Function Fetch

core/fetch/fetch.go:49–84

Fetch runs in a loop, fetching blocks from the configured peer (e.g. the generator) and applying them to the local Chain. It returns when its context is canceled. After each attempt to fetch and apply a block, it calls health to report either an error or nil to indicate success.

(ctx context.Context, c *protocol.Chain, peer *rpc.Client, health func(error))

// After each attempt to fetch and apply a block, it calls health
// to report either an error or nil to indicate success.
func Fetch(ctx context.Context, c *protocol.Chain, peer *rpc.Client, health func(error)) {
	blockch, errch := DownloadBlocks(ctx, peer, c.Height()+1)

	var err error
	var nfailures uint
	for {
		select {
		case <-ctx.Done():
			log.Printf(ctx, "Deposed, Fetch exiting")
			return
		case err = <-errch:
			health(err)
			logNetworkError(ctx, err)
		case b := <-blockch:
			prevBlock, prevSnapshot := c.State()
			for {
				err = applyBlock(ctx, c, prevSnapshot, prevBlock, b)
				if err == protocol.ErrBadBlock {
					log.Fatalkv(ctx, log.KeyError, err)
				} else if err != nil {
					// This is a serious I/O error.
					health(err)
					log.Error(ctx, err)
					nfailures++

					time.Sleep(backoffDur(nfailures))
					continue
				}
				break
			}

			health(nil)
			nfailures = 0
		}
	}
}

// DownloadBlocks starts a goroutine to download blocks from
// the given peer, starting at the given height and incrementing from there.