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|
package transform
import (
"bytes"
"io"
"net/url"
"strings"
"unicode/utf8"
)
type matchState int
const (
matchStateNone matchState = iota
matchStateWhitespace
matchStatePartial
matchStateFull
)
type contentlexer struct {
content []byte
pos int // input position
start int // item start position
width int // width of last element
matchers []absURLMatcher
state stateFunc
ms matchState
matches [3]bool // track matches of the 3 prefixes
idx int // last index in matches checked
w io.Writer
}
type stateFunc func(*contentlexer) stateFunc
type prefix struct {
r []rune
f func(l *contentlexer)
}
var prefixes = []*prefix{
&prefix{r: []rune{'s', 'r', 'c', '='}, f: checkCandidateBase},
&prefix{r: []rune{'h', 'r', 'e', 'f', '='}, f: checkCandidateBase},
&prefix{r: []rune{'s', 'r', 'c', 's', 'e', 't', '='}, f: checkCandidateSrcset},
}
type absURLMatcher struct {
match []byte
quote []byte
replacementURL []byte
}
func (l *contentlexer) match(r rune) {
var found bool
// note, the prefixes can start off on the same foot, i.e.
// src and srcset.
if l.ms == matchStateWhitespace {
l.idx = 0
for j, p := range prefixes {
if r == p.r[l.idx] {
l.matches[j] = true
found = true
if l.checkMatchState(r, j) {
return
}
} else {
l.matches[j] = false
}
}
if !found {
l.ms = matchStateNone
}
return
}
l.idx++
for j, m := range l.matches {
// still a match?
if m {
if prefixes[j].r[l.idx] == r {
found = true
if l.checkMatchState(r, j) {
return
}
} else {
l.matches[j] = false
}
}
}
if found {
return
}
l.ms = matchStateNone
}
func (l *contentlexer) checkMatchState(r rune, idx int) bool {
if r == '=' {
l.ms = matchStateFull
for k := range l.matches {
if k != idx {
l.matches[k] = false
}
}
return true
}
l.ms = matchStatePartial
return false
}
func (l *contentlexer) emit() {
l.w.Write(l.content[l.start:l.pos])
l.start = l.pos
}
func checkCandidateBase(l *contentlexer) {
for _, m := range l.matchers {
if !bytes.HasPrefix(l.content[l.pos:], m.match) {
continue
}
// check for schemaless URLs
posAfter := l.pos + len(m.match)
if posAfter >= len(l.content) {
return
}
r, _ := utf8.DecodeRune(l.content[posAfter:])
if r == '/' {
// schemaless: skip
return
}
if l.pos > l.start {
l.emit()
}
l.pos += len(m.match)
l.w.Write(m.quote)
l.w.Write(m.replacementURL)
l.start = l.pos
}
}
func checkCandidateSrcset(l *contentlexer) {
// special case, not frequent (me think)
for _, m := range l.matchers {
if !bytes.HasPrefix(l.content[l.pos:], m.match) {
continue
}
// check for schemaless URLs
posAfter := l.pos + len(m.match)
if posAfter >= len(l.content) {
return
}
r, _ := utf8.DecodeRune(l.content[posAfter:])
if r == '/' {
// schemaless: skip
continue
}
posLastQuote := bytes.Index(l.content[l.pos+1:], m.quote)
// safe guard
if posLastQuote < 0 || posLastQuote > 2000 {
return
}
if l.pos > l.start {
l.emit()
}
section := l.content[l.pos+len(m.quote) : l.pos+posLastQuote+1]
fields := bytes.Fields(section)
l.w.Write([]byte(m.quote))
for i, f := range fields {
if f[0] == '/' {
l.w.Write(m.replacementURL)
l.w.Write(f[1:])
} else {
l.w.Write(f)
}
if i < len(fields)-1 {
l.w.Write([]byte(" "))
}
}
l.w.Write(m.quote)
l.pos += len(section) + (len(m.quote) * 2)
l.start = l.pos
}
}
func (l *contentlexer) replace() {
contentLength := len(l.content)
var r rune
for {
if l.pos >= contentLength {
l.width = 0
break
}
var width = 1
r = rune(l.content[l.pos])
if r >= utf8.RuneSelf {
r, width = utf8.DecodeRune(l.content[l.
|