vidforward: add config file watcher

This change adds a file watcher and then uses this file watcher
to perform updates based on changes in a configuration file. This
configuration file contains logging parameters for the time being
in the hope that it will help with debugging.

Testing was also added for this functionality.

cmd/vidforward/main.go

@@ -32,6 +32,7 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"net"
 	"net/http"
 	"os"
@@ -46,6 +47,10 @@ import (
 	"gopkg.in/natefinch/lumberjack.v2"
 )
 
+// This is the path to the vidforward configuration.
+// This contains parameters such as log level and logging filters.
+const configFileName = "/etc/vidforward/config.json"
+
 // Server defaults.
 const (
 	defaultPort = "8080"
@@ -125,6 +130,49 @@ func terminationCallback(m *broadcastManager) func() {
 	}
 }
 
+// loadConfig loads the vidforward configuration file. This primarily concerns logging
+// configuration for the time being, with the intended use case of debugging.
+func (m *broadcastManager) loadConfig() error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	data, err := ioutil.ReadFile(configFileName)
+	if err != nil {
+		return fmt.Errorf("could not read config file: %w", err)
+	}
+
+	var cfg struct {
+		LogLevel         string   `json:"LogLevel"`
+		LogSuppress      bool     `json:"LogSuppress"`
+		LogCallerFilters []string `json:"LogCallerFilters"`
+	}
+
+	if err = json.Unmarshal(data, &cfg); err != nil {
+		return fmt.Errorf("could not unmarshal config file: %w", err)
+	}
+
+	m.log.(*logging.JSONLogger).SetLevel(map[string]int8{
+		"debug":   logging.Debug,
+		"info":    logging.Info,
+		"warning": logging.Warning,
+		"error":   logging.Error,
+		"fatal":   logging.Fatal,
+	}[cfg.LogLevel])
+	m.log.(*logging.JSONLogger).SetSuppress(cfg.LogSuppress)
+	m.log.(*logging.JSONLogger).SetCallerFilters(cfg.LogCallerFilters...)
+
+	return nil
+}
+
+// This is a callback that can be used by file watchers to reload the config.
+func (m *broadcastManager) onConfigChange() {
+	err := m.loadConfig()
+	if err != nil {
+		m.log.Error("could not load config", "error", err)
+		return
+	}
+}
+
 // recvHandler handles recv requests for video forwarding. The MAC is firstly
 // checked to ensure it is "active" i.e. should be sending data, and then the
 // video is extracted from the request body and provided to the revid pipeline
@@ -413,6 +461,16 @@ func main() {
 		log.Warning("could not load previous state", "error", err)
 	}
 
+	// Try to load the config file.
+	err = m.loadConfig()
+	if err != nil {
+		log.Warning("could not load config file", "error", err)
+	}
+
+	// Set up a file watcher to watch the config file. This will allow us
+	// to perform updates to configuration while the service is running.
+	watchFile(configFileName, m.onConfigChange, log)
+
 	http.HandleFunc("/recv", m.recv)
 	http.HandleFunc("/control", m.control)
 	http.HandleFunc("/slate", m.slate)

cmd/vidforward/watcher.go

@@ -0,0 +1,79 @@
+/*
+DESCRIPTION
+
+	watcher.go provides a tool for watching a file for modifications and
+	performing an action when the file is modified.
+
+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 (
+	"fmt"
+	"path"
+
+	"bitbucket.org/ausocean/utils/logging"
+	"github.com/fsnotify/fsnotify"
+)
+
+// watchFile watches a file for modifications and calls onWrite when the file
+// is modified. Technically, the directory is watched instead of the file.
+// This is because watching the file itself will cause problems if changes
+// are done atomically.
+// See fsnotify documentation:
+// https://godocs.io/github.com/fsnotify/fsnotify#hdr-Watching_files
+func watchFile(file string, onWrite func(), l logging.Logger) error {
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return fmt.Errorf("could not create watcher: %w", err)
+	}
+
+	go func() {
+		for {
+			select {
+			case event, ok := <-watcher.Events:
+				if !ok {
+					l.Warning("watcher events chan closed, terminating")
+					return
+				}
+				if event.Op&fsnotify.Write == fsnotify.Write && event.Name == file {
+					l.Info("file modification event", "file", file)
+					onWrite()
+				}
+			case err, ok := <-watcher.Errors:
+				if !ok {
+					l.Warning("watcher error chan closed, terminating")
+					return
+				}
+				l.Error("file watcher error", "error", err)
+			}
+		}
+	}()
+
+	// Watch the directory over the file.
+	err = watcher.Add(path.Dir(file))
+	if err != nil {
+		return fmt.Errorf("could not add file %s to watcher: %w", file, err)
+	}
+	return nil
+}

cmd/vidforward/watcher_test.go

@@ -0,0 +1,124 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"bitbucket.org/ausocean/utils/logging"
+)
+
+// Delay between changing a file and the file watcher picking up the change.
+const watchTimeAllowance = 1 * time.Second
+
+// TestWatchFile tests the watchFile function. It creates a temporary file,
+// watches it, writes to it, and checks if the onWrite function was called.
+func TestWatchFile(t *testing.T) {
+	tmpFile, err := ioutil.TempFile("", "example")
+	if err != nil {
+		t.Fatalf("could not create temporary file: %v", err)
+	}
+	defer os.Remove(tmpFile.Name())
+
+	// We'll check this to see if the onWrite function was called.
+	called := false
+
+	err = watchFile(tmpFile.Name(), func() {
+		called = true
+	}, (*logging.TestLogger)(t))
+	if err != nil {
+		t.Fatalf("watchFile failed: %v", err)
+	}
+
+	if _, err := tmpFile.Write([]byte("hello world")); err != nil {
+		t.Fatalf("could not write to temporary file: %v", err)
+	}
+	if err := tmpFile.Close(); err != nil {
+		t.Fatalf("could not close temporary file: %v", err)
+	}
+
+	// Allow some time for the file watcher to pick up the change.
+	time.Sleep(watchTimeAllowance)
+
+	if !called {
+		t.Errorf("onWrite was not called after modifying the file")
+	}
+}
+
+// TestWatchFileFileNotExistYet tests the watchFile function in the case
+// that the file to be watched does not exist on the first call to watchFile.
+// It creates a temporary directory, watches a file in that directory, creates
+// and writes to the file, and checks if the onWrite function was called.
+func TestWatchFileFileNotExistYet(t *testing.T) {
+	// Create a temporary directory.
+	tmpDir, err := ioutil.TempDir("", "example")
+	if err != nil {
+		t.Fatalf("could not create temporary directory: %v", err)
+	}
+	defer os.Remove(tmpDir) // clean up
+
+	// File that does not exist yet but will be created in the temporary directory.
+	fileName := filepath.Join(tmpDir, "testfile")
+
+	called := false
+	err = watchFile(fileName, func() {
+		called = true
+	}, (*logging.TestLogger)(t))
+	if err != nil {
+		t.Fatalf("watchFile failed: %v", err)
+	}
+
+	// Create and write to the file.
+	err = ioutil.WriteFile(fileName, []byte("hello world"), 0666)
+	if err != nil {
+		t.Fatalf("could not write to file: %v", err)
+	}
+
+	// Allow some time for the file watcher to pick up the change.
+	time.Sleep(watchTimeAllowance)
+
+	if !called {
+		t.Errorf("onWrite was not called after creating and modifying the file")
+	}
+}
+
+// TestWatchFileMultipleChanges tests the watchFile function in the case
+// that the file to be watched is modified multiple times. It creates a
+// temporary file, watches it, writes to it twice, and checks if the onWrite
+// function was called twice.
+func TestWatchFileMultipleChanges(t *testing.T) {
+	tmpfile, err := ioutil.TempFile("", "example")
+	if err != nil {
+		t.Fatalf("could not create temporary file: %v", err)
+	}
+	defer os.Remove(tmpfile.Name())
+
+	// We'll count how many times onWrite was called.
+	calledCount := 0
+
+	err = watchFile(tmpfile.Name(), func() {
+		calledCount++
+	}, (*logging.TestLogger)(t))
+	if err != nil {
+		t.Fatalf("watchFile failed: %v", err)
+	}
+
+	// Write to the file twice.
+	for i := 0; i < 2; i++ {
+		if _, err := tmpfile.Write([]byte("hello world")); err != nil {
+			t.Fatalf("could not write to temporary file: %v", err)
+		}
+		if err := tmpfile.Sync(); err != nil {
+			t.Fatalf("could not sync temporary file: %v", err)
+		}
+
+		// Allow some time for the file watcher to pick up the change.
+		time.Sleep(watchTimeAllowance)
+	}
+
+	if calledCount != 2 {
+		t.Errorf("onWrite was not called the expected number of times after modifying the file")
+	}
+}

go.mod

@@ -4,7 +4,7 @@ go 1.18
 
 require (
 	bitbucket.org/ausocean/iot v1.4.1
-	bitbucket.org/ausocean/utils v1.3.2
+	bitbucket.org/ausocean/utils v1.4.0
 	github.com/Comcast/gots v0.0.0-20190305015453-8d56e473f0f7
 	github.com/coreos/go-systemd v0.0.0-20191104093116-d3cd4ed1dbcf
 	github.com/go-audio/audio v0.0.0-20181013203223-7b2a6ca21480
@@ -22,6 +22,8 @@ require (
 	gopkg.in/natefinch/lumberjack.v2 v2.0.0
 )
 
+require github.com/fsnotify/fsnotify v1.6.0
+
 require (
 	github.com/ajstarks/svgo v0.0.0-20180226025133-644b8db467af // indirect
 	github.com/fogleman/gg v1.3.0 // indirect
@@ -35,4 +37,5 @@ require (
 	go.uber.org/multierr v1.1.0 // indirect
 	go.uber.org/zap v1.10.0 // indirect
 	golang.org/x/image v0.0.0-20210216034530-4410531fe030 // indirect
+	golang.org/x/sys v0.0.0-20220908164124-27713097b956 // indirect
 )

go.sum

@@ -3,8 +3,8 @@ bitbucket.org/ausocean/iot v1.4.1 h1:PcRu9dS5CbKyw1FZjEc4MR9CQ+ku9MkH9ZjA0f6Mm1c
 bitbucket.org/ausocean/iot v1.4.1/go.mod h1:NbEg2PvYSHDdUsy5eMmihBySpWfqaHiMdspQDZdDe8o=
 bitbucket.org/ausocean/utils v1.2.11/go.mod h1:uXzX9z3PLemyURTMWRhVI8uLhPX4uuvaaO85v2hcob8=
 bitbucket.org/ausocean/utils v1.3.0/go.mod h1:yWsulKjbBgwL17/w55MQ6cIT9jmNeOkwpd2gUIxAcIY=
-bitbucket.org/ausocean/utils v1.3.2 h1:U+jNixVPH1Ih0QpOckI4djhEc/T6FAzt9znADRcJ07s=
-bitbucket.org/ausocean/utils v1.3.2/go.mod h1:XgvCH4DQLCd6NYMzsSqwhHmPr+qzYks5M8IDpdNnZiU=
+bitbucket.org/ausocean/utils v1.4.0 h1:ceNRscC49fAVY9tIOAN3Jyg7g+A9JTKjqgxEGb7A+9E=
+bitbucket.org/ausocean/utils v1.4.0/go.mod h1:XgvCH4DQLCd6NYMzsSqwhHmPr+qzYks5M8IDpdNnZiU=
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
 gioui.org v0.0.0-20210308172011-57750fc8a0a6/go.mod h1:RSH6KIUZ0p2xy5zHDxgAM4zumjgTw83q2ge/PI+yyw8=
 github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
@@ -36,6 +36,8 @@ github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSs
 github.com/fogleman/gg v1.2.1-0.20190220221249-0403632d5b90/go.mod h1:R/bRT+9gY/C5z7JzPU0zXsXHKM4/ayA+zqcVNZzPa1k=
 github.com/fogleman/gg v1.3.0 h1:/7zJX8F6AaYQc57WQCyN9cAIz+4bCJGO9B+dyW29am8=
 github.com/fogleman/gg v1.3.0/go.mod h1:R/bRT+9gY/C5z7JzPU0zXsXHKM4/ayA+zqcVNZzPa1k=
+github.com/fsnotify/fsnotify v1.6.0 h1:n+5WquG0fcWoWp6xPWfHdbskMCQaFnG6PfBrh1Ky4HY=
+github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbSClcnxKAGw=
 github.com/go-audio/aiff v0.0.0-20180403003018-6c3a8a6aff12/go.mod h1:AMSAp6W1zd0koOdX6QDgGIuBDTUvLa2SLQtm7d9eM3c=
 github.com/go-audio/audio v0.0.0-20180206231410-b697a35b5608/go.mod h1:6uAu0+H2lHkwdGsAY+j2wHPNPpPoeg5AaEFh9FlA+Zs=
 github.com/go-audio/audio v0.0.0-20181013203223-7b2a6ca21480 h1:4sGU+UABMMsRJyD+Y2yzMYxq0GJFUsRRESI0P1gZ2ig=
@@ -141,6 +143,8 @@ golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210304124612-50617c2ba197/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20210909193231-528a39cd75f3/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220908164124-27713097b956 h1:XeJjHH1KiLpKGb6lvMiksZ9l0fVUh+AmGcm0nOMEBOY=
+golang.org/x/sys v0.0.0-20220908164124-27713097b956/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=