nmon/internal/librenms/detect.go

package librenms

import (
	"fmt"
	"regexp"
	"strings"
)

var numericOIDRE = regexp.MustCompile(`^\.?[0-9]+(\.[0-9]+)+$`)

// match is the profile match: section built from an os_detection file.
type match struct {
	sysObjectID []string
	sysDescr    []string
	notes       []string // conditions that could not be carried over
}

// phpRegex converts a PHP /pattern/flags regular expression to a Go one.
func phpRegex(s string) (string, error) {
	s = strings.TrimSpace(s)
	if len(s) < 2 {
		return "", fmt.Errorf("not delimited")
	}
	d := s[0]
	end := strings.LastIndexByte(s, d)
	if end <= 0 {
		return "", fmt.Errorf("no closing delimiter")
	}
	pat, flags := s[1:end], s[end+1:]
	prefix := ""
	for _, f := range flags {
		switch f {
		case 'i', 's', 'm':
			prefix += string(f)
		case 'u', 'D', 'U':
		default:
			return "", fmt.Errorf("unsupported flag %q", string(f))
		}
	}
	if prefix != "" {
		pat = "(?" + prefix + ")" + pat
	}
	if _, err := regexp.Compile(pat); err != nil {
		return "", err
	}
	return pat, nil
}

// parseDetection maps the discovery: list of an os_detection file.
func parseDetection(doc map[string]any) match {
	var m match
	for gi, g := range asList(doc["discovery"]) {
		e := asMap(g)
		if e == nil {
			m.notes = append(m.notes, fmt.Sprintf("discovery[%d]: not a mapping, skipped", gi))
			continue
		}
		oids, descr := parseDetectionGroup(&m, gi, e)
		if len(oids) > 0 && len(descr) > 0 {
			m.notes = append(m.notes, fmt.Sprintf("discovery[%d] requires sysObjectID AND sysDescr; "+
				"only sysObjectID is used, so this match is broader than LibreNMS's", gi))
			descr = nil
		}
		m.sysObjectID = appendNew(m.sysObjectID, oids...)
		m.sysDescr = appendNew(m.sysDescr, descr...)
	}
	return m
}

// parseDetectionGroup reads one discovery entry, recording what it cannot express in m.notes.
func parseDetectionGroup(m *match, gi int, e map[string]any) (oids, descr []string) {
	for _, k := range sortedKeys(e) {
		switch k {
		case "sysObjectID":
			for _, o := range strs(e[k]) {
				if !numericOIDRE.MatchString(strings.TrimSpace(o)) {
					m.notes = append(m.notes, fmt.Sprintf("discovery[%d].sysObjectID %q is not a numeric OID, skipped", gi, o))
					continue
				}
				oids = append(oids, strings.TrimPrefix(strings.TrimSpace(o), "."))
			}
		case "sysDescr":
			for _, d := range strs(e[k]) {
				descr = append(descr, regexp.QuoteMeta(d))
			}
		case "sysDescr_regex":
			for _, d := range strs(e[k]) {
				re, err := phpRegex(d)
				if err != nil {
					m.notes = append(m.notes, fmt.Sprintf("discovery[%d].sysDescr_regex %q skipped: %v", gi, oneLine(d), err))
					continue
				}
				descr = append(descr, re)
			}
		default:
			m.notes = append(m.notes, fmt.Sprintf("discovery[%d] has an extra condition %q that profile match cannot express "+
				"(LibreNMS requires it in addition)", gi, k))
		}
	}
	return oids, descr
}

func appendNew(dst []string, v ...string) []string {
outer:
	for _, x := range v {
		for _, y := range dst {
			if x == y {
				continue outer
			}
		}
		dst = append(dst, x)
	}
	return dst
}