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: text_parse.go
    path of file: ./repos/gotosocial/vendor/github.com/prometheus/common/expfmt
    
    the code of the file until where you have to start completion: // Copyright 2014 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package expfmt

import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"math"
	"strconv"
	"strings"

	dto "github.com/prometheus/client_model/go"

	"github.com/prometheus/common/model"
	"google.golang.org/protobuf/proto"
)

// A stateFn is a function that represents a state in a state machine. By
// executing it, the state is progressed to the next state. The stateFn returns
// another stateFn, which represents the new state. The end state is represented
// by nil.
type stateFn func() stateFn

// ParseError signals 
    
func (p *TextParser) startLabelValue() stateFn {
	if p.skipBlankTab(); p.err != nil {
		return nil // Unexpected end of input.
	}
	if p.currentByte != '"' {
		p.parseError(fmt.Sprintf("expected '\"' at start of label value, found %q", p.currentByte))
		return nil
	}
	if p.readTokenAsLabelValue(); p.err != nil {
		return nil
	}
	if !model.LabelValue(p.currentToken.String()).IsValid() {
		p.parseError(fmt.Sprintf("invalid label value %q", p.currentToken.String()))
		return nil
	}
	p.currentLabelPair.Value = proto.String(p.currentToken.String())
	// Special treatment of summaries:
	// - Quantile labels are special, will result in dto.Quantile later.
	// - Other labels have to be added to currentLabels for signature calculation.
	if p.currentMF.GetType() == dto.MetricType_SUMMARY {
		if p.currentLabelPair.GetName() == model.QuantileLabel {
			if p.currentQuantile, p.err = parseFloat(p.currentLabelPair.GetValue()); p.err != nil {
				// Create a more helpful error message.
				p.parseError(fmt.Sprintf("expected float as value for 'quantile' label, got %q", p.currentLabelPair.GetValue()))
				return nil
			}
		} else {
			p.currentLabels[p.currentLabelPair.GetName()] = p.currentLabelPair.GetValue()
		}
	}
	// Similar special treatment of histograms.
	if p.currentMF.GetType() == dto.MetricType_HISTOGRAM {
		if p.currentLabelPair.GetName() == model.BucketLabel {
			if p.currentBucket, p.err = parseFloat(p.currentLabelPair.GetValue()); p.err != nil {
				// Create a more helpful error message.
				p.parseError(fmt.Sprintf("expected float as value for 'le' label, got %q", p.currentLabelPair.GetValue()))
				return nil
			}
		} else {
			p.currentLabels[p.currentLabelPair.GetName()] = p.currentLabelPair.GetValue()
		}
	}
	if p.skipBlankTab(); p.err != nil {
		return nil // Unexpected end of input.
	}
	switch p.currentByte {
	case ',':
		return p.startLabelName

	case '}':
		if p.skipBlankTab(); p.err != nil {
			return nil // Unexpected end of input.
		}
		return p.readingValue
	default:
		p.parseError(fmt.Sprintf("unexpected end of label value %q", p.currentLabelPair.GetValue()))
		return nil
	}