CoreSuite.Connectivity 1.0.2

Connectivity

A lightweight internet availability checker and connection monitor for .NET 8, included in CoreSuite.

Overview

Connectivity checks whether at least one of several well-known HTTPS endpoints can be reached. It can perform a single synchronous or asynchronous check, or remain active in the background and notify the application whenever the detected connection state changes.

The service is suitable for availability indicators, offline-mode transitions, retry coordination, synchronization scheduling, and other scenarios that need a practical internet reachability signal. A positive result confirms that one tested endpoint responded successfully; it does not guarantee that every remote service used by the application is available.

Key features

• Performs synchronous and asynchronous availability checks.
• Monitors connectivity continuously in the background.
• Uses several independent HTTPS endpoints instead of relying on a single host.
• Considers the internet available as soon as one endpoint responds successfully.
• Supports a configurable interval between monitoring checks.
• Raises general status-change, connected, and disconnected events.
• Exposes the current monitoring state and last stored connection state.
• Uses a shared HttpClient with a three-second request timeout.
• Falls back from HEAD to GET when an endpoint rejects HEAD requests.
• Stops active monitoring through IDisposable.
• Has no external package dependencies.
• Includes XML documentation and NuGet symbol generation.

Requirements

• .NET 8 (net8.0) or a compatible target framework
• A reference to CoreSuite.Connectivity

The service has no runtime dependency on another CoreSuite package and can be used by console, desktop, web, worker, and service applications.

Installation

dotnet add package CoreSuite.Connectivity

Or add Connectivity/Connectivity.vbproj as a project reference when working directly with the CoreSuite solution.

Quick start: check once

Import the service namespace and prefer the asynchronous API when the caller can use Await.

Imports CoreSuite.Services
Public Async Function CheckInternetAsync() As Task
    Using connectivityService As New Connectivity()
        Dim isOnline As Boolean = Await connectivityService.IsAvailableAsync()
        Console.WriteLine($"Internet available: {isOnline}")
    End Using
End Function

IsAvailableAsync() performs a fresh check each time it is called and returns True as soon as one configured endpoint responds successfully.

Synchronous check

Use IsAvailable() only when blocking the current thread is acceptable.

Imports CoreSuite.Services
Using connectivityService As New Connectivity()
    Dim isOnline As Boolean = connectivityService.IsAvailable()
End Using

In UI applications, prefer IsAvailableAsync() so the interface remains responsive while network requests are in progress.

Continuous monitoring

Configure MonitoringInterval, subscribe to the desired events, and call StartMonitoring().

Imports CoreSuite.Services
Public Class MainForm
    Private ReadOnly connectivityService As New Connectivity()
    Public Sub New()
        InitializeComponent()
        connectivityService.MonitoringInterval = TimeSpan.FromSeconds(2)
        AddHandler connectivityService.ConnectivityChanged, AddressOf ConnectivityService_ConnectivityChanged
        AddHandler connectivityService.Connected, AddressOf ConnectivityService_Connected
        AddHandler connectivityService.Disconnected, AddressOf ConnectivityService_Disconnected
        connectivityService.StartMonitoring()
    End Sub
    Private Sub ConnectivityService_ConnectivityChanged(sender As Object, e As ConnectivityEventArgs)
        Debug.WriteLine($"Internet available: {e.InternetAvailable}")
    End Sub
    Private Sub ConnectivityService_Connected(sender As Object, e As EventArgs)
        Debug.WriteLine("Connected")
    End Sub
    Private Sub ConnectivityService_Disconnected(sender As Object, e As EventArgs)
        Debug.WriteLine("Disconnected")
    End Sub
    Protected Overrides Sub OnFormClosed(e As FormClosedEventArgs)
        connectivityService.Dispose()
        MyBase.OnFormClosed(e)
    End Sub
End Class

Calling StartMonitoring() while monitoring is already active has no effect. The first check establishes the comparison baseline; events are raised only when a later check detects a different state.

Updating a Windows Forms interface

Monitoring continues outside the UI thread, so event handlers must marshal interface changes back to the form when required.

Private Sub ConnectivityService_ConnectivityChanged(sender As Object, e As ConnectivityEventArgs)
    If InvokeRequired Then
        BeginInvoke(Sub() UpdateConnectivityStatus(e.InternetAvailable))
        Return
    End If
    UpdateConnectivityStatus(e.InternetAvailable)
End Sub
Private Sub UpdateConnectivityStatus(isOnline As Boolean)
    StatusLabel.Text = If(isOnline, "Online", "Offline")
    StatusLabel.ForeColor = If(isOnline, Color.Green, Color.Firebrick)
End Sub

The service does not capture a Windows Forms, WPF, ASP.NET, or other synchronization context.

Main properties

MonitoringInterval should be a positive TimeSpan. Very short intervals can generate unnecessary requests and should be avoided.

Methods

Events

All three events describe transitions detected by continuous monitoring. One-time calls to IsAvailable() and IsAvailableAsync() return their results directly and do not raise these events.

ConnectivityEventArgs

Private Sub ConnectivityService_ConnectivityChanged(sender As Object, e As ConnectivityEventArgs)
    If e.InternetAvailable Then
        Debug.WriteLine("The connection is available again.")
    Else
        Debug.WriteLine("The connection is unavailable.")
    End If
End Sub

Endpoint-checking behavior

For each configured HTTPS address, the service:

1. sends a HEAD request;
2. returns True immediately when the response is successful;
3. retries the same address with GET when the server returns 405 Method Not Allowed;
4. continues with the next address after an unsuccessful response or network error;
5. returns False when no address responds successfully.

The shared HTTP client applies a three-second timeout to each request. Because the service tests endpoints sequentially, a completely unavailable connection can take longer than three seconds to report when several requests must time out.

Starting and stopping monitoring

Monitoring can be paused and started again with the same instance.

connectivityService.StartMonitoring()
' Application continues running...
connectivityService.StopMonitoring()
' Monitoring can be started again later.
connectivityService.StartMonitoring()

StopMonitoring() cancels the current monitoring operation and releases its cancellation source. Dispose the instance when its owning application component shuts down.

Monitoring notes

• Connectivity means that at least one tested public endpoint responded successfully.
• A positive result does not confirm DNS, authentication, authorization, or availability of the application's own API.
• The first monitoring check establishes a baseline and does not raise ConnectivityChanged, Connected, or Disconnected.
• Later events are raised only when the result differs from the preceding monitored result.
• Event handlers may execute on a background thread.
• IsConnected represents stored monitoring state; use IsAvailableAsync() when a fresh result is required.
• Network and HTTP failures are treated as unsuccessful endpoint checks instead of being exposed as connectivity exceptions.
• Stopping or disposing the service cancels the active monitoring operation.
• Long-lived instances should be disposed by their owner.

License

CoreSuite is licensed under the MIT License.