statsd_exporter/pkg/mapper/fsm/formatter.go

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// Copyright 2018 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 fsm
import (
"fmt"
"regexp"
"strconv"
"strings"
)
var (
templateReplaceCaptureRE = regexp.MustCompile(`\$\{?([a-zA-Z0-9_\$]+)\}?`)
)
type TemplateFormatter struct {
captureIndexes []int
captureCount int
fmtString string
}
// NewTemplateFormatter instantiates a TemplateFormatter
// from given template string and the maximum amount of captures.
func NewTemplateFormatter(template string, captureCount int) *TemplateFormatter {
matches := templateReplaceCaptureRE.FindAllStringSubmatch(template, -1)
if len(matches) == 0 {
// if no regex reference found, keep it as it is
return &TemplateFormatter{captureCount: 0, fmtString: template}
}
var indexes []int
valueFormatter := template
for _, match := range matches {
idx, err := strconv.Atoi(match[len(match)-1])
if err != nil || idx > captureCount || idx < 1 {
// if index larger than captured count or using unsupported named capture group,
// replace with empty string
valueFormatter = strings.Replace(valueFormatter, match[0], "", -1)
} else {
valueFormatter = strings.Replace(valueFormatter, match[0], "%s", -1)
// note: the regex reference variable $? starts from 1
indexes = append(indexes, idx-1)
}
}
return &TemplateFormatter{
captureIndexes: indexes,
captureCount: len(indexes),
fmtString: valueFormatter,
}
}
// Format accepts a list containing captured strings and returns the formatted
// string using the template stored in current TemplateFormatter.
func (formatter *TemplateFormatter) Format(captures []string) string {
if formatter.captureCount == 0 {
// no label substitution, keep as it is
return formatter.fmtString
}
indexes := formatter.captureIndexes
vargs := make([]interface{}, formatter.captureCount)
for i, idx := range indexes {
vargs[i] = captures[idx]
}
return fmt.Sprintf(formatter.fmtString, vargs...)
}