github.com/pokt-network/tendermint@v0.32.11-0.20230426215212-59310158d3e9/docs/architecture/adr-039-peer-behaviour.md (about)

     1  # ADR 039: Peer Behaviour Interface
     2  
     3  ## Changelog
     4  * 07-03-2019: Initial draft
     5  * 14-03-2019: Updates from feedback
     6  
     7  ## Context
     8  
     9  The responsibility for signaling and acting upon peer behaviour lacks a single 
    10  owning component and is heavily coupled with the network stack[<sup>1</sup>](#references). Reactors
    11  maintain a reference to the `p2p.Switch` which they use to call 
    12  `switch.StopPeerForError(...)` when a peer misbehaves and 
    13  `switch.MarkAsGood(...)` when a peer contributes in some meaningful way. 
    14  While the switch handles `StopPeerForError` internally, the `MarkAsGood` 
    15  method delegates to another component, `p2p.AddrBook`. This scheme of delegation 
    16  across Switch obscures the responsibility for handling peer behaviour
    17  and ties up the reactors in a larger dependency graph when testing.
    18  
    19  ## Decision
    20  
    21  Introduce a `PeerBehaviour` interface and concrete implementations which
    22  provide methods for reactors to signal peer behaviour without direct
    23  coupling `p2p.Switch`.  Introduce a ErrorBehaviourPeer to provide
    24  concrete reasons for stopping peers. Introduce GoodBehaviourPeer to provide
    25  concrete ways in which a peer contributes.
    26  
    27  ### Implementation Changes
    28  
    29  PeerBehaviour then becomes an interface for signaling peer errors as well
    30  as for marking peers as `good`.
    31  
    32  ```go
    33  type PeerBehaviour interface {
    34      Behaved(peer Peer, reason GoodBehaviourPeer)
    35      Errored(peer Peer, reason ErrorBehaviourPeer)
    36  }
    37  ```
    38  
    39  Instead of signaling peers to stop with arbitrary reasons:
    40  `reason interface{}` 
    41  
    42  We introduce a concrete error type ErrorBehaviourPeer:
    43  ```go
    44  type ErrorBehaviourPeer int
    45  
    46  const (
    47      ErrorBehaviourUnknown = iota
    48      ErrorBehaviourBadMessage
    49      ErrorBehaviourMessageOutofOrder
    50      ...
    51  )
    52  ```
    53  
    54  To provide additional information on the ways a peer contributed, we introduce
    55  the GoodBehaviourPeer type.
    56  
    57  ```go
    58  type GoodBehaviourPeer int
    59  
    60  const (
    61      GoodBehaviourVote = iota
    62      GoodBehaviourBlockPart
    63      ...
    64  )
    65  ```
    66  
    67  As a first iteration we provide a concrete implementation which wraps
    68  the switch:
    69  ```go
    70  type SwitchedPeerBehaviour struct {
    71      sw *Switch
    72  }
    73  
    74  func (spb *SwitchedPeerBehaviour) Errored(peer Peer, reason ErrorBehaviourPeer) {
    75      spb.sw.StopPeerForError(peer, reason)
    76  }
    77  
    78  func (spb *SwitchedPeerBehaviour) Behaved(peer Peer, reason GoodBehaviourPeer) {
    79      spb.sw.MarkPeerAsGood(peer)
    80  }
    81  
    82  func NewSwitchedPeerBehaviour(sw *Switch) *SwitchedPeerBehaviour {
    83      return &SwitchedPeerBehaviour{
    84          sw: sw,
    85      }
    86  }
    87  ```
    88  
    89  Reactors, which are often difficult to unit test[<sup>2</sup>](#references) could use an implementation which exposes the signals produced by the reactor in
    90  manufactured scenarios:
    91  
    92  ```go
    93  type ErrorBehaviours map[Peer][]ErrorBehaviourPeer
    94  type GoodBehaviours map[Peer][]GoodBehaviourPeer
    95  
    96  type StorePeerBehaviour struct {
    97      eb ErrorBehaviours
    98      gb GoodBehaviours
    99  }
   100  
   101  func NewStorePeerBehaviour() *StorePeerBehaviour{
   102      return &StorePeerBehaviour{
   103          eb: make(ErrorBehaviours),
   104          gb: make(GoodBehaviours),
   105      }
   106  }
   107  
   108  func (spb StorePeerBehaviour) Errored(peer Peer, reason ErrorBehaviourPeer) {
   109      if _, ok := spb.eb[peer]; !ok {
   110          spb.eb[peer] = []ErrorBehaviours{reason}
   111      } else {
   112          spb.eb[peer] = append(spb.eb[peer], reason)
   113      }
   114  }
   115  
   116  func (mpb *StorePeerBehaviour) GetErrored() ErrorBehaviours {
   117      return mpb.eb
   118  }
   119  
   120  
   121  func (spb StorePeerBehaviour) Behaved(peer Peer, reason GoodBehaviourPeer) {
   122      if _, ok := spb.gb[peer]; !ok {
   123          spb.gb[peer] = []GoodBehaviourPeer{reason}
   124      } else {
   125          spb.gb[peer] = append(spb.gb[peer], reason)
   126      }
   127  }
   128  
   129  func (spb *StorePeerBehaviour) GetBehaved() GoodBehaviours {
   130      return spb.gb
   131  }
   132  ```
   133  
   134  ## Status
   135  
   136  Accepted
   137  
   138  ## Consequences
   139  
   140  ### Positive
   141  
   142      * De-couple signaling from acting upon peer behaviour.
   143      * Reduce the coupling of reactors and the Switch and the network
   144        stack
   145      * The responsibility of managing peer behaviour can be migrated to
   146        a single component instead of split between the switch and the
   147        address book.
   148  
   149  ### Negative
   150  
   151      * The first iteration will simply wrap the Switch and introduce a
   152        level of indirection.
   153  
   154  ### Neutral
   155  
   156  ## References
   157  
   158  1. Issue [#2067](https://github.com/tendermint/tendermint/issues/2067): P2P Refactor
   159  2. PR: [#3506](https://github.com/tendermint/tendermint/pull/3506): ADR 036: Blockchain Reactor Refactor