Offline complex object mutations cause React Native Apps to crash

[matthiaszyx]

Do you want to request a feature or report a bug? Bug

What is the current behavior? In React Native, using the AWSAppSyncClient to upload a complex object (i.e. a file) to S3 causes the App to freeze and/or crash if the file is at least a few megabytes in size and the offline capability of the AWSAppSyncClient is not disabled (i.e. disableOffline is set to false). (Note: if the file is very small or if the offline feature of the AWSAppSyncClient is disabled uploading files does work).

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Upload a file using the AWSAppSyncClient like this:

const fileBuffer = new Buffer(await RNFetchBlob.fs.readFile(file.uri, "base64"), "base64");
client.mutate({
    mutation: gql(`
        mutation createItem($file:S3ObjectInput!) {
            createItem(file: $file) { id file { bucket region key } }
        }
    `,
    variables: {
        file: {
            bucket: 'mybucket',
            region: 'eu-central-1',
            key: 'mykey',
            mimeType: file.type,
            localUri: fileBuffer
        }
    }
});

What is the expected behavior? No crashes or freezes.

Which versions and which environment (browser, react-native, nodejs) / OS are affected by this issue? Did this work in previous versions? Environment: react-native, Versions: any that I have tried, for example the current ones: react-native@0.62.2, aws-appsync@3.0.3