feat: implement syslog logging (#181)

* feat: implement syslog logging

With this functionality in tree, macOS users could easily access
ooniprobe logs by filtering by process name in the console app.

Part of https://github.com/ooni/probe/issues/1289

* fix: build on windows

* fix: all build issues

cmd/ooniprobe/main.go

@@ -1,9 +1,8 @@
 package main
 
 import (
-	// commands
-
 	"github.com/apex/log"
+	"github.com/ooni/probe-cli/internal/cli/app"
 	_ "github.com/ooni/probe-cli/internal/cli/geoip"
 	_ "github.com/ooni/probe-cli/internal/cli/info"
 	_ "github.com/ooni/probe-cli/internal/cli/list"
@@ -15,13 +14,10 @@ import (
 	_ "github.com/ooni/probe-cli/internal/cli/upload"
 	_ "github.com/ooni/probe-cli/internal/cli/version"
 	"github.com/ooni/probe-cli/internal/crashreport"
-
-	"github.com/ooni/probe-cli/internal/cli/app"
 )
 
 func main() {
-	err, _ := crashreport.CapturePanic(app.Run, nil)
+	if err, _ := crashreport.CapturePanic(app.Run, nil); err != nil {
-	if err != nil {
 		log.WithError(err.(error)).Error("panic in app.Run")
 		crashreport.Wait()
 	}

internal/cli/root/root.go

@@ -5,6 +5,7 @@ import (
 	"github.com/apex/log"
 	"github.com/ooni/probe-cli/internal/log/handlers/batch"
 	"github.com/ooni/probe-cli/internal/log/handlers/cli"
+	"github.com/ooni/probe-cli/internal/log/handlers/syslog"
 	"github.com/ooni/probe-cli/internal/ooni"
 	"github.com/ooni/probe-cli/internal/utils"
 	"github.com/ooni/probe-cli/internal/version"
@@ -33,6 +34,9 @@ func init() {
 
 	isVerbose := Cmd.Flag("verbose", "Enable verbose log output.").Short('v').Bool()
 	isBatch := Cmd.Flag("batch", "Enable batch command line usage.").Bool()
+	logHandler := Cmd.Flag(
+		"log-handler", "Set the desired log handler (one of: batch, cli, syslog)",
+	).String()
 
 	softwareName := Cmd.Flag(
 		"software-name", "Override application name",
@@ -42,10 +46,23 @@ func init() {
 	).Default(version.Version).String()
 
 	Cmd.PreAction(func(ctx *kingpin.ParseContext) error {
+		// TODO(bassosimone): we need to properly deprecate --batch
+		// in favour of more granular command line flags.
+		if *isBatch && *logHandler != "" {
+			log.Fatal("cannot specify --batch and --log-handler together")
+		}
 		if *isBatch {
+			*logHandler = "batch"
+		}
+		switch *logHandler {
+		case "batch":
 			log.SetHandler(batch.Default)
-		} else {
+		case "cli", "":
 			log.SetHandler(cli.Default)
+		case "syslog":
+			log.SetHandler(syslog.Default)
+		default:
+			log.Fatalf("unknown --log-handler: %s", *logHandler)
 		}
 		if *isVerbose {
 			log.SetLevel(log.DebugLevel)

internal/log/handlers/syslog/syslog.c

@@ -0,0 +1,39 @@
+#ifndef _WIN32
+#include <syslog.h>
+#endif
+
+void ooniprobe_openlog(void) {
+#ifndef _WIN32
+    (void)openlog("ooniprobe", LOG_PID, LOG_USER);
+#endif
+}
+
+void ooniprobe_log_debug(const char *message) {
+#ifndef _WIN32
+    (void)syslog(LOG_DEBUG, "%s", message);
+#endif
+}
+
+void ooniprobe_log_info(const char *message) {
+#ifndef _WIN32
+    (void)syslog(LOG_INFO, "%s", message);
+#endif
+}
+
+void ooniprobe_log_warning(const char *message) {
+#ifndef _WIN32
+    (void)syslog(LOG_WARNING, "%s", message);
+#endif
+}
+
+void ooniprobe_log_err(const char *message) {
+#ifndef _WIN32
+    (void)syslog(LOG_ERR, "%s", message);
+#endif
+}
+
+void ooniprobe_log_crit(const char *message) {
+#ifndef _WIN32
+    (void)syslog(LOG_CRIT, "%s", message);
+#endif
+}

internal/log/handlers/syslog/syslog.go

@@ -0,0 +1,53 @@
+// Package syslog contains a syslog handler.
+//
+// We use this handler on macOS systems to log messages
+// when ooniprobe is running in the background.
+package syslog
+
+import (
+	"fmt"
+	"unsafe"
+
+	"github.com/apex/log"
+)
+
+/*
+#include<stdlib.h>
+
+void ooniprobe_openlog(void);
+void ooniprobe_log_debug(const char *message);
+void ooniprobe_log_info(const char *message);
+void ooniprobe_log_warning(const char *message);
+void ooniprobe_log_err(const char *message);
+void ooniprobe_log_crit(const char *message);
+*/
+import "C"
+
+// Default is the handler that emits logs with syslog
+var Default log.Handler = newhandler()
+
+type handler struct{}
+
+func newhandler() handler {
+	C.ooniprobe_openlog()
+	return handler{}
+}
+
+func (h handler) HandleLog(e *log.Entry) error {
+	message := fmt.Sprintf("%s %+v", e.Message, e.Fields)
+	cstr := C.CString(message)
+	defer C.free(unsafe.Pointer(cstr))
+	switch e.Level {
+	case log.DebugLevel:
+		C.ooniprobe_log_debug(cstr)
+	case log.InfoLevel:
+		C.ooniprobe_log_info(cstr)
+	case log.WarnLevel:
+		C.ooniprobe_log_warning(cstr)
+	case log.ErrorLevel:
+		C.ooniprobe_log_err(cstr)
+	default:
+		C.ooniprobe_log_crit(cstr)
+	}
+	return nil
+}