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// Copyright 2020 New Relic Corporation. All rights reserved.
// SPDX-License-Identifier: Apache-2.0
package internal
// https://newrelic.atlassian.net/wiki/display/eng/Language+agent+transaction+segment+terms+rules
import (
"encoding/json"
"strings"
)
const (
placeholder = "*"
separator = "/"
)
type segmentRule struct {
Prefix string `json:"prefix"`
Terms []string `json:"terms"`
TermsMap map[string]struct{}
}
// segmentRules is keyed by each segmentRule's Prefix field with any trailing
// slash removed.
type segmentRules map[string]*segmentRule
func buildTermsMap(terms []string) map[string]struct{} {
m := make(map[string]struct{}, len(terms))
for _, t := range terms {
m[t] = struct{}{}
}
return m
}
func (rules *segmentRules) UnmarshalJSON(b []byte) error {
var raw []*segmentRule
if err := json.Unmarshal(b, &raw); nil != err {
return err
}
rs := make(map[string]*segmentRule)
for _, rule := range raw {
prefix := strings.TrimSuffix(rule.Prefix, "/")
if len(strings.Split(prefix, "/")) != 2 {
// TODO
// Warn("invalid segment term rule prefix",
// {"prefix": rule.Prefix})
continue
}
if nil == rule.Terms {
// TODO
// Warn("segment term rule has missing terms",
// {"prefix": rule.Prefix})
continue
}
rule.TermsMap = buildTermsMap(rule.Terms)
rs[prefix] = rule
}
*rules = rs
return nil
}
func (rule *segmentRule) apply(name string) string {
if !strings.HasPrefix(name, rule.Prefix) {
return name
}
s := strings.TrimPrefix(name, rule.Prefix)
leadingSlash := ""
if strings.HasPrefix(s, separator) {
leadingSlash = separator
s = strings.TrimPrefix(s, separator)
}
if "" != s {
segments := strings.Split(s, separator)
for i, segment := range segments {
_, allowed := rule.TermsMap[segment]
if allowed {
segments[i] = segment
} else {
segments[i] = placeholder
}
}
segments = collapsePlaceholders(segments)
s = strings.Join(segments, separator)
}
return rule.Prefix + leadingSlash + s
}
func (rules segmentRules) apply(name string) string {
if nil == rules {
return name
}
rule, ok := rules[firstTwoSegments(name)]
if !ok {
return name
}
return rule.apply(name)
}
func firstTwoSegments(name string) string {
firstSlashIdx := strings.Index(name, separator)
if firstSlashIdx == -1 {
return name
}
secondSlashIdx := strings.Index(name[firstSlashIdx+1:], separator)
if secondSlashIdx == -1 {
return name
}
return name[0 : firstSlashIdx+secondSlashIdx+1]
}
func collapsePlaceholders(segments []string) []string {
j := 0
prevStar := false
for i := 0; i < len(segments); i++ {
segment := segments[i]
if placeholder == segment {
if prevStar {
continue
}
segments[j] = placeholder
j++
prevStar = true
} else {
segments[j] = segment
j++
prevStar = false
}
}
return segments[0:j]
}
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