Retry installing Visual Studio Build Tools on failure

We've seen occasional failures to install the Visual Studio Build Tools
due to flakey responses from the server.

Attempt to make this script more robust by adding a retry with
exponential backoff, attempting up to 10 times before eventually giving
up. This adds the same logic to both the VSB and Swift toolchain
downloads.

Author: plemarquand

.github/workflows/scripts/windows/install-vsb.ps1

@@ -14,8 +14,30 @@ $VSB_SHA256='C792BDB0FD46155DE19955269CAC85D52C4C63C23DB2CF43D96B9390146F9390'
 Set-Variable ErrorActionPreference Stop
 Set-Variable ProgressPreference SilentlyContinue
 Write-Host -NoNewLine ('Downloading {0} ... ' -f ${VSB})
-Invoke-WebRequest -Uri $VSB -OutFile $env:TEMP\vs_buildtools.exe
-Write-Host 'SUCCESS'
+$MaxRetries = 10
+$BaseDelay = 1
+$Attempt = 0
+$Success = $false
+
+while (-not $Success -and $Attempt -lt $MaxRetries) {
+    $Attempt++
+    try {
+        Invoke-WebRequest -Uri $VSB -OutFile $env:TEMP\vs_buildtools.exe
+        $Success = $true
+        Write-Host 'SUCCESS'
+    }
+    catch {
+        if ($Attempt -eq $MaxRetries) {
+            Write-Host "FAILED after $MaxRetries attempts: $($_.Exception.Message)"
+            exit 1
+        }
+
+        # Calculate exponential backoff delay (2^attempt * base delay)
+        $Delay = $BaseDelay * [Math]::Pow(2, $Attempt - 1)
+        Write-Host "Attempt $Attempt failed, retrying in $Delay seconds..."
+        Start-Sleep -Seconds $Delay
+    }
+}
 Write-Host -NoNewLine ('Verifying SHA256 ({0}) ... ' -f $VSB_SHA256)
 $Hash = Get-FileHash $env:TEMP\vs_buildtools.exe -Algorithm sha256
 if ($Hash.Hash -eq $VSB_SHA256) {

.github/workflows/scripts/windows/swift/install-swift.ps1

@@ -17,8 +17,30 @@ function Install-Swift {
     Set-Variable ErrorActionPreference Stop
     Set-Variable ProgressPreference SilentlyContinue
     Write-Host -NoNewLine ('Downloading {0} ... ' -f $url)
-    Invoke-WebRequest -Uri $url -OutFile installer.exe
-    Write-Host 'SUCCESS'
+    $MaxRetries = 10
+    $BaseDelay = 1
+    $Attempt = 0
+    $Success = $false
+
+    while (-not $Success -and $Attempt -lt $MaxRetries) {
+        $Attempt++
+        try {
+            Invoke-WebRequest -Uri $url -OutFile installer.exe
+            $Success = $true
+            Write-Host 'SUCCESS'
+        }
+        catch {
+            if ($Attempt -eq $MaxRetries) {
+                Write-Host "FAILED after $MaxRetries attempts: $($_.Exception.Message)"
+                exit 1
+            }
+
+            # Calculate exponential backoff delay (2^attempt * base delay)
+            $Delay = $BaseDelay * [Math]::Pow(2, $Attempt - 1)
+            Write-Host "Attempt $Attempt failed, retrying in $Delay seconds..."
+            Start-Sleep -Seconds $Delay
+        }
+    }
     Write-Host -NoNewLine ('Verifying SHA256 ({0}) ... ' -f $Sha256)
     $Hash = Get-FileHash installer.exe -Algorithm sha256
     if ($Hash.Hash -eq $Sha256 -or $Sha256 -eq "") {