID(getRoom(room)),
+		event.EventMessage,
+		format.RenderMarkdown(payload.Text, true, true),
+	)
+	if err != nil {
+		fmt.Println("Failed sending to Matrix", err)
+		if httpErr, ok := err.(mautrix.HTTPError); ok {
+			return c.Status(httpErr.Response.StatusCode).SendString(httpErr.RespError.Err)
+		}
+		return fiber.ErrInternalServerError
+	}
+
+	return c.SendStatus(fiber.StatusOK)
+}