Uploading a File to AWS S3

· 309 words · 2 minutes read

This example shows how to upload a local file onto an S3 bucket using the Go AWS SDK. Our first step is to step up the session using the NewSession function. We've then created an AddFileToS3 function which can be called multiple times when wanting to upload many files.

Within the PutObjectInput you can specify options when uploading the file and in our example we show how you can enable AES256 encryption on your files (when at rest).

For this to work you'll need to have your AWS credentials setup (with AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY) and you'll need to fill in the S3_REGION and S3_BUCKET constants (More info on bucket regions here).

package main

import (


// TODO fill these in!
const (
    S3_REGION = ""
    S3_BUCKET = ""

func main() {

    // Create a single AWS session (we can re use this if we're uploading many files)
    s, err := session.NewSession(&aws.Config{Region: aws.String(S3_REGION)})
    if err != nil {

    // Upload
    err = AddFileToS3(s, "result.csv")
    if err != nil {

// AddFileToS3 will upload a single file to S3, it will require a pre-built aws session
// and will set file info like content type and encryption on the uploaded file.
func AddFileToS3(s *session.Session, fileDir string) error {

    // Open the file for use
    file, err := os.Open(fileDir)
    if err != nil {
        return err
    defer file.Close()

    // Get file size and read the file content into a buffer
    fileInfo, _ := file.Stat()
    var size int64 = fileInfo.Size()
    buffer := make([]byte, size)

    // Config settings: this is where you choose the bucket, filename, content-type etc.
    // of the file you're uploading.
    _, err = s3.New(s).PutObject(&s3.PutObjectInput{
        Bucket:               aws.String(S3_BUCKET),
        Key:                  aws.String(fileDir),
        ACL:                  aws.String("private"),
        Body:                 bytes.NewReader(buffer),
        ContentLength:        aws.Int64(size),
        ContentType:          aws.String(http.DetectContentType(buffer)),
        ContentDisposition:   aws.String("attachment"),
        ServerSideEncryption: aws.String("AES256"),
    return err
Image of Author Edd Turtle

Author:  Edd Turtle

Edd is the Lead Developer at Hoowla, a prop-tech startup, where he spends much of his time working on production-ready Go and PHP code. He loves coding, but also enjoys cycling and camping in his spare time.

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