Printing | Blazor

Both printing models work in Blazor WebAssembly and Blazor Server.

builder.Services.AddBrowserPrinting();   // Shiny.Printers.Blazor - thermal, over browser device APIs
builder.Services.AddBlazorPrinting();    // Shiny.Printing.Blazor - IPrintService over window.print()

Thermal printers from the browser

Shiny.Printers.Blazor plugs three browser transports into the same IPrinterConnection seam as Bluetooth LE and TCP, so the identical PrintDocument and EscPosProtocol drive them.

@inject BrowserPrinterManager Printers
@implements IAsyncDisposable

<button @onclick="Connect" disabled="@(!support.Bluetooth)">Connect printer</button>

@code {
    BrowserPrintingSupport support = new(false, false, false, false);
    BrowserPrinter? printer;

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        if (firstRender)
        {
            support = await Printers.GetSupport();   // JS interop is only legal after the first render
            StateHasChanged();
        }
    }

    async Task Connect()
    {
        try
        {
            // must run from a user gesture - the browser rejects the chooser otherwise
            printer = await Printers.RequestBluetooth();   // ...or RequestSerial() / RequestUsb()

            await printer.Print(new PrintDocument()
                .AlignCenter().Bold().Line("SHINY MART").ResetStyle()
                .QrCode("https://shinylib.net")
                .Feed(3));
        }
        catch (OperationCanceledException)
        {
            // the user dismissed the device chooser
        }
    }

    // BrowserPrinter owns its connection - dispose it to hand the device back to the browser
    public ValueTask DisposeAsync() => printer?.DisposeAsync() ?? ValueTask.CompletedTask;
}

There is no scanner. Every browser device API opens a chooser that only the user can dismiss, and only from a user gesture, so RequestBluetooth(), RequestSerial() and RequestUsb() do the scan and the connect in one call. Call them from a click handler - never from OnInitialized or OnAfterRender.

Transport	Browser API	Best for	Browsers
RequestBluetooth()	navigator.bluetooth	Cheap 58/80mm BLE printers - the same GATT fingerprints as Shiny.Printers.BluetoothLE	Chrome, Edge, Opera - desktop and Android
RequestSerial()	navigator.serial	USB-serial / RS-232 receipt printers	Chrome, Edge - desktop only
RequestUsb()	navigator.usb	Devices with a raw bulk OUT endpoint	Chrome, Edge - desktop and Android

All three are Chromium-only - never Safari, Firefox or anything on iOS - and need a secure context (HTTPS or localhost). GetSupport() reports all four in one call.

Each transport has its own config, carrying the same Capabilities and ProtocolFactory as the native ones:

printer = await Printers.RequestSerial(new()
{
    BaudRate = 19200,                          // default 9600 8N1
    FlowControl = WebSerialFlowControl.Hardware,
    Capabilities = PrinterCapabilities.Paper80mm
});

Config	Notable settings
WebBluetoothPrinterConfig	Profiles (defaults to KnownWebPrinterProfiles.All), AcceptAllDevices, WriteWithoutResponse, ChunkSize (180)
WebSerialPrinterConfig	BaudRate, DataBits, StopBits, Parity, FlowControl, UsbVendorIds, ChunkSize (1024)
WebUsbPrinterConfig	Filters (default: USB printer class 7), ChunkSize (4096)

• Web Bluetooth never exposes the negotiated MTU, so the chunk size cannot be derived the way the native BLE transport does - it defaults to a safe 180 bytes. Web Bluetooth also needs full 128-bit lowercase UUIDs.
• WebUSB claims the interface directly and so competes with the OS printer driver; on Windows and macOS a printer installed in the system print queue usually cannot be claimed. Prefer Web Serial where the device has a port.
• Port-9100 printers are out of reach from WebAssembly - browsers cannot open raw TCP sockets. Under Blazor Server, Shiny.Printers.Network works as-is because the socket runs on the server.

BrowserPrinter.Connection exposes the transport, device Name, Id, a diagnostic Detail (matched profile, baud rate, USB endpoint) and WhenStatusChanged(), which fires when the browser reports the device has gone.

The browser print dialog

Shiny.Printing.Blazor is the IPrintService for the web. PDF, image and HTML content is rendered into a hidden iframe and printed with window.print():

@inject IPrintService Print

var result = await Print.Print(PrintJob.Html("<h1>Hello</h1>"));

The browser always shows its own dialog, so silent printing and printer enumeration are not available, and PrintJob.File fails - there is no file system to read from. PrintJob.HtmlUrl loads a page into the iframe, which the browser only allows for same-origin URLs.