[feature] Initial Prometheus metrics implementation (#2334)

* feat: Initial OTEL metrics

* docs: add metrics documentation

* fix: metrics endpoint conditional check

* feat: metrics endpoint basic auth

* fix: make metrics-auth-enabled default false

* fix: go fmt helpers.gen.go

* fix: add metric-related env vars to envparsing.sh

* fix: metrics docs

* fix: metrics related stuff in envparsing.sh

* fix: metrics docs

* chore: metrics docs wording

* fix: metrics stuff in envparsing?

* bump otel versions

---------

Co-authored-by: Tsuribori <user@acertaindebian>
Co-authored-by: Tsuribori <none@example.org>
Co-authored-by: tsmethurst <tobi.smethurst@protonmail.com>

vendor/github.com/prometheus/procfs/mountinfo.go

@@ -0,0 +1,180 @@
+// Copyright 2019 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 procfs
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/prometheus/procfs/internal/util"
+)
+
+// A MountInfo is a type that describes the details, options
+// for each mount, parsed from /proc/self/mountinfo.
+// The fields described in each entry of /proc/self/mountinfo
+// is described in the following man page.
+// http://man7.org/linux/man-pages/man5/proc.5.html
+type MountInfo struct {
+	// Unique ID for the mount
+	MountID int
+	// The ID of the parent mount
+	ParentID int
+	// The value of `st_dev` for the files on this FS
+	MajorMinorVer string
+	// The pathname of the directory in the FS that forms
+	// the root for this mount
+	Root string
+	// The pathname of the mount point relative to the root
+	MountPoint string
+	// Mount options
+	Options map[string]string
+	// Zero or more optional fields
+	OptionalFields map[string]string
+	// The Filesystem type
+	FSType string
+	// FS specific information or "none"
+	Source string
+	// Superblock options
+	SuperOptions map[string]string
+}
+
+// Reads each line of the mountinfo file, and returns a list of formatted MountInfo structs.
+func parseMountInfo(info []byte) ([]*MountInfo, error) {
+	mounts := []*MountInfo{}
+	scanner := bufio.NewScanner(bytes.NewReader(info))
+	for scanner.Scan() {
+		mountString := scanner.Text()
+		parsedMounts, err := parseMountInfoString(mountString)
+		if err != nil {
+			return nil, err
+		}
+		mounts = append(mounts, parsedMounts)
+	}
+
+	err := scanner.Err()
+	return mounts, err
+}
+
+// Parses a mountinfo file line, and converts it to a MountInfo struct.
+// An important check here is to see if the hyphen separator, as if it does not exist,
+// it means that the line is malformed.
+func parseMountInfoString(mountString string) (*MountInfo, error) {
+	var err error
+
+	mountInfo := strings.Split(mountString, " ")
+	mountInfoLength := len(mountInfo)
+	if mountInfoLength < 10 {
+		return nil, fmt.Errorf("%w: Too few fields in mount string: %s", ErrFileParse, mountString)
+	}
+
+	if mountInfo[mountInfoLength-4] != "-" {
+		return nil, fmt.Errorf("%w: couldn't find separator in expected field: %s", ErrFileParse, mountInfo[mountInfoLength-4])
+	}
+
+	mount := &MountInfo{
+		MajorMinorVer:  mountInfo[2],
+		Root:           mountInfo[3],
+		MountPoint:     mountInfo[4],
+		Options:        mountOptionsParser(mountInfo[5]),
+		OptionalFields: nil,
+		FSType:         mountInfo[mountInfoLength-3],
+		Source:         mountInfo[mountInfoLength-2],
+		SuperOptions:   mountOptionsParser(mountInfo[mountInfoLength-1]),
+	}
+
+	mount.MountID, err = strconv.Atoi(mountInfo[0])
+	if err != nil {
+		return nil, fmt.Errorf("%w: mount ID: %q", ErrFileParse, mount.MountID)
+	}
+	mount.ParentID, err = strconv.Atoi(mountInfo[1])
+	if err != nil {
+		return nil, fmt.Errorf("%w: parent ID: %q", ErrFileParse, mount.ParentID)
+	}
+	// Has optional fields, which is a space separated list of values.
+	// Example: shared:2 master:7
+	if mountInfo[6] != "" {
+		mount.OptionalFields, err = mountOptionsParseOptionalFields(mountInfo[6 : mountInfoLength-4])
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", ErrFileParse, err)
+		}
+	}
+	return mount, nil
+}
+
+// mountOptionsIsValidField checks a string against a valid list of optional fields keys.
+func mountOptionsIsValidField(s string) bool {
+	switch s {
+	case
+		"shared",
+		"master",
+		"propagate_from",
+		"unbindable":
+		return true
+	}
+	return false
+}
+
+// mountOptionsParseOptionalFields parses a list of optional fields strings into a double map of strings.
+func mountOptionsParseOptionalFields(o []string) (map[string]string, error) {
+	optionalFields := make(map[string]string)
+	for _, field := range o {
+		optionSplit := strings.SplitN(field, ":", 2)
+		value := ""
+		if len(optionSplit) == 2 {
+			value = optionSplit[1]
+		}
+		if mountOptionsIsValidField(optionSplit[0]) {
+			optionalFields[optionSplit[0]] = value
+		}
+	}
+	return optionalFields, nil
+}
+
+// mountOptionsParser parses the mount options, superblock options.
+func mountOptionsParser(mountOptions string) map[string]string {
+	opts := make(map[string]string)
+	options := strings.Split(mountOptions, ",")
+	for _, opt := range options {
+		splitOption := strings.Split(opt, "=")
+		if len(splitOption) < 2 {
+			key := splitOption[0]
+			opts[key] = ""
+		} else {
+			key, value := splitOption[0], splitOption[1]
+			opts[key] = value
+		}
+	}
+	return opts
+}
+
+// GetMounts retrieves mountinfo information from `/proc/self/mountinfo`.
+func GetMounts() ([]*MountInfo, error) {
+	data, err := util.ReadFileNoStat("/proc/self/mountinfo")
+	if err != nil {
+		return nil, err
+	}
+	return parseMountInfo(data)
+}
+
+// GetProcMounts retrieves mountinfo information from a processes' `/proc/<pid>/mountinfo`.
+func GetProcMounts(pid int) ([]*MountInfo, error) {
+	data, err := util.ReadFileNoStat(fmt.Sprintf("/proc/%d/mountinfo", pid))
+	if err != nil {
+		return nil, err
+	}
+	return parseMountInfo(data)
+}