Dependency MQTTnet out of date and has breaking changes.

[Clockwork-Muse]

The dependency for MQTTnet is now at version 4.3.1.873, which includes some breaking changes (or at least some binary incompatibilities).

Attempting a project like so:

<Project Sdk="Microsoft.NET.Sdk.BlazorWebAssembly">

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="CloudNative.CloudEvents" Version="2.7.1" />
    <PackageReference Include="CloudNative.CloudEvents.Mqtt" Version="2.7.1" />
    <PackageReference Include="CloudNative.CloudEvents.SystemTextJson" Version="2.7.1" />
    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly" Version="6.0.18" />
    <PackageReference Include="Microsoft.AspNetCore.Components.WebAssembly.DevServer" Version="6.0.18" PrivateAssets="all" />
    <PackageReference Include="MQTTnet" Version="3.1.2" />
  </ItemGroup>

</Project>

... ends up yielding

dotnet build
MSBuild version 17.3.2+561848881 for .NET
  Determining projects to restore...
  All projects are up-to-date for restore.
/workspaces/event-client/Pages/FetchData.razor(64,30): error CS0012: The type 'MqttApplicationMessage' is defined in an assembly that is not referenced. You must add a reference to assembly 'MQTTnet, Version=3.0.15.0, Culture=neutral, PublicKeyToken=b69712f52770c0a7'. [/workspaces/event-client/event-client.csproj]
/workspaces/event-client/Pages/FetchData.razor(65,37): warning CS8602: Dereference of a possibly null reference. [/workspaces/event-client/event-client.csproj]
/workspaces/event-client/Pages/FetchData.razor(65,26): warning CS8604: Possible null reference argument for parameter 'item' in 'void List<string>.Add(string item)'. [/workspaces/event-client/event-client.csproj]

Build FAILED.

/workspaces/event-client/Pages/FetchData.razor(65,37): warning CS8602: Dereference of a possibly null reference. [/workspaces/event-client/event-client.csproj]
/workspaces/event-client/Pages/FetchData.razor(65,26): warning CS8604: Possible null reference argument for parameter 'item' in 'void List<string>.Add(string item)'. [/workspaces/event-client/event-client.csproj]
/workspaces/event-client/Pages/FetchData.razor(64,30): error CS0012: The type 'MqttApplicationMessage' is defined in an assembly that is not referenced. You must add a reference to assembly 'MQTTnet, Version=3.0.15.0, Culture=neutral, PublicKeyToken=b69712f52770c0a7'. [/workspaces/event-client/event-client.csproj]
    2 Warning(s)
    1 Error(s)

Time Elapsed 00:00:00.73

[jskeet]

Thanks - we'll need to have a think about what to do here. We'd need a new major version (at least for the MQTT package) if we just bump the dependency - and at that point, anyone still using v3 would have problems.

I wonder whether the right approach is to create a new package, CloudNative.CloudEvents.Mqtt4. What do you think?

[Clockwork-Muse]

On a personal level I get annoyed with versioning in the package/namespace name. I understand why people sometimes do it though.

[jskeet]

On a personal level I get annoyed with versioning in the package/namespace name. I understand why people sometimes do it though.

So what would your proposal be as an alternative? How would you suggest we support v3 users and v4 users? Or just not support v3 users any more?

[Clockwork-Muse]

Take the breaking change, drop v3 support (which hasn't been updated in > 18 mos).
If v3 support is still needed for some reason, release/maintenance branch.

[jskeet]

Right. And presumably release this as a new major version of just the MQTT CE package. (We don't want to disrupt other users, but we do want to signal the breaking change to MQTT users.) This is something I've thought we'll probably end up needing for a while - this is just the forcing function. I think "release everything all at the same time" is probably still appropriate, and we can keep a common minor/patch version, but vary major version by package...