// GetBlock attempts to retrieve a particular block from peers within the
// deadline enforced by the context.
func (bs *Bitswap) GetBlock(parent context.Context, k key.Key) (*blocks.Block, error) {
// Any async work initiated by this function must end when this function
// returns. To ensure this, derive a new context. Note that it is okay to
// listen on parent in this scope, but NOT okay to pass |parent| to
// functions called by this one. Otherwise those functions won't return
// when this context's cancel func is executed. This is difficult to
// enforce. May this comment keep you safe.
ctx, cancelFunc := context.WithCancel(parent)
ctx = eventlog.ContextWithLoggable(ctx, eventlog.Uuid("GetBlockRequest"))
log.Event(ctx, "Bitswap.GetBlockRequest.Start", &k)
defer log.Event(ctx, "Bitswap.GetBlockRequest.End", &k)
defer func() {
cancelFunc()
}()
promise, err := bs.GetBlocks(ctx, []key.Key{k})
if err != nil {
return nil, err
}
select {
case block, ok := <-promise:
if !ok {
select {
case <-ctx.Done():
return nil, ctx.Err()
default:
return nil, errors.New("promise channel was closed")
}
}
return block, nil
case <-parent.Done():
return nil, parent.Err()
}
}
func (c *Client) FindProvidersAsync(ctx context.Context, k key.Key, max int) <-chan peer.PeerInfo {
ctx = eventlog.ContextWithLoggable(ctx, eventlog.Uuid("findProviders"))
defer log.EventBegin(ctx, "findProviders", &k).Done()
ch := make(chan peer.PeerInfo)
go func() {
defer close(ch)
request := pb.NewMessage(pb.Message_GET_PROVIDERS, string(k), 0)
response, err := c.proxy.SendRequest(ctx, request)
if err != nil {
log.Debug(err)
return
}
for _, p := range pb.PBPeersToPeerInfos(response.GetProviderPeers()) {
select {
case <-ctx.Done():
log.Debug(ctx.Err())
return
case ch <- p:
}
}
}()
return ch
}