Fix synchronous API

[david-preston-triad]

What problem does the pull request solve?

Earlier this year, I submitted Pull Request https://github.com/alphagov/notifications-net-client/pull/83 to add an asynchronous version of the NotificationClient API. Subsequently, an issue was found with the synchronous version of the API whereby the affected code appears to "hang" when the API is called. The issue occurs in specific scenarios, and most commonly affects the following project types:

• ASP.NET (Framework) websites
• .NET (Framework) Windows Forms applications

The issue is less likely to affect .NET (Framework) Console applications or .NET Core projects. It is caused because the methods of the synchronous API are now implemented by calling the corresponding asynchronous API methods and waiting for the result. This can lead to a deadlock on the main thread used by Windows Forms and ASP.NET applications. The issue and work-around are described at https://medium.com/bynder-tech/c-why-you-should-use-configureawait-false-in-your-library-code-d7837dce3d7f.

I have tested the fix successfully with the following types of project:

• .NET (Framework) Console application
• .NET (Framework) Windows Forms application
• ASP.NET (Framework) website
• .NET (Core) Console application
• ASP.NET (Core) website

Checklist

• [x] I’ve used the pull request template
• [ ] I’ve written unit tests for these changes
• [x] I’ve update the documentation (in DOCUMENTATION.md and CHANGELOG.md)
• [x] I’ve bumped the version number (in src/Notify/Notify.csproj)

[ghost]

Can one of the admins verify this patch?

[quis]

@govuk-notify-jenkins test this please

[quis]

@david-preston-triad thanks for looking into this. We’ll find an appropriate person to review it.

[leohemsted]

@david-preston-triad hi, thanks for the PR! Really sorry for how long it's taken for us to get round to this, but we think this looks good (though we're not domain experts here). We'll get this deployed this evening or tomorrow morning (but from another PR just so I could rebase it - https://github.com/alphagov/notifications-net-client/pull/105 )