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| 1 // Copyright 2015 The Chromium Authors. All rights reserved. | |
| 2 // Use of this source code is governed by a BSD-style license that can be | |
| 3 // found in the LICENSE file. | |
| 4 | |
| 5 package featureBreaker | |
| 6 | |
| 7 import ( | |
| 8 "errors" | |
| 9 "fmt" | |
| 10 "runtime" | |
| 11 "strings" | |
| 12 "sync" | |
| 13 ) | |
| 14 | |
| 15 // FeatureBreaker is the state-access interface for all Filter* functions in | |
| 16 // this package. A feature is the Name of some method on the filtered service. | |
| 17 // So if you had: | |
| 18 // c, fb := FilterMC(...) | |
| 19 // mc := gae.GetMC(c) | |
| 20 // | |
| 21 // you could do: | |
| 22 // fb.BreakFeatures(memcache.ErrServerError, "Add", "Set") | |
| 23 // | |
| 24 // and then | |
| 25 // mc.Add(...) and mc.Set(...) | |
| 26 // | |
| 27 // would return the error. | |
| 28 // | |
| 29 // You may also pass nil as the error for BreakFeatures, and the fake will | |
| 30 // provide the DefaultError which you passed to the Filter function. | |
| 31 // | |
| 32 // This interface can only break features which return errors. | |
| 33 type FeatureBreaker interface { | |
| 34 BreakFeatures(err error, feature ...string) | |
| 35 UnbreakFeatures(feature ...string) | |
| 36 } | |
| 37 | |
| 38 // ErrBrokenFeaturesBroken is returned from RunIfNotBroken when BrokenFeatures | |
| 39 // itself isn't working correctly. | |
| 40 var ErrBrokenFeaturesBroken = errors.New("featureBreaker: Unable to retrieve cal
ler information") | |
| 41 | |
| 42 type state struct { | |
| 43 sync.Mutex | |
| 44 | |
| 45 broken map[string]error | |
| 46 | |
| 47 // defaultError is the default error to return when you call | |
| 48 // BreakFeatures(nil, ...). If this is unset and the user calls BreakFea
tures | |
| 49 // with nil, BrokenFeatures will return a generic error. | |
| 50 defaultError error | |
| 51 } | |
| 52 | |
| 53 func newState(dflt error) *state { | |
| 54 return &state{ | |
| 55 broken: map[string]error{}, | |
| 56 defaultError: dflt, | |
| 57 } | |
| 58 } | |
| 59 | |
| 60 // BreakFeatures allows you to specify an MCSingleReadWriter function name | |
| 61 // to cause it to return memcache.ErrServerError. e.g. | |
| 62 // | |
| 63 // m.SetBrokenFeatures("Add") | |
| 64 // | |
| 65 // would return memcache.ErrServerError. You can reverse this by calling | |
| 66 // UnbreakFeatures("Add"). | |
| 67 func (s *state) BreakFeatures(err error, feature ...string) { | |
| 68 s.Lock() | |
| 69 defer s.Unlock() | |
| 70 for _, f := range feature { | |
| 71 s.broken[f] = err | |
| 72 } | |
| 73 } | |
| 74 | |
| 75 // UnbreakFeatures is the inverse of BreakFeatures, and will return the named | |
| 76 // features back to their original functionality. | |
| 77 func (s *state) UnbreakFeatures(feature ...string) { | |
| 78 s.Lock() | |
| 79 defer s.Unlock() | |
| 80 for _, f := range feature { | |
| 81 delete(s.broken, f) | |
| 82 } | |
| 83 } | |
| 84 | |
| 85 func (s *state) run(f func() error) error { | |
| 86 if s.noBrokenFeatures() { | |
| 87 return f() | |
| 88 } | |
| 89 | |
| 90 pc, _, _, _ := runtime.Caller(1) | |
| 91 fullName := runtime.FuncForPC(pc).Name() | |
| 92 fullNameParts := strings.Split(fullName, ".") | |
| 93 name := fullNameParts[len(fullNameParts)-1] | |
| 94 | |
| 95 s.Lock() | |
| 96 err, ok := s.broken[name] | |
| 97 dflt := s.defaultError | |
| 98 s.Unlock() | |
| 99 | |
| 100 if ok { | |
| 101 if err != nil { | |
| 102 return err | |
| 103 } | |
| 104 if dflt != nil { | |
| 105 return dflt | |
| 106 } | |
| 107 return fmt.Errorf("feature %q is broken", name) | |
| 108 } | |
| 109 | |
| 110 return f() | |
| 111 } | |
| 112 | |
| 113 func (s *state) noBrokenFeatures() bool { | |
| 114 s.Lock() | |
| 115 defer s.Unlock() | |
| 116 return len(s.broken) == 0 | |
| 117 } | |
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