Update vendor

1 files changed, 859 insertions, 0 deletions

diff --git a/vendor/golang.org/x/text/language/parse.go b/vendor/golang.org/x/text/language/parse.go
new file mode 100644
index 00000000..cfa28f56
--- /dev/null
+++ b/vendor/golang.org/x/text/language/parse.go
@@ -0,0 +1,859 @@
+// Copyright 2013 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 language
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+
+	"golang.org/x/text/internal/tag"
+)
+
+// isAlpha returns true if the byte is not a digit.
+// b must be an ASCII letter or digit.
+func isAlpha(b byte) bool {
+	return b > '9'
+}
+
+// isAlphaNum returns true if the string contains only ASCII letters or digits.
+func isAlphaNum(s []byte) bool {
+	for _, c := range s {
+		if !('a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || '0' <= c && c <= '9') {
+			return false
+		}
+	}
+	return true
+}
+
+// errSyntax is returned by any of the parsing functions when the
+// input is not well-formed, according to BCP 47.
+// TODO: return the position at which the syntax error occurred?
+var errSyntax = errors.New("language: tag is not well-formed")
+
+// ValueError is returned by any of the parsing functions when the
+// input is well-formed but the respective subtag is not recognized
+// as a valid value.
+type ValueError struct {
+	v [8]byte
+}
+
+func mkErrInvalid(s []byte) error {
+	var e ValueError
+	copy(e.v[:], s)
+	return e
+}
+
+func (e ValueError) tag() []byte {
+	n := bytes.IndexByte(e.v[:], 0)
+	if n == -1 {
+		n = 8
+	}
+	return e.v[:n]
+}
+
+// Error implements the error interface.
+func (e ValueError) Error() string {
+	return fmt.Sprintf("language: subtag %q is well-formed but unknown", e.tag())
+}
+
+// Subtag returns the subtag for which the error occurred.
+func (e ValueError) Subtag() string {
+	return string(e.tag())
+}
+
+// scanner is used to scan BCP 47 tokens, which are separated by _ or -.
+type scanner struct {
+	b     []byte
+	bytes [max99thPercentileSize]byte
+	token []byte
+	start int // start position of the current token
+	end   int // end position of the current token
+	next  int // next point for scan
+	err   error
+	done  bool
+}
+
+func makeScannerString(s string) scanner {
+	scan := scanner{}
+	if len(s) <= len(scan.bytes) {
+		scan.b = scan.bytes[:copy(scan.bytes[:], s)]
+	} else {
+		scan.b = []byte(s)
+	}
+	scan.init()
+	return scan
+}
+
+// makeScanner returns a scanner using b as the input buffer.
+// b is not copied and may be modified by the scanner routines.
+func makeScanner(b []byte) scanner {
+	scan := scanner{b: b}
+	scan.init()
+	return scan
+}
+
+func (s *scanner) init() {
+	for i, c := range s.b {
+		if c == '_' {
+			s.b[i] = '-'
+		}
+	}
+	s.scan()
+}
+
+// restToLower converts the string between start and end to lower case.
+func (s *scanner) toLower(start, end int) {
+	for i := start; i < end; i++ {
+		c := s.b[i]
+		if 'A' <= c && c <= 'Z' {
+			s.b[i] += 'a' - 'A'
+		}
+	}
+}
+
+func (s *scanner) setError(e error) {
+	if s.err == nil || (e == errSyntax && s.err != errSyntax) {
+		s.err = e
+	}
+}
+
+// resizeRange shrinks or grows the array at position oldStart such that
+// a new string of size newSize can fit between oldStart and oldEnd.
+// Sets the scan point to after the resized range.
+func (s *scanner) resizeRange(oldStart, oldEnd, newSize int) {
+	s.start = oldStart
+	if end := oldStart + newSize; end != oldEnd {
+		diff := end - oldEnd
+		if end < cap(s.b) {
+			b := make([]byte, len(s.b)+diff)
+			copy(b, s.b[:oldStart])
+			copy(b[end:], s.b[oldEnd:])
+			s.b = b
+		} else {
+			s.b = append(s.b[end:], s.b[oldEnd:]...)
+		}
+		s.next = end + (s.next - s.end)
+		s.end = end
+	}
+}
+
+// replace replaces the current token with repl.
+func (s *scanner) replace(repl string) {
+	s.resizeRange(s.start, s.end, len(repl))
+	copy(s.b[s.start:], repl)
+}
+
+// gobble removes the current token from the input.
+// Caller must call scan after calling gobble.
+func (s *scanner) gobble(e error) {
+	s.setError(e)
+	if s.start == 0 {
+		s.b = s.b[:+copy(s.b, s.b[s.next:])]
+		s.end = 0
+	} else {
+		s.b = s.b[:s.start-1+copy(s.b[s.start-1:], s.b[s.end:])]
+		s.end = s.start - 1
+	}
+	s.next = s.start
+}
+
+// deleteRange removes the given range from s.b before the current token.
+func (s *scanner) deleteRange(start, end int) {
+	s.setError(errSyntax)
+	s.b = s.b[:start+copy(s.b[start:], s.b[end:])]
+	diff := end - start
+	s.next -= diff
+	s.start -= diff
+	s.end -= diff
+}
+
+// scan parses the next token of a BCP 47 string.  Tokens that are larger
+// than 8 characters or include non-alphanumeric characters result in an error
+// and are gobbled and removed from the output.
+// It returns the end position of the last token consumed.
+func (s *scanner) scan() (end int) {
+	end = s.end
+	s.token = nil
+	for s.start = s.next; s.next < len(s.b); {
+		i := bytes.IndexByte(s.b[s.next:], '-')
+		if i == -1 {
+			s.end = len(s.b)
+			s.next = len(s.b)
+			i = s.end - s.start
+		} else {
+			s.end = s.next + i
+			s.next = s.end + 1
+		}
+		token := s.b[s.start:s.end]
+		if i < 1 || i > 8 || !isAlphaNum(token) {
+			s.gobble(errSyntax)
+			continue
+		}
+		s.token = token
+		return end
+	}
+	if n := len(s.b); n > 0 && s.b[n-1] == '-' {
+		s.setError(errSyntax)
+		s.b = s.b[:len(s.b)-1]
+	}
+	s.done = true
+	return end
+}
+
+// acceptMinSize parses multiple tokens of the given size or greater.
+// It returns the end position of the last token consumed.
+func (s *scanner) acceptMinSize(min int) (end int) {
+	end = s.end
+	s.scan()
+	for ; len(s.token) >= min; s.scan() {
+		end = s.end
+	}
+	return end
+}
+
+// Parse parses the given BCP 47 string and returns a valid Tag. If parsing
+// failed it returns an error and any part of the tag that could be parsed.
+// If parsing succeeded but an unknown value was found, it returns
+// ValueError. The Tag returned in this case is just stripped of the unknown
+// value. All other values are preserved. It accepts tags in the BCP 47 format
+// and extensions to this standard defined in
+// http://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
+// The resulting tag is canonicalized using the default canonicalization type.
+func Parse(s string) (t Tag, err error) {
+	return Default.Parse(s)
+}
+
+// Parse parses the given BCP 47 string and returns a valid Tag. If parsing
+// failed it returns an error and any part of the tag that could be parsed.
+// If parsing succeeded but an unknown value was found, it returns
+// ValueError. The Tag returned in this case is just stripped of the unknown
+// value. All other values are preserved. It accepts tags in the BCP 47 format
+// and extensions to this standard defined in
+// http://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
+// The resulting tag is canonicalized using the the canonicalization type c.
+func (c CanonType) Parse(s string) (t Tag, err error) {
+	// TODO: consider supporting old-style locale key-value pairs.
+	if s == "" {
+		return und, errSyntax
+	}
+	if len(s) <= maxAltTaglen {
+		b := [maxAltTaglen]byte{}
+		for i, c := range s {
+			// Generating invalid UTF-8 is okay as it won't match.
+			if 'A' <= c && c <= 'Z' {
+				c += 'a' - 'A'
+			} else if c == '_' {
+				c = '-'
+			}
+			b[i] = byte(c)
+		}
+		if t, ok := grandfathered(b); ok {
+			return t, nil
+		}
+	}
+	scan := makeScannerString(s)
+	t, err = parse(&scan, s)
+	t, changed := t.canonicalize(c)
+	if changed {
+		t.remakeString()
+	}
+	return t, err
+}
+
+func parse(scan *scanner, s string) (t Tag, err error) {
+	t = und
+	var end int
+	if n := len(scan.token); n <= 1 {
+		scan.toLower(0, len(scan.b))
+		if n == 0 || scan.token[0] != 'x' {
+			return t, errSyntax
+		}
+		end = parseExtensions(scan)
+	} else if n >= 4 {
+		return und, errSyntax
+	} else { // the usual case
+		t, end = parseTag(scan)
+		if n := len(scan.token); n == 1 {
+			t.pExt = uint16(end)
+			end = parseExtensions(scan)
+		} else if end < len(scan.b) {
+			scan.setError(errSyntax)
+			scan.b = scan.b[:end]
+		}
+	}
+	if int(t.pVariant) < len(scan.b) {
+		if end < len(s) {
+			s = s[:end]
+		}
+		if len(s) > 0 && tag.Compare(s, scan.b) == 0 {
+			t.str = s
+		} else {
+			t.str = string(scan.b)
+		}
+	} else {
+		t.pVariant, t.pExt = 0, 0
+	}
+	return t, scan.err
+}
+
+// parseTag parses language, script, region and variants.
+// It returns a Tag and the end position in the input that was parsed.
+func parseTag(scan *scanner) (t Tag, end int) {
+	var e error
+	// TODO: set an error if an unknown lang, script or region is encountered.
+	t.lang, e = getLangID(scan.token)
+	scan.setError(e)
+	scan.replace(t.lang.String())
+	langStart := scan.start
+	end = scan.scan()
+	for len(scan.token) == 3 && isAlpha(scan.token[0]) {
+		// From http://tools.ietf.org/html/bcp47, <lang>-<extlang> tags are equivalent
+		// to a tag of the form <extlang>.
+		lang, e := getLangID(scan.token)
+		if lang != 0 {
+			t.lang = lang
+			copy(scan.b[langStart:], lang.String())
+			scan.b[langStart+3] = '-'
+			scan.start = langStart + 4
+		}
+		scan.gobble(e)
+		end = scan.scan()
+	}
+	if len(scan.token) == 4 && isAlpha(scan.token[0]) {
+		t.script, e = getScriptID(script, scan.token)
+		if t.script == 0 {
+			scan.gobble(e)
+		}
+		end = scan.scan()
+	}
+	if n := len(scan.token); n >= 2 && n <= 3 {
+		t.region, e = getRegionID(scan.token)
+		if t.region == 0 {
+			scan.gobble(e)
+		} else {
+			scan.replace(t.region.String())
+		}
+		end = scan.scan()
+	}
+	scan.toLower(scan.start, len(scan.b))
+	t.pVariant = byte(end)
+	end = parseVariants(scan, end, t)
+	t.pExt = uint16(end)
+	return t, end
+}
+
+var separator = []byte{'-'}
+
+// parseVariants scans tokens as long as each token is a valid variant string.
+// Duplicate variants are removed.
+func parseVariants(scan *scanner, end int, t Tag) int {
+	start := scan.start
+	varIDBuf := [4]uint8{}
+	variantBuf := [4][]byte{}
+	varID := varIDBuf[:0]
+	variant := variantBuf[:0]
+	last := -1
+	needSort := false
+	for ; len(scan.token) >= 4; scan.scan() {
+		// TODO: measure the impact of needing this conversion and redesign
+		// the data structure if there is an issue.
+		v, ok := variantIndex[string(scan.token)]
+		if !ok {
+			// unknown variant
+			// TODO: allow user-defined variants?
+			scan.gobble(mkErrInvalid(scan.token))
+			continue
+		}
+		varID = append(varID, v)
+		variant = append(variant, scan.token)
+		if !needSort {
+			if last < int(v) {
+				last = int(v)
+			} else {
+				needSort = true
+				// There is no legal combinations of more than 7 variants
+				// (and this is by no means a useful sequence).
+				const maxVariants = 8
+				if len(varID) > maxVariants {
+					break
+				}
+			}
+		}
+		end = scan.end
+	}
+	if needSort {
+		sort.Sort(variantsSort{varID, variant})
+		k, l := 0, -1
+		for i, v := range varID {
+			w := int(v)
+			if l == w {
+				// Remove duplicates.
+				continue
+			}
+			varID[k] = varID[i]
+			variant[k] = variant[i]
+			k++
+			l = w
+		}
+		if str := bytes.Join(variant[:k], separator); len(str) == 0 {
+			end = start - 1
+		} else {
+			scan.resizeRange(start, end, len(str))
+			copy(scan.b[scan.start:], str)
+			end = scan.end
+		}
+	}
+	return end
+}
+
+type variantsSort struct {
+	i []uint8
+	v [][]byte
+}
+
+func (s variantsSort) Len() int {
+	return len(s.i)
+}
+
+func (s variantsSort) Swap(i, j int) {
+	s.i[i], s.i[j] = s.i[j], s.i[i]
+	s.v[i], s.v[j] = s.v[j], s.v[i]
+}
+
+func (s variantsSort) Less(i, j int) bool {
+	return s.i[i] < s.i[j]
+}
+
+type bytesSort [][]byte
+
+func (b bytesSort) Len() int {
+	return len(b)
+}
+
+func (b bytesSort) Swap(i, j int) {
+	b[i], b[j] = b[j], b[i]
+}
+
+func (b bytesSort) Less(i, j int) bool {
+	return bytes.Compare(b[i], b[j]) == -1
+}
+
+// parseExtensions parses and normalizes the extensions in the buffer.
+// It returns the last position of scan.b that is part of any extension.
+// It also trims scan.b to remove excess parts accordingly.
+func parseExtensions(scan *scanner) int {
+	start := scan.start
+	exts := [][]byte{}
+	private := []byte{}
+	end := scan.end
+	for len(scan.token) == 1 {
+		extStart := scan.start
+		ext := scan.token[0]
+		end = parseExtension(scan)
+		extension := scan.b[extStart:end]
+		if len(extension) < 3 || (ext != 'x' && len(extension) < 4) {
+			scan.setError(errSyntax)
+			end = extStart
+			continue
+		} else if start == extStart && (ext == 'x' || scan.start == len(scan.b)) {
+			scan.b = scan.b[:end]
+			return end
+		} else if ext == 'x' {
+			private = extension
+			break
+		}
+		exts = append(exts, extension)
+	}
+	sort.Sort(bytesSort(exts))
+	if len(private) > 0 {
+		exts = append(exts, private)
+	}
+	scan.b = scan.b[:start]
+	if len(exts) > 0 {
+		scan.b = append(scan.b, bytes.Join(exts, separator)...)
+	} else if start > 0 {
+		// Strip trailing '-'.
+		scan.b = scan.b[:start-1]
+	}
+	return end
+}
+
+// parseExtension parses a single extension and returns the position of
+// the extension end.
+func parseExtension(scan *scanner) int {
+	start, end := scan.start, scan.end
+	switch scan.token[0] {
+	case 'u':
+		attrStart := end
+		scan.scan()
+		for last := []byte{}; len(scan.token) > 2; scan.scan() {
+			if bytes.Compare(scan.token, last) != -1 {
+				// Attributes are unsorted. Start over from scratch.
+				p := attrStart + 1
+				scan.next = p
+				attrs := [][]byte{}
+				for scan.scan(); len(scan.token) > 2; scan.scan() {
+					attrs = append(attrs, scan.token)
+					end = scan.end
+				}
+				sort.Sort(bytesSort(attrs))
+				copy(scan.b[p:], bytes.Join(attrs, separator))
+				break
+			}
+			last = scan.token
+			end = scan.end
+		}
+		var last, key []byte
+		for attrEnd := end; len(scan.token) == 2; last = key {
+			key = scan.token
+			keyEnd := scan.end
+			end = scan.acceptMinSize(3)
+			// TODO: check key value validity
+			if keyEnd == end || bytes.Compare(key, last) != 1 {
+				// We have an invalid key or the keys are not sorted.
+				// Start scanning keys from scratch and reorder.
+				p := attrEnd + 1
+				scan.next = p
+				keys := [][]byte{}
+				for scan.scan(); len(scan.token) == 2; {
+					keyStart, keyEnd := scan.start, scan.end
+					end = scan.acceptMinSize(3)
+					if keyEnd != end {
+						keys = append(keys, scan.b[keyStart:end])
+					} else {
+						scan.setError(errSyntax)
+						end = keyStart
+					}
+				}
+				sort.Sort(bytesSort(keys))
+				reordered := bytes.Join(keys, separator)
+				if e := p + len(reordered); e < end {
+					scan.deleteRange(e, end)
+					end = e
+				}
+				copy(scan.b[p:], bytes.Join(keys, separator))
+				break
+			}
+		}
+	case 't':
+		scan.scan()
+		if n := len(scan.token); n >= 2 && n <= 3 && isAlpha(scan.token[1]) {
+			_, end = parseTag(scan)
+			scan.toLower(start, end)
+		}
+		for len(scan.token) == 2 && !isAlpha(scan.token[1]) {
+			end = scan.acceptMinSize(3)
+		}
+	case 'x':
+		end = scan.acceptMinSize(1)
+	default:
+		end = scan.acceptMinSize(2)
+	}
+	return end
+}
+
+// Compose creates a Tag from individual parts, which may be of type Tag, Base,
+// Script, Region, Variant, []Variant, Extension, []Extension or error. If a
+// Base, Script or Region or slice of type Variant or Extension is passed more
+// than once, the latter will overwrite the former. Variants and Extensions are
+// accumulated, but if two extensions of the same type are passed, the latter
+// will replace the former. A Tag overwrites all former values and typically
+// only makes sense as the first argument. The resulting tag is returned after
+// canonicalizing using the Default CanonType. If one or more errors are
+// encountered, one of the errors is returned.
+func Compose(part ...interface{}) (t Tag, err error) {
+	return Default.Compose(part...)
+}
+
+// Compose creates a Tag from individual parts, which may be of type Tag, Base,
+// Script, Region, Variant, []Variant, Extension, []Extension or error. If a
+// Base, Script or Region or slice of type Variant or Extension is passed more
+// than once, the latter will overwrite the former. Variants and Extensions are
+// accumulated, but if two extensions of the same type are passed, the latter
+// will replace the former. A Tag overwrites all former values and typically
+// only makes sense as the first argument. The resulting tag is returned after
+// canonicalizing using CanonType c. If one or more errors are encountered,
+// one of the errors is returned.
+func (c CanonType) Compose(part ...interface{}) (t Tag, err error) {
+	var b builder
+	if err = b.update(part...); err != nil {
+		return und, err
+	}
+	t, _ = b.tag.canonicalize(c)
+
+	if len(b.ext) > 0 || len(b.variant) > 0 {
+		sort.Sort(sortVariant(b.variant))
+		sort.Strings(b.ext)
+		if b.private != "" {
+			b.ext = append(b.ext, b.private)
+		}
+		n := maxCoreSize + tokenLen(b.variant...) + tokenLen(b.ext...)
+		buf := make([]byte, n)
+		p := t.genCoreBytes(buf)
+		t.pVariant = byte(p)
+		p += appendTokens(buf[p:], b.variant...)
+		t.pExt = uint16(p)
+		p += appendTokens(buf[p:], b.ext...)
+		t.str = string(buf[:p])
+	} else if b.private != "" {
+		t.str = b.private
+		t.remakeString()
+	}
+	return
+}
+
+type builder struct {
+	tag Tag
+
+	private string // the x extension
+	ext     []string
+	variant []string
+
+	err error
+}
+
+func (b *builder) addExt(e string) {
+	if e == "" {
+	} else if e[0] == 'x' {
+		b.private = e
+	} else {
+		b.ext = append(b.ext, e)
+	}
+}
+
+var errInvalidArgument = errors.New("invalid Extension or Variant")
+
+func (b *builder) update(part ...interface{}) (err error) {
+	replace := func(l *[]string, s string, eq func(a, b string) bool) bool {
+		if s == "" {
+			b.err = errInvalidArgument
+			return true
+		}
+		for i, v := range *l {
+			if eq(v, s) {
+				(*l)[i] = s
+				return true
+			}
+		}
+		return false
+	}
+	for _, x := range part {
+		switch v := x.(type) {
+		case Tag:
+			b.tag.lang = v.lang
+			b.tag.region = v.region
+			b.tag.script = v.script
+			if v.str != "" {
+				b.variant = nil
+				for x, s := "", v.str[v.pVariant:v.pExt]; s != ""; {
+					x, s = nextToken(s)
+					b.variant = append(b.variant, x)
+				}
+				b.ext, b.private = nil, ""
+				for i, e := int(v.pExt), ""; i < len(v.str); {
+					i, e = getExtension(v.str, i)
+					b.addExt(e)
+				}
+			}
+		case Base:
+			b.tag.lang = v.langID
+		case Script:
+			b.tag.script = v.scriptID
+		case Region:
+			b.tag.region = v.regionID
+		case Variant:
+			if !replace(&b.variant, v.variant, func(a, b string) bool { return a == b }) {
+				b.variant = append(b.variant, v.variant)
+			}
+		case Extension:
+			if !replace(&b.ext, v.s, func(a, b string) bool { return a[0] == b[0] }) {
+				b.addExt(v.s)
+			}
+		case []Variant:
+			b.variant = nil
+			for _, x := range v {
+				b.update(x)
+			}
+		case []Extension:
+			b.ext, b.private = nil, ""
+			for _, e := range v {
+				b.update(e)
+			}
+		// TODO: support parsing of raw strings based on morphology or just extensions?
+		case error:
+			err = v
+		}
+	}
+	return
+}
+
+func tokenLen(token ...string) (n int) {
+	for _, t := range token {
+		n += len(t) + 1
+	}
+	return
+}
+
+func appendTokens(b []byte, token ...string) int {
+	p := 0
+	for _, t := range token {
+		b[p] = '-'
+		copy(b[p+1:], t)
+		p += 1 + len(t)
+	}
+	return p
+}
+
+type sortVariant []string
+
+func (s sortVariant) Len() int {
+	return len(s)
+}
+
+func (s sortVariant) Swap(i, j int) {
+	s[j], s[i] = s[i], s[j]
+}
+
+func (s sortVariant) Less(i, j int) bool {
+	return variantIndex[s[i]] < variantIndex[s[j]]
+}
+
+func findExt(list []string, x byte) int {
+	for i, e := range list {
+		if e[0] == x {
+			return i
+		}
+	}
+	return -1
+}
+
+// getExtension returns the name, body and end position of the extension.
+func getExtension(s string, p int) (end int, ext string) {
+	if s[p] == '-' {
+		p++
+	}
+	if s[p] == 'x' {
+		return len(s), s[p:]
+	}
+	end = nextExtension(s, p)
+	return end, s[p:end]
+}
+
+// nextExtension finds the next extension within the string, searching
+// for the -<char>- pattern from position p.
+// In the fast majority of cases, language tags will have at most
+// one extension and extensions tend to be small.
+func nextExtension(s string, p int) int {
+	for n := len(s) - 3; p < n; {
+		if s[p] == '-' {
+			if s[p+2] == '-' {
+				return p
+			}
+			p += 3
+		} else {
+			p++
+		}
+	}
+	return len(s)
+}
+
+var errInvalidWeight = errors.New("ParseAcceptLanguage: invalid weight")
+
+// ParseAcceptLanguage parses the contents of a Accept-Language header as
+// defined in http://www.ietf.org/rfc/rfc2616.txt and returns a list of Tags and
+// a list of corresponding quality weights. It is more permissive than RFC 2616
+// and may return non-nil slices even if the input is not valid.
+// The Tags will be sorted by highest weight first and then by first occurrence.
+// Tags with a weight of zero will be dropped. An error will be returned if the
+// input could not be parsed.
+func ParseAcceptLanguage(s string) (tag []Tag, q []float32, err error) {
+	var entry string
+	for s != "" {
+		if entry, s = split(s, ','); entry == "" {
+			continue
+		}
+
+		entry, weight := split(entry, ';')
+
+		// Scan the language.
+		t, err := Parse(entry)
+		if err != nil {
+			id, ok := acceptFallback[entry]
+			if !ok {
+				return nil, nil, err
+			}
+			t = Tag{lang: id}
+		}
+
+		// Scan the optional weight.
+		w := 1.0
+		if weight != "" {
+			weight = consume(weight, 'q')
+			weight = consume(weight, '=')
+			// consume returns the empty string when a token could not be
+			// consumed, resulting in an error for ParseFloat.
+			if w, err = strconv.ParseFloat(weight, 32); err != nil {
+				return nil, nil, errInvalidWeight
+			}
+			// Drop tags with a quality weight of 0.
+			if w <= 0 {
+				continue
+			}
+		}
+
+		tag = append(tag, t)
+		q = append(q, float32(w))
+	}
+	sortStable(&tagSort{tag, q})
+	return tag, q, nil
+}
+
+// consume removes a leading token c from s and returns the result or the empty
+// string if there is no such token.
+func consume(s string, c byte) string {
+	if s == "" || s[0] != c {
+		return ""
+	}
+	return strings.TrimSpace(s[1:])
+}
+
+func split(s string, c byte) (head, tail string) {
+	if i := strings.IndexByte(s, c); i >= 0 {
+		return strings.TrimSpace(s[:i]), strings.TrimSpace(s[i+1:])
+	}
+	return strings.TrimSpace(s), ""
+}
+
+// Add hack mapping to deal with a small number of cases that that occur
+// in Accept-Language (with reasonable frequency).
+var acceptFallback = map[string]langID{
+	"english": _en,
+	"deutsch": _de,
+	"italian": _it,
+	"french":  _fr,
+	"*":       _mul, // defined in the spec to match all languages.
+}
+
+type tagSort struct {
+	tag []Tag
+	q   []float32
+}
+
+func (s *tagSort) Len() int {
+	return len(s.q)
+}
+
+func (s *tagSort) Less(i, j int) bool {
+	return s.q[i] > s.q[j]
+}
+
+func (s *tagSort) Swap(i, j int) {
+	s.tag[i], s.tag[j] = s.tag[j], s.tag[i]
+	s.q[i], s.q[j] = s.q[j], s.q[i]
+}