aws4fetch

A compact (6.4kb minified, 2.5kb gzipped) AWS client for environments that support
fetch and
SubtleCrypto – that is, modern web browsers and
JS platforms like Cloudflare Workers. Also retries
requests with an exponential backoff with full jitter
strategy by default.

Example

``js
import { AwsClient } from 'aws4fetch'

const aws = new AwsClient({ accessKeyId: MY_ACCESS_KEY, secretAccessKey: MY_SECRET_KEY })

// https://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html
const LAMBDA_FN_API = 'https://lambda.us-east-1.amazonaws.com/2015-03-31/functions'

async function invokeMyLambda(event) {
const res = await aws.fetch(${LAMBDA_FN_API}/my-lambda/invocations, { body: JSON.stringify(event) })

// res is a standard Response object: https://developer.mozilla.org/en-US/docs/Web/API/Response
return res.json()
}

invokeMyLambda({my: 'event'}).then(json => console.log(json))
`

You can see a more detailed example, a Cloudflare Worker script you can use as
a replacement for API Gateway, in the example directory.

API

aws4fetch exports two classes: AwsClient and AwsV4Signer

new AwsClient(options)

You can use the same instance of AwsClient for all your service calls as the service and region will be determined
at fetch time – or you can create separate instances if you have different needs, eg no retrying for some service.

`js
import { AwsClient } from 'aws4fetch'

const aws = new AwsClient({
accessKeyId, // required, akin to AWS_ACCESS_KEY_ID
secretAccessKey, // required, akin to AWS_SECRET_ACCESS_KEY
sessionToken, // akin to AWS_SESSION_TOKEN if using temp credentials
service, // AWS service, by default parsed at fetch time
region, // AWS region, by default parsed at fetch time
cache, // credential cache, defaults to new Map()
retries, // number of retries before giving up, defaults to 10, set to 0 for no retrying
initRetryMs, // defaults to 50 – timeout doubles each retry
})
`

$3

Has the same signature as the global fetch function

`js
import { AwsClient } from 'aws4fetch'

const aws = new AwsClient(opts)

async function doFetch() {

const response = await aws.fetch(url, {

method, // if not supplied, will default to 'POST' if there's a body, otherwise 'GET'
headers, // standard JS object literal, or Headers instance
body, // optional, String or ArrayBuffer/ArrayBufferView – ie, remember to stringify your JSON

// and any other standard fetch options, eg keepalive, etc

// optional, largely if you want to override options in the AwsClient instance
aws: {
signQuery, // set to true to sign the query string instead of the Authorization header
accessKeyId, // same as in AwsClient constructor above
secretAccessKey, // same as in AwsClient constructor above
sessionToken, // same as in AwsClient constructor above
service, // same as in AwsClient constructor above
region, // same as in AwsClient constructor above
cache, // same as in AwsClient constructor above
datetime, // defaults to now, to override use the form '20150830T123600Z'
appendSessionToken, // set to true to add X-Amz-Security-Token after signing, defaults to true for iot
allHeaders, // set to true to force all headers to be signed instead of the defaults
singleEncode, // set to true to only encode %2F once (usually only needed for testing)
},
})

console.log(await response.json())
}
`

NB: Due to the way bodies are handled in Request
instances, it's faster to invoke the function as above – using a URL as the input
argument and passing the body in the init argument – instead of the form of
invocation that uses a Request object directly as input.

If you don't know which URL to call for the AWS service you want, the full list
of AWS endpoints can be found here:
https://docs.aws.amazon.com/general/latest/gr/rande.html

And the APIs are documented here: https://docs.aws.amazon.com/ (the REST APIs
are usually documented under "API Reference" for each service)

$3

Returns a Promise that resolves to an
AWS4
signed Request –
has the same signature as fetch. Use this to create a Request you can send
using fetch() yourself.

`js
import { AwsClient } from 'aws4fetch'

const aws = new AwsClient(opts)

async function doFetch() {

const request = await aws.sign(url, {

method, // if not supplied, will default to 'POST' if there's a body, otherwise 'GET'
headers, // standard JS object literal, or Headers instance
body, // optional, String or ArrayBuffer/ArrayBufferView – ie, remember to stringify your JSON

// and any other standard fetch options, eg keepalive, etc

// optional, largely if you want to override options in the AwsClient instance
aws: {
signQuery, // set to true to sign the query string instead of the Authorization header
accessKeyId, // same as in AwsClient constructor above
secretAccessKey, // same as in AwsClient constructor above
sessionToken, // same as in AwsClient constructor above
service, // same as in AwsClient constructor above
region, // same as in AwsClient constructor above
cache, // same as in AwsClient constructor above
datetime, // defaults to now, to override use the form '20150830T123600Z'
appendSessionToken, // set to true to add X-Amz-Security-Token after signing, defaults to true for iot
allHeaders, // set to true to force all headers to be signed instead of the defaults
singleEncode, // set to true to only encode %2F once (usually only needed for testing)
},
})

const response = await fetch(request)

console.log(await response.json())
}
`

new AwsV4Signer(options)

The underlying signing class for a request – use this if you just want to deal
with the raw AWS4 signed method/url/headers/body.

`js
import { AwsV4Signer } from 'aws4fetch'

const signer = new AwsV4Signer({
url, // required, the AWS endpoint to sign
accessKeyId, // required, akin to AWS_ACCESS_KEY_ID
secretAccessKey, // required, akin to AWS_SECRET_ACCESS_KEY
sessionToken, // akin to AWS_SESSION_TOKEN if using temp credentials
method, // if not supplied, will default to 'POST' if there's a body, otherwise 'GET'
headers, // standard JS object literal, or Headers instance
body, // optional, String or ArrayBuffer/ArrayBufferView – ie, remember to stringify your JSON
signQuery, // set to true to sign the query string instead of the Authorization header
service, // AWS service, by default parsed at fetch time
region, // AWS region, by default parsed at fetch time
cache, // credential cache, defaults to new Map()
datetime, // defaults to now, to override use the form '20150830T123600Z'
appendSessionToken, // set to true to add X-Amz-Security-Token after signing, defaults to true for iot
allHeaders, // set to true to force all headers to be signed instead of the defaults
singleEncode, // set to true to only encode %2F once (usually only needed for testing)
})
`

$3

Actually perform the signing of the request and return a Promise that resolves
to an object containing the signed method, url, headers and body.

method will be a String, url will be an instance of URL,
headers will be an instance of Headers and
body will unchanged from the argument you supply to the constructor.

`js
import { AwsV4Signer } from 'aws4fetch'

const signer = new AwsV4Signer(opts)

async function sign() {
const { method, url, headers, body } = await signer.sign()

console.log(method, url, [...headers], body)
}
`

$3

Returns a Promise that resolves to the signed string to use in the
Authorization header

Used by the sign() method – you shouldn't need to access this directly unless you're constructing your own requests.

$3

Returns a Promise that resolves to the
hex signature

Used by the sign() method – you shouldn't need to access this directly unless you're constructing your own requests.

Installation

With npm do:

`
npm install aws4fetch
``