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// 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 file.
package format
import (
"reflect"
"unicode/utf8"
)
// A Parser parses a format string. The result from the parse are set in the
// struct fields.
type Parser struct {
Verb rune
WidthPresent bool
PrecPresent bool
Minus bool
Plus bool
Sharp bool
Space bool
Zero bool
// For the formats %+v %#v, we set the plusV/sharpV flags
// and clear the plus/sharp flags since %+v and %#v are in effect
// different, flagless formats set at the top level.
PlusV bool
SharpV bool
HasIndex bool
Width int
Prec int // precision
// retain arguments across calls.
Args []interface{}
// retain current argument number across calls
ArgNum int
// reordered records whether the format string used argument reordering.
Reordered bool
// goodArgNum records whether the most recent reordering directive was valid.
goodArgNum bool
// position info
format string
startPos int
endPos int
Status Status
}
// Reset initializes a parser to scan format strings for the given args.
func (p *Parser) Reset(args []interface{}) {
p.Args = args
p.ArgNum = 0
p.startPos = 0
p.Reordered = false
}
// Text returns the part of the format string that was parsed by the last call
// to Scan. It returns the original substitution clause if the current scan
// parsed a substitution.
func (p *Parser) Text() string { return p.format[p.startPos:p.endPos] }
// SetFormat sets a new format string to parse. It does not reset the argument
// count.
func (p *Parser) SetFormat(format string) {
p.format = format
p.startPos = 0
p.endPos = 0
}
// Status indicates the result type of a call to Scan.
type Status int
const (
StatusText Status = iota
StatusSubstitution
StatusBadWidthSubstitution
StatusBadPrecSubstitution
StatusNoVerb
StatusBadArgNum
StatusMissingArg
)
// ClearFlags reset the parser to default behavior.
func (p *Parser) ClearFlags() {
p.WidthPresent = false
p.PrecPresent = false
p.Minus = false
p.Plus = false
p.Sharp = false
p.Space = false
p.Zero = false
p.PlusV = false
p.SharpV = false
p.HasIndex = false
}
// Scan scans the next part of the format string and sets the status to
// indicate whether it scanned a string literal, substitution or error.
func (p *Parser) Scan() bool {
p.Status = StatusText
format := p.format
end := len(format)
if p.endPos >= end {
return false
}
afterIndex := false // previous item in format was an index like [3].
p.startPos = p.endPos
p.goodArgNum = true
i := p.startPos
for i < end && format[i] != '%' {
i++
}
if i > p.startPos {
p.endPos = i
return true
}
// Process one verb
i++
p.Status = StatusSubstitution
// Do we have flags?
p.ClearFlags()
simpleFormat:
for ; i < end; i++ {
c := p.format[i]
switch c {
case '#':
p.Sharp = true
case '0':
p.Zero = !p.Minus // Only allow zero padding to the left.
case '+':
p.Plus = true
case '-':
p.Minus = true
p.Zero = false // Do not pad with zeros to the right.
case ' ':
p.Space = true
default:
// Fast path for common case of ascii lower case simple verbs
// without precision or width or argument indices.
if 'a' <= c && c <= 'z' && p.ArgNum < len(p.Args) {
if c == 'v' {
// Go syntax
p.SharpV = p.Sharp
p.Sharp = false
// Struct-field syntax
p.PlusV = p.Plus
p.Plus = false
}
p.Verb = rune(c)
p.ArgNum++
p.endPos = i + 1
return true
}
// Format is more complex than simple flags and a verb or is malformed.
break simpleFormat
}
}
// Do we have an explicit argument index?
i, afterIndex = p.updateArgNumber(format, i)
// Do we have width?
if i < end && format[i] == '*' {
i++
p.Width, p.WidthPresent = p.intFromArg()
if !p.WidthPresent {
p.Status = StatusBadWidthSubstitution
}
// We have a negative width, so take its value and ensure
// that the minus flag is set
if p.Width < 0 {
p.Width = -p.Width
p.Minus = true
p.Zero = false // Do not pad with zeros to the right.
}
afterIndex = false
} else {
p.Width, p.WidthPresent, i = parsenum(format, i, end)
if afterIndex && p.WidthPresent { // "%[3]2d"
p.goodArgNum = false
}
}
// Do we have precision?
if i+1 < end && format[i] == '.' {
i++
if afterIndex { // "%[3].2d"
p.goodArgNum = false
}
i, afterIndex = p.updateArgNumber(format, i)
if i < end && format[i] == '*' {
i++
p.Prec, p.PrecPresent = p.intFromArg()
// Negative precision arguments don't make sense
if p.Prec < 0 {
p.Prec = 0
p.PrecPresent = false
}
if !p.PrecPresent {
p.Status = StatusBadPrecSubstitution
}
afterIndex = false
} else {
p.Prec, p.PrecPresent, i = parsenum(format, i, end)
if !p.PrecPresent {
p.Prec = 0
p.PrecPresent = true
}
}
}
if !afterIndex {
i, afterIndex = p.updateArgNumber(format, i)
}
p.HasIndex = afterIndex
if i >= end {
p.endPos = i
p.Status = StatusNoVerb
return true
}
verb, w := utf8.DecodeRuneInString(format[i:])
p.endPos = i + w
p.Verb = verb
switch {
case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
p.startPos = p.endPos - 1
p.Status = StatusText
case !p.goodArgNum:
p.Status = StatusBadArgNum
case p.ArgNum >= len(p.Args): // No argument left over to print for the current verb.
p.Status = StatusMissingArg
case verb == 'v':
// Go syntax
p.SharpV = p.Sharp
p.Sharp = false
// Struct-field syntax
p.PlusV = p.Plus
p.Plus = false
fallthrough
default:
p.ArgNum++
}
return true
}
// intFromArg gets the ArgNumth element of Args. On return, isInt reports
// whether the argument has integer type.
func (p *Parser) intFromArg() (num int, isInt bool) {
if p.ArgNum < len(p.Args) {
arg := p.Args[p.ArgNum]
num, isInt = arg.(int) // Almost always OK.
if !isInt {
// Work harder.
switch v := reflect.ValueOf(arg); v.Kind() {
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
n := v.Int()
if int64(int(n)) == n {
num = int(n)
isInt = true
}
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
n := v.Uint()
if int64(n) >= 0 && uint64(int(n)) == n {
num = int(n)
isInt = true
}
default:
// Already 0, false.
}
}
p.ArgNum++
if tooLarge(num) {
num = 0
isInt = false
}
}
return
}
// parseArgNumber returns the value of the bracketed number, minus 1
// (explicit argument numbers are one-indexed but we want zero-indexed).
// The opening bracket is known to be present at format[0].
// The returned values are the index, the number of bytes to consume
// up to the closing paren, if present, and whether the number parsed
// ok. The bytes to consume will be 1 if no closing paren is present.
func parseArgNumber(format string) (index int, wid int, ok bool) {
// There must be at least 3 bytes: [n].
if len(format) < 3 {
return 0, 1, false
}
// Find closing bracket.
for i := 1; i < len(format); i++ {
if format[i] == ']' {
width, ok, newi := parsenum(format, 1, i)
if !ok || newi != i {
return 0, i + 1, false
}
return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
}
}
return 0, 1, false
}
// updateArgNumber returns the next argument to evaluate, which is either the value of the passed-in
// argNum or the value of the bracketed integer that begins format[i:]. It also returns
// the new value of i, that is, the index of the next byte of the format to process.
func (p *Parser) updateArgNumber(format string, i int) (newi int, found bool) {
if len(format) <= i || format[i] != '[' {
return i, false
}
p.Reordered = true
index, wid, ok := parseArgNumber(format[i:])
if ok && 0 <= index && index < len(p.Args) {
p.ArgNum = index
return i + wid, true
}
p.goodArgNum = false
return i + wid, ok
}
// tooLarge reports whether the magnitude of the integer is
// too large to be used as a formatting width or precision.
func tooLarge(x int) bool {
const max int = 1e6
return x > max || x < -max
}
// parsenum converts ASCII to integer. num is 0 (and isnum is false) if no number present.
func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
if start >= end {
return 0, false, end
}
for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
if tooLarge(num) {
return 0, false, end // Overflow; crazy long number most likely.
}
num = num*10 + int(s[newi]-'0')
isnum = true
}
return
}