Input report reader library

The input_report_reader library facilitates the implementation of input drivers by providing one of the commonly required functionalities: managing and keeping track of upstream drivers that want to receive reports.

InputReportReaderManager in the library creates and manages InputReportReaders, which implement fuchsia.input.report.InputReportsReader. The manager can send reports to all existing InputReportReaders.

An upstream driver that wants to read input reports from an input device may register with InputReportReaderManager by calling the CreateReader method. When an input report arrives (whether in the form of HID reports or device readings by polling and so on), the report is pushed to all the registered readers using the SendReportToAllReaders method. The report is then translated to fuchsia_input_report::InputReport. When the InputReportReaderManager instance is destructed, all of the existing InputReportReaders are freed.

How to use

The steps below walk through how to use the input report reader library in an input device:

Define a class that holds all the data that needs to be reported (this struct must declare the required ToFidlInputReport method), for example:

struct MyExampleMouseReport {
  zx::time event_time;
  int64_t x;
  int64_t y;

  void ToFidlInputReport(fidl::WireTableBuilder<::fuchsia_input_report::wire::InputReport>&
                         input_report, fidl::AnyArena& allocator) const;
}

Implement the ToFidlInputReport method, for example:

void MyExampleMouseReport::ToFidlInputReport(
    fidl::WireTableBuilder<::fuchsia_input_report::wire::InputReport>& input_report,
    fidl::AnyArena& allocator) const {
  auto mouse_input_rpt = fuchsia_input_report::wire::MouseInputReport::Builder(allocator);
  mouse_input_rpt.movement_x(x);
  mouse_input_rpt.movement_y(y);

  input_report.mouse(mouse_input_rpt.Build());
  input_report.event_time(event_time.get());
}

In your input device, declare an instance of InputReportReaderManager templated on your struct, for example:
```
input_report_reader::InputReportReaderManager<MyExampleMouseReport> readers_;
```
When a report arrives, parse the report, fill out MyExampleMouseReport with the report data, and call the SendReportToAllReaders method, for example:
```
readers_.SendReportToAllReaders(report);
```

In the implementation of fuchsia.input.report.InputDevice.GetInputReportsReader, call the CreateReader method, for example:

void MyExampleInputDevice::GetInputReportsReader(GetInputReportsReaderRequestView request,
                                              GetInputReportsReaderCompleter::Sync& completer) {
  auto status = readers_.CreateReader(dispatcher_, std::move(request->reader));
  if (status != ZX_OK) {
     // ...
  }
}