aws-sdk-kotlin

You must generate an Access Key before getting started. All examples will utilize access_key_id and access_key_secret variables which represent the Access Key ID and Secret Access Key values you generated.

This example uses the aws-sdk-kotlin ↗. You must pass in the R2 configuration credentials when instantiating your S3 client:

Basic Usage

Kotlin

import aws.sdk.kotlin.runtime.auth.credentials.StaticCredentialsProvider
import aws.sdk.kotlin.services.s3.S3Client
import aws.sdk.kotlin.services.s3.listObjects
import aws.sdk.kotlin.services.s3.model.GetObjectRequest
import aws.sdk.kotlin.services.s3.model.PutObjectRequest
import aws.sdk.kotlin.services.s3.presigners.presignGetObject
import aws.sdk.kotlin.services.s3.presigners.presignPutObject
import aws.smithy.kotlin.runtime.auth.awscredentials.Credentials
import aws.smithy.kotlin.runtime.net.url.Url
import kotlinx.coroutines.runBlocking
import kotlin.time.Duration.Companion.minutes

val ACCOUNT_ID = "<ACCOUNT_ID>"
val ACCESS_KEY = "<ACCESS_KEY>"
val SECRET_KEY = "<SECRET_KEY>"

fun main() = runBlocking {
    val r2Client = S3Client.fromEnvironment {
        region = "auto" // Required by SDK, but not used by R2
        endpointUrl = Url.parse("https://${ACCOUNT_ID}.r2.cloudflarestorage.com")
        credentialsProvider = StaticCredentialsProvider(
            Credentials(
                accessKeyId = ACCESS_KEY,
                secretAccessKey = SECRET_KEY
            ),
        )
    }

    println("Available buckets:")
    r2Client.listBuckets().buckets?.forEach { bucket ->
        println("* ${bucket.name}")
    }

    val bucketName = "<BUCKET_NAME>"
    println("\nObjects in bucket '${bucketName}':")
    r2Client.listObjects { bucket = bucketName }.contents?.forEach {
        println("* ${it.key} (size: ${it.size} bytes, modified: ${it.lastModified})")
    }

    r2Client.close()
}

Available buckets:
* my-bucket-1
* my-bucket-2

Objects in bucket 'my-bucket-1':
* image1.png (size: 253167 bytes, modified: 2026-01-17T11:30:58.896Z)
* image2.png (size: 247027 bytes, modified: 2026-01-17T11:30:57.779Z)

Generate presigned URLs

You can also generate presigned links that can be used to temporarily share public read or write access to a bucket.

Kotlin

val uploadUrl = r2Client.presignPutObject(
    input = PutObjectRequest {
        bucket = bucketName
        key = "README.md"
    },
    duration = 15.minutes,
).url
println(uploadUrl)

val getUrl = r2Client.presignGetObject(
    input = GetObjectRequest {
        bucket = bucketName
        key = "README.md"
    },
    duration = 15.minutes,
).url
println(getUrl)

You can use these presigned URLs with any HTTP client. For example, to upload a file using the PUT URL:

curl -X PUT "https://<your-presigned-put-url>" -H "Content-Type: application/octet-stream" --data-binary "@local-file.txt"

To download a file using the GET URL:

curl -X GET "https://<your-presigned-get-url>" -o downloaded-file.txt