Adding upstream version 1.16.10.upstream/1.16.10upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 838 insertions, 0 deletions

diff --git a/src/net/mail/message.go b/src/net/mail/message.go
new file mode 100644
index 0000000..47bbf6c
--- /dev/null
+++ b/src/net/mail/message.go
@@ -0,0 +1,838 @@
+// Copyright 2011 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 mail implements parsing of mail messages.
+
+For the most part, this package follows the syntax as specified by RFC 5322 and
+extended by RFC 6532.
+Notable divergences:
+	* Obsolete address formats are not parsed, including addresses with
+	  embedded route information.
+	* The full range of spacing (the CFWS syntax element) is not supported,
+	  such as breaking addresses across lines.
+	* No unicode normalization is performed.
+	* The special characters ()[]:;@\, are allowed to appear unquoted in names.
+*/
+package mail
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"mime"
+	"net/textproto"
+	"strings"
+	"sync"
+	"time"
+	"unicode/utf8"
+)
+
+var debug = debugT(false)
+
+type debugT bool
+
+func (d debugT) Printf(format string, args ...interface{}) {
+	if d {
+		log.Printf(format, args...)
+	}
+}
+
+// A Message represents a parsed mail message.
+type Message struct {
+	Header Header
+	Body   io.Reader
+}
+
+// ReadMessage reads a message from r.
+// The headers are parsed, and the body of the message will be available
+// for reading from msg.Body.
+func ReadMessage(r io.Reader) (msg *Message, err error) {
+	tp := textproto.NewReader(bufio.NewReader(r))
+
+	hdr, err := tp.ReadMIMEHeader()
+	if err != nil {
+		return nil, err
+	}
+
+	return &Message{
+		Header: Header(hdr),
+		Body:   tp.R,
+	}, nil
+}
+
+// Layouts suitable for passing to time.Parse.
+// These are tried in order.
+var (
+	dateLayoutsBuildOnce sync.Once
+	dateLayouts          []string
+)
+
+func buildDateLayouts() {
+	// Generate layouts based on RFC 5322, section 3.3.
+
+	dows := [...]string{"", "Mon, "}   // day-of-week
+	days := [...]string{"2", "02"}     // day = 1*2DIGIT
+	years := [...]string{"2006", "06"} // year = 4*DIGIT / 2*DIGIT
+	seconds := [...]string{":05", ""}  // second
+	// "-0700 (MST)" is not in RFC 5322, but is common.
+	zones := [...]string{"-0700", "MST"} // zone = (("+" / "-") 4DIGIT) / "GMT" / ...
+
+	for _, dow := range dows {
+		for _, day := range days {
+			for _, year := range years {
+				for _, second := range seconds {
+					for _, zone := range zones {
+						s := dow + day + " Jan " + year + " 15:04" + second + " " + zone
+						dateLayouts = append(dateLayouts, s)
+					}
+				}
+			}
+		}
+	}
+}
+
+// ParseDate parses an RFC 5322 date string.
+func ParseDate(date string) (time.Time, error) {
+	dateLayoutsBuildOnce.Do(buildDateLayouts)
+	// CR and LF must match and are tolerated anywhere in the date field.
+	date = strings.ReplaceAll(date, "\r\n", "")
+	if strings.Index(date, "\r") != -1 {
+		return time.Time{}, errors.New("mail: header has a CR without LF")
+	}
+	// Re-using some addrParser methods which support obsolete text, i.e. non-printable ASCII
+	p := addrParser{date, nil}
+	p.skipSpace()
+
+	// RFC 5322: zone = (FWS ( "+" / "-" ) 4DIGIT) / obs-zone
+	// zone length is always 5 chars unless obsolete (obs-zone)
+	if ind := strings.IndexAny(p.s, "+-"); ind != -1 && len(p.s) >= ind+5 {
+		date = p.s[:ind+5]
+		p.s = p.s[ind+5:]
+	} else {
+		ind := strings.Index(p.s, "T")
+		if ind == 0 {
+			// In this case we have the following date formats:
+			// * Thu, 20 Nov 1997 09:55:06 MDT
+			// * Thu, 20 Nov 1997 09:55:06 MDT (MDT)
+			// * Thu, 20 Nov 1997 09:55:06 MDT (This comment)
+			ind = strings.Index(p.s[1:], "T")
+			if ind != -1 {
+				ind++
+			}
+		}
+
+		if ind != -1 && len(p.s) >= ind+5 {
+			// The last letter T of the obsolete time zone is checked when no standard time zone is found.
+			// If T is misplaced, the date to parse is garbage.
+			date = p.s[:ind+1]
+			p.s = p.s[ind+1:]
+		}
+	}
+	if !p.skipCFWS() {
+		return time.Time{}, errors.New("mail: misformatted parenthetical comment")
+	}
+	for _, layout := range dateLayouts {
+		t, err := time.Parse(layout, date)
+		if err == nil {
+			return t, nil
+		}
+	}
+	return time.Time{}, errors.New("mail: header could not be parsed")
+}
+
+// A Header represents the key-value pairs in a mail message header.
+type Header map[string][]string
+
+// Get gets the first value associated with the given key.
+// It is case insensitive; CanonicalMIMEHeaderKey is used
+// to canonicalize the provided key.
+// If there are no values associated with the key, Get returns "".
+// To access multiple values of a key, or to use non-canonical keys,
+// access the map directly.
+func (h Header) Get(key string) string {
+	return textproto.MIMEHeader(h).Get(key)
+}
+
+var ErrHeaderNotPresent = errors.New("mail: header not in message")
+
+// Date parses the Date header field.
+func (h Header) Date() (time.Time, error) {
+	hdr := h.Get("Date")
+	if hdr == "" {
+		return time.Time{}, ErrHeaderNotPresent
+	}
+	return ParseDate(hdr)
+}
+
+// AddressList parses the named header field as a list of addresses.
+func (h Header) AddressList(key string) ([]*Address, error) {
+	hdr := h.Get(key)
+	if hdr == "" {
+		return nil, ErrHeaderNotPresent
+	}
+	return ParseAddressList(hdr)
+}
+
+// Address represents a single mail address.
+// An address such as "Barry Gibbs <bg@example.com>" is represented
+// as Address{Name: "Barry Gibbs", Address: "bg@example.com"}.
+type Address struct {
+	Name    string // Proper name; may be empty.
+	Address string // user@domain
+}
+
+// ParseAddress parses a single RFC 5322 address, e.g. "Barry Gibbs <bg@example.com>"
+func ParseAddress(address string) (*Address, error) {
+	return (&addrParser{s: address}).parseSingleAddress()
+}
+
+// ParseAddressList parses the given string as a list of addresses.
+func ParseAddressList(list string) ([]*Address, error) {
+	return (&addrParser{s: list}).parseAddressList()
+}
+
+// An AddressParser is an RFC 5322 address parser.
+type AddressParser struct {
+	// WordDecoder optionally specifies a decoder for RFC 2047 encoded-words.
+	WordDecoder *mime.WordDecoder
+}
+
+// Parse parses a single RFC 5322 address of the
+// form "Gogh Fir <gf@example.com>" or "foo@example.com".
+func (p *AddressParser) Parse(address string) (*Address, error) {
+	return (&addrParser{s: address, dec: p.WordDecoder}).parseSingleAddress()
+}
+
+// ParseList parses the given string as a list of comma-separated addresses
+// of the form "Gogh Fir <gf@example.com>" or "foo@example.com".
+func (p *AddressParser) ParseList(list string) ([]*Address, error) {
+	return (&addrParser{s: list, dec: p.WordDecoder}).parseAddressList()
+}
+
+// String formats the address as a valid RFC 5322 address.
+// If the address's name contains non-ASCII characters
+// the name will be rendered according to RFC 2047.
+func (a *Address) String() string {
+	// Format address local@domain
+	at := strings.LastIndex(a.Address, "@")
+	var local, domain string
+	if at < 0 {
+		// This is a malformed address ("@" is required in addr-spec);
+		// treat the whole address as local-part.
+		local = a.Address
+	} else {
+		local, domain = a.Address[:at], a.Address[at+1:]
+	}
+
+	// Add quotes if needed
+	quoteLocal := false
+	for i, r := range local {
+		if isAtext(r, false, false) {
+			continue
+		}
+		if r == '.' {
+			// Dots are okay if they are surrounded by atext.
+			// We only need to check that the previous byte is
+			// not a dot, and this isn't the end of the string.
+			if i > 0 && local[i-1] != '.' && i < len(local)-1 {
+				continue
+			}
+		}
+		quoteLocal = true
+		break
+	}
+	if quoteLocal {
+		local = quoteString(local)
+
+	}
+
+	s := "<" + local + "@" + domain + ">"
+
+	if a.Name == "" {
+		return s
+	}
+
+	// If every character is printable ASCII, quoting is simple.
+	allPrintable := true
+	for _, r := range a.Name {
+		// isWSP here should actually be isFWS,
+		// but we don't support folding yet.
+		if !isVchar(r) && !isWSP(r) || isMultibyte(r) {
+			allPrintable = false
+			break
+		}
+	}
+	if allPrintable {
+		return quoteString(a.Name) + " " + s
+	}
+
+	// Text in an encoded-word in a display-name must not contain certain
+	// characters like quotes or parentheses (see RFC 2047 section 5.3).
+	// When this is the case encode the name using base64 encoding.
+	if strings.ContainsAny(a.Name, "\"#$%&'(),.:;<>@[]^`{|}~") {
+		return mime.BEncoding.Encode("utf-8", a.Name) + " " + s
+	}
+	return mime.QEncoding.Encode("utf-8", a.Name) + " " + s
+}
+
+type addrParser struct {
+	s   string
+	dec *mime.WordDecoder // may be nil
+}
+
+func (p *addrParser) parseAddressList() ([]*Address, error) {
+	var list []*Address
+	for {
+		p.skipSpace()
+
+		// allow skipping empty entries (RFC5322 obs-addr-list)
+		if p.consume(',') {
+			continue
+		}
+
+		addrs, err := p.parseAddress(true)
+		if err != nil {
+			return nil, err
+		}
+		list = append(list, addrs...)
+
+		if !p.skipCFWS() {
+			return nil, errors.New("mail: misformatted parenthetical comment")
+		}
+		if p.empty() {
+			break
+		}
+		if p.peek() != ',' {
+			return nil, errors.New("mail: expected comma")
+		}
+
+		// Skip empty entries for obs-addr-list.
+		for p.consume(',') {
+			p.skipSpace()
+		}
+		if p.empty() {
+			break
+		}
+	}
+	return list, nil
+}
+
+func (p *addrParser) parseSingleAddress() (*Address, error) {
+	addrs, err := p.parseAddress(true)
+	if err != nil {
+		return nil, err
+	}
+	if !p.skipCFWS() {
+		return nil, errors.New("mail: misformatted parenthetical comment")
+	}
+	if !p.empty() {
+		return nil, fmt.Errorf("mail: expected single address, got %q", p.s)
+	}
+	if len(addrs) == 0 {
+		return nil, errors.New("mail: empty group")
+	}
+	if len(addrs) > 1 {
+		return nil, errors.New("mail: group with multiple addresses")
+	}
+	return addrs[0], nil
+}
+
+// parseAddress parses a single RFC 5322 address at the start of p.
+func (p *addrParser) parseAddress(handleGroup bool) ([]*Address, error) {
+	debug.Printf("parseAddress: %q", p.s)
+	p.skipSpace()
+	if p.empty() {
+		return nil, errors.New("mail: no address")
+	}
+
+	// address = mailbox / group
+	// mailbox = name-addr / addr-spec
+	// group = display-name ":" [group-list] ";" [CFWS]
+
+	// addr-spec has a more restricted grammar than name-addr,
+	// so try parsing it first, and fallback to name-addr.
+	// TODO(dsymonds): Is this really correct?
+	spec, err := p.consumeAddrSpec()
+	if err == nil {
+		var displayName string
+		p.skipSpace()
+		if !p.empty() && p.peek() == '(' {
+			displayName, err = p.consumeDisplayNameComment()
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		return []*Address{{
+			Name:    displayName,
+			Address: spec,
+		}}, err
+	}
+	debug.Printf("parseAddress: not an addr-spec: %v", err)
+	debug.Printf("parseAddress: state is now %q", p.s)
+
+	// display-name
+	var displayName string
+	if p.peek() != '<' {
+		displayName, err = p.consumePhrase()
+		if err != nil {
+			return nil, err
+		}
+	}
+	debug.Printf("parseAddress: displayName=%q", displayName)
+
+	p.skipSpace()
+	if handleGroup {
+		if p.consume(':') {
+			return p.consumeGroupList()
+		}
+	}
+	// angle-addr = "<" addr-spec ">"
+	if !p.consume('<') {
+		atext := true
+		for _, r := range displayName {
+			if !isAtext(r, true, false) {
+				atext = false
+				break
+			}
+		}
+		if atext {
+			// The input is like "foo.bar"; it's possible the input
+			// meant to be "foo.bar@domain", or "foo.bar <...>".
+			return nil, errors.New("mail: missing '@' or angle-addr")
+		}
+		// The input is like "Full Name", which couldn't possibly be a
+		// valid email address if followed by "@domain"; the input
+		// likely meant to be "Full Name <...>".
+		return nil, errors.New("mail: no angle-addr")
+	}
+	spec, err = p.consumeAddrSpec()
+	if err != nil {
+		return nil, err
+	}
+	if !p.consume('>') {
+		return nil, errors.New("mail: unclosed angle-addr")
+	}
+	debug.Printf("parseAddress: spec=%q", spec)
+
+	return []*Address{{
+		Name:    displayName,
+		Address: spec,
+	}}, nil
+}
+
+func (p *addrParser) consumeGroupList() ([]*Address, error) {
+	var group []*Address
+	// handle empty group.
+	p.skipSpace()
+	if p.consume(';') {
+		p.skipCFWS()
+		return group, nil
+	}
+
+	for {
+		p.skipSpace()
+		// embedded groups not allowed.
+		addrs, err := p.parseAddress(false)
+		if err != nil {
+			return nil, err
+		}
+		group = append(group, addrs...)
+
+		if !p.skipCFWS() {
+			return nil, errors.New("mail: misformatted parenthetical comment")
+		}
+		if p.consume(';') {
+			p.skipCFWS()
+			break
+		}
+		if !p.consume(',') {
+			return nil, errors.New("mail: expected comma")
+		}
+	}
+	return group, nil
+}
+
+// consumeAddrSpec parses a single RFC 5322 addr-spec at the start of p.
+func (p *addrParser) consumeAddrSpec() (spec string, err error) {
+	debug.Printf("consumeAddrSpec: %q", p.s)
+
+	orig := *p
+	defer func() {
+		if err != nil {
+			*p = orig
+		}
+	}()
+
+	// local-part = dot-atom / quoted-string
+	var localPart string
+	p.skipSpace()
+	if p.empty() {
+		return "", errors.New("mail: no addr-spec")
+	}
+	if p.peek() == '"' {
+		// quoted-string
+		debug.Printf("consumeAddrSpec: parsing quoted-string")
+		localPart, err = p.consumeQuotedString()
+		if localPart == "" {
+			err = errors.New("mail: empty quoted string in addr-spec")
+		}
+	} else {
+		// dot-atom
+		debug.Printf("consumeAddrSpec: parsing dot-atom")
+		localPart, err = p.consumeAtom(true, false)
+	}
+	if err != nil {
+		debug.Printf("consumeAddrSpec: failed: %v", err)
+		return "", err
+	}
+
+	if !p.consume('@') {
+		return "", errors.New("mail: missing @ in addr-spec")
+	}
+
+	// domain = dot-atom / domain-literal
+	var domain string
+	p.skipSpace()
+	if p.empty() {
+		return "", errors.New("mail: no domain in addr-spec")
+	}
+	// TODO(dsymonds): Handle domain-literal
+	domain, err = p.consumeAtom(true, false)
+	if err != nil {
+		return "", err
+	}
+
+	return localPart + "@" + domain, nil
+}
+
+// consumePhrase parses the RFC 5322 phrase at the start of p.
+func (p *addrParser) consumePhrase() (phrase string, err error) {
+	debug.Printf("consumePhrase: [%s]", p.s)
+	// phrase = 1*word
+	var words []string
+	var isPrevEncoded bool
+	for {
+		// word = atom / quoted-string
+		var word string
+		p.skipSpace()
+		if p.empty() {
+			break
+		}
+		isEncoded := false
+		if p.peek() == '"' {
+			// quoted-string
+			word, err = p.consumeQuotedString()
+		} else {
+			// atom
+			// We actually parse dot-atom here to be more permissive
+			// than what RFC 5322 specifies.
+			word, err = p.consumeAtom(true, true)
+			if err == nil {
+				word, isEncoded, err = p.decodeRFC2047Word(word)
+			}
+		}
+
+		if err != nil {
+			break
+		}
+		debug.Printf("consumePhrase: consumed %q", word)
+		if isPrevEncoded && isEncoded {
+			words[len(words)-1] += word
+		} else {
+			words = append(words, word)
+		}
+		isPrevEncoded = isEncoded
+	}
+	// Ignore any error if we got at least one word.
+	if err != nil && len(words) == 0 {
+		debug.Printf("consumePhrase: hit err: %v", err)
+		return "", fmt.Errorf("mail: missing word in phrase: %v", err)
+	}
+	phrase = strings.Join(words, " ")
+	return phrase, nil
+}
+
+// consumeQuotedString parses the quoted string at the start of p.
+func (p *addrParser) consumeQuotedString() (qs string, err error) {
+	// Assume first byte is '"'.
+	i := 1
+	qsb := make([]rune, 0, 10)
+
+	escaped := false
+
+Loop:
+	for {
+		r, size := utf8.DecodeRuneInString(p.s[i:])
+
+		switch {
+		case size == 0:
+			return "", errors.New("mail: unclosed quoted-string")
+
+		case size == 1 && r == utf8.RuneError:
+			return "", fmt.Errorf("mail: invalid utf-8 in quoted-string: %q", p.s)
+
+		case escaped:
+			//  quoted-pair = ("\" (VCHAR / WSP))
+
+			if !isVchar(r) && !isWSP(r) {
+				return "", fmt.Errorf("mail: bad character in quoted-string: %q", r)
+			}
+
+			qsb = append(qsb, r)
+			escaped = false
+
+		case isQtext(r) || isWSP(r):
+			// qtext (printable US-ASCII excluding " and \), or
+			// FWS (almost; we're ignoring CRLF)
+			qsb = append(qsb, r)
+
+		case r == '"':
+			break Loop
+
+		case r == '\\':
+			escaped = true
+
+		default:
+			return "", fmt.Errorf("mail: bad character in quoted-string: %q", r)
+
+		}
+
+		i += size
+	}
+	p.s = p.s[i+1:]
+	return string(qsb), nil
+}
+
+// consumeAtom parses an RFC 5322 atom at the start of p.
+// If dot is true, consumeAtom parses an RFC 5322 dot-atom instead.
+// If permissive is true, consumeAtom will not fail on:
+// - leading/trailing/double dots in the atom (see golang.org/issue/4938)
+// - special characters (RFC 5322 3.2.3) except '<', '>', ':' and '"' (see golang.org/issue/21018)
+func (p *addrParser) consumeAtom(dot bool, permissive bool) (atom string, err error) {
+	i := 0
+
+Loop:
+	for {
+		r, size := utf8.DecodeRuneInString(p.s[i:])
+		switch {
+		case size == 1 && r == utf8.RuneError:
+			return "", fmt.Errorf("mail: invalid utf-8 in address: %q", p.s)
+
+		case size == 0 || !isAtext(r, dot, permissive):
+			break Loop
+
+		default:
+			i += size
+
+		}
+	}
+
+	if i == 0 {
+		return "", errors.New("mail: invalid string")
+	}
+	atom, p.s = p.s[:i], p.s[i:]
+	if !permissive {
+		if strings.HasPrefix(atom, ".") {
+			return "", errors.New("mail: leading dot in atom")
+		}
+		if strings.Contains(atom, "..") {
+			return "", errors.New("mail: double dot in atom")
+		}
+		if strings.HasSuffix(atom, ".") {
+			return "", errors.New("mail: trailing dot in atom")
+		}
+	}
+	return atom, nil
+}
+
+func (p *addrParser) consumeDisplayNameComment() (string, error) {
+	if !p.consume('(') {
+		return "", errors.New("mail: comment does not start with (")
+	}
+	comment, ok := p.consumeComment()
+	if !ok {
+		return "", errors.New("mail: misformatted parenthetical comment")
+	}
+
+	// TODO(stapelberg): parse quoted-string within comment
+	words := strings.FieldsFunc(comment, func(r rune) bool { return r == ' ' || r == '\t' })
+	for idx, word := range words {
+		decoded, isEncoded, err := p.decodeRFC2047Word(word)
+		if err != nil {
+			return "", err
+		}
+		if isEncoded {
+			words[idx] = decoded
+		}
+	}
+
+	return strings.Join(words, " "), nil
+}
+
+func (p *addrParser) consume(c byte) bool {
+	if p.empty() || p.peek() != c {
+		return false
+	}
+	p.s = p.s[1:]
+	return true
+}
+
+// skipSpace skips the leading space and tab characters.
+func (p *addrParser) skipSpace() {
+	p.s = strings.TrimLeft(p.s, " \t")
+}
+
+func (p *addrParser) peek() byte {
+	return p.s[0]
+}
+
+func (p *addrParser) empty() bool {
+	return p.len() == 0
+}
+
+func (p *addrParser) len() int {
+	return len(p.s)
+}
+
+// skipCFWS skips CFWS as defined in RFC5322.
+func (p *addrParser) skipCFWS() bool {
+	p.skipSpace()
+
+	for {
+		if !p.consume('(') {
+			break
+		}
+
+		if _, ok := p.consumeComment(); !ok {
+			return false
+		}
+
+		p.skipSpace()
+	}
+
+	return true
+}
+
+func (p *addrParser) consumeComment() (string, bool) {
+	// '(' already consumed.
+	depth := 1
+
+	var comment string
+	for {
+		if p.empty() || depth == 0 {
+			break
+		}
+
+		if p.peek() == '\\' && p.len() > 1 {
+			p.s = p.s[1:]
+		} else if p.peek() == '(' {
+			depth++
+		} else if p.peek() == ')' {
+			depth--
+		}
+		if depth > 0 {
+			comment += p.s[:1]
+		}
+		p.s = p.s[1:]
+	}
+
+	return comment, depth == 0
+}
+
+func (p *addrParser) decodeRFC2047Word(s string) (word string, isEncoded bool, err error) {
+	if p.dec != nil {
+		word, err = p.dec.Decode(s)
+	} else {
+		word, err = rfc2047Decoder.Decode(s)
+	}
+
+	if err == nil {
+		return word, true, nil
+	}
+
+	if _, ok := err.(charsetError); ok {
+		return s, true, err
+	}
+
+	// Ignore invalid RFC 2047 encoded-word errors.
+	return s, false, nil
+}
+
+var rfc2047Decoder = mime.WordDecoder{
+	CharsetReader: func(charset string, input io.Reader) (io.Reader, error) {
+		return nil, charsetError(charset)
+	},
+}
+
+type charsetError string
+
+func (e charsetError) Error() string {
+	return fmt.Sprintf("charset not supported: %q", string(e))
+}
+
+// isAtext reports whether r is an RFC 5322 atext character.
+// If dot is true, period is included.
+// If permissive is true, RFC 5322 3.2.3 specials is included,
+// except '<', '>', ':' and '"'.
+func isAtext(r rune, dot, permissive bool) bool {
+	switch r {
+	case '.':
+		return dot
+
+	// RFC 5322 3.2.3. specials
+	case '(', ')', '[', ']', ';', '@', '\\', ',':
+		return permissive
+
+	case '<', '>', '"', ':':
+		return false
+	}
+	return isVchar(r)
+}
+
+// isQtext reports whether r is an RFC 5322 qtext character.
+func isQtext(r rune) bool {
+	// Printable US-ASCII, excluding backslash or quote.
+	if r == '\\' || r == '"' {
+		return false
+	}
+	return isVchar(r)
+}
+
+// quoteString renders a string as an RFC 5322 quoted-string.
+func quoteString(s string) string {
+	var buf strings.Builder
+	buf.WriteByte('"')
+	for _, r := range s {
+		if isQtext(r) || isWSP(r) {
+			buf.WriteRune(r)
+		} else if isVchar(r) {
+			buf.WriteByte('\\')
+			buf.WriteRune(r)
+		}
+	}
+	buf.WriteByte('"')
+	return buf.String()
+}
+
+// isVchar reports whether r is an RFC 5322 VCHAR character.
+func isVchar(r rune) bool {
+	// Visible (printing) characters.
+	return '!' <= r && r <= '~' || isMultibyte(r)
+}
+
+// isMultibyte reports whether r is a multi-byte UTF-8 character
+// as supported by RFC 6532
+func isMultibyte(r rune) bool {
+	return r >= utf8.RuneSelf
+}
+
+// isWSP reports whether r is a WSP (white space).
+// WSP is a space or horizontal tab (RFC 5234 Appendix B).
+func isWSP(r rune) bool {
+	return r == ' ' || r == '\t'
+}