toggledlog: convert remaing naked fmt.Print*

Several fatal errors were just printed to stdout, which
meant they were invisible when running the test suite.

Fix this by introducing toggledlog.Fatal and convert as
follows:

Fatal errors     -> toggledlog.Fatal
Warnings         -> toggledlog.Warn
Password prompts -> fmt.Fprintf

3 files changed, 17 insertions, 9 deletions

diff --git a/internal/configfile/kdf.go b/internal/configfile/kdf.go
index f1a7a40..e77a743 100644
--- a/internal/configfile/kdf.go
+++ b/internal/configfile/kdf.go
@@ -1,13 +1,14 @@
 package configfile
 
 import (
-	"fmt"
+	"log"
 	"math"
 	"os"
 
 	"golang.org/x/crypto/scrypt"
 
 	"github.com/rfjakob/gocryptfs/internal/cryptocore"
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
 )
 
 const (
@@ -31,7 +32,7 @@ func NewScryptKdf(logN int) scryptKdf {
 		s.N = 1 << ScryptDefaultLogN
 	} else {
 		if logN < 10 {
-			fmt.Println("Error: scryptn below 10 is too low to make sense. Aborting.")
+			toggledlog.Fatal.Println("Error: scryptn below 10 is too low to make sense. Aborting.")
 			os.Exit(1)
 		}
 		s.N = 1 << uint32(logN)
@@ -45,7 +46,7 @@ func NewScryptKdf(logN int) scryptKdf {
 func (s *scryptKdf) DeriveKey(pw string) []byte {
 	k, err := scrypt.Key([]byte(pw), s.Salt, s.N, s.R, s.P, s.KeyLen)
 	if err != nil {
-		panic(fmt.Sprintf("DeriveKey failed: %s", err.Error()))
+		log.Panicf("DeriveKey failed: %v", err)
 	}
 	return k
 }
diff --git a/internal/prefer_openssl/prefer.go b/internal/prefer_openssl/prefer.go
index 16788e0..0bc24b4 100644
--- a/internal/prefer_openssl/prefer.go
+++ b/internal/prefer_openssl/prefer.go
@@ -1,9 +1,10 @@
 package prefer_openssl
 
 import (
-	"fmt"
 	"io/ioutil"
 	"regexp"
+
+	"github.com/rfjakob/gocryptfs/internal/toggledlog"
 )
 
 // filePreferOpenSSL tells us if OpenSSL is faster than Go GCM on this machine.
@@ -17,12 +18,12 @@ import (
 func filePreferOpenSSL(file string) bool {
 	ci, err := ioutil.ReadFile(file)
 	if err != nil {
-		fmt.Println(err)
+		toggledlog.Warn.Println(err)
 		return true
 	}
 	haveAes, err := regexp.Match(`(?m)^flags.*\baes\b`, ci)
 	if err != nil {
-		fmt.Println(err)
+		toggledlog.Warn.Println(err)
 		return true
 	}
 	return !haveAes
diff --git a/internal/toggledlog/log.go b/internal/toggledlog/log.go
index 7f437c8..23d7347 100644
--- a/internal/toggledlog/log.go
+++ b/internal/toggledlog/log.go
@@ -49,18 +49,24 @@ func (l *toggledLogger) Println(v ...interface{}) {
 	}
 }
 
-// As defined by http://elinux.org/Debugging_by_printing#Log_Levels
 // Debug messages
+// Can be enabled by passing "-d"
 var Debug *toggledLogger
 
-// Informational message e.g. startup information
+// Informational message
+// Can be disabled by passing "-q"
 var Info *toggledLogger
 
-// A warning, meaning nothing serious by itself but might indicate problems
+// A warning, meaning nothing serious by itself but might indicate problems.
+// Passing "-wpanic" will make this function panic after printing the message.
 var Warn *toggledLogger
 
+// Fatal error, we are about to exit
+var Fatal *toggledLogger
+
 func init() {
 	Debug = &toggledLogger{false, false, log.New(os.Stdout, "", 0)}
 	Info = &toggledLogger{true, false, log.New(os.Stdout, "", 0)}
 	Warn = &toggledLogger{true, false, log.New(os.Stderr, "", 0)}
+	Fatal = &toggledLogger{true, false, log.New(os.Stderr, "", 0)}
 }