@acusti/appsync-fetch

@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 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

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

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,
    },
);

With TypeScript

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:

import { ListItemsQuery } from 'API';

const itemsResult = await appsyncFetch<ListItemsQuery>(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.