anandkunal

AWS SigV4 & SES Walkthrough in Go

A few years ago, I helped a non-profit organization build and deploy a series of web applications and micro-services on top of AWS. One of the services was responsible for sending out email notifications to people via AWS SES.

Back then, I wrote a really simple program in Go that made direct calls to the AWS API. Instead of using an official library, I read the API specification, learned how to authenticate requests, and implemented a fairly trivial SDK. The code was succinct, readable, and worked perfectly for 3 years without any issues.

That is until this past week…

AWS recently updated the specification, we’re now at Signature Version 4 (SigV4), for how API requests must be formed and signed by clients. In this walkthrough, I’ll share the full Go source code (~130 LOC) that I put together to make valid authenticated calls to AWS for SES. You don’t need to be knowledgeable about Go to grok code in this post. In fact, code in this post will translate pretty cleanly to

anandkunal

Keybase proof

I hereby claim:

• I am anandkunal on github.
• I am kunalanand (https://keybase.io/kunalanand) on keybase.
• I have a public key ASBB49TMrvEQLZhvjuWQsz6Poc28_OuAEcKicNB-7AGnSAo

To claim this, I am signing this object:

anandkunal

PASS
ok  	_/Users/ka/rpc_tutorial  	0.038s

anandkunal

func TestColdGet(t *testing.T) {
  item, _ := c.Get(cacheItem.Key)
  if item != nil {
    t.Errorf("Cache key should not exist: %s\n", cacheItem.Key)
  }
}

func TestPut(t *testing.T) {
  _, err := c.Put(cacheItem)
  if err != nil {

anandkunal

var (
  c   *Client
  err error

  dsn       = "localhost:9876"
  cacheItem = &CacheItem{Key: "some key", Value: "some value"}
)

func init() {
  c, err = NewClient(dsn, time.Millisecond*500)

anandkunal

func (c *Client) Get(key string) (*CacheItem, error) {
  var item *CacheItem
  err := c.connection.Call("RPC.Get", key, &item)
  return item, err
}

func (c *Client) Put(item *CacheItem) (bool, error) {
  var added bool
  err := c.connection.Call("RPC.Put", item, &added)
  return added, err

anandkunal

type (
  Client struct {
    connection *rpc.Client
  }
)

func NewClient(dsn string, timeout time.Duration) (*Client, error) {
  connection, err := net.DialTimeout("tcp", dsn, timeout)
  if err != nil {
    return nil, err

anandkunal

package main

import (
  "log"
  "net"
  "net/rpc"
  "runtime"
)

func init() {

anandkunal

func (r *RPC) Stats(skip bool, requests *Requests) error {
  *requests = *r.requests
  return nil
}

anandkunal

func (r *RPC) Clear(skip bool, ack *bool) error {
  r.mu.Lock()
  defer r.mu.Unlock()

  r.cache = make(map[string]string)
  *ack = true

  r.requests.Clear++
  return nil
}