Web search restrictions after internal content (#1074)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/Tests/Tools/ToolCalling/LoopbackWebServer.cs

@@ -0,0 +1,79 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+
+namespace AIStudio.Tests.Tools.ToolCalling;
+
+/// <summary>
+/// A minimal HTTP server on the loopback address, which stands in for the intranet in tests: it
+/// is the one non-public address a test can serve from.
+/// </summary>
+/// <remarks>
+/// /redirect sends the client on, to /page of this server unless the test names another address,
+/// and every other path answers with a small HTML page.
+/// </remarks>
+internal sealed class LoopbackWebServer : IDisposable
+{
+    private readonly TcpListener listener = new(IPAddress.Loopback, 0);
+    private readonly CancellationTokenSource stop = new();
+    private readonly string? redirectLocation;
+
+    /// <param name="redirectLocation">Where /redirect sends the client, or null for /page of this server.</param>
+    public LoopbackWebServer(string? redirectLocation = null)
+    {
+        this.redirectLocation = redirectLocation;
+        this.listener.Start();
+        _ = this.ServeAsync();
+    }
+
+    public int Port => ((IPEndPoint)this.listener.LocalEndpoint).Port;
+
+    public Uri Address(string path) => new($"http://127.0.0.1:{this.Port}{path}");
+
+    private async Task ServeAsync()
+    {
+        try
+        {
+            while (!this.stop.IsCancellationRequested)
+            {
+                using var client = await this.listener.AcceptTcpClientAsync(this.stop.Token);
+                await using var stream = client.GetStream();
+                var request = await ReadRequestHeadAsync(stream, this.stop.Token);
+                var response = request.StartsWith("GET /redirect ", StringComparison.Ordinal)
+                    ? $"HTTP/1.1 302 Found\r\nLocation: {this.redirectLocation ?? this.Address("/page").ToString()}\r\nContent-Length: 0\r\nConnection: close\r\n\r\n"
+                    : Page("<html><head><title>Travel</title></head><body><main><p>The travel policy of the intranet.</p></main></body></html>");
+
+                await stream.WriteAsync(Encoding.UTF8.GetBytes(response), this.stop.Token);
+            }
+        }
+        catch (Exception exception) when (exception is OperationCanceledException or ObjectDisposedException or SocketException)
+        {
+            // The test is over.
+        }
+    }
+
+    private static string Page(string html) => $"HTTP/1.1 200 OK\r\nContent-Type: text/html; charset=utf-8\r\nContent-Length: {Encoding.UTF8.GetByteCount(html)}\r\nConnection: close\r\n\r\n{html}";
+
+    private static async Task<string> ReadRequestHeadAsync(NetworkStream stream, CancellationToken token)
+    {
+        var head = new StringBuilder();
+        var buffer = new byte[1024];
+        while (!head.ToString().Contains("\r\n\r\n", StringComparison.Ordinal))
+        {
+            var read = await stream.ReadAsync(buffer, token);
+            if (read == 0)
+                break;
+
+            head.Append(Encoding.ASCII.GetString(buffer, 0, read));
+        }
+
+        return head.ToString();
+    }
+
+    public void Dispose()
+    {
+        this.stop.Cancel();
+        this.listener.Stop();
+        this.stop.Dispose();
+    }
+}