multipartform.kt

internal class MultiPartContent(val parts: List<Part>) : OutgoingContent.WriteChannelContent() {
    //val uuid = "RANDOM234"
    //val time = System.currentTimeMillis()
    //val time = "123134234234"
    //val boundary = "***ktor-$uuid-ktor-$time***"
    val boundary = generateBoundary()

    private fun generateBoundary(): String = buildString {
        repeat(32) {
            append(Random.nextInt().absoluteValue.toString(16))
        }
    }.take(70)


    data class Part(val name: String, val size: Long, val filename: String? = null, val headers: Headers = Headers.Empty, val writer: suspend ByteWriteChannel.() -> Unit)

    override suspend fun writeTo(channel: ByteWriteChannel) {
        for (part in parts) {
            channel.writeStringUtf8("--$boundary\r\n")
            val partHeaders = Headers.build {
                val fileNamePart = if (part.filename != null) "; filename=\"${part.filename}\"" else ""
                append(HttpHeaders.ContentDisposition, "form-data; name=\"${part.name}\"$fileNamePart")
                append(HttpHeaders.ContentLength, part.size.toString())
                appendAll(part.headers)
            }
            for ((key, value) in partHeaders.flattenEntries()) {
                channel.writeStringUtf8("$key: $value\r\n")
            }
            channel.writeStringUtf8("\r\n")
            part.writer(channel)
            channel.writeStringUtf8("\r\n")
        }
        channel.writeStringUtf8("--$boundary--\r\n")
    }

    override val contentType = ContentType.MultiPart.FormData
        .withParameter("boundary", boundary)

    override val contentLength: Long?
        get() {
            var length = 0L
            for (part in parts) {
                length += ("--$boundary\r\n").length
                val partHeaders = Headers.build {
                    val fileNamePart = if (part.filename != null) "; filename=\"${part.filename}\"" else ""
                    append(HttpHeaders.ContentDisposition, "form-data; name=\"${part.name}\"$fileNamePart")
                    append(HttpHeaders.ContentLength, part.size.toString())
                    appendAll(part.headers)
                }
                for ((key, value) in partHeaders.flattenEntries()) {
                    length += ("$key: $value\r\n").length
                }
                length += ("\r\n").length
                length += part.size
                length += ("\r\n").length
            }
            length += ("--$boundary--\r\n").length
            print("CONTENT LENGTH: $length")
            return length
        }

    class Builder {
        val parts = arrayListOf<Part>()

        private fun add(part: Part) {
            parts += part
        }

        private fun add(name: String, size: Long, filename: String? = null, contentType: ContentType? = null, headers: Headers = Headers.Empty, writer: suspend ByteWriteChannel.() -> Unit) {
            val contentTypeHeaders: Headers = if (contentType != null) headersOf(HttpHeaders.ContentType, contentType.toString()) else headersOf()
            add(Part(name, size, filename, headers + contentTypeHeaders, writer))
        }

        fun add(name: String, size: Long, text: String, contentType: ContentType? = null, filename: String? = null) {
            add(name, size, filename, contentType) { writeStringUtf8(text) }
        }

        fun add(name: String, size: Long, data: ByteArray, contentType: ContentType? = ContentType.Application.OctetStream, filename: String? = null) {
            add(name, size, filename, contentType) { writeFully(data) }
        }

        internal fun build(): MultiPartContent = MultiPartContent(parts.toList())
    }

    companion object {
        fun build(callback: Builder.() -> Unit) = Builder().apply(callback).build()
    }
}

private operator fun Headers.plus(other: Headers): Headers = when {
    this.isEmpty() -> other
    other.isEmpty() -> this
    else -> Headers.build {
        appendAll(this@plus)
        appendAll(other)
    }
}