a command that (partially works and) downloads mxc media

commands.go

package connector

import (
	"encoding/base64"
	"encoding/json"
	"fmt"
	"log"
	"net/url"
	"os"
	"strings"

	"maunium.net/go/mautrix/bridgev2/commands"
	"maunium.net/go/mautrix/event"
	"maunium.net/go/mautrix/id"
)

var cmdDownload = &commands.FullHandler{
	Func: fnDownload,
	Name: "download",
	Help: commands.HelpMeta{
		Description: "download media",
		Args:        "<_mxc-url_>",
	},
}

func fnDownload(ce *commands.Event) {
	if len(ce.Args) == 0 {
		ce.Reply("Usage: `$cmdprefix download <mxc url>`")
		return
	}
	uri := ce.Args[0]

	parsedUrl, err := url.Parse(uri)
	if err != nil {
		log.Printf("Failed to parse URL: %v", err)
		return
	}

	queryParams := parsedUrl.Query()

	// Get specific query parameter by key
	fileInfoJSONB64 := queryParams.Get("encryptedFileInfoJSON")

	if len(fileInfoJSONB64)%4 != 0 {
		fileInfoJSONB64 += strings.Repeat("=", 4-(len(fileInfoJSONB64)%4))
	}

	fileInfoJSON, err := base64.URLEncoding.DecodeString(fileInfoJSONB64)

	if err != nil {
		log.Printf("Failed to turn b64url to json: %v", err)
		return
	}

	encryptedFile := event.EncryptedFileInfo{}
	err = json.Unmarshal(fileInfoJSON, &encryptedFile)
	if err != nil {
		log.Printf("Failed to parse encrypted file info: %v", err)
		return
	}

	parsedUrl.RawQuery = ""

	err = ce.Bridge.Bot.DownloadMediaToFile(ce.Ctx, id.ContentURIString(parsedUrl.String()), &encryptedFile, true, func(file *os.File) error {
		ce.Reply(fmt.Sprintf("Saved to %v", file.Name()))
		return nil
	})

	if err != nil {
		log.Fatalf("Failed to parse encrypted file info: %v", err)
	}
}