1. Using the right networking APIs for your Universal Windows app
Sidharth Nabar, Himadri Sarkar
Windows Networking team

2. Considerations when writing a networking app
Server-side support
Scenario requirements
Foreground vs background
Portability requirements
Performance considerations
Ease of coding
Which API should you use?

3. Discuss 4 networking scenarios &
In this talk
Discuss 4 networking scenarios &
API Choices for each
HTTPS with user authentication
Device-Cloud bi-directional communication
Network communication between devices over sockets
Download/Upload content to cloud in the background

4. HTTPS with User Authentication
Scenario 1
HTTPS with User Authentication

5. Recommended API: HttpClient
Features
Client Authentication
Username/Password or certificate?
UI or Programmatic?
Server Authentication
Well-known or private CA?
Custom validation/Certificate pinning?
Recommended API: HttpClient

6. API Choices Windows.Web.Http & System.Net.Http √ √ (new!) Feature
Programming Language support
All UWP languages
C#/VB
Private CA/Self-signed certificate √
Custom validation of server certificate
√ (new!)
X (on roadmap)
Integration with native UI for Auth X
Client Certificate Support
Partial
Cross-platform support (Xamarin)

7. Programming Pattern – Windows.Web.Http
1. Create an HttpBaseProtocolFilter instance (optional)
var filter = new HttpBaseProtocolFilter();
2. Modify settings on the filter (optional)
filter.ClientCertificate = myCertificate;
3. Create an HttpClient instance
var client = new HttpClient(); OR
var client = new HttpClient(filter);
4. Send requests from client
HttpResponseMessage response = await client.GetAsync(uri);

8. Demo: Online Auction App
Requirements:
Custom server certificate validation
Client Certificate
API Choice:
Windows.Web.Http.HttpClient

9. Summary: HTTPS with User Authentication
Windows.Web.Http
Supports wide range of HTTP security and authentication features
Available for all UWP programming languages
System.Net.Http
Supports programmatic use of credentials and certificates
Available cross-platform for C#/VB developers
(For more info and code snippets, see

10. Device-Cloud Bidirectional Communication
Scenario 2
Device-Cloud Bidirectional Communication

11. Features Communication Model Server Endpoint
Truly bidirectional or client-initiated?
Half-duplex or full-duplex?
Server Endpoint
REST API or simple message exchange?
Supports WebSockets?
Performance Requirements/Optimizations
Caching/Data Compression required?
Latency/delay requirements?

12. API Choices Windows.Web.Http.HttpClient&
Windows.Networking.Sockets.WebSockets
Feature
HttpClient
WebSockets
Messaging pattern
Request-response
Bidirectional
Duplex communication?
Half
Full
Latency/overhead
Higher
Lower
Proxy/Firewall traversal √
Server certificate custom validation
√(new!)
√ (new!)
REST support, CRUD semantics
Built-in
Needs additional code
Caching and data compression

13. API Choices (Contd.) MessageWebSocket & StreamWebSocket √ Feature
Message Format
Discrete WebSocket messages
Continuous data stream
UTF-8 Strings/JSON data √ X
Binary data
Recommended data size
Small (bytes/KB)
Large (MB)
Recommended content types
Strings, JSON content
Audio, Video, Photos

14. Programming Pattern – MessageWebSocket
1. Create an instance of WebSocket
var socket= new MessageWebSocket();
2. Register MessageReceived event handler
socket.MessageReceived = myReceivingHandler;
3. Register Closed event handler
socket.Closed = myClosedHandler;
4. Connect to server and send data. Close connection with status code at the end.
await socket.ConnectAsync(serverUri);
// Send data.
socket.Close(code, reason);

15. Demo: Online Auction App
Requirements:
Client-Server bidirectional communication
Server relays others’ bids independent of client’s bids
Minimum latency and overhead
API Choice:
Windows.Networking.Sockets.MessageWebSocket

16. Network Traffic Comparison
Bytes on the wire
Wireshark trace for HttpClient run
Wireshark trace for WebSocket run

17. Summary: Device-Cloud bidirectional communication
HttpClient
Ideal for request-response communication
Built-in support for REST API and message handling semantics
WebSockets
Ideal for low latency bidirectional communication
Message format and semantics need to be implemented on top

18. Network communication between devices over sockets
Scenario 3
Network communication between devices over sockets

19. Features Lifespan of the socket Language Choice Pre-existing code
Foreground only or Background also
Language Choice
C#/VB, JavaScript or C++
Pre-existing code
Win32 or .NET libraries

20. API Choices Windows.Networking.Sockets, System.Net.Sockets and Winsock
Feature
Windows.Networking.Sockets
System.Net.Sockets
WinSock
Language Support
C++/CX √ X
JavaScript
C#/VB
Activity Support in Background

21. Sockets – Listening in Background
Special trigger to start a background task – SocketActivityTrigger
App can transfer ownership of socket to the OS while suspending
OS keeps the socket alive even when the app is not running

22. Programming Pattern – Sockets in Background
1. Create a task with trigger type SocketActivityTrigger
socketTaskBuilder.TaskEntryPoint = "SocketActivityBackgroundTask.SocketActivity Task";
var trigger = new SocketActivityTrigger();
socketTaskBuilder.SetTrigger(trigger);
var task = socketTaskBuilder.Register();
2. Associate Socket with the task and connect to the remote device
socket.EnableTransferOwnership(task.TaskId, SocketActivityConnectedStandbyAction.Wake);
await socket.ConnectAsync(target, port);

23. Programming Pattern – Sockets in Background
3. Transfer the ownership when suspending foreground app or Background Task cancellation
socket.TransferOwnership(socketId);
Things to note:
At any point ownership of the socket can be only in one component
Find the list of sockets owned by the service using:
SocketActivityInformation.AllSockets
Socket not in the list means socket is already closed or retrieved

24. Demo: Multi-player Game
Requirements:
App communication between devices over sockets
Listening on the socket activity even when the app is not running
API Choice:
Windows.Networking.Sockets

25. Listening on Socket in background
Summary
Sockets APIs in UWP
Recommended: Windows.Networking.Sockets
Also available: System.Net.Socket, Winsock
Listening on Socket in background
Use SocketActivityTrigger

26. Download/Upload content to cloud in the background
Scenario 4
Download/Upload content to cloud in the background

27. Features Protocol Destination location Content Size
HTTP/ FTP
Destination location
Memory/File
Content Size
Small (in KBs)/Big (in MBs)
Resiliency to reboot and network outage
Resource Awareness
Battery/Network cost

28. Windows.Networking.BackgroundTransfer
API Choices
HttpClient (in background task) & BackgroundTransfer
Feature
HttpClient in BG Task
Windows.Networking.BackgroundTransfer
Protocol
HTTP
HTTP/FTP
Destination Location
In memory & File
File only
Recommended file size
Small (KBs)
Large (MBs)
Resiliency (network connection drop/reboot)
Needs additional code
Can be resumed where left off
Network Cost Awareness
Built-in
Battery Saver Awareness

29. Programming Pattern – Windows.Networking.BackgroundTransfer
1. Create an DownloadOperation instance
BackgroundDownloader downloader = new BackgroundDownloader(); DownloadOperation download = downloader.CreateDownload(new Uri(downloadlocation), file);
Task<DownloadOperation> startTask = download.StartAsync().AsTask();
2. Start the transfer
downloads = await BackgroundDownloader.GetCurrentDownloadsAsync ();
await download.AttachAsync().AsTask(cts.Token, progressCallback);
3. Retrieve and attach to the transfers

30. Programming Pattern – Windows.Networking.BackgroundTransfer
4.Handling of Completion in foreground app
Task<DownloadOperation> startTask = download.StartAsync().AsTask(); Task continueTask = startTask.ContinueWith(OnDownloadCompleted);
5.Handling of Completion using a background task
BackgroundTransferCompletionGroup completionGroup = new BackgroundTransferCompletionGroup();
//Create background task builder
builder.SetTrigger(completionGroup.Trigger);
BackgroundDownloader downloader = new BackgroundDownloader(completionGroup);

31. Demo: Multi-player Game
Requirements:
Download a new game level in the Background
Show a toast notification on completion of the download
API Choice:
Windows.Networking.BackgroundTransfer

32. Summary – Download/Upload content in Background
BackgroundTransfer APIs in UWP
Recommended for large files
For smaller size/in-memory content - HTTPClient in background task
Automatic completion handling
Use trigger in BackgroundTransferCompletionGroup

33. References and More Info
MSDN:
GitHub Universal Samples:
HttpClient
WebSockets
SocketActivityStreamSocket
BackgroundTransfer
API Feedback:

34. Thank You!