How to do a Pre-signed POST upload to AWS S3 in Go?

Question

I would like to do a pre-signed POST to upload files to an AWS S3 bucket - how would this be done in Go?

Please note that this is not the same as Pre-signed upload w

Answer 1

Here is an alternative approach from https://github.com/minio/minio-go that you might like for a full programmatic way of generating presigned post policy.

package main

import (
    "fmt"
    "log"
    "time"

    "github.com/minio/minio-go"
)

func main() {
    policy := minio.NewPostPolicy()
    policy.SetKey("myobject")
    policy.SetBucket("mybucket")
    policy.SetExpires(time.Now().UTC().AddDate(0, 0, 10)) // expires in 10 days
    config := minio.Config{
        AccessKeyID:     "YOUR-ACCESS-KEY-HERE",
        SecretAccessKey: "YOUR-PASSWORD-HERE",
        Endpoint:        "https://s3.amazonaws.com",
    }
    s3Client, err := minio.New(config)
    if err != nil {
        log.Fatalln(err)
    }
    m, err := s3Client.PresignedPostPolicy(policy)
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Printf("curl ")
    for k, v := range m {
        fmt.Printf("-F %s=%s ", k, v)
    }
    fmt.Printf("-F file=@/etc/bashrc ")
    fmt.Printf(config.Endpoint + "/mybucket\n")
}

---

Step 1:

    policy := minio.NewPostPolicy()
    policy.SetKey("myobject")
    policy.SetBucket("mybucket")
    policy.SetExpires(time.Now().UTC().AddDate(0, 0, 10)) // expires in 10 days

Instantiate a new policy structure, this policy structure implements following methods.

func NewPostPolicy() *PostPolicy
func (p *PostPolicy) SetBucket(bucket string) error
func (p *PostPolicy) SetContentLength(min, max int) error
func (p *PostPolicy) SetContentType(contentType string) error
func (p *PostPolicy) SetExpires(t time.Time) error
func (p *PostPolicy) SetKey(key string) error
func (p *PostPolicy) SetKeyStartsWith(keyStartsWith string) error
func (p PostPolicy) String() string

---

Step 2:

    m, err := s3Client.PresignedPostPolicy(policy)
    if err != nil {
        fmt.Println(err)
        return
    }

Now PresignedPostPolicy() takes the PostPolicy structure and returns back a map of "key/values" which can be used in your HTML form or curl command to upload data to s3.