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dbus: fix support for CentOS 7 by using introspection
Fix extracted from: elastic/beats#16902
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,182 @@ | ||
| // Licensed to Elasticsearch B.V. under one or more contributor | ||
| // license agreements. See the NOTICE file distributed with | ||
| // this work for additional information regarding copyright | ||
| // ownership. Elasticsearch B.V. licenses this file to you 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. | ||
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| //+build !netbsd | ||
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| package main | ||
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| import ( | ||
| "encoding/xml" | ||
| "fmt" | ||
| "os" | ||
| "path/filepath" | ||
| "strconv" | ||
| "strings" | ||
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| "github.com/coreos/go-systemd/v22/dbus" | ||
| dbusRaw "github.com/godbus/dbus" | ||
| "github.com/pkg/errors" | ||
| ) | ||
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| type unitFetcher func(conn *dbus.Conn, states, patterns []string) ([]dbus.UnitStatus, error) | ||
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| // instrospectForUnitMethods determines what methods are available via dbus for listing systemd units. | ||
| // We have a number of functions, some better than others, for getting and filtering unit lists. | ||
| // This will attempt to find the most optimal method, and move down to methods that require more work. | ||
| func instrospectForUnitMethods() (unitFetcher, error) { | ||
| //setup a dbus connection | ||
| conn, err := dbusRaw.SystemBusPrivate() | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error getting connection to system bus") | ||
| } | ||
|
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| auth := dbusRaw.AuthExternal(strconv.Itoa(os.Getuid())) | ||
| err = conn.Auth([]dbusRaw.Auth{auth}) | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error authenticating") | ||
| } | ||
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| err = conn.Hello() | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error in Hello") | ||
| } | ||
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| var props string | ||
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| //call "introspect" on the systemd1 path to see what ListUnit* methods are available | ||
| obj := conn.Object("org.freedesktop.systemd1", dbusRaw.ObjectPath("/org/freedesktop/systemd1")) | ||
| err = obj.Call("org.freedesktop.DBus.Introspectable.Introspect", 0).Store(&props) | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error calling dbus") | ||
| } | ||
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| unitMap, err := parseXMLAndReturnMethods(props) | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error handling XML") | ||
| } | ||
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| //return a function callback ordered by desirability | ||
| if _, ok := unitMap["ListUnitsByPatterns"]; ok { | ||
| return listUnitsByPatternWrapper, nil | ||
| } else if _, ok := unitMap["ListUnitsFiltered"]; ok { | ||
| return listUnitsFilteredWrapper, nil | ||
| } else if _, ok := unitMap["ListUnits"]; ok { | ||
| return listUnitsWrapper, nil | ||
| } | ||
| return nil, fmt.Errorf("no supported list Units function: %v", unitMap) | ||
| } | ||
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| func parseXMLAndReturnMethods(str string) (map[string]bool, error) { | ||
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| type Method struct { | ||
| Name string `xml:"name,attr"` | ||
| } | ||
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| type Iface struct { | ||
| Name string `xml:"name,attr"` | ||
| Method []Method `xml:"method"` | ||
| } | ||
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| type IntrospectData struct { | ||
| XMLName xml.Name `xml:"node"` | ||
| Interface []Iface `xml:"interface"` | ||
| } | ||
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| methods := IntrospectData{} | ||
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| err := xml.Unmarshal([]byte(str), &methods) | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error unmarshalling XML") | ||
| } | ||
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| if len(methods.Interface) == 0 { | ||
| return nil, errors.Wrap(err, "no methods found on introspect") | ||
| } | ||
| methodMap := make(map[string]bool) | ||
| for _, iface := range methods.Interface { | ||
| for _, method := range iface.Method { | ||
| if strings.Contains(method.Name, "ListUnits") { | ||
| methodMap[method.Name] = true | ||
| } | ||
| } | ||
| } | ||
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| return methodMap, nil | ||
| } | ||
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| // listUnitsByPatternWrapper is a bare wrapper for the unitFetcher type | ||
| func listUnitsByPatternWrapper(conn *dbus.Conn, states, patterns []string) ([]dbus.UnitStatus, error) { | ||
| return conn.ListUnitsByPatterns(states, patterns) | ||
| } | ||
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| //listUnitsFilteredWrapper wraps the dbus ListUnitsFiltered method | ||
| func listUnitsFilteredWrapper(conn *dbus.Conn, states, patterns []string) ([]dbus.UnitStatus, error) { | ||
| units, err := conn.ListUnitsFiltered(states) | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "ListUnitsFiltered error") | ||
| } | ||
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| return matchUnitPatterns(patterns, units) | ||
| } | ||
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| // listUnitsWrapper wraps the dbus ListUnits method | ||
| func listUnitsWrapper(conn *dbus.Conn, states, patterns []string) ([]dbus.UnitStatus, error) { | ||
| units, err := conn.ListUnits() | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "ListUnits error") | ||
| } | ||
| if len(patterns) > 0 { | ||
| units, err = matchUnitPatterns(patterns, units) | ||
| if err != nil { | ||
| return nil, errors.Wrap(err, "error matching unit patterns") | ||
| } | ||
| } | ||
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| if len(states) > 0 { | ||
| var finalUnits []dbus.UnitStatus | ||
| for _, unit := range units { | ||
| for _, state := range states { | ||
| if unit.LoadState == state || unit.ActiveState == state || unit.SubState == state { | ||
| finalUnits = append(finalUnits, unit) | ||
| break | ||
| } | ||
| } | ||
| } | ||
| return finalUnits, nil | ||
| } | ||
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| return units, nil | ||
| } | ||
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| // matchUnitPatterns returns a list of units that match the pattern list. | ||
| // This algo, including filepath.Match, is designed to (somewhat) emulate the behavior of ListUnitsByPatterns, which uses `fnmatch`. | ||
| func matchUnitPatterns(patterns []string, units []dbus.UnitStatus) ([]dbus.UnitStatus, error) { | ||
| var matchUnits []dbus.UnitStatus | ||
| for _, unit := range units { | ||
| for _, pattern := range patterns { | ||
| match, err := filepath.Match(pattern, unit.Name) | ||
| if err != nil { | ||
| return nil, errors.Wrapf(err, "error matching with pattern %s", pattern) | ||
| } | ||
| if match { | ||
| matchUnits = append(matchUnits, unit) | ||
| break | ||
| } | ||
| } | ||
| } | ||
| return matchUnits, nil | ||
| } |
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