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315 lines
8.4 KiB
315 lines
8.4 KiB
package statesync
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import (
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"context"
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"errors"
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"fmt"
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"sync"
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"github.com/tendermint/tendermint/internal/p2p"
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"github.com/tendermint/tendermint/light/provider"
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ssproto "github.com/tendermint/tendermint/proto/tendermint/statesync"
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tmproto "github.com/tendermint/tendermint/proto/tendermint/types"
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"github.com/tendermint/tendermint/types"
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)
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var (
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errNoConnectedPeers = errors.New("no available peers to dispatch request to")
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errUnsolicitedResponse = errors.New("unsolicited light block response")
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errPeerAlreadyBusy = errors.New("peer is already processing a request")
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errDisconnected = errors.New("dispatcher disconnected")
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)
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// A Dispatcher multiplexes concurrent requests by multiple peers for light blocks.
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// Only one request per peer can be sent at a time. Subsequent concurrent requests will
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// report an error from the LightBlock method.
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// NOTE: It is not the responsibility of the dispatcher to verify the light blocks.
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type Dispatcher struct {
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// the channel with which to send light block requests on
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requestCh *p2p.Channel
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mtx sync.Mutex
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// all pending calls that have been dispatched and are awaiting an answer
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calls map[types.NodeID]chan *types.LightBlock
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}
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func NewDispatcher(requestChannel *p2p.Channel) *Dispatcher {
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return &Dispatcher{
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requestCh: requestChannel,
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calls: make(map[types.NodeID]chan *types.LightBlock),
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}
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}
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// LightBlock uses the request channel to fetch a light block from a given peer
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// tracking, the call and waiting for the reactor to pass back the response. A nil
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// LightBlock response is used to signal that the peer doesn't have the requested LightBlock.
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func (d *Dispatcher) LightBlock(ctx context.Context, height int64, peer types.NodeID) (*types.LightBlock, error) {
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// dispatch the request to the peer
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callCh, err := d.dispatch(ctx, peer, height)
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if err != nil {
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return nil, err
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}
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// clean up the call after a response is returned
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defer func() {
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d.mtx.Lock()
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defer d.mtx.Unlock()
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if call, ok := d.calls[peer]; ok {
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delete(d.calls, peer)
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close(call)
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}
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}()
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// wait for a response, cancel or timeout
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select {
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case resp := <-callCh:
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return resp, nil
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case <-ctx.Done():
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return nil, ctx.Err()
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}
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}
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// dispatch takes a peer and allocates it a channel so long as it's not already
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// busy and the receiving channel is still running. It then dispatches the message
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func (d *Dispatcher) dispatch(ctx context.Context, peer types.NodeID, height int64) (chan *types.LightBlock, error) {
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d.mtx.Lock()
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defer d.mtx.Unlock()
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select {
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case <-ctx.Done():
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return nil, errDisconnected
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default:
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}
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ch := make(chan *types.LightBlock, 1)
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// check if a request for the same peer has already been made
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if _, ok := d.calls[peer]; ok {
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close(ch)
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return ch, errPeerAlreadyBusy
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}
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d.calls[peer] = ch
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// send request
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if err := d.requestCh.Send(ctx, p2p.Envelope{
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To: peer,
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Message: &ssproto.LightBlockRequest{
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Height: uint64(height),
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},
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}); err != nil {
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close(ch)
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return ch, err
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}
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return ch, nil
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}
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// Respond allows the underlying process which receives requests on the
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// requestCh to respond with the respective light block. A nil response is used to
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// represent that the receiver of the request does not have a light block at that height.
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func (d *Dispatcher) Respond(ctx context.Context, lb *tmproto.LightBlock, peer types.NodeID) error {
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d.mtx.Lock()
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defer d.mtx.Unlock()
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// check that the response came from a request
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answerCh, ok := d.calls[peer]
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if !ok {
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// this can also happen if the response came in after the timeout
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return errUnsolicitedResponse
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}
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// If lb is nil we take that to mean that the peer didn't have the requested light
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// block and thus pass on the nil to the caller.
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if lb == nil {
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select {
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case answerCh <- nil:
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return nil
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case <-ctx.Done():
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return ctx.Err()
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}
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}
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block, err := types.LightBlockFromProto(lb)
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if err != nil {
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return err
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}
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select {
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case <-ctx.Done():
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return ctx.Err()
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case answerCh <- block:
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return nil
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}
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}
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// Close shuts down the dispatcher and cancels any pending calls awaiting responses.
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// Peers awaiting responses that have not arrived are delivered a nil block.
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func (d *Dispatcher) Close() {
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d.mtx.Lock()
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defer d.mtx.Unlock()
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for peer := range d.calls {
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delete(d.calls, peer)
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// don't close the channel here as it's closed in
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// other handlers, and would otherwise get garbage
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// collected.
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}
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}
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//----------------------------------------------------------------
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// BlockProvider is a p2p based light provider which uses a dispatcher connected
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// to the state sync reactor to serve light blocks to the light client
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//
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// TODO: This should probably be moved over to the light package but as we're
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// not yet officially supporting p2p light clients we'll leave this here for now.
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//
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// NOTE: BlockProvider will return an error with concurrent calls. However, we don't
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// need a mutex because a light client (and the backfill process) will never call a
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// method more than once at the same time
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type BlockProvider struct {
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peer types.NodeID
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chainID string
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dispatcher *Dispatcher
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}
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// Creates a block provider which implements the light client Provider interface.
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func NewBlockProvider(peer types.NodeID, chainID string, dispatcher *Dispatcher) *BlockProvider {
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return &BlockProvider{
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peer: peer,
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chainID: chainID,
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dispatcher: dispatcher,
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}
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}
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// LightBlock fetches a light block from the peer at a specified height returning either a
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// light block or an appropriate error.
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func (p *BlockProvider) LightBlock(ctx context.Context, height int64) (*types.LightBlock, error) {
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lb, err := p.dispatcher.LightBlock(ctx, height, p.peer)
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switch err {
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case nil:
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if lb == nil {
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return nil, provider.ErrLightBlockNotFound
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}
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case context.DeadlineExceeded, context.Canceled:
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return nil, err
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case errPeerAlreadyBusy:
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return nil, provider.ErrLightBlockNotFound
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default:
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return nil, provider.ErrUnreliableProvider{Reason: err.Error()}
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}
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// check that the height requested is the same one returned
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if lb.Height != height {
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return nil, provider.ErrBadLightBlock{
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Reason: fmt.Errorf("expected height %d, got height %d", height, lb.Height),
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}
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}
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// perform basic validation
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if err := lb.ValidateBasic(p.chainID); err != nil {
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return nil, provider.ErrBadLightBlock{Reason: err}
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}
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return lb, nil
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}
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// ReportEvidence should allow for the light client to report any light client
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// attacks. This is a no op as there currently isn't a way to wire this up to
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// the evidence reactor (we should endeavor to do this in the future but for now
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// it's not critical for backwards verification)
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func (p *BlockProvider) ReportEvidence(ctx context.Context, ev types.Evidence) error {
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return nil
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}
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// String implements stringer interface
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func (p *BlockProvider) String() string { return string(p.peer) }
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//----------------------------------------------------------------
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// peerList is a rolling list of peers. This is used to distribute the load of
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// retrieving blocks over all the peers the reactor is connected to
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type peerList struct {
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mtx sync.Mutex
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peers []types.NodeID
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waiting []chan types.NodeID
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}
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func newPeerList() *peerList {
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return &peerList{
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peers: make([]types.NodeID, 0),
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waiting: make([]chan types.NodeID, 0),
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}
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}
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func (l *peerList) Len() int {
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l.mtx.Lock()
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defer l.mtx.Unlock()
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return len(l.peers)
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}
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func (l *peerList) Pop(ctx context.Context) types.NodeID {
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l.mtx.Lock()
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if len(l.peers) == 0 {
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// if we don't have any peers in the list we block until a peer is
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// appended
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wait := make(chan types.NodeID, 1)
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l.waiting = append(l.waiting, wait)
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// unlock whilst waiting so that the list can be appended to
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l.mtx.Unlock()
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select {
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case peer := <-wait:
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return peer
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case <-ctx.Done():
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return ""
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}
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}
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peer := l.peers[0]
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l.peers = l.peers[1:]
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l.mtx.Unlock()
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return peer
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}
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func (l *peerList) Append(peer types.NodeID) {
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l.mtx.Lock()
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defer l.mtx.Unlock()
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if len(l.waiting) > 0 {
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wait := l.waiting[0]
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l.waiting = l.waiting[1:]
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wait <- peer
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close(wait)
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} else {
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l.peers = append(l.peers, peer)
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}
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}
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func (l *peerList) Remove(peer types.NodeID) {
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l.mtx.Lock()
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defer l.mtx.Unlock()
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for i, p := range l.peers {
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if p == peer {
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l.peers = append(l.peers[:i], l.peers[i+1:]...)
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return
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}
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}
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}
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func (l *peerList) All() []types.NodeID {
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l.mtx.Lock()
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defer l.mtx.Unlock()
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return l.peers
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}
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func (l *peerList) Contains(id types.NodeID) bool {
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l.mtx.Lock()
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defer l.mtx.Unlock()
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for _, p := range l.peers {
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if id == p {
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return true
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}
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}
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return false
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}
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