src/mime/mediatype.go - go - Git at Google

 // Copyright 2010 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 mime

 import (
 	"errors"
 	"fmt"
 	"maps"
 	"slices"
 	"strings"
 	"unicode"
 )

 // FormatMediaType serializes mediatype t and the parameters
 // param as a media type conforming to RFC 2045 and RFC 2616.
 // The type and parameter names are written in lower-case.
 // When any of the arguments result in a standard violation then
 // FormatMediaType returns the empty string.
 func FormatMediaType(t string, param map[string]string) string {
 	var b strings.Builder
 	if major, sub, ok := strings.Cut(t, "/"); !ok {
 		if !isToken(t) {
 			return ""
 		}
 		b.WriteString(strings.ToLower(t))
 	} else {
 		if !isToken(major) || !isToken(sub) {
 			return ""
 		}
 		b.WriteString(strings.ToLower(major))
 		b.WriteByte('/')
 		b.WriteString(strings.ToLower(sub))
 	}

 	for _, attribute := range slices.Sorted(maps.Keys(param)) {
 		value := param[attribute]
 		b.WriteByte(';')
 		b.WriteByte(' ')
 		if !isToken(attribute) {
 			return ""
 		}
 		b.WriteString(strings.ToLower(attribute))

 		needEnc := needsEncoding(value)
 		if needEnc {
 			// RFC 2231 section 4
 			b.WriteByte('*')
 		}
 		b.WriteByte('=')

 		if needEnc {
 			b.WriteString("utf-8''")

 			offset := 0
 			for index := 0; index < len(value); index++ {
 				ch := value[index]
 				// {RFC 2231 section 7}
 				// attribute-char := <any (US-ASCII) CHAR except SPACE, CTLs, "*", "'", "%", or tspecials>
 				if ch <= ' ' || ch >= 0x7F ||
 					ch == '*' || ch == '\'' || ch == '%' ||
 					isTSpecial(ch) {

 					b.WriteString(value[offset:index])
 					offset = index + 1

 					b.WriteByte('%')
 					b.WriteByte(upperhex[ch>>4])
 					b.WriteByte(upperhex[ch&0x0F])
 				}
 			}
 			b.WriteString(value[offset:])
 			continue
 		}

 		if isToken(value) {
 			b.WriteString(value)
 			continue
 		}

 		b.WriteByte('"')
 		offset := 0
 		for index := 0; index < len(value); index++ {
 			character := value[index]
 			if character == '"' || character == '\\' {
 				b.WriteString(value[offset:index])
 				offset = index
 				b.WriteByte('\\')
 			}
 		}
 		b.WriteString(value[offset:])
 		b.WriteByte('"')
 	}
 	return b.String()
 }

 func checkMediaTypeDisposition(s string) error {
 	typ, rest := consumeToken(s)
 	if typ == "" {
 		return errNoMediaType
 	}
 	if rest == "" {
 		return nil
 	}
 	var ok bool
 	if rest, ok = strings.CutPrefix(rest, "/"); !ok {
 		return errNoSlashAfterFirstToken
 	}
 	subtype, rest := consumeToken(rest)
 	if subtype == "" {
 		return errNoTokenAfterSlash
 	}
 	if rest != "" {
 		return errUnexpectedContentAfterMediaSubtype
 	}
 	return nil
 }

 var (
 	errNoMediaType                        = errors.New("mime: no media type")
 	errNoSlashAfterFirstToken             = errors.New("mime: expected slash after first token")
 	errNoTokenAfterSlash                  = errors.New("mime: expected token after slash")
 	errUnexpectedContentAfterMediaSubtype = errors.New("mime: unexpected content after media subtype")
 )

 // ErrInvalidMediaParameter is returned by [ParseMediaType] if
 // the media type value was found but there was an error parsing
 // the optional parameters
 var ErrInvalidMediaParameter = errors.New("mime: invalid media parameter")

 // ParseMediaType parses a media type value and any optional
 // parameters, per RFC 1521.  Media types are the values in
 // Content-Type and Content-Disposition headers (RFC 2183).
 // On success, ParseMediaType returns the media type converted
 // to lowercase and trimmed of white space and a non-nil map.
 // If there is an error parsing the optional parameter,
 // the media type will be returned along with the error
 // [ErrInvalidMediaParameter].
 // The returned map, params, maps from the lowercase
 // attribute to the attribute value with its case preserved.
 func ParseMediaType(v string) (mediatype string, params map[string]string, err error) {
 	base, _, _ := strings.Cut(v, ";")
 	mediatype = strings.TrimSpace(strings.ToLower(base))

 	err = checkMediaTypeDisposition(mediatype)
 	if err != nil {
 		return "", nil, err
 	}

 	params = make(map[string]string)

 	// Map of base parameter name -> parameter name -> value
 	// for parameters containing a '*' character.
 	// Lazily initialized.
 	var continuation map[string]map[string]string

 	v = v[len(base):]
 	for len(v) > 0 {
 		v = strings.TrimLeftFunc(v, unicode.IsSpace)
 		if len(v) == 0 {
 			break
 		}
 		key, value, rest := consumeMediaParam(v)
 		if key == "" {
 			if strings.TrimSpace(rest) == ";" {
 				// Ignore trailing semicolons.
 				// Not an error.
 				break
 			}
 			// Parse error.
 			return mediatype, nil, ErrInvalidMediaParameter
 		}

 		pmap := params
 		if baseName, _, ok := strings.Cut(key, "*"); ok {
 			if continuation == nil {
 				continuation = make(map[string]map[string]string)
 			}
 			if pmap, ok = continuation[baseName]; !ok {
 				continuation[baseName] = make(map[string]string)
 				pmap = continuation[baseName]
 			}
 		}
 		if v, exists := pmap[key]; exists && v != value {
 			// Duplicate parameter names are incorrect, but we allow them if they are equal.
 			return "", nil, errDuplicateParamName
 		}
 		pmap[key] = value
 		v = rest
 	}

 	// Stitch together any continuations or things with stars
 	// (i.e. RFC 2231 things with stars: "foo*0" or "foo*")
 	var buf strings.Builder
 	for key, pieceMap := range continuation {
 		singlePartKey := key + "*"
 		if v, ok := pieceMap[singlePartKey]; ok {
 			if decv, ok := decode2231Enc(v); ok {
 				params[key] = decv
 			}
 			continue
 		}

 		buf.Reset()
 		valid := false
 		for n := 0; ; n++ {
 			simplePart := fmt.Sprintf("%s*%d", key, n)
 			if v, ok := pieceMap[simplePart]; ok {
 				valid = true
 				buf.WriteString(v)
 				continue
 			}
 			encodedPart := simplePart + "*"
 			v, ok := pieceMap[encodedPart]
 			if !ok {
 				break
 			}
 			valid = true
 			if n == 0 {
 				if decv, ok := decode2231Enc(v); ok {
 					buf.WriteString(decv)
 				}
 			} else {
 				decv, _ := percentHexUnescape(v)
 				buf.WriteString(decv)
 			}
 		}
 		if valid {
 			params[key] = buf.String()
 		}
 	}

 	return
 }

 var errDuplicateParamName = errors.New("mime: duplicate parameter name")

 func decode2231Enc(v string) (string, bool) {
 	charset, v, ok := strings.Cut(v, "'")
 	if !ok {
 		return "", false
 	}
 	// TODO: ignoring the language part for now. If anybody needs it, we'll
 	// need to decide how to expose it in the API. But I'm not sure
 	// anybody uses it in practice.
 	_, extOtherVals, ok := strings.Cut(v, "'")
 	if !ok {
 		return "", false
 	}
 	charset = strings.ToLower(charset)
 	switch charset {
 	case "us-ascii", "utf-8":
 	default:
 		// Empty or unsupported encoding.
 		return "", false
 	}
 	return percentHexUnescape(extOtherVals)
 }

 // consumeToken consumes a token from the beginning of provided
 // string, per RFC 2045 section 5.1 (referenced from 2183), and return
 // the token consumed and the rest of the string. Returns ("", v) on
 // failure to consume at least one character.
 func consumeToken(v string) (token, rest string) {
 	for i := range len(v) {
 		if !isTokenChar(v[i]) {
 			return v[:i], v[i:]
 		}
 	}
 	return v, ""
 }

 // consumeValue consumes a "value" per RFC 2045, where a value is
 // either a 'token' or a 'quoted-string'.  On success, consumeValue
 // returns the value consumed (and de-quoted/escaped, if a
 // quoted-string) and the rest of the string. On failure, returns
 // ("", v).
 func consumeValue(v string) (value, rest string) {
 	if v == "" {
 		return
 	}
 	if v[0] != '"' {
 		return consumeToken(v)
 	}

 	// parse a quoted-string
 	buffer := new(strings.Builder)
 	for i := 1; i < len(v); i++ {
 		r := v[i]
 		if r == '"' {
 			return buffer.String(), v[i+1:]
 		}
 		// When MSIE sends a full file path (in "intranet mode"), it does not
 		// escape backslashes: "C:\dev\go\foo.txt", not "C:\\dev\\go\\foo.txt".
 		//
 		// No known MIME generators emit unnecessary backslash escapes
 		// for simple token characters like numbers and letters.
 		//
 		// If we see an unnecessary backslash escape, assume it is from MSIE
 		// and intended as a literal backslash. This makes Go servers deal better
 		// with MSIE without affecting the way they handle conforming MIME
 		// generators.
 		if r == '\\' && i+1 < len(v) && isTSpecial(v[i+1]) {
 			buffer.WriteByte(v[i+1])
 			i++
 			continue
 		}
 		if r == '\r' || r == '\n' {
 			return "", v
 		}
 		buffer.WriteByte(v[i])
 	}
 	// Did not find end quote.
 	return "", v
 }

 func consumeMediaParam(v string) (param, value, rest string) {
 	rest = strings.TrimLeftFunc(v, unicode.IsSpace)
 	var ok bool
 	if rest, ok = strings.CutPrefix(rest, ";"); !ok {
 		return "", "", v
 	}

 	rest = strings.TrimLeftFunc(rest, unicode.IsSpace)
 	param, rest = consumeToken(rest)
 	param = strings.ToLower(param)
 	if param == "" {
 		return "", "", v
 	}

 	rest = strings.TrimLeftFunc(rest, unicode.IsSpace)
 	if rest, ok = strings.CutPrefix(rest, "="); !ok {
 		return "", "", v
 	}
 	rest = strings.TrimLeftFunc(rest, unicode.IsSpace)
 	value, rest2 := consumeValue(rest)
 	if value == "" && rest2 == rest {
 		return "", "", v
 	}
 	rest = rest2
 	return param, value, rest
 }

 func percentHexUnescape(s string) (string, bool) {
 	// Count %, check that they're well-formed.
 	percents := 0
 	for i := 0; i < len(s); {
 		if s[i] != '%' {
 			i++
 			continue
 		}
 		percents++
 		if i+2 >= len(s) || !ishex(s[i+1]) || !ishex(s[i+2]) {
 			return "", false
 		}
 		i += 3
 	}
 	if percents == 0 {
 		return s, true
 	}

 	t := make([]byte, len(s)-2*percents)
 	j := 0
 	for i := 0; i < len(s); {
 		switch s[i] {
 		case '%':
 			t[j] = unhex(s[i+1])<<4 | unhex(s[i+2])
 			j++
 			i += 3
 		default:
 			t[j] = s[i]
 			j++
 			i++
 		}
 	}
 	return string(t), true
 }

 func ishex(c byte) bool {
 	switch {
 	case '0' <= c && c <= '9':
 		return true
 	case 'a' <= c && c <= 'f':
 		return true
 	case 'A' <= c && c <= 'F':
 		return true
 	}
 	return false
 }

 func unhex(c byte) byte {
 	switch {
 	case '0' <= c && c <= '9':
 		return c - '0'
 	case 'a' <= c && c <= 'f':
 		return c - 'a' + 10
 	case 'A' <= c && c <= 'F':
 		return c - 'A' + 10
 	}
 	return 0
 }
	// Copyright 2010 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 mime

	import (
	"errors"
	"fmt"
	"maps"
	"slices"
	"strings"
	"unicode"
	)

	// FormatMediaType serializes mediatype t and the parameters
	// param as a media type conforming to RFC 2045 and RFC 2616.
	// The type and parameter names are written in lower-case.
	// When any of the arguments result in a standard violation then
	// FormatMediaType returns the empty string.
	func FormatMediaType(t string, param map[string]string) string {
	var b strings.Builder
	if major, sub, ok := strings.Cut(t, "/"); !ok {
	if !isToken(t) {
	return ""
	}
	b.WriteString(strings.ToLower(t))
	} else {
	if !isToken(major) \|\| !isToken(sub) {
	return ""
	}
	b.WriteString(strings.ToLower(major))
	b.WriteByte('/')
	b.WriteString(strings.ToLower(sub))
	}

	for _, attribute := range slices.Sorted(maps.Keys(param)) {
	value := param[attribute]
	b.WriteByte(';')
	b.WriteByte(' ')
	if !isToken(attribute) {
	return ""
	}
	b.WriteString(strings.ToLower(attribute))

	needEnc := needsEncoding(value)
	if needEnc {
	// RFC 2231 section 4
	b.WriteByte('*')
	}
	b.WriteByte('=')

	if needEnc {
	b.WriteString("utf-8''")

	offset := 0
	for index := 0; index < len(value); index++ {
	ch := value[index]
	// {RFC 2231 section 7}
	// attribute-char := <any (US-ASCII) CHAR except SPACE, CTLs, "*", "'", "%", or tspecials>
	if ch <= ' ' \|\| ch >= 0x7F \|\|
	ch == '*' \|\| ch == '\'' \|\| ch == '%' \|\|
	isTSpecial(ch) {

	b.WriteString(value[offset:index])
	offset = index + 1

	b.WriteByte('%')
	b.WriteByte(upperhex[ch>>4])
	b.WriteByte(upperhex[ch&0x0F])
	}
	}
	b.WriteString(value[offset:])
	continue
	}

	if isToken(value) {
	b.WriteString(value)
	continue
	}

	b.WriteByte('"')
	offset := 0
	for index := 0; index < len(value); index++ {
	character := value[index]
	if character == '"' \|\| character == '\\' {
	b.WriteString(value[offset:index])
	offset = index
	b.WriteByte('\\')
	}
	}
	b.WriteString(value[offset:])
	b.WriteByte('"')
	}
	return b.String()
	}

	func checkMediaTypeDisposition(s string) error {
	typ, rest := consumeToken(s)
	if typ == "" {
	return errNoMediaType
	}
	if rest == "" {
	return nil
	}
	var ok bool
	if rest, ok = strings.CutPrefix(rest, "/"); !ok {
	return errNoSlashAfterFirstToken
	}
	subtype, rest := consumeToken(rest)
	if subtype == "" {
	return errNoTokenAfterSlash
	}
	if rest != "" {
	return errUnexpectedContentAfterMediaSubtype
	}
	return nil
	}

	var (
	errNoMediaType = errors.New("mime: no media type")
	errNoSlashAfterFirstToken = errors.New("mime: expected slash after first token")
	errNoTokenAfterSlash = errors.New("mime: expected token after slash")
	errUnexpectedContentAfterMediaSubtype = errors.New("mime: unexpected content after media subtype")
	)

	// ErrInvalidMediaParameter is returned by [ParseMediaType] if
	// the media type value was found but there was an error parsing
	// the optional parameters
	var ErrInvalidMediaParameter = errors.New("mime: invalid media parameter")

	// ParseMediaType parses a media type value and any optional
	// parameters, per RFC 1521. Media types are the values in
	// Content-Type and Content-Disposition headers (RFC 2183).
	// On success, ParseMediaType returns the media type converted
	// to lowercase and trimmed of white space and a non-nil map.
	// If there is an error parsing the optional parameter,
	// the media type will be returned along with the error
	// [ErrInvalidMediaParameter].
	// The returned map, params, maps from the lowercase
	// attribute to the attribute value with its case preserved.
	func ParseMediaType(v string) (mediatype string, params map[string]string, err error) {
	base, _, _ := strings.Cut(v, ";")
	mediatype = strings.TrimSpace(strings.ToLower(base))

	err = checkMediaTypeDisposition(mediatype)
	if err != nil {
	return "", nil, err
	}

	params = make(map[string]string)

	// Map of base parameter name -> parameter name -> value
	// for parameters containing a '*' character.
	// Lazily initialized.
	var continuation map[string]map[string]string

	v = v[len(base):]
	for len(v) > 0 {
	v = strings.TrimLeftFunc(v, unicode.IsSpace)
	if len(v) == 0 {
	break
	}
	key, value, rest := consumeMediaParam(v)
	if key == "" {
	if strings.TrimSpace(rest) == ";" {
	// Ignore trailing semicolons.
	// Not an error.
	break
	}
	// Parse error.
	return mediatype, nil, ErrInvalidMediaParameter
	}

	pmap := params
	if baseName, _, ok := strings.Cut(key, "*"); ok {
	if continuation == nil {
	continuation = make(map[string]map[string]string)
	}
	if pmap, ok = continuation[baseName]; !ok {
	continuation[baseName] = make(map[string]string)
	pmap = continuation[baseName]
	}
	}
	if v, exists := pmap[key]; exists && v != value {
	// Duplicate parameter names are incorrect, but we allow them if they are equal.
	return "", nil, errDuplicateParamName
	}
	pmap[key] = value
	v = rest
	}

	// Stitch together any continuations or things with stars
	// (i.e. RFC 2231 things with stars: "foo0" or "foo")
	var buf strings.Builder
	for key, pieceMap := range continuation {
	singlePartKey := key + "*"
	if v, ok := pieceMap[singlePartKey]; ok {
	if decv, ok := decode2231Enc(v); ok {
	params[key] = decv
	}
	continue
	}

	buf.Reset()
	valid := false
	for n := 0; ; n++ {
	simplePart := fmt.Sprintf("%s*%d", key, n)
	if v, ok := pieceMap[simplePart]; ok {
	valid = true
	buf.WriteString(v)
	continue
	}
	encodedPart := simplePart + "*"
	v, ok := pieceMap[encodedPart]
	if !ok {
	break
	}
	valid = true
	if n == 0 {
	if decv, ok := decode2231Enc(v); ok {
	buf.WriteString(decv)
	}
	} else {
	decv, _ := percentHexUnescape(v)
	buf.WriteString(decv)
	}
	}
	if valid {
	params[key] = buf.String()
	}
	}

	return
	}

	var errDuplicateParamName = errors.New("mime: duplicate parameter name")

	func decode2231Enc(v string) (string, bool) {
	charset, v, ok := strings.Cut(v, "'")
	if !ok {
	return "", false
	}
	// TODO: ignoring the language part for now. If anybody needs it, we'll
	// need to decide how to expose it in the API. But I'm not sure
	// anybody uses it in practice.
	_, extOtherVals, ok := strings.Cut(v, "'")
	if !ok {
	return "", false
	}
	charset = strings.ToLower(charset)
	switch charset {
	case "us-ascii", "utf-8":
	default:
	// Empty or unsupported encoding.
	return "", false
	}
	return percentHexUnescape(extOtherVals)
	}

	// consumeToken consumes a token from the beginning of provided
	// string, per RFC 2045 section 5.1 (referenced from 2183), and return
	// the token consumed and the rest of the string. Returns ("", v) on
	// failure to consume at least one character.
	func consumeToken(v string) (token, rest string) {
	for i := range len(v) {
	if !isTokenChar(v[i]) {
	return v[:i], v[i:]
	}
	}
	return v, ""
	}

	// consumeValue consumes a "value" per RFC 2045, where a value is
	// either a 'token' or a 'quoted-string'. On success, consumeValue
	// returns the value consumed (and de-quoted/escaped, if a
	// quoted-string) and the rest of the string. On failure, returns
	// ("", v).
	func consumeValue(v string) (value, rest string) {
	if v == "" {
	return
	}
	if v[0] != '"' {
	return consumeToken(v)
	}

	// parse a quoted-string
	buffer := new(strings.Builder)
	for i := 1; i < len(v); i++ {
	r := v[i]
	if r == '"' {
	return buffer.String(), v[i+1:]
	}
	// When MSIE sends a full file path (in "intranet mode"), it does not
	// escape backslashes: "C:\dev\go\foo.txt", not "C:\\dev\\go\\foo.txt".
	//
	// No known MIME generators emit unnecessary backslash escapes
	// for simple token characters like numbers and letters.
	//
	// If we see an unnecessary backslash escape, assume it is from MSIE
	// and intended as a literal backslash. This makes Go servers deal better
	// with MSIE without affecting the way they handle conforming MIME
	// generators.
	if r == '\\' && i+1 < len(v) && isTSpecial(v[i+1]) {
	buffer.WriteByte(v[i+1])
	i++
	continue
	}
	if r == '\r' \|\| r == '\n' {
	return "", v
	}
	buffer.WriteByte(v[i])
	}
	// Did not find end quote.
	return "", v
	}

	func consumeMediaParam(v string) (param, value, rest string) {
	rest = strings.TrimLeftFunc(v, unicode.IsSpace)
	var ok bool
	if rest, ok = strings.CutPrefix(rest, ";"); !ok {
	return "", "", v
	}

	rest = strings.TrimLeftFunc(rest, unicode.IsSpace)
	param, rest = consumeToken(rest)
	param = strings.ToLower(param)
	if param == "" {
	return "", "", v
	}

	rest = strings.TrimLeftFunc(rest, unicode.IsSpace)
	if rest, ok = strings.CutPrefix(rest, "="); !ok {
	return "", "", v
	}
	rest = strings.TrimLeftFunc(rest, unicode.IsSpace)
	value, rest2 := consumeValue(rest)
	if value == "" && rest2 == rest {
	return "", "", v
	}
	rest = rest2
	return param, value, rest
	}

	func percentHexUnescape(s string) (string, bool) {
	// Count %, check that they're well-formed.
	percents := 0
	for i := 0; i < len(s); {
	if s[i] != '%' {
	i++
	continue
	}
	percents++
	if i+2 >= len(s) \|\| !ishex(s[i+1]) \|\| !ishex(s[i+2]) {
	return "", false
	}
	i += 3
	}
	if percents == 0 {
	return s, true
	}

	t := make([]byte, len(s)-2*percents)
	j := 0
	for i := 0; i < len(s); {
	switch s[i] {
	case '%':
	t[j] = unhex(s[i+1])<<4 \| unhex(s[i+2])
	j++
	i += 3
	default:
	t[j] = s[i]
	j++
	i++
	}
	}
	return string(t), true
	}

	func ishex(c byte) bool {
	switch {
	case '0' <= c && c <= '9':
	return true
	case 'a' <= c && c <= 'f':
	return true
	case 'A' <= c && c <= 'F':
	return true
	}
	return false
	}

	func unhex(c byte) byte {
	switch {
	case '0' <= c && c <= '9':
	return c - '0'
	case 'a' <= c && c <= 'f':
	return c - 'a' + 10
	case 'A' <= c && c <= 'F':
	return c - 'A' + 10
	}
	return 0
	}