root: config: implement config watching

Signed-off-by: Marc 'risson' Schmitt <marc.schmitt@risson.space>

go.mod

@@ -42,6 +42,7 @@ require (
 	github.com/cespare/xxhash/v2 v2.2.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/felixge/httpsnoop v1.0.1 // indirect
+	github.com/fsnotify/fsnotify v1.6.0 // indirect
 	github.com/go-asn1-ber/asn1-ber v1.5.4 // indirect
 	github.com/go-http-utils/fresh v0.0.0-20161124030543-7231e26a4b27 // indirect
 	github.com/go-http-utils/headers v0.0.0-20181008091004-fed159eddc2a // indirect

go.sum

@@ -66,6 +66,8 @@ github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1m
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
 github.com/felixge/httpsnoop v1.0.1 h1:lvB5Jl89CsZtGIWuTcDM1E/vkVs49/Ml7JJe07l8SPQ=
 github.com/felixge/httpsnoop v1.0.1/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
+github.com/fsnotify/fsnotify v1.6.0 h1:n+5WquG0fcWoWp6xPWfHdbskMCQaFnG6PfBrh1Ky4HY=
+github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbSClcnxKAGw=
 github.com/garyburd/redigo v1.6.4 h1:LFu2R3+ZOPgSMWMOL+saa/zXRjw0ID2G8FepO53BGlg=
 github.com/garyburd/redigo v1.6.4/go.mod h1:rTb6epsqigu3kYKBnaF028A7Tf/Aw5s0cqA47doKKqw=
 github.com/getsentry/sentry-go v0.20.0 h1:bwXW98iMRIWxn+4FgPW7vMrjmbym6HblXALmhjHmQaQ=
@@ -486,6 +488,7 @@ golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.0.0-20220908164124-27713097b956/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.7.0 h1:3jlCCIQZPdOYu1h8BkNvLz8Kgwtae2cagcG/VamtZRU=
 golang.org/x/sys v0.7.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=

internal/config/config.go

@@ -8,8 +8,10 @@ import (
 	"path/filepath"
 	"reflect"
 	"strings"
+	"time"
 
 	env "github.com/Netflix/go-env"
+	"github.com/fsnotify/fsnotify"
 	log "github.com/sirupsen/logrus"
 	"gopkg.in/yaml.v2"
 )
@@ -53,6 +55,71 @@ func getConfigPaths() []string {
 	return computedConfigPaths
 }
 
+func WatchChanges(callback func()) (*fsnotify.Watcher, error) {
+	configPaths := getConfigPaths()
+
+	w, err := fsnotify.NewWatcher()
+	if err != nil {
+		return nil, err
+	}
+
+	// Start listening for events
+	go func() {
+		reload := false
+		for {
+			select {
+			// Read from errors
+			case err, ok := <-w.Errors:
+				if !ok {
+					// Channel was closed (i.e. Watcher.Close() was called)
+					return
+				}
+				log.WithError(err).Warning("failed to watch for file changes")
+			// Read from events
+			case ev, ok := <-w.Events:
+				if !ok {
+					// Channel was closed (i.e. Watcher.Close() was called)
+					return
+				}
+
+				// Ignores files we're not interested in
+				// We get the whole list again in case a file in a directory we're watching was created
+				// and that file is of interest
+				for _, f := range getConfigPaths() {
+					if f == ev.Name {
+						reload = true
+						log.Debugf("%s file change, setting configuration to be reloaded", ev.Name)
+					}
+				}
+			default:
+				if reload {
+					log.Infof("configuration files changed, reloading configuration")
+					Reload()
+					callback()
+					// Cooldown after configuration reloading
+					time.Sleep(14 * time.Second)
+				}
+				// Otherwise `select` fires all of the time
+				time.Sleep(1 * time.Second)
+				reload = false
+			}
+		}
+	}()
+
+	// Register the files to be watch
+	for _, p := range configPaths {
+		// Actually, watch the directory, not the files, as that's how fsnotify works
+		// We assume we're only getting valid files as getConfigPaths already handles all the necessary checks
+		err = w.Add(filepath.Dir(p))
+		log.Warningf("watching for changes for file %s in dir %s", p, filepath.Dir(p))
+		if err != nil {
+			return w, err
+		}
+	}
+
+	return w, nil
+}
+
 func Get() *Config {
 	if cfg == nil {
 		c := &Config{}
@@ -62,6 +129,12 @@ func Get() *Config {
 	return cfg
 }
 
+func Reload() {
+	c := &Config{}
+	c.Setup(getConfigPaths()...)
+	cfg = c
+}
+
 func (c *Config) Setup(paths ...string) {
 	for _, path := range paths {
 		err := c.LoadConfig(path)