Add efficient implementation of fmt and use for errors.

common/errors.go

@@ -10,16 +10,19 @@ import (
 
 type Error interface {
 	Error() string
-	Trace(msg string) Error
-	TraceCause(cause error, msg string) Error
+	Trace(format string, a ...interface{}) Error
+	TraceCause(cause error, format string, a ...interface{}) Error
 	Cause() error
 }
 
-func NewError(msg string) Error {
+func NewError(format string, a ...interface{}) Error {
+	msg := Fmt(format, a...)
 	return newError(msg, nil)
+
 }
 
-func NewErrorWithCause(cause error, msg string) Error {
+func NewErrorWithCause(cause error, format string, a ...interface{}) Error {
+	msg := Fmt(format, a...)
 	return newError(msg, cause)
 }
 
@@ -39,6 +42,7 @@ type cmnError struct {
 	traces []traceItem
 }
 
+// NOTE: Do not expose, it's not very friendly.
 func newError(msg string, cause error) *cmnError {
 	return &cmnError{
 		msg:    msg,
@@ -52,13 +56,15 @@ func (err *cmnError) Error() string {
 }
 
 // Add tracing information with msg.
-func (err *cmnError) Trace(msg string) Error {
+func (err *cmnError) Trace(format string, a ...interface{}) Error {
+	msg := Fmt(format, a...)
 	return err.doTrace(msg, 2)
 }
 
 // Add tracing information with cause and msg.
 // If a cause was already set before, it is overwritten.
-func (err *cmnError) TraceCause(cause error, msg string) Error {
+func (err *cmnError) TraceCause(cause error, format string, a ...interface{}) Error {
+	msg := Fmt(format, a...)
 	err.cause = cause
 	return err.doTrace(msg, 2)
 }

common/string.go

@@ -6,8 +6,14 @@ import (
 	"strings"
 )
 
-// Fmt shorthand, XXX DEPRECATED
-var Fmt = fmt.Sprintf
+// Like fmt.Sprintf, but skips formatting if args are empty.
+var Fmt = func(format string, a ...interface{}) string {
+	if len(a) == 0 {
+		return format
+	} else {
+		return fmt.Sprintf(format, a...)
+	}
+}
 
 // RightPadString adds spaces to the right of a string to make it length totalLength
 func RightPadString(s string, totalLength int) string {