Ability to download attachments

[bosukas]

Summary

Currently there is no way to download attachments without creating your own function for it, however I feel like it would be a nice extension function with kord-extensions.

Preferred Behaviour

Maybe an extension function for attachments could be added, something like:

attachment.downloadToFile(fileUrl)

attachment.downloadToPath(pathUrl)

Suggestions

I have an extension function for the http client that lets you download from URLs. I don't know if its the best approach but it works.

suspend fun HttpClient.downloadToFile(file: File, url: String) {
    // create file if it does not exist
    if(!file.exists()) {
        withContext(Dispatchers.IO) {
            file.createNewFile()
        }
    }

    // check if we can write to the file
    require(file.canWrite()) { "Cannot write to file '${file.name}'"}

    val bytes = get<ByteReadChannel>(url)
    val bufferSize = 1024*100
    val buffer = ByteArray(bufferSize)

    // download the content at the url and write that content to the file
    withContext(Dispatchers.IO) {
        FileOutputStream(file).use {
            do {
                val currentRead = bytes.readAvailable(buffer)

                // channel has closed
                if(currentRead == -1) {
                    break
                }

                it.write(buffer, 0, currentRead)
            } while (currentRead >= 0)
        }
    }
}

[gdude2002]

Done, see the utils docs for info after they build.