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Copy pathprintf.go
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197 lines (171 loc) · 4.17 KB
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// Package printf implements a parser for fmt.Printf-style format
// strings.
//
// It parses verbs according to the following syntax:
// Numeric -> '0'-'9'
// Letter -> 'a'-'z' | 'A'-'Z'
// Index -> '[' Numeric+ ']'
// Star -> '*'
// Star -> Index '*'
//
// Precision -> Numeric+ | Star
// Width -> Numeric+ | Star
//
// WidthAndPrecision -> Width '.' Precision
// WidthAndPrecision -> Width '.'
// WidthAndPrecision -> Width
// WidthAndPrecision -> '.' Precision
// WidthAndPrecision -> '.'
//
// Flag -> '+' | '-' | '#' | ' ' | '0'
// Verb -> Letter | '%'
//
// Input -> '%' [ Flag+ ] [ WidthAndPrecision ] [ Index ] Verb
package printf
import (
"errors"
"regexp"
"strconv"
"strings"
)
// ErrInvalid is returned for invalid format strings or verbs.
var ErrInvalid = errors.New("invalid format string")
type Verb struct {
Letter rune
Flags string
Width Argument
Precision Argument
// Which value in the argument list the verb uses.
// -1 denotes the next argument,
// values > 0 denote explicit arguments.
// The value 0 denotes that no argument is consumed. This is the case for %%.
Value int
Raw string
}
// Argument is an implicit or explicit width or precision.
type Argument interface {
isArgument()
}
// The Default value, when no width or precision is provided.
type Default struct{}
// Zero is the implicit zero value.
// This value may only appear for precisions in format strings like %6.f
type Zero struct{}
// Star is a * value, which may either refer to the next argument (Index == -1) or an explicit argument.
type Star struct{ Index int }
// A Literal value, such as 6 in %6d.
type Literal int
func (Default) isArgument() {}
func (Zero) isArgument() {}
func (Star) isArgument() {}
func (Literal) isArgument() {}
// Parse parses f and returns a list of actions.
// An action may either be a literal string, or a Verb.
func Parse(f string) ([]interface{}, error) {
var out []interface{}
for len(f) > 0 {
if f[0] == '%' {
v, n, err := ParseVerb(f)
if err != nil {
return nil, err
}
f = f[n:]
out = append(out, v)
} else {
n := strings.IndexByte(f, '%')
if n > -1 {
out = append(out, f[:n])
f = f[n:]
} else {
out = append(out, f)
f = ""
}
}
}
return out, nil
}
func atoi(s string) int {
n, _ := strconv.Atoi(s)
return n
}
// ParseVerb parses the verb at the beginning of f.
// It returns the verb, how much of the input was consumed, and an error, if any.
func ParseVerb(f string) (Verb, int, error) {
if len(f) < 2 {
return Verb{}, 0, ErrInvalid
}
const (
flags = 1
width = 2
widthStar = 3
widthIndex = 5
dot = 6
prec = 7
precStar = 8
precIndex = 10
verbIndex = 11
verb = 12
)
m := re.FindStringSubmatch(f)
if m == nil {
return Verb{}, 0, ErrInvalid
}
v := Verb{
Letter: []rune(m[verb])[0],
Flags: m[flags],
Raw: m[0],
}
if m[width] != "" {
// Literal width
v.Width = Literal(atoi(m[width]))
} else if m[widthStar] != "" {
// Star width
if m[widthIndex] != "" {
v.Width = Star{atoi(m[widthIndex])}
} else {
v.Width = Star{-1}
}
} else {
// Default width
v.Width = Default{}
}
if m[dot] == "" {
// default precision
v.Precision = Default{}
} else {
if m[prec] != "" {
// Literal precision
v.Precision = Literal(atoi(m[prec]))
} else if m[precStar] != "" {
// Star precision
if m[precIndex] != "" {
v.Precision = Star{atoi(m[precIndex])}
} else {
v.Precision = Star{-1}
}
} else {
// Zero precision
v.Precision = Zero{}
}
}
if m[verb] == "%" {
v.Value = 0
} else if m[verbIndex] != "" {
v.Value = atoi(m[verbIndex])
} else {
v.Value = -1
}
return v, len(m[0]), nil
}
const (
flags = `([+#0 -]*)`
verb = `([a-zA-Z%])`
index = `(?:\[([0-9]+)\])`
star = `((` + index + `)?\*)`
width1 = `([0-9]+)`
width2 = star
width = `(?:` + width1 + `|` + width2 + `)`
precision = width
widthAndPrecision = `(?:(?:` + width + `)?(?:(\.)(?:` + precision + `)?)?)`
)
var re = regexp.MustCompile(`^%` + flags + widthAndPrecision + `?` + index + `?` + verb)