You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: decode_string.go
    path of file: ./repos/plumber/vendor/google.golang.org/protobuf/internal/encoding/text
    
    the code of the file until where you have to start completion: // Copyright 2018 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 text

import (
	"bytes"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf16"
	"unicode/utf8"

	"google.golang.org/protobuf/internal/strs"
)

// parseStringValue parses string field token.
// This differs from parseString since the text format allows
// multiple back-to-back string literals where they are semantically treated
// as a single large string with all values concatenated.
//
// E.g., `"foo" "bar" "baz"` => "foobarbaz"
func (d *Decoder) parseStringValue() (Token, error) {
	// Note that the ending quote is sufficient to unambiguously mark the end
	// of a string. Thus, the text grammar does not require intervening
	// whitespace or control characters in-between strings.
	// Thus, the following is valid:
	//	`"foo"'bar'"baz"` => "foobarbaz"
	in0 := d.in
	var ss []string
	for len(d.in) > 0 && (d.in[0] == '"' || d.in[0] == '\'') {
		s, err := d.parseString()
		if err != nil {
			return Token{}, err
		}
		ss = append(ss, s)
	}
	// d.in already points to the end of the value at this point.
	return Token{
		kind:  Scalar,
		attrs: stringValue,
		pos:   len(d.orig) - len(in0),
		raw:   in0[:len(in0)-len(d.in)],
		str:   strings.Join(ss, ""),
	}, nil
}

// parseString parses a string value enclosed in " or '.
func (d *Decoder) parseString() (string, error) {
	in := d.in
	if len(in) == 0 {
		return "", ErrUnexpectedEOF
	}
	quote := in[0]
	in = in[1:]
	i := indexNeedEscapeInBytes(in)
	in, out := in[i:], in[:i:i] // set cap to prevent mutations
	for len(in) > 0 {
		switch r, n := utf8.DecodeRune(in); {
		case r == utf8.RuneError && n == 1:
			return "", d.newSyntaxError("invalid UTF-8 detected")
		case r == 0 || r == '\n':
			return "", d.newSyntaxError("invalid character %q in string", r)
		case r == rune(quote):
			in = in[1:]
			d.consume(len(d.in) - len(in))
			return string(out), nil
		case r == '\\':
			if len(in) < 2 {
				return "", ErrUnexpectedEOF
			}
			switch r := in[1]; r {
			case '"', '\'', '\\', '?':
				in, out = in[2:], append(out, r)
			case 'a':
				in, out = in[2:], append(out, '\a')
			case 'b':
				in, out = in[2:], append(out, '\b')
			case 'n':
				in, out = in[2:], append(out, '\n')
			case 'r':
				in, out = in[2:], append(out, '\r')
			case 't':
				i
    
func (d *Decoder) parseString() (string, error) {
	in := d.in
	if len(in) == 0 {
		return "", ErrUnexpectedEOF
	}
	quote := in[0]
	in = in[1:]
	i := indexNeedEscapeInBytes(in)
	in, out := in[i:], in[:i:i] // set cap to prevent mutations
	for len(in) > 0 {
		switch r, n := utf8.DecodeRune(in); {
		case r == utf8.RuneError && n == 1:
			return "", d.newSyntaxError("invalid UTF-8 detected")
		case r == 0 || r == '\n':
			return "", d.newSyntaxError("invalid character %q in string", r)
		case r == rune(quote):
			in = in[1:]
			d.consume(len(d.in) - len(in))
			return string(out), nil
		case r == '\\':
			if len(in) < 2 {
				return "", ErrUnexpectedEOF
			}
			switch r := in[1]; r {
			case '"', '\'', '\\', '?':
				in, out = in[2:], append(out, r)
			case 'a':
				in, out = in[2:], append(out, '\a')
			case 'b':
				in, out = in[2:], append(out, '\b')
			case 'n':
				in, out = in[2:], append(out, '\n')
			case 'r':
				in, out = in[2:], append(out, '\r')
			case 't':
				in, out = in[2:], append(out, '\t')
			case 'v':
				in, out = in[2:], append(out, '\v')
			case 'f':
				in, out = in[2:], append(out, '\f')
			case '0', '1', '2', '3', '4', '5', '6', '7':
				// One, two, or three octal characters.
				n := len(in[1:]) - len(bytes.TrimLeft(in[1:], "01234567"))
				if n > 3 {
					n = 3
				}
				v, err := strconv.ParseUint(string(in[1:1+n]), 8, 8)
				if err != nil {
					return "", d.newSyntaxError("invalid octal escape code %q in string", in[:1+n])
				}
				in, out = in[1+n:], append(out, byte(v))
			case 'x':
				// One or two hexadecimal characters.
				n := len(in[2:]) - len(bytes.TrimLeft(in[2:], "0123456789abcdefABCDEF"))
				if n > 2 {
					n = 2
				}
				v, err := strconv.ParseUint(string(in[2:2+n]), 16, 8)
				if err != nil {
					return "", d.newSyntaxError("invalid hex escape code %q in string", in[:2+n])
				}
				in, out = in[2+n:], append(out, byte(v))
			case 'u', 'U':
				// Four or eight hexadecimal characters
				n := 6
				if r == 'U' {
					n = 10
				}
				if len(in) < n {
					return "", ErrUnexpectedEOF
				}
				v, err := strconv.ParseUint(string(in[2:n]), 16, 32)
				if utf8.MaxRune < v || err != nil {
					return "", d.newSyntaxError("invalid Unicode escape code %q in string", in[:n])
				}
				in = in[n:]

				r := rune(v)
				if utf16.IsSurrogate(r) {
					if len(in) < 6 {
						return "", ErrUnexpectedEOF
					}
					v, err := strconv.ParseUint(string(in[2:6]), 16, 16)
					r = utf16.DecodeRune(r, rune(v))
					if in[0] != '\\' || in[1] != 'u' || r == unicode.ReplacementChar || err != nil {
						return "", d.newSyntaxError("invalid Unicode escape code %q in string", in[:6])
					}
					in = in[6:]
				}
				out = append(out, string(r)...)
			default:
				return "", d.newSyntaxError("invalid escape code %q in string", in[:2])
			}
		default:
			i := indexNeedEscapeInBytes(in[n:])
			in, out = in[n+i:], append(out, in[:n+i]...)
		}
	}
	return "", ErrUnexpectedEOF
}