statsd_exporter/pkg/mapper/escape.go

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// Copyright 2020 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 mapper
import (
"strings"
"unicode/utf8"
)
// EscapeMetricName replaces invalid characters in the metric name with "_"
// Valid characters are a-z, A-Z, 0-9, and _
func EscapeMetricName(metricName string) string {
metricLen := len(metricName)
if metricLen == 0 {
return ""
}
escaped := false
var sb strings.Builder
// If a metric starts with a digit, allocate the memory and prepend an
// underscore.
if metricName[0] >= '0' && metricName[0] <= '9' {
escaped = true
sb.Grow(metricLen + 1)
sb.WriteByte('_')
}
// This is an character replacement method optimized for this limited
// use case. It is much faster than using a regex.
offset := 0
var prevChar rune
for i, c := range metricName {
// Seek forward, skipping valid characters until we find one that needs
// to be replaced, then add all the characters we've seen so far to the
// string.Builder.
if (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ||
(c >= '0' && c <= '9') || (c == '_') {
// Character is valid, so skip over it without doing anything.
} else {
// Double-dashes are allowed if there is a corresponding mapping.
// For consistency, double-dashes should also be allowed in the default case.
if c == '-' && prevChar == '-' {
offset = i + utf8.RuneLen(c)
continue
}
if !escaped {
// Up until now we've been lazy and avoided actually allocating
// memory. Unfortunately we've now determined this string needs
// escaping, so allocate the buffer for the whole string.
escaped = true
sb.Grow(metricLen)
}
sb.WriteString(metricName[offset:i])
offset = i + utf8.RuneLen(c)
sb.WriteByte('_')
}
prevChar = c
}
if !escaped {
// This is the happy path where nothing had to be escaped, so we can
// avoid doing anything.
return metricName
}
if offset < metricLen {
sb.WriteString(metricName[offset:])
}
return sb.String()
}