Escl: HTTPS support, security policies, and HTTPS->HTTP fallback

#338

NAPS2.Escl.Server/EsclApiController.cs

@@ -14,20 +14,24 @@ internal class EsclApiController : WebApiController
 
     private readonly EsclDeviceConfig _deviceConfig;
     private readonly EsclServerState _serverState;
+    private readonly EsclSecurityPolicy _securityPolicy;
     private readonly ILogger _logger;
 
-    internal EsclApiController(EsclDeviceConfig deviceConfig, EsclServerState serverState, ILogger logger)
+    internal EsclApiController(EsclDeviceConfig deviceConfig, EsclServerState serverState,
+        EsclSecurityPolicy securityPolicy, ILogger logger)
     {
         _deviceConfig = deviceConfig;
         _serverState = serverState;
+        _securityPolicy = securityPolicy;
         _logger = logger;
     }
 
     [Route(HttpVerbs.Get, "/ScannerCapabilities")]
     public async Task GetScannerCapabilities()
     {
         var caps = _deviceConfig.Capabilities;
-        var iconUri = caps.IconPng != null ? $"http://naps2-{caps.Uuid}.local.:{_deviceConfig.Port}/eSCL/icon.png" : "";
+        var protocol = _securityPolicy.HasFlag(EsclSecurityPolicy.ServerRequireHttps) ? "https" : "http";
+        var iconUri = caps.IconPng != null ? $"{protocol}://naps2-{caps.Uuid}.local.:{_deviceConfig.Port}/eSCL/icon.png" : "";
         var doc =
             EsclXmlHelper.CreateDocAsString(
                 new XElement(ScanNs + "ScannerCapabilities",
@@ -169,7 +173,13 @@ public void CreateScanJob()
         _serverState.IsProcessing = true;
         var jobInfo = JobInfo.CreateNewJob(_serverState, _deviceConfig.CreateJob(settings));
         _serverState.AddJob(jobInfo);
-        Response.Headers.Add("Location", $"{Request.Url}/{jobInfo.Id}");
+        var uri = Request.Url;
+        if (Request.IsSecureConnection)
+        {
+            // Fix https://github.com/unosquare/embedio/issues/593
+            uri = new UriBuilder(uri) { Scheme = "https" }.Uri;
+        }
+        Response.Headers.Add("Location", $"{uri}/{jobInfo.Id}");
         Response.StatusCode = 201; // Created
     }
 

NAPS2.Escl.Server/EsclServer.cs

@@ -1,3 +1,4 @@
+using System.Security.Cryptography.X509Certificates;
 using EmbedIO;
 using EmbedIO.WebApi;
 using Microsoft.Extensions.Logging;
@@ -11,11 +12,15 @@ static EsclServer()
     {
         Swan.Logging.Logger.NoLogging();
     }
-    
+
     private readonly Dictionary<EsclDeviceConfig, DeviceContext> _devices = new();
     private bool _started;
     private CancellationTokenSource? _cts;
 
+    public EsclSecurityPolicy SecurityPolicy { get; set; }
+
+    public X509Certificate2? Certificate { get; set; }
+
     public ILogger Logger { get; set; } = NullLogger.Instance;
 
     public void AddDevice(EsclDeviceConfig deviceConfig)
@@ -45,6 +50,11 @@ public Task Start()
         {
             return Task.CompletedTask;
         }
+        if (SecurityPolicy.HasFlag(EsclSecurityPolicy.ServerRequireHttps) && Certificate == null)
+        {
+            throw new EsclSecurityPolicyViolationException(
+                $"EsclSecurityPolicy of {SecurityPolicy} needs a certificate to be specified");
+        }
         _started = true;
         _cts = new CancellationTokenSource();
 
@@ -63,24 +73,39 @@ private async Task StartServerAndAdvertise(DeviceContext deviceCtx)
         var cancelToken = CancellationTokenSource.CreateLinkedTokenSource(_cts!.Token, deviceCtx.Cts.Token).Token;
         // Try to run the server with the port specified in the EsclDeviceConfig first. If that fails, try random ports
         // instead, and store the actually-used port back in EsclDeviceConfig so it can be advertised correctly.
-        await PortFinder.RunWithSpecifiedOrRandomPort(deviceCtx.Config.Port, async port =>
+        bool hasHttp = !SecurityPolicy.HasFlag(EsclSecurityPolicy.ServerRequireHttps);
+        bool hasHttps = Certificate != null;
+        if (hasHttp)
         {
-            await StartServer(deviceCtx, port, cancelToken);
-            deviceCtx.Config.Port = port;
-        }, cancelToken);
-        deviceCtx.Advertiser.AdvertiseDevice(deviceCtx.Config);
+            await PortFinder.RunWithSpecifiedOrRandomPort(deviceCtx.Config.Port, async port =>
+            {
+                await StartServer(deviceCtx, port, false, cancelToken);
+                deviceCtx.Config.Port = port;
+            }, cancelToken);
+        }
+        if (hasHttps)
+        {
+            await PortFinder.RunWithSpecifiedOrRandomPort(deviceCtx.Config.TlsPort, async tlsPort =>
+            {
+                await StartServer(deviceCtx, tlsPort, true, cancelToken);
+                deviceCtx.Config.TlsPort = tlsPort;
+            }, cancelToken);
+        }
+        deviceCtx.Advertiser.AdvertiseDevice(deviceCtx.Config, hasHttp, hasHttps);
     }
 
-    private async Task StartServer(DeviceContext deviceCtx, int port, CancellationToken cancelToken)
+    private async Task StartServer(DeviceContext deviceCtx, int port, bool tls, CancellationToken cancelToken)
     {
-        var url = $"http://+:{port}/";
+        var protocol = tls ? "https" : "http";
+        var url = $"{protocol}://+:{port}/";
         deviceCtx.ServerState = new EsclServerState();
         var server = new WebServer(o => o
                 .WithMode(HttpListenerMode.EmbedIO)
-                .WithUrlPrefix(url))
+                .WithUrlPrefix(url)
+                .WithCertificate((tls ? Certificate : null)!))
             .HandleUnhandledException(UnhandledServerException)
             .WithWebApi("/eSCL",
-                m => m.WithController(() => new EsclApiController(deviceCtx.Config, deviceCtx.ServerState, Logger)));
+                m => m.WithController(() => new EsclApiController(deviceCtx.Config, deviceCtx.ServerState, SecurityPolicy, Logger)));
         await server.StartAsync(cancelToken);
     }
 

NAPS2.Escl.Server/MdnsAdvertiser.cs

@@ -1,55 +1,147 @@
 using Makaretu.Dns;
+using Makaretu.Dns.Resolving;
 
 namespace NAPS2.Escl.Server;
 
 public class MdnsAdvertiser : IDisposable
 {
     private readonly ServiceDiscovery _sd;
     private readonly Dictionary<string, ServiceProfile> _serviceProfiles = new();
+    private readonly Dictionary<string, ServiceProfile> _serviceProfiles2 = new();
 
     public MdnsAdvertiser()
     {
         _sd = new ServiceDiscovery();
     }
 
-    public void AdvertiseDevice(EsclDeviceConfig deviceConfig)
+    public void AdvertiseDevice(EsclDeviceConfig deviceConfig, bool hasHttp, bool hasHttps)
     {
         var caps = deviceConfig.Capabilities;
         if (caps.Uuid == null)
         {
             throw new ArgumentException("UUID must be specified");
         }
+        if (!hasHttp && !hasHttps)
+        {
+            return;
+        }
         var name = caps.MakeAndModel;
-        var service = new ServiceProfile(name, "_uscan._tcp", (ushort) deviceConfig.Port);
+
+        // HTTP+HTTPS should be handled by responding with the relevant records for both _uscan and _uscans when either
+        // is queried. This isn't handled out-of-the-box by the MDNS library so we need to do some extra work.
+        var httpProfile = new ServiceProfile(name, "_uscan._tcp", (ushort) deviceConfig.Port);
+        var httpsProfile = new ServiceProfile(name, "_uscans._tcp", (ushort) deviceConfig.TlsPort);
+        // If only one of HTTP or HTTPS is enabled, then we use that as the service. If both are enabled, we use the
+        // HTTP service as a baseline and then hack in the HTTPS records later.
+        var service = hasHttp ? httpProfile : httpsProfile;
+
         var domain = $"naps2-{caps.Uuid}";
-        service.HostName = DomainName.Join(domain, service.Domain);
-        service.AddProperty("txtvers", "1");
-        service.AddProperty("Vers", "2.0"); // TODO: verify
-        if (deviceConfig.Capabilities.IconPng != null)
+        var hostName = DomainName.Join(domain, service.Domain);
+
+        // Replace the default TXT record with the first TXT record (HTTP if used, HTTPS otherwise)
+        service.Resources.RemoveAll(x => x is TXTRecord);
+        service.Resources.Add(CreateTxtRecord(deviceConfig, hasHttp, service, caps, name));
+
+        // NSEC records are recommended by RFC6762 to annotate that there's no more info for this host
+        service.Resources.Add(new NSECRecord
+            { Name = hostName, NextOwnerName = hostName, Types = [DnsType.A, DnsType.AAAA] });
+
+        if (hasHttp && hasHttps)
         {
-            service.AddProperty("representation", $"http://naps2-{caps.Uuid}.local.:{deviceConfig.Port}/eSCL/icon.png");
+            // If both HTTP and HTTPS are enabled, we add the extra HTTPS records here
+            service.Resources.Add(new PTRRecord
+            {
+                Name = httpsProfile.QualifiedServiceName,
+                DomainName = httpsProfile.FullyQualifiedName
+            });
+            service.Resources.Add(new SRVRecord
+            {
+                Name = httpsProfile.FullyQualifiedName,
+                Port = (ushort) deviceConfig.TlsPort
+            });
+            service.Resources.Add(CreateTxtRecord(deviceConfig, false, httpsProfile, caps, name));
         }
-        service.AddProperty("rs", "eSCL");
-        service.AddProperty("ty", name);
-        service.AddProperty("pdl", "application/pdf,image/jpeg,image/png");
-        // TODO: Actual adf/duplex, etc.
-        service.AddProperty("uuid", caps.Uuid);
-        service.AddProperty("cs", "color,grayscale,binary");
-        service.AddProperty("is", "platen"); // and ,adf
-        service.AddProperty("duplex", "F");
+
+        // The default HostName isn't correct, it should be "naps2-uuid.local" (the actual host) instead of
+        // "name._uscan.local" (the service name)
+        service.HostName = hostName;
+
+        // Send the full set of HTTP/HTTPS records to anyone currently listening
         _sd.Announce(service);
+
+        // Set up to respond to _uscan/_uscans queries with our records.
         _sd.Advertise(service);
+        if (hasHttp && hasHttps)
+        {
+            // Add _uscans to the available services (_uscan was already mapped in Advertise())
+            _sd.NameServer.Catalog[ServiceDiscovery.ServiceName].Resources.Add(new PTRRecord
+                { Name = ServiceDiscovery.ServiceName, DomainName = httpsProfile.QualifiedServiceName });
+            // Cross-reference _uscan to the HTTPS records
+            _sd.NameServer.Catalog[httpProfile.QualifiedServiceName].Resources.Add(new PTRRecord
+                { Name = httpsProfile.QualifiedServiceName, DomainName = httpsProfile.FullyQualifiedName });
+            // Add a _uscans reference with both HTTP and HTTPS records
+            _sd.NameServer.Catalog[httpsProfile.QualifiedServiceName] = new Node
+            {
+                Name = httpsProfile.QualifiedServiceName, Authoritative = true, Resources =
+                {
+                    new PTRRecord
+                        { Name = httpProfile.QualifiedServiceName, DomainName = httpProfile.FullyQualifiedName },
+                    new PTRRecord
+                        { Name = httpsProfile.QualifiedServiceName, DomainName = httpsProfile.FullyQualifiedName }
+                }
+            };
+        }
+
+        // Persist the profiles so they can be unadvertised later
         _serviceProfiles.Add(caps.Uuid, service);
+        if (hasHttp && hasHttps)
+        {
+            _serviceProfiles2.Add(caps.Uuid, httpsProfile);
+        }
+    }
+
+    private static TXTRecord CreateTxtRecord(EsclDeviceConfig deviceConfig, bool http, ServiceProfile service,
+        EsclCapabilities caps, string? name)
+    {
+        var record = new TXTRecord();
+        record.Name = service.FullyQualifiedName;
+        record.Strings.Add("txtvers=1");
+        record.Strings.Add("Vers=2.0"); // TODO: verify
+        if (deviceConfig.Capabilities.IconPng != null)
+        {
+            record.Strings.Add(
+                http
+                    ? $"representation=http://naps2-{caps.Uuid}.local.:{deviceConfig.Port}/eSCL/icon.png"
+                    : $"representation=https://naps2-{caps.Uuid}.local.:{deviceConfig.TlsPort}/eSCL/icon.png");
+        }
+        record.Strings.Add("rs=eSCL");
+        record.Strings.Add($"ty={name}");
+        record.Strings.Add("pdl=application/pdf,image/jpeg,image/png");
+        // TODO: Actual adf/duplex, etc.
+        record.Strings.Add($"uuid={caps.Uuid}");
+        record.Strings.Add("cs=color,grayscale,binary");
+        record.Strings.Add("is=platen"); // and ,adf
+        record.Strings.Add("duplex=F");
+        return record;
     }
 
     public void UnadvertiseDevice(EsclDeviceConfig deviceConfig)
     {
-        if (deviceConfig.Capabilities.Uuid == null)
+        var uuid = deviceConfig.Capabilities.Uuid;
+        if (uuid == null)
         {
             throw new ArgumentException("UUID must be specified");
         }
-        _sd.Unadvertise(_serviceProfiles[deviceConfig.Capabilities.Uuid]);
-        _serviceProfiles.Remove(deviceConfig.Capabilities.Uuid);
+        if (_serviceProfiles.ContainsKey(uuid))
+        {
+            _sd.Unadvertise(_serviceProfiles[uuid]);
+            _serviceProfiles.Remove(uuid);
+        }
+        if (_serviceProfiles2.ContainsKey(uuid))
+        {
+            _sd.Unadvertise(_serviceProfiles2[uuid]);
+            _serviceProfiles2.Remove(uuid);
+        }
     }
 
     public void Dispose()

NAPS2.Escl.Tests/ClientServerTests.cs

@@ -34,6 +34,7 @@ public async Task ClientServer()
             Host = $"[{IPAddress.IPv6Loopback}]",
             RemoteEndpoint = IPAddress.IPv6Loopback,
             Port = deviceConfig.Port,
+            TlsPort = deviceConfig.TlsPort,
             RootUrl = "eSCL",
             Tls = false,
             Uuid = uuid
@@ -43,4 +44,12 @@ public async Task ClientServer()
         Assert.Equal("HP Blah", caps.MakeAndModel);
         Assert.Equal("123abc", caps.SerialNumber);
     }
+
+    [Fact]
+    public async Task StartTlsServerWithoutCertificate()
+    {
+        using var server = new EsclServer();
+        server.SecurityPolicy = EsclSecurityPolicy.RequireHttps;
+        await Assert.ThrowsAsync<EsclSecurityPolicyViolationException>(() => server.Start());
+    }
 }

NAPS2.Escl.Usb/EsclUsbContext.cs

@@ -52,6 +52,7 @@ public void ConnectToDevice()
             Host = IPAddress.Loopback.ToString(),
             RemoteEndpoint = IPAddress.Loopback,
             Port = port,
+            TlsPort = 0,
             RootUrl = "eSCL",
             Tls = false,
             Uuid = Guid.Empty.ToString("D")