Configure `aws-sdk-go` for R2

This example uses version 2 of the aws-sdk-go Open external link package. You must pass in the R2 configuration credentials when instantiating your S3 service client:

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/credentials"
	"github.com/aws/aws-sdk-go-v2/service/s3"
	"log"
)

func main() {
	var bucketName = "sdk-example"
	var accountId = "<accountid>"
	var accessKeyId = "<access_key_id>"
	var accessKeySecret = "<access_key_secret>"

	r2Resolver := aws.EndpointResolverWithOptionsFunc(func(service, region string, options ...interface{}) (aws.Endpoint, error) {
		return aws.Endpoint{
			URL: fmt.Sprintf("https://%s.r2.cloudflarestorage.com", accountId),
		}, nil
	})

	cfg, err := config.LoadDefaultConfig(context.TODO(),
		config.WithEndpointResolverWithOptions(r2Resolver),
		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(accessKeyId, accessKeySecret, "")),
	)
	if err != nil {
		log.Fatal(err)
	}

	client := s3.NewFromConfig(cfg)

	listObjectsOutput, err := client.ListObjectsV2(context.TODO(), &s3.ListObjectsV2Input{
		Bucket: &bucketName,
	})
	if err != nil {
		log.Fatal(err)
	}

	for _, object := range listObjectsOutput.Contents {
		obj, _ := json.MarshalIndent(object, "", "\t")
		fmt.Println(string(obj))
	}

	//  {
	//  	"ChecksumAlgorithm": null,
	//  	"ETag": "\"eb2b891dc67b81755d2b726d9110af16\"",
	//  	"Key": "ferriswasm.png",
	//  	"LastModified": "2022-05-18T17:20:21.67Z",
	//  	"Owner": null,
	//  	"Size": 87671,
	//  	"StorageClass": "STANDARD"
	//  }

	listBucketsOutput, err := client.ListBuckets(context.TODO(), &s3.ListBucketsInput{})
	if err != nil {
		log.Fatal(err)
	}

	for _, object := range listBucketsOutput.Buckets {
		obj, _ := json.MarshalIndent(object, "", "\t")
		fmt.Println(string(obj))
	}

	// {
	// 		"CreationDate": "2022-05-18T17:19:59.645Z",
	// 		"Name": "sdk-example"
	// }
}

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

presignClient := s3.NewPresignClient(client)

	presignResult, err := presignClient.PresignPutObject(context.TODO(), &s3.PutObjectInput{
		Bucket: aws.String(bucketName),
		Key:    aws.String("example.txt"),
	})

	if err != nil {
		panic("Couldn't get presigned URL for PutObject")
	}

	fmt.Printf("Presigned URL For object: %s\n", presignResult.URL)