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poll.go
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poll.go
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package client
import (
"context"
"time"
"github.com/drand/drand/chain"
"github.com/drand/drand/log"
)
// PollingWatcher generalizes the `Watch` interface for clients which learn new values
// by asking for them once each group period.
func PollingWatcher(ctx context.Context, c Client, chainInfo *chain.Info, l log.Logger) <-chan Result {
ch := make(chan Result, 1)
r := c.RoundAt(time.Now())
val, err := c.Get(ctx, r)
if err != nil {
l.Error("polling_client", "failed to watch", "err", err)
close(ch)
return ch
}
ch <- val
go func() {
defer close(ch)
// Initially, wait to synchronize to the round boundary.
_, nextTime := chain.NextRound(time.Now().Unix(), chainInfo.Period, chainInfo.GenesisTime)
select {
case <-ctx.Done():
return
case <-time.After(time.Duration(nextTime-time.Now().Unix()) * time.Second):
}
r, err := c.Get(ctx, c.RoundAt(time.Now()))
if err == nil {
ch <- r
} else {
l.Error("polling_client", "failed to watch", "err", err)
}
// Then tick each period.
t := time.NewTicker(chainInfo.Period)
defer t.Stop()
for {
select {
case <-t.C:
r, err := c.Get(ctx, c.RoundAt(time.Now()))
if err == nil {
ch <- r
} else {
l.Error("polling_client", "failed to watch", "err", err)
}
// TODO: keep trying on errors?
case <-ctx.Done():
return
}
}
}()
return ch
}