RequestBodyUtil.kt

import android.content.Context
import android.net.Uri
import android.provider.MediaStore
import okhttp3.MediaType
import okhttp3.RequestBody
import okio.BufferedSink
import okio.Okio


fun createRequestBody(uri: Uri, context: Context): RequestBody {
    val contentResolver = context.contentResolver
    val contentType = MediaType.parse(contentResolver.getType(uri))

    val projection = arrayOf(MediaStore.MediaColumns.SIZE)
    val length = contentResolver
            .query(uri, projection, null, null, null)
            ?.use {
                if (it.moveToFirst()) {
                    it.getLong(0)
                } else {
                    null
                }
            } ?: throw IllegalArgumentException("uriからファイルサイズを取得できません")

    return object : RequestBody() {

        override fun contentLength(): Long = length

        override fun contentType(): MediaType? = contentType

        override fun writeTo(sink: BufferedSink) {
            Okio
                    .source(context.contentResolver.openInputStream(uri))
                    .use {
                        sink.writeAll(it)
                    }
        }

    }
}