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Michael Fomenko
Michael Fomenko

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Developing Send-To-Kindle Telegram Bot

#go #kindle #books

Lately, I've been using the Kindle app on my tablet a lot and it was always a hustle to send my e-books to my tablet. You need to convert to a proper format, transfer it somehow... meh...

So I decided to create a Telegram bot that does all this for you. You send it a book - it appears on your Kindle. Any format supported. That's it - that simple!

I decided to use Go as a language because I wanted to practice it more.

Programmatically converting books to .mobi

It was the main challenge. I did not want to code a converter myself so I started googling other ways to do it. Also, I decided not to go with some online conversion tools with an API as I did not want to rely on them.
So after a while, I stumbled upon the fact that Calibre - popular software for managing e-books - has CLI tools. They had everything, that's perfect!

So I started coding.
The conversion itself looks like this. A simple method that accepts input and output paths for an e-book and passes them to the ebook-convert CLI Tool.

func convert(in, out string) error { cmd := exec.Command("ebook-convert", in, out) if err := cmd.Run(); err != nil { return err } if err := cmd.Wait(); err != nil { return err } if _, err := os.Stat(out); errors.Is(err, os.ErrNotExist) { return errConversion } return nil }
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Telegram integration

Up next was telegram integration. That's easy.

Created bot credentials using BotFather
For integration with Telegram, I found a bot framework for Go - Telebot
The setup was pretty easy:

func (b *SendToKindleBot) Start() error { bot, err := tb.NewBot(tb.Settings{ Token: b.Token, Poller: &tb.LongPoller{Timeout: 10 * time.Second}, }) if err != nil { return ErrStartup } bot.Start() return nil }
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Sending via email

I created an email that my bot would use to send e-books.
Then don't forget to add it to Approved Personal Document Email List in your kindle settings.

And the method itself is pretty simple:

func (b *SendToKindleBot) sendFileViaEmail(path string) error { msg := email.NewMessage("", "") msg.From = mail.Address{Name: "From", Address: b.EmailFrom} msg.To = []string{b.EmailTo} if err := msg.Attach(path); err != nil { return err } auth := smtp.PlainAuth("", b.EmailFrom, b.Password, b.SMTPHost) addr := fmt.Sprintf("%s:%s", b.SMTPHost, b.SMTPPort) if err := email.Send(addr, auth, msg); err != nil { return err } return nil }
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Putting things together

So next I wrote all the insides of the telegram bot with the main thing being - a handler that would receive a file and send it to my kindle.

func (b *SendToKindleBot) documentHandler(bot *tb.Bot) func(msg *tb.Message) { return func(msg *tb.Message) { doc := msg.Document nameParts := strings.Split(doc.FileName, ".") fileNameWithoutExtension := strings.Join(nameParts[:len(nameParts)-1], "") extension := nameParts[len(nameParts)-1] originalFilePath := tmpFilesPath + doc.FileName if err := bot.Download(&doc.File, originalFilePath); err != nil { log.Println("could not download file", err) respond(bot, msg, "Sorry. I could not download file") } defer removeSilently(originalFilePath) fileToSend := originalFilePath if needToConvert(extension) { outputFilePath := tmpFilesPath + fileNameWithoutExtension + ".mobi" if err := convert(originalFilePath, outputFilePath); err != nil { log.Println("could not convert file", err) respond(bot, msg, "Sorry. I could not convert file") } fileToSend = outputFilePath defer removeSilently(outputFilePath) } if err := b.sendFileViaEmail(fileToSend); err != nil { log.Println("could not send file", err) respond(bot, msg, "Sorry. I could not send file") } } }
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And registered it in the bot:

... bot.Handle(tb.OnDocument, b.documentHandler(bot)) ...
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Creating docker container

I wanted to put this app inside a docker container so I can deploy it easily in DigitalOcean and have it running 24/7.
This came to be a bit tricky. Installation of Calibre Tools was not straightforward. Still, after lots of tries, I came up with the following Dockerfile:

FROM amd64/ubuntu COPY --from=golang:1.16.11-bullseye /usr/local/go/ /usr/local/go/ ENV PATH="/usr/local/go/bin:${PATH}" RUN go env -w GOPROXY=direct GOFLAGS="-insecure" ENV TZ=Europe/Minsk RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone RUN apt-get update && \  apt-get upgrade -y && \  apt-get install -y git && \  apt-get install wget && \  apt-get install -y python RUN apt-get install -y ffmpeg libsm6 libxext6 RUN wget -nv -O- https://download.calibre-ebook.com/linux-installer.sh | sh /dev/stdin RUN mkdir -p files WORKDIR /app COPY . . RUN go build RUN chmod +x ./send-to-kindle-telegram-bot CMD ["./send-to-kindle-telegram-bot"]
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Conclusion

After a lot of testing, I finally got the app up and running on DigitalOcean.

Hope you find this bot useful!
Full code you can find on my GitHub: https://github.com/michaelfmnk/send-to-kindle-telegram-bot
I'm open to any suggestions, ideas, or collaboration :)

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