// Copyright 2017, The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE.md file.
// Package value provides functionality for reflect.Value types.
package value
import (
"fmt"
"reflect"
"strconv"
"strings"
"unicode"
)
var stringerIface = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
// Format formats the value v as a string.
//
// This is similar to fmt.Sprintf("%+v", v) except this:
// * Prints the type unless it can be elided
// * Avoids printing struct fields that are zero
// * Prints a nil-slice as being nil, not empty
// * Prints map entries in deterministic order
func Format(v reflect.Value, conf FormatConfig) string {
conf.printType = true
conf.followPointers = true
conf.realPointers = true
return formatAny(v, conf, nil)
}
type FormatConfig struct {
UseStringer bool // Should the String method be used if available?
printType bool // Should we print the type before the value?
PrintPrimitiveType bool // Should we print the type of primitives?
followPointers bool // Should we recursively follow pointers?
realPointers bool // Should we print the real address of pointers?
}
func formatAny(v reflect.Value, conf FormatConfig, visited map[uintptr]bool) string {
// TODO: Should this be a multi-line printout in certain situations?
if !v.IsValid() {
return "<non-existent>"
}
if conf.UseStringer && v.Type().Implements(stringerIface) && v.CanInterface() {
if (v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface) && v.IsNil() {
return "<nil>"
}
const stringerPrefix = "s" // Indicates that the String method was used
s := v.Interface().(fmt.Stringer).String()
return stringerPrefix + formatString(s)
}
switch v.Kind() {
case reflect.Bool:
return formatPrimitive(v.Type(), v.Bool(), conf)
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return formatPrimitive(v.Type(), v.Int(), conf)
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
if v.Type().PkgPath() == "" || v.Kind() == reflect.Uintptr {
// Unnamed uints are usually bytes or words, so use hexadecimal.
return formatPrimitive(v.Type(), formatHex(v.Uint()), conf)
}
return formatPrimitive(v.Type(), v.Uint(), conf)
case reflect.Float32, reflect.Float64:
return formatPrimitive(v.Type(), v.Float(), conf)
case reflect.Complex64, reflect.Complex128:
return formatPrimitive(v.Type(), v.Complex(), conf)
case reflect.String:
return formatPrimitive(v.Type(), formatString(v.String()), conf)
case reflect.UnsafePointer, reflect.Chan, reflect.Func:
return formatPointer(v, conf)
case reflect.Ptr:
if v.IsNil() {
if conf.printType {
return fmt.Sprintf("(%v)(nil)", v.Type())
}
return "<nil>"
}
if visited[v.Pointer()] || !conf.followPointers {
return formatPointer(v, conf)
}
visited = insertPointer(visited, v.Pointer())
return "&" + formatAny(v.Elem(), conf, visited)
case reflect.Interface:
if v.IsNil() {
if conf.printType {
return fmt.Sprintf("%v(nil)", v.Type())
}
return "<nil>"
}
return formatAny(v.Elem(), conf, visited)
case reflect.Slice:
if v.IsNil() {
if conf.printType {
return fmt.Sprintf("%v(nil)", v.Type())
}
return "<nil>"
}
if visited[v.Pointer()] {
return formatPointer(v, conf)
}
visited = insertPointer(visited, v.Pointer())
fallthrough
case reflect.Array:
var ss []string
subConf := conf
subConf.printType = v.Type().Elem().Kind() == reflect.Interface
for i := 0; i < v.Len(); i++ {
s := formatAny(v.Index(i), subConf, visited)
ss = append(ss, s)
}
s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
if conf.printType {
return v.Type().String() + s
}
return s
case reflect.Map:
if v.IsNil() {
if conf.printType {
return fmt.Sprintf("%v(nil)", v.Type())
}
return "<nil>"
}
if visited[v.Pointer()] {
return formatPointer(v, conf)
}
visited = insertPointer(visited, v.Pointer())
var ss []string
keyConf, valConf := conf, conf
keyConf.printType = v.Type().Key().Kind() == reflect.Interface
keyConf.followPointers = false
valConf.printType = v.Type().Elem().Kind() == reflect.Interface
for _, k := range SortKeys(v.MapKeys()) {
sk := formatAny(k, keyConf, visited)
sv := formatAny(v.MapIndex(k), valConf, visited)
ss = append(ss, fmt.Sprintf("%s: %s", sk, sv))
}
s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
if conf.printType {
return v.Type().String() + s
}
return s
case reflect.Struct:
var ss []string
subConf := conf
subConf.printType = true
for i := 0; i < v.NumField(); i++ {
vv := v.Field(i)
if isZero(vv) {
continue // Elide zero value fields
}
name := v.Type().Field(i).Name
subConf.UseStringer = conf.UseStringer
s := formatAny(vv, subConf, visited)
ss = append(ss, fmt.Sprintf("%s: %s", name, s))
}
s := fmt.Sprintf("{%s}", strings.Join(ss, ", "))
if conf.printType {
return v.Type().String() + s
}
return s
default:
panic(fmt.Sprintf("%v kind not handled", v.Kind()))
}
}
func formatString(s string) string {
// Use quoted string if it the same length as a raw string literal.
// Otherwise, attempt to use the raw string form.
qs := strconv.Quote(s)
if len(qs) == 1+len(s)+1 {
return qs
}
// Disallow newlines to ensure output is a single line.
// Only allow printable runes for readability purposes.
rawInvalid := func(r rune) bool {
return r == '`' || r == '\n' || !unicode.IsPrint(r)
}
if strings.IndexFunc(s, rawInvalid) < 0 {
return "`" + s + "`"
}
return qs
}
func formatPrimitive(t reflect.Type, v interface{}, conf FormatConfig) string {
if conf.printType && (conf.PrintPrimitiveType || t.PkgPath() != "") {
return fmt.Sprintf("%v(%v)", t, v)
}
return fmt.Sprintf("%v", v)
}
func formatPointer(v reflect.Value, conf FormatConfig) string {
p := v.Pointer()
if !conf.realPointers {
p = 0 // For deterministic printing purposes
}
s := formatHex(uint64(p))
if conf.printType {
return fmt.Sprintf("(%v)(%s)", v.Type(), s)
}
return s
}
func formatHex(u uint64) string {
var f string
switch {
case u <= 0xff:
f = "0x%02x"
case u <= 0xffff:
f = "0x%04x"
case u <= 0xffffff:
f = "0x%06x"
case u <= 0xffffffff:
f = "0x%08x"
case u <= 0xffffffffff:
f = "0x%010x"
case u <= 0xffffffffffff:
f = "0x%012x"
case u <= 0xffffffffffffff:
f = "0x%014x"
case u <= 0xffffffffffffffff:
f = "0x%016x"
}
return fmt.Sprintf(f, u)
}
// insertPointer insert p into m, allocating m if necessary.
func insertPointer(m map[uintptr]bool, p uintptr) map[uintptr]bool {
if m == nil {
m = make(map[uintptr]bool)
}
m[p] = true
return m
}
// isZero reports whether v is the zero value.
// This does not rely on Interface and so can be used on unexported fields.
func isZero(v reflect.Value) bool {
switch v.Kind() {
case reflect.Bool:
return v.Bool() == false
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return v.Int() == 0
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return v.Uint() == 0
case reflect.Float32, reflect.Float64:
return v.Float() == 0
case reflect.Complex64, reflect.Complex128:
return v.Complex() == 0
case reflect.String:
return v.String() == ""
case reflect.UnsafePointer:
return v.Pointer() == 0
case reflect.Chan, reflect.Func, reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
return v.IsNil()
case reflect.Array:
for i := 0; i < v.Len(); i++ {
if !isZero(v.Index(i)) {
return false
}
}
return true
case reflect.Struct:
for i := 0; i < v.NumField(); i++ {
if !isZero(v.Field(i)) {
return false
}
}
return true
}
return false
}
