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restic/vendor/go.opencensus.io/resource/resource.go
2019-04-24 15:17:48 +02:00

165 lines
4.7 KiB
Go

// Copyright 2018, OpenCensus 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 resource provides functionality for resource, which capture
// identifying information about the entities for which signals are exported.
package resource
import (
"context"
"fmt"
"os"
"regexp"
"sort"
"strconv"
"strings"
)
// Environment variables used by FromEnv to decode a resource.
const (
EnvVarType = "OC_RESOURCE_TYPE"
EnvVarLabels = "OC_RESOURCE_LABELS"
)
// Resource describes an entity about which identifying information and metadata is exposed.
// For example, a type "k8s.io/container" may hold labels describing the pod name and namespace.
type Resource struct {
Type string
Labels map[string]string
}
// EncodeLabels encodes a labels map to a string as provided via the OC_RESOURCE_LABELS environment variable.
func EncodeLabels(labels map[string]string) string {
sortedKeys := make([]string, 0, len(labels))
for k := range labels {
sortedKeys = append(sortedKeys, k)
}
sort.Strings(sortedKeys)
s := ""
for i, k := range sortedKeys {
if i > 0 {
s += ","
}
s += k + "=" + strconv.Quote(labels[k])
}
return s
}
var labelRegex = regexp.MustCompile(`^\s*([[:ascii:]]{1,256}?)=("[[:ascii:]]{0,256}?")\s*,`)
// DecodeLabels decodes a serialized label map as used in the OC_RESOURCE_LABELS variable.
// A list of labels of the form `<key1>="<value1>",<key2>="<value2>",...` is accepted.
// Domain names and paths are accepted as label keys.
// Most users will want to use FromEnv instead.
func DecodeLabels(s string) (map[string]string, error) {
m := map[string]string{}
// Ensure a trailing comma, which allows us to keep the regex simpler
s = strings.TrimRight(strings.TrimSpace(s), ",") + ","
for len(s) > 0 {
match := labelRegex.FindStringSubmatch(s)
if len(match) == 0 {
return nil, fmt.Errorf("invalid label formatting, remainder: %s", s)
}
v := match[2]
if v == "" {
v = match[3]
} else {
var err error
if v, err = strconv.Unquote(v); err != nil {
return nil, fmt.Errorf("invalid label formatting, remainder: %s, err: %s", s, err)
}
}
m[match[1]] = v
s = s[len(match[0]):]
}
return m, nil
}
// FromEnv is a detector that loads resource information from the OC_RESOURCE_TYPE
// and OC_RESOURCE_labelS environment variables.
func FromEnv(context.Context) (*Resource, error) {
res := &Resource{
Type: strings.TrimSpace(os.Getenv(EnvVarType)),
}
labels := strings.TrimSpace(os.Getenv(EnvVarLabels))
if labels == "" {
return res, nil
}
var err error
if res.Labels, err = DecodeLabels(labels); err != nil {
return nil, err
}
return res, nil
}
var _ Detector = FromEnv
// merge resource information from b into a. In case of a collision, a takes precedence.
func merge(a, b *Resource) *Resource {
if a == nil {
return b
}
if b == nil {
return a
}
res := &Resource{
Type: a.Type,
Labels: map[string]string{},
}
if res.Type == "" {
res.Type = b.Type
}
for k, v := range b.Labels {
res.Labels[k] = v
}
// Labels from resource a overwrite labels from resource b.
for k, v := range a.Labels {
res.Labels[k] = v
}
return res
}
// Detector attempts to detect resource information.
// If the detector cannot find resource information, the returned resource is nil but no
// error is returned.
// An error is only returned on unexpected failures.
type Detector func(context.Context) (*Resource, error)
// MultiDetector returns a Detector that calls all input detectors in order and
// merges each result with the previous one. In case a type of label key is already set,
// the first set value is takes precedence.
// It returns on the first error that a sub-detector encounters.
func MultiDetector(detectors ...Detector) Detector {
return func(ctx context.Context) (*Resource, error) {
return detectAll(ctx, detectors...)
}
}
// detectall calls all input detectors sequentially an merges each result with the previous one.
// It returns on the first error that a sub-detector encounters.
func detectAll(ctx context.Context, detectors ...Detector) (*Resource, error) {
var res *Resource
for _, d := range detectors {
r, err := d(ctx)
if err != nil {
return nil, err
}
res = merge(res, r)
}
return res, nil
}