hugo/parser/page.go

279 lines
6 KiB
Go
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package parser
import (
"bufio"
"bytes"
"fmt"
"io"
"unicode"
)
const (
HTML_LEAD = "<"
YAML_LEAD = "-"
YAML_DELIM_UNIX = "---\n"
YAML_DELIM_DOS = "---\r\n"
YAML_DELIM = "---"
TOML_LEAD = "+"
TOML_DELIM_UNIX = "+++\n"
TOML_DELIM_DOS = "+++\r\n"
TOML_DELIM = "+++"
JSON_LEAD = "{"
)
var (
delims = [][]byte{
[]byte(YAML_DELIM_UNIX),
[]byte(YAML_DELIM_DOS),
[]byte(TOML_DELIM_UNIX),
[]byte(TOML_DELIM_DOS),
[]byte(JSON_LEAD),
}
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UnixEnding = []byte("\n")
DosEnding = []byte("\r\n")
)
type FrontMatter []byte
type Content []byte
type Page interface {
FrontMatter() FrontMatter
Content() Content
IsRenderable() bool
Metadata() (interface{}, error)
}
type page struct {
render bool
frontmatter FrontMatter
content Content
}
func (p *page) Content() Content {
return p.content
}
func (p *page) FrontMatter() FrontMatter {
return p.frontmatter
}
func (p *page) IsRenderable() bool {
return p.render
}
func (p *page) Metadata() (meta interface{}, err error) {
frontmatter := p.FrontMatter()
if len(frontmatter) != 0 {
fm := DetectFrontMatter(rune(frontmatter[0]))
meta, err = fm.Parse(frontmatter)
if err != nil {
return
}
}
return
}
// ReadFrom reads the content from an io.Reader and constructs a page.
func ReadFrom(r io.Reader) (p Page, err error) {
reader := bufio.NewReader(r)
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if err = chompWhitespace(reader); err != nil && err != io.EOF {
return
}
firstLine, err := peekLine(reader)
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if err != nil && err != io.EOF {
return
}
newp := new(page)
newp.render = shouldRender(firstLine)
if newp.render && isFrontMatterDelim(firstLine) {
left, right := determineDelims(firstLine)
fm, err := extractFrontMatterDelims(reader, left, right)
if err != nil {
return nil, err
}
newp.frontmatter = fm
}
content, err := extractContent(reader)
if err != nil {
return nil, err
}
newp.content = content
return newp, nil
}
func chompWhitespace(r io.RuneScanner) (err error) {
for {
c, _, err := r.ReadRune()
if err != nil {
return err
}
if !unicode.IsSpace(c) {
r.UnreadRune()
return nil
}
}
}
func peekLine(r *bufio.Reader) (line []byte, err error) {
firstFive, err := r.Peek(5)
if err != nil {
return
}
idx := bytes.IndexByte(firstFive, '\n')
if idx == -1 {
return firstFive, nil
}
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idx++ // include newline.
return firstFive[:idx], nil
}
func shouldRender(lead []byte) (frontmatter bool) {
if len(lead) <= 0 {
return
}
if bytes.Equal(lead[:1], []byte(HTML_LEAD)) {
return
}
return true
}
func isFrontMatterDelim(data []byte) bool {
for _, d := range delims {
if bytes.HasPrefix(data, d) {
return true
}
}
return false
}
func determineDelims(firstLine []byte) (left, right []byte) {
switch len(firstLine) {
case 5:
fallthrough
case 4:
if firstLine[0] == YAML_LEAD[0] {
return []byte(YAML_DELIM), []byte(YAML_DELIM)
}
return []byte(TOML_DELIM), []byte(TOML_DELIM)
case 3:
fallthrough
case 2:
fallthrough
case 1:
return []byte(JSON_LEAD), []byte("}")
default:
panic(fmt.Sprintf("Unable to determine delims from %q", firstLine))
}
}
// extractFrontMatterDelims takes a frontmatter from the content bufio.Reader.
// Begining white spaces of the bufio.Reader must be trimmed before call this
// function.
func extractFrontMatterDelims(r *bufio.Reader, left, right []byte) (fm FrontMatter, err error) {
var (
c byte
buf bytes.Buffer
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level int
sameDelim = bytes.Equal(left, right)
)
// Frontmatter must start with a delimiter. To check it first,
// pre-reads beginning delimiter length - 1 bytes from Reader
for i := 0; i < len(left)-1; i++ {
if c, err = r.ReadByte(); err != nil {
return nil, fmt.Errorf("unable to read frontmatter at filepos %d: %s", buf.Len(), err)
}
if err = buf.WriteByte(c); err != nil {
return nil, err
}
}
// Reads a character from Reader one by one and checks it matches the
// last character of one of delemiters to find the last character of
// frontmatter. If it matches, makes sure it contains the delimiter
// and if so, also checks it is followed by CR+LF or LF when YAML,
// TOML case. In JSON case, nested delimiters must be parsed and it
// is expected that the delimiter only contains one character.
for {
if c, err = r.ReadByte(); err != nil {
return nil, fmt.Errorf("unable to read frontmatter at filepos %d: %s", buf.Len(), err)
}
if err = buf.WriteByte(c); err != nil {
return nil, err
}
switch c {
case left[len(left)-1]:
if sameDelim { // YAML, TOML case
if bytes.HasSuffix(buf.Bytes(), left) {
c, err = r.ReadByte()
if err != nil {
// It is ok that the end delimiter ends with EOF
if err != io.EOF || level != 1 {
return nil, fmt.Errorf("unable to read frontmatter at filepos %d: %s", buf.Len(), err)
}
} else {
switch c {
case '\n':
// ok
case '\r':
if err = buf.WriteByte(c); err != nil {
return nil, err
}
if c, err = r.ReadByte(); err != nil {
return nil, fmt.Errorf("unable to read frontmatter at filepos %d: %s", buf.Len(), err)
}
if c != '\n' {
return nil, fmt.Errorf("frontmatter delimiter must be followed by CR+LF or LF but those can't be found at filepos %d", buf.Len())
}
default:
return nil, fmt.Errorf("frontmatter delimiter must be followed by CR+LF or LF but those can't be found at filepos %d", buf.Len())
}
if err = buf.WriteByte(c); err != nil {
return nil, err
}
}
if level == 0 {
level = 1
} else {
level = 0
}
}
} else { // JSON case
level++
}
case right[len(right)-1]: // JSON case only reaches here
level--
}
if level == 0 {
// Consumes white spaces immediately behind frontmatter
if err = chompWhitespace(r); err != nil {
if err != io.EOF {
return nil, err
}
}
return buf.Bytes(), nil
}
}
}
func extractContent(r io.Reader) (content Content, err error) {
wr := new(bytes.Buffer)
if _, err = wr.ReadFrom(r); err != nil {
return
}
return wr.Bytes(), nil
}