b = bufio.NewReader(bytes.NewBuffer(data))

b = bytes.NewReader(data)

package main

import (
	"bufio"
	"bytes"
	"context"
	"io"
	"log"
	"net/http"

	"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"
)

var AWS_KEY string = "<redacted>"
var AWS_SECRET string = "<redacted>"
var ENDPOINT string = "https://s3.eu-west-3.amazonaws.com/"
var BUCKET string = "hupload-test"

func main() {
	c, err := config.LoadDefaultConfig(
		context.Background(),
		config.WithRegion("eu-west-3"),
		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(AWS_KEY, AWS_SECRET, "")),
		config.WithHTTPClient(&http.Client{
			Timeout: 0,
		}),
	)
	if err != nil {
		log.Fatal(err)
	}

	data := []byte{}

	var b io.Reader

	OPTION := 1

	switch OPTION {
	case 1:
		// Fails
		b = bufio.NewReader(bytes.NewBuffer(data))
	case 2:
		// Works
		b = bytes.NewReader(data)
	case 3:
		// Fails
		b = io.LimitReader(bytes.NewReader(data), 1024)
	}
	client := s3.NewFromConfig(c, func(o *s3.Options) {
		o.UsePathStyle = true
		o.BaseEndpoint = &ENDPOINT
	})
	size := int64(len(data))
	key := "sample/testFile"
	input := &s3.PutObjectInput{
		Bucket:        &BUCKET,
		Key:           &key,
		Body:          b,
		ContentLength: &size,
	}
	_, err = client.PutObject(context.Background(), input)
	if err != nil {
		log.Fatal(err)
	}
}