tlog: always trim trailing newlines

The messages we print through tlog sometimes do, sometimes do
not contain a trailing newline. The stdlib logger usually drops
trailing newlines automatically, but tlog postfixes ColorReset to
the caller's message, so the logger logic does not work when we
print colored output.

Drop the newlines on our own, and add a test.

Fixes the blank lines in fsck output:

~/go/src/github.com/rfjakob/gocryptfs/tests/fsck$ ./run_fsck.bash
Reading password from extpass program
Decrypting master key
OpenDir "": invalid entry "invalid_file_name.3": illegal base64 data at input byte 17
OpenDir "": invalid entry "invalid_file_name_2": bad message
fsck: corrupt entry in dir "": "invalid_file_name.3"
fsck: corrupt entry in dir "": "invalid_file_name_2"
OpenDir "": invalid entry "invalid_file_name____1": bad message
fsck: corrupt entry in dir "": "invalid_file_name____1"
doRead 4327225: corrupt block #0: stupidgcm: message authentication failed
fsck: error reading file "corrupt_file" (inum 4327225): 5=input/output error
cipherSize 40 < overhead 50: corrupt file

doRead 4327074: corrupt header: ParseHeader: invalid version, want=2 have=22616
cipherSize 40 < overhead 50: corrupt file

fsck: error reading file "corrupt_file_2" (inum 4327074): 5=input/output error
Readlink "s-P7PcQDUcVkoeMDnC3EYA": decrypting target failed: stupidgcm: message authentication failed
fsck: error reading symlink "corrupt_symlink": 5=input/output error
Readlink "iI0MtUdzELPeOAZYwYZFee169hpGgd3l2PXQBcc9sl4": decrypting target failed: illegal base64 data at input byte 0
fsck: error reading symlink "corrupt_symlink_2": 5=input/output error
OpenDir "yrwcjj2qoC4IYvhw9sbfRg": could not read gocryptfs.diriv: wanted 16 bytes, got 17
fsck: error opening dir "diriv_too_long": 5=input/output error
OpenDir "trqecbMNXdzLqzpk7fSfKw": could not read gocryptfs.diriv: wanted 16 bytes, got 3
fsck: error opening dir "diriv_too_short": 5=input/output error
cipherSize 8 < header size 18: corrupt file

readFileID 4327049: incomplete file, got 8 instead of 19 bytes
fsck: corrupt file "incomplete_file_1" (inode 4327049)
readFileID 4327038: incomplete file, got 18 instead of 19 bytes
fsck: corrupt file "incomplete_file_2" (inode 4327038)
cipherSize 1 < header size 18: corrupt file

readFileID 4327063: incomplete file, got 1 instead of 19 bytes
fsck: corrupt file "incomplete_file_3" (inode 4327063)
fsck: error opening dir "missing_diriv": 2=no such file or directory
ListXAttr: invalid xattr name "user.gocryptfs.0a5e7yWl0SGUGeWB0Sy2K0": bad message
fsck: corrupt xattr name on file "xattr_corrupt_name": "user.gocryptfs.0a5e7yWl0SGUGeWB0Sy2K0"
GetXAttr: stupidgcm: message authentication failed
fsck: error reading xattr "user.foo" from "xattr_corrupt_value": 5=input/output error
fsck summary: 15 corrupt files

2 files changed, 43 insertions, 4 deletions

diff --git a/internal/tlog/log.go b/internal/tlog/log.go
index 9277abd..9ebe535 100644
--- a/internal/tlog/log.go
+++ b/internal/tlog/log.go
@@ -57,22 +57,35 @@ type toggledLogger struct {
 	Logger *log.Logger
 }
 
+// trimNewline removes one trailing newline from "msg"
+func trimNewline(msg string) string {
+	if len(msg) == 0 {
+		return msg
+	}
+	if msg[len(msg)-1] == '\n' {
+		return msg[:len(msg)-1]
+	}
+	return msg
+}
+
 func (l *toggledLogger) Printf(format string, v ...interface{}) {
 	if !l.Enabled {
 		return
 	}
-	l.Logger.Printf(l.prefix + fmt.Sprintf(format, v...) + l.postfix)
+	msg := trimNewline(fmt.Sprintf(format, v...))
+	l.Logger.Printf(l.prefix + msg + l.postfix)
 	if l.Wpanic {
-		l.Logger.Panic(wpanicMsg + fmt.Sprintf(format, v...))
+		l.Logger.Panic(wpanicMsg + msg)
 	}
 }
 func (l *toggledLogger) Println(v ...interface{}) {
 	if !l.Enabled {
 		return
 	}
-	l.Logger.Println(l.prefix + fmt.Sprint(v...) + l.postfix)
+	msg := trimNewline(fmt.Sprint(v...))
+	l.Logger.Println(l.prefix + msg + l.postfix)
 	if l.Wpanic {
-		l.Logger.Panic(wpanicMsg + fmt.Sprint(v...))
+		l.Logger.Panic(wpanicMsg + msg)
 	}
 }
 
diff --git a/internal/tlog/tlog_test.go b/internal/tlog/tlog_test.go
new file mode 100644
index 0000000..2e1c034
--- /dev/null
+++ b/internal/tlog/tlog_test.go
@@ -0,0 +1,26 @@
+package tlog
+
+import (
+	"testing"
+)
+
+// Test that trimNewline() works as expected
+func TestTrimNewline(t *testing.T) {
+	testTable := []struct {
+		in   string
+		want string
+	}{
+		{"...\n", "..."},
+		{"\n...\n", "\n..."},
+		{"", ""},
+		{"\n", ""},
+		{"\n\n", "\n"},
+		{"   ", "   "},
+	}
+	for _, v := range testTable {
+		have := trimNewline(v.in)
+		if v.want != have {
+			t.Errorf("want=%q have=%q", v.want, have)
+		}
+	}
+}