av/cmd/vidforward/slate.go

/*
DESCRIPTION
  slate.go houses vidforward slate functionality including the slate writing
  routine and HTTP request handlers for receiving of new slate videos.

AUTHORS
  Saxon A. Nelson-Milton <saxon@ausocean.org>

LICENSE
  Copyright (C) 2022 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
*/

package main

import (
	"errors"
	"fmt"
	"io"
	"time"

	"bitbucket.org/ausocean/av/codec/h264"
	"bitbucket.org/ausocean/av/device/file"
	"bitbucket.org/ausocean/utils/logging"
)

// @note this is temporary; slate names will be created based on device mac so that we can
// have a slate per device (or maybe multiple slates per device).
const slateFileName = "/home/saxon/go/src/bitbucket.org/ausocean/av/cmd/vidforward/slate.h264"

func writeSlateAndCheckErrors(dst io.Writer, signalCh chan struct{}, log logging.Logger) error {
	// Also create an errCh that will be used to communicate errors from the
	// writeSlate routine.
	errCh := make(chan error)

	go writeSlate(dst, errCh, signalCh, log)

	// We'll watch out for any errors that happen within a 5 second window. This
	// will indicate something seriously wrong with init, like a missing file etc.
	const startupWindowDuration = 5 * time.Second
	startupWindow := time.NewTimer(startupWindowDuration)
	select {

	// If this triggers first, we're all good.
	case <-startupWindow.C:
		log.Debug("out of error window")

		// We consider any errors after this either to be normal i.e. as a result
		// of stopping the slate input, or something that can not be handled, and
		// only logged, therefore we can close the error channel errCh now.
		// This will also let the routine know that errors can no longer be sent
		// down errCh.
		close(errCh)

	// This means we got a slate error pretty early and need to let caller know.
	case err := <-errCh:
		return fmt.Errorf("could not write slate image: %w", err)
	}
	return nil
}

// writeSlate is a routine that employs a file input device and h264 lexer to
// write a h264 encoded slate image to the provided revid pipeline.
func writeSlate(dst io.Writer, errCh chan error, exitSignal chan struct{}, log logging.Logger) {
	log.Info("writing slate")
	const (
		// Assume 25fps until this becomes configurable.
		slateFrameRate = 25

		loopSetting = true
		frameDelay  = time.Second / slateFrameRate
	)

	fileInput := file.NewWith(log, slateFileName, loopSetting)
	err := fileInput.Start()
	if err != nil {
		errCh <- err
		return
	}

	// This will wait for a signal from the provided slateExitSignal (or from a
	// timeout) to stop writing the slate by "Stopping" the file input which will
	// terminate the Lex function.
	go func() {
		slateTimeoutTimer := time.NewTimer(24 * time.Hour)
		select {
		case <-slateTimeoutTimer.C:
			log.Warning("slate timeout")
		case <-exitSignal:
			log.Info("slate exit signal")
		}
		log.Info("stopping file input")
		fileInput.Stop()
	}()

	// Begin lexing the slate file and send frames to rv pipeline. We'll stay in
	// here until file input closes or there's an unexpected error.
	err = h264.Lex(dst, fileInput, frameDelay)

	// If we get to this point, it means that the we've finished lexing for some
	// reason; let's figure out why.
	select {
	// The only reason we'd get a receive on errCh from this side is if its been
	// closed. This means that we've exceeded the "startup error" period, and that
	// either the error is normal from stopping the input, or we can no longer inform
	// the caller and just need to log the problem.
	case <-errCh:
		if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
			log.Debug("got expected error", "error", err)
			return
		}
		log.Error("got unexpected error", "error", err)

	// This means that a problem occured pretty early in lexing.
	default:
		log.Error("unexpected error during lex startup", "error", err)
		errCh <- err
	}
	log.Error("finished writing slate")
}