@acusti/appsync-fetch


appsync-fetch is a lightweight node.js module that uses [@acusti/post][]
to make requests to an AWS AppSync graphql API. It expands on
@acusti/post’s API with an optional third argument for passing in AWS
credentials, as well as the region. If AWS credentials aren’t provided, it
uses the same algorithm as @aws-sdk/credential-providers’s [fromEnv
helper][fromenv] to get credentials from the standard AWS environment
variables made available in lambdas. It then uses those credentials to
construct the appropriate [AWS SigV4][] authorization headers for IAM-based
authorization.

There are two primary reasons it’s worth using:

1. it relies on the native node.js http/https modules for fetching (via
@acusti/post) and on the native node.js crypto module for its
cryptographic logic; this makes it way lighter weight than alternatives
and results in faster start times in your lambdas
2. its DX ergonomics are carefully tuned for interacting with AppSync
GraphQL APIs

[@acusti/post]: https://github.com/acusti/uikit/tree/main/packages/post
[aws sigv4]:
https://docs.aws.amazon.com/general/latest/gr/signature-version-4.html
[fetch]:
http://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch
[fromenv]:
https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/modules/_aws_sdk_credential_providers.html#fromenv

Usage

``
npm install @acusti/appsync-fetch


or


yarn add @acusti/appsync-fetch
`

The package exports appsyncFetch, a function that takes similar arguments
to [window.fetch][] (note that method is always POST) and returns a
promise. The promise is resolved with the parsed JSON version of the
request’s response (i.e. return await response.json() when using the
Fetch API), because that’s what you wanted anyways. It also sets all
required headers, including AWS authorization headers, a Date header, and
Content-Type.

In addition, the second argument can take a query property (string) and a
variables property (object), which it will JSON.stringify into a valid
GraphQL request body. You can also pass in body as a string directly, but
if you pass in a query, the body will be overwritten (you will get a
type error in typescript if you try to pass both).

The function also takes an optional third argument where you can manually
pass in AWS credentials if you don’t wish to rely on the built-in
credentials handling, which will extract credentials from environment
variables via process.env. Usage is illustrated in the code example
below.

And lastly, if the response is an error (4xx or 5xx), appsyncFetch will
throw an Error object with the response HTTP error and message as the Error
object message and with the following additional properties:

- Error.response: the node.js response IncomingMessage object
- Error.responseJSON: if the response body can be parsed as JSON, the
JSON representation returned from calling JSON.parse() on it
- Error.responseText: the response body as text

[window.fetch]: http://developer.mozilla.org/en-US/docs/Web/API/fetch

`js
import { appsyncFetch } from '@acusti/appsync-fetch';

const appsyncURL = 'https://_.appsync-api.us-west-2.amazonaws.com/graphql';

// In its simplest usage, environment variables are used for authorization
const itemsResult = await appsyncFetch(appsyncURL, {
query:
query ListItems {
listItems {
items {
id
text
}
}
},
});
// itemsResult is the parsed JSON from the response, e.g.:
// const response = await fetch(...);
// const itemsResult = await response.json();

// You can also pass in variables
const createdItemResult = await appsyncFetch(appsyncURL, {
query:
mutation CreateItem($input: CreateItemInput!) {
createItem(input: $input) {
id
}
},
variables: {
input: {
text: 'Here is the text of a new item',
},
},
});

// You can also provide the authentication variables manually
const manualAuthenticationResult = await appsyncFetch(
appsyncURL,
{ query: 'query {...}' },
{
accessKeyId,
secretAccessKey,
sessionToken,
},
);
`

$3

You can pass in the expected data result from the GraphQL query as a
generic to appsyncFetch. This works very well with the [codegen GraphQL
API types][] provided by AWS amplify:

`ts
import { ListItemsQuery } from 'API';

const itemsResult = await appsyncFetch(appsyncURL, {
query:
query ListItems {
listItems {
items {
id
text
}
}
},
});
`

The type of itemsResult will be
{ data?: ListItemsQuery, errors?: GraphQLResponseError[] }, where
GraphQLResponseError` is the shape of GraphQL errors returned by appsync
as illustrated [in the docs][].

[codegen graphql api types]:
https://docs.amplify.aws/cli/graphql/client-code-generation/
[in the docs]:
https://docs.aws.amazon.com/appsync/latest/devguide/troubleshooting-and-common-mistakes.html