feat(dns): Add real-time DNS speed benchmark and 'Fastest' auto-selection option (#4935)

* feat(dns): Add real-time DNS speed benchmark and 'Fastest' auto-selection option

* fix(dns): Address CodeRabbit & Codex PR review feedback

* fix(ci): Remove .biomeignore to keep repository root clean

* Fix Fastest DNS eligibility and failed probe handling

---------

Co-authored-by: Chris Titus <contact@christitus.com>

functions/private/Get-WinUtilDNSBenchmark.ps1

@@ -0,0 +1,84 @@
+function Get-WinUtilDNSBenchmark {
+    <#
+
+    .SYNOPSIS
+        Benchmarks neutral DNS providers by measuring TCP port 53 latency (RTT in ms) to determine the fastest DNS server.
+
+    .PARAMETER TimeoutMs
+        Maximum timeout in milliseconds for each connection test. Default is 1500ms.
+
+    .OUTPUTS
+        Array of PSCustomObjects containing Provider, PrimaryIP, and LatencyMs sorted by lowest latency.
+
+    .EXAMPLE
+        $results = Get-WinUtilDNSBenchmark
+        $fastest = $results[0]
+
+    #>
+    [CmdletBinding()]
+    param(
+        [ValidateRange(1, 9998)]
+        [int]$TimeoutMs = 1500
+    )
+
+    Write-WinUtilLog -Component "DNS" -Message "Starting DNS latency benchmark scan (TCP port 53)..."
+
+    $dnsConfigs = $sync.configs.dns
+    if ($null -eq $dnsConfigs) {
+        Write-Warning "DNS configurations not found in `$sync.configs.dns."
+        Write-WinUtilLog -Level "ERROR" -Component "DNS" -Message "DNS configurations not found in `$sync.configs.dns."
+        return @()
+    }
+
+    $results = [System.Collections.Generic.List[PSObject]]::new()
+
+    foreach ($prop in $dnsConfigs.PSObject.Properties) {
+        $providerName = $prop.Name
+        $primaryIp = $prop.Value.Primary
+        if (-not $primaryIp) { continue }
+
+        # Providers must explicitly opt in so new filtering services are never auto-selected.
+        if ($prop.Value.BenchmarkEligible -ne $true) {
+            continue
+        }
+
+        $latency = 9999
+        $client = $null
+        try {
+            $client = New-Object System.Net.Sockets.TcpClient
+            $stopwatch = [System.Diagnostics.Stopwatch]::StartNew()
+            $asyncResult = $client.BeginConnect($primaryIp, 53, $null, $null)
+            $success = $asyncResult.AsyncWaitHandle.WaitOne($TimeoutMs, $false)
+            $stopwatch.Stop()
+
+            if ($success) {
+                $client.EndConnect($asyncResult)
+                $latency = [int]$stopwatch.ElapsedMilliseconds
+            } else {
+                $latency = 9999
+            }
+        } catch {
+            $latency = 9999
+        } finally {
+            if ($null -ne $client) {
+                $client.Dispose()
+            }
+        }
+
+        $results.Add([PSCustomObject]@{
+            Provider  = $providerName
+            PrimaryIP = $primaryIp
+            LatencyMs = $latency
+        })
+    }
+
+    $sortedResults = @($results | Sort-Object LatencyMs)
+    if ($sortedResults.Count -gt 0 -and $sortedResults[0].LatencyMs -lt 9999) {
+        $fastest = $sortedResults[0]
+        Write-WinUtilLog -Component "DNS" -Message "DNS Benchmark completed. Fastest neutral provider: $($fastest.Provider) ($($fastest.LatencyMs) ms)"
+    } else {
+        Write-WinUtilLog -Component "DNS" -Message "DNS Benchmark completed. Could not determine latency for providers."
+    }
+
+    return $sortedResults
+}

functions/private/Set-WinUtilDNS.ps1

@@ -18,6 +18,21 @@ function Set-WinUtilDNS {
         return $true
     }
 
+    if($DNSProvider -eq "Fastest") {
+        Write-WinUtilLog -Component "DNS" -Message "Auto-detecting fastest DNS provider via latency benchmark..."
+        $benchmark = Get-WinUtilDNSBenchmark
+        $validFastest = $benchmark | Where-Object { $_.LatencyMs -lt 9999 } | Select-Object -First 1
+        if ($validFastest) {
+            $DNSProvider = $validFastest.Provider
+            Write-Host "Auto-selected fastest DNS provider: $DNSProvider ($($validFastest.LatencyMs) ms)"
+            Write-WinUtilLog -Component "DNS" -Message "Auto-selected fastest DNS provider: $DNSProvider ($($validFastest.LatencyMs) ms)"
+        } else {
+            Write-Warning "Could not measure DNS latency to any provider; keeping current network adapter DNS settings."
+            Write-WinUtilLog -Component "DNS" -Message "Benchmark timeout or all probes failed; aborting DNS change to preserve existing settings."
+            return $false
+        }
+    }
+
     try {
         $Adapters = Get-NetAdapter | Where-Object {$_.Status -eq "Up"}
         Write-Host "Ensuring DNS is set to $DNSProvider on the following interfaces:"