Address the review comments.

Make the truncating function not exportable outside package.
Improve name for AppName max chars constant.
Put constant local to the formatter module.

constants.go

@@ -12,7 +12,6 @@ type Priority int
 
 const severityMask = 0x07
 const facilityMask = 0xf8
-const appNameMax = 48 // limit to 48 chars as per RFC5424
 
 const (
 	// Severity.

formatter.go

@@ -6,6 +6,8 @@ import (
 	"time"
 )
 
+const appNameMaxLength = 48 // limit to 48 chars as per RFC5424
+
 // Formatter is a type of function that takes the consituent parts of a
 // syslog message and returns a formatted string. A different Formatter is
 // defined for each different syslog protocol we support.
@@ -38,7 +40,7 @@ func RFC3164Formatter(p Priority, hostname, tag, content string) string {
 }
 
 // if string's length is greater than max, then use the last part
-func TruncateStartStr(s string, max int) string {
+func truncateStartStr(s string, max int) string {
 	if (len(s) > max) {
 		return s[len(s) - max:]
 	}
@@ -49,7 +51,7 @@ func TruncateStartStr(s string, max int) string {
 func RFC5424Formatter(p Priority, hostname, tag, content string) string {
 	timestamp := time.Now().Format(time.RFC3339)
 	pid := os.Getpid()
-	appName := TruncateStartStr(os.Args[0], appNameMax)
+	appName := truncateStartStr(os.Args[0], appNameMaxLength)
 	msg := fmt.Sprintf("<%d>%d %s %s %s %d %s - %s",
 		p, 1, timestamp, hostname, appName, pid, tag, content)
 	return msg

formatter_test.go

@@ -38,19 +38,19 @@ func TestRFC3164Formatter(t *testing.T) {
 func TestRFC5424Formatter(t *testing.T) {
 	out := RFC5424Formatter(LOG_ERR, "hostname", "tag", "content")
 	expected := fmt.Sprintf("<%d>%d %s %s %s %d %s - %s",
-		LOG_ERR, 1, time.Now().Format(time.RFC3339), "hostname", TruncateStartStr(os.Args[0], appNameMax),
+		LOG_ERR, 1, time.Now().Format(time.RFC3339), "hostname", truncateStartStr(os.Args[0], appNameMaxLength),
 			os.Getpid(), "tag", "content")
 	if out != expected {
 		t.Errorf("expected %v got %v", expected, out)
 	}
 }
 
 func TestTruncateStartStr(t *testing.T) {
-	out := TruncateStartStr("abcde", 3)
+	out := truncateStartStr("abcde", 3)
 	if strings.Compare(out, "cde" ) != 0 {
 		t.Errorf("expected \"cde\" got %v", out)
 	}
-	out = TruncateStartStr("abcde", 5)
+	out = truncateStartStr("abcde", 5)
 	if strings.Compare(out, "abcde" ) != 0 {
 		t.Errorf("expected \"abcde\" got %v", out)
 	}