Implement facility based logger, debugging via REST API

This implements a new debug/trace infrastructure based on a slightly
hacked up logger. Instead of the traditional "if debug { ... }" I've
rewritten the logger to have no-op Debugln and Debugf, unless debugging
has been enabled for a given "facility". The "facility" is just a
string, typically a package name.

This will be slightly slower than before; but not that much as it's
mostly a function call that returns immediately. For the cases where it
matters (the Debugln takes a hex.Dump() of something for example, and
it's not in a very occasional "if err != nil" branch) there is an
l.ShouldDebug(facility) that is fast enough to be used like the old "if
debug".

The point of all this is that we can now toggle debugging for the
various packages on and off at runtime. There's a new method
/rest/system/debug that can be POSTed a set of facilities to enable and
disable debug for, or GET from to get a list of facilities with
descriptions and their current debug status.

Similarly a /rest/system/log?since=... can grab the latest log entries,
up to 250 of them (hardcoded constant in main.go) plus the initial few.

Not implemented in this commit (but planned) is a simple debug GUI
available on /debug that shows the current log in an easily pasteable
format and has checkboxes to enable the various debug facilities.

The debug instructions to a user then becomes "visit this URL, check
these boxes, reproduce your problem, copy and paste the log". The actual
log viewer on the hypothetical /debug URL can poll regularly for new log
entries and this bypass the 250 line limit.

The existing STTRACE=foo variable is still obeyed and just sets the
start state of the system.

cmd/syncthing/gui.go

@@ -20,16 +20,17 @@ import (
 	"path/filepath"
 	"reflect"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
 
-	"github.com/calmh/logger"
 	"github.com/syncthing/syncthing/lib/auto"
 	"github.com/syncthing/syncthing/lib/config"
 	"github.com/syncthing/syncthing/lib/db"
 	"github.com/syncthing/syncthing/lib/discover"
 	"github.com/syncthing/syncthing/lib/events"
+	"github.com/syncthing/syncthing/lib/logger"
 	"github.com/syncthing/syncthing/lib/model"
 	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
@@ -41,15 +42,8 @@ import (
 	"golang.org/x/crypto/bcrypt"
 )
 
-type guiError struct {
-	Time  time.Time `json:"time"`
-	Error string    `json:"error"`
-}
-
 var (
 	configInSync = true
-	guiErrors    = []guiError{}
-	guiErrorsMut = sync.NewMutex()
 	startTime    = time.Now()
 )
 
@@ -65,9 +59,12 @@ type apiSvc struct {
 	fss             *folderSummarySvc
 	stop            chan struct{}
 	systemConfigMut sync.Mutex
+
+	guiErrors *logger.Recorder
+	systemLog *logger.Recorder
 }
 
-func newAPISvc(id protocol.DeviceID, cfg *config.Wrapper, assetDir string, m *model.Model, eventSub *events.BufferedSubscription, discoverer *discover.CachingMux, relaySvc *relay.Svc) (*apiSvc, error) {
+func newAPISvc(id protocol.DeviceID, cfg *config.Wrapper, assetDir string, m *model.Model, eventSub *events.BufferedSubscription, discoverer *discover.CachingMux, relaySvc *relay.Svc, errors, systemLog *logger.Recorder) (*apiSvc, error) {
 	svc := &apiSvc{
 		id:              id,
 		cfg:             cfg,
@@ -77,6 +74,8 @@ func newAPISvc(id protocol.DeviceID, cfg *config.Wrapper, assetDir string, m *mo
 		discoverer:      discoverer,
 		relaySvc:        relaySvc,
 		systemConfigMut: sync.NewMutex(),
+		guiErrors:       errors,
+		systemLog:       systemLog,
 	}
 
 	var err error
@@ -138,8 +137,6 @@ func (s *apiSvc) getListener(cfg config.GUIConfiguration) (net.Listener, error)
 func (s *apiSvc) Serve() {
 	s.stop = make(chan struct{})
 
-	l.AddHandler(logger.LevelWarn, s.showGuiError)
-
 	// The GET handlers
 	getRestMux := http.NewServeMux()
 	getRestMux.HandleFunc("/rest/db/completion", s.getDBCompletion)              // device folder
@@ -164,6 +161,9 @@ func (s *apiSvc) Serve() {
 	getRestMux.HandleFunc("/rest/system/status", s.getSystemStatus)              // -
 	getRestMux.HandleFunc("/rest/system/upgrade", s.getSystemUpgrade)            // -
 	getRestMux.HandleFunc("/rest/system/version", s.getSystemVersion)            // -
+	getRestMux.HandleFunc("/rest/system/debug", s.getSystemDebug)                // -
+	getRestMux.HandleFunc("/rest/system/log", s.getSystemLog)                    // [since]
+	getRestMux.HandleFunc("/rest/system/log.txt", s.getSystemLogTxt)             // [since]
 
 	// The POST handlers
 	postRestMux := http.NewServeMux()
@@ -181,6 +181,7 @@ func (s *apiSvc) Serve() {
 	postRestMux.HandleFunc("/rest/system/upgrade", s.postSystemUpgrade)        // -
 	postRestMux.HandleFunc("/rest/system/pause", s.postSystemPause)            // device
 	postRestMux.HandleFunc("/rest/system/resume", s.postSystemResume)          // device
+	postRestMux.HandleFunc("/rest/system/debug", s.postSystemDebug)            // [enable] [disable]
 
 	// Debug endpoints, not for general use
 	getRestMux.HandleFunc("/rest/debug/peerCompletion", s.getPeerCompletion)
@@ -223,9 +224,7 @@ func (s *apiSvc) Serve() {
 		handler = redirectToHTTPSMiddleware(handler)
 	}
 
-	if debugHTTP {
-		handler = debugMiddleware(handler)
-	}
+	handler = debugMiddleware(handler)
 
 	srv := http.Server{
 		Handler:     handler,
@@ -379,6 +378,36 @@ func (s *apiSvc) getSystemVersion(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+func (s *apiSvc) getSystemDebug(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	names := l.Facilities()
+	enabled := l.FacilityDebugging()
+	sort.Strings(enabled)
+	json.NewEncoder(w).Encode(map[string]interface{}{
+		"facilities": names,
+		"enabled":    enabled,
+	})
+}
+
+func (s *apiSvc) postSystemDebug(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	q := r.URL.Query()
+	for _, f := range strings.Split(q.Get("enable"), ",") {
+		if f == "" {
+			continue
+		}
+		l.SetDebug(f, true)
+		l.Infof("Enabled debug data for %q", f)
+	}
+	for _, f := range strings.Split(q.Get("disable"), ",") {
+		if f == "" {
+			continue
+		}
+		l.SetDebug(f, false)
+		l.Infof("Disabled debug data for %q", f)
+	}
+}
+
 func (s *apiSvc) getDBBrowse(w http.ResponseWriter, r *http.Request) {
 	qs := r.URL.Query()
 	folder := qs.Get("folder")
@@ -684,30 +713,41 @@ func (s *apiSvc) getSystemStatus(w http.ResponseWriter, r *http.Request) {
 
 func (s *apiSvc) getSystemError(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
-	guiErrorsMut.Lock()
-	json.NewEncoder(w).Encode(map[string][]guiError{"errors": guiErrors})
-	guiErrorsMut.Unlock()
+	json.NewEncoder(w).Encode(map[string][]logger.Line{
+		"errors": s.guiErrors.Since(time.Time{}),
+	})
 }
 
 func (s *apiSvc) postSystemError(w http.ResponseWriter, r *http.Request) {
 	bs, _ := ioutil.ReadAll(r.Body)
 	r.Body.Close()
-	s.showGuiError(0, string(bs))
+	l.Warnln(string(bs))
 }
 
 func (s *apiSvc) postSystemErrorClear(w http.ResponseWriter, r *http.Request) {
-	guiErrorsMut.Lock()
-	guiErrors = []guiError{}
-	guiErrorsMut.Unlock()
+	s.guiErrors.Clear()
 }
 
-func (s *apiSvc) showGuiError(l logger.LogLevel, err string) {
-	guiErrorsMut.Lock()
-	guiErrors = append(guiErrors, guiError{time.Now(), err})
-	if len(guiErrors) > 5 {
-		guiErrors = guiErrors[len(guiErrors)-5:]
+func (s *apiSvc) getSystemLog(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	since, err := time.Parse(time.RFC3339, q.Get("since"))
+	l.Debugln(err)
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+
+	json.NewEncoder(w).Encode(map[string][]logger.Line{
+		"messages": s.systemLog.Since(since),
+	})
+}
+
+func (s *apiSvc) getSystemLogTxt(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	since, err := time.Parse(time.RFC3339, q.Get("since"))
+	l.Debugln(err)
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+
+	for _, line := range s.systemLog.Since(since) {
+		fmt.Fprintf(w, "%s: %s\n", line.When.Format(time.RFC3339), line.Message)
 	}
-	guiErrorsMut.Unlock()
 }
 
 func (s *apiSvc) getSystemDiscovery(w http.ResponseWriter, r *http.Request) {