L2CAP Options

L2CapChannelOptions (L2CapChannelOptions) configures the L2CAP channel represented by IBluetoothRemoteL2CapChannel — a connection-oriented channel useful for higher-throughput bulk transfer than individual GATT characteristic writes. It controls MTU sizing, whether a background read loop is used, write-flush behavior, and the background read buffer size. DI-configured via IOptions<L2CapChannelOptions>.

It does not configure per-operation timeouts — OpenAsync, CloseAsync, ReadAsync, and WriteAsync each accept their own optional timeout parameter directly.

Basic Configuration

builder.Services.Configure<L2CapChannelOptions>(options =>
{
    options.Mtu = null; // let the platform negotiate; falls back to DefaultMtu
    options.DefaultMtu = 512;
    options.EnableBackgroundReading = true;
    options.AutoFlushWrites = true;
    options.ReadBufferSize = 512;
});

await channel.OpenAsync(TimeSpan.FromSeconds(30), cancellationToken);
channel.DataReceived += (_, args) => ProcessReceivedData(args.Data);
await channel.WriteAsync(data, TimeSpan.FromSeconds(10), cancellationToken);
await channel.CloseAsync(cancellationToken: cancellationToken);

Bulk Transfer (Firmware Update / File Transfer)

builder.Services.Configure<L2CapChannelOptions>(options =>
{
    options.DefaultMtu = 4096;        // larger MTU for throughput
    options.AutoFlushWrites = false;  // let the platform batch writes where it can
    options.ReadBufferSize = 4096;
});

await channel.OpenAsync(TimeSpan.FromSeconds(60), cancellationToken);
await channel.WriteAsync(largeChunk, TimeSpan.FromMinutes(2), cancellationToken);

Pull-Based Reading

builder.Services.Configure<L2CapChannelOptions>(options => options.EnableBackgroundReading = false);

var buffer = new byte[1024];
var bytesRead = await channel.ReadAsync(buffer, TimeSpan.FromSeconds(10), cancellationToken);

Platform Considerations

  • iOS/macOS: real implementation, but CoreBluetooth doesn't expose the real negotiated L2CAP MTU — DefaultMtu is always used in its place.
  • Android: real implementation, negotiated MTU is reported correctly.
  • Windows: not supported. NativeOpenL2CapChannelAsync throws NotSupportedException.
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