// NewDownloader initiates the download request loop with a host, and returns a
// Downloader.
func NewDownloader(host modules.HostDBEntry, contract modules.RenterContract) (*Downloader, error) {
// check that contract has enough value to support a download
if len(contract.LastRevision.NewValidProofOutputs) != 2 {
return nil, errors.New("invalid contract")
}
sectorPrice := host.DownloadBandwidthPrice.Mul64(modules.SectorSize)
if contract.RenterFunds().Cmp(sectorPrice) < 0 {
return nil, errors.New("contract has insufficient funds to support download")
}
// initiate download loop
conn, err := net.DialTimeout("tcp", string(contract.NetAddress), 15*time.Second)
if err != nil {
return nil, err
}
// allot 2 minutes for RPC request + revision exchange
extendDeadline(conn, modules.NegotiateRecentRevisionTime)
defer extendDeadline(conn, time.Hour)
if err := encoding.WriteObject(conn, modules.RPCDownload); err != nil {
conn.Close()
return nil, errors.New("couldn't initiate RPC: " + err.Error())
}
if err := verifyRecentRevision(conn, contract); err != nil {
conn.Close() // TODO: close gracefully if host has entered revision loop
return nil, err
}
// the host is now ready to accept revisions
return &Downloader{
contract: contract,
host: host,
conn: conn,
}, nil
}
