prysm-pulse/beacon-chain/sync/context.go

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package sync
import (
"github.com/libp2p/go-libp2p-core/network"
"github.com/pkg/errors"
"github.com/prysmaticlabs/prysm/beacon-chain/blockchain"
"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
"github.com/prysmaticlabs/prysm/beacon-chain/p2p"
)
// Specifies the fixed size context length.
const forkDigestLength = 4
// writes peer's current context for the expected payload to the stream.
func writeContextToStream(objCtx []byte, stream network.Stream, chain blockchain.ChainInfoFetcher) error {
// The rpc context for our v2 methods is the fork-digest of
// the relevant payload. We write the associated fork-digest(context)
// into the stream for the payload.
rpcCtx, err := rpcContext(stream, chain)
if err != nil {
return err
}
// Exit early if there is an empty context.
if len(rpcCtx) == 0 {
return nil
}
// Always choose the object's context when writing to the stream.
if objCtx != nil {
rpcCtx = objCtx
}
_, err = stream.Write(rpcCtx)
return err
}
// reads any attached context-bytes to the payload.
func readContextFromStream(stream network.Stream, chain blockchain.ChainInfoFetcher) ([]byte, error) {
rpcCtx, err := rpcContext(stream, chain)
if err != nil {
return nil, err
}
if len(rpcCtx) == 0 {
return []byte{}, nil
}
// Read context (fork-digest) from stream
b := make([]byte, forkDigestLength)
if _, err := stream.Read(b); err != nil {
return nil, err
}
return b, nil
}
// retrieve expected context depending on rpc topic schema version.
func rpcContext(stream network.Stream, chain blockchain.ChainInfoFetcher) ([]byte, error) {
_, _, version, err := p2p.TopicDeconstructor(string(stream.Protocol()))
if err != nil {
return nil, err
}
switch version {
case p2p.SchemaVersionV1:
// Return empty context for a v1 method.
return []byte{}, nil
case p2p.SchemaVersionV2:
currFork := chain.CurrentFork()
genRoot := chain.GenesisValidatorRoot()
digest, err := helpers.ComputeForkDigest(currFork.CurrentVersion, genRoot[:])
if err != nil {
return nil, err
}
return digest[:], nil
default:
return nil, errors.New("invalid version of %s registered for topic: %s")
}
}