Shows how to generate an OFFLINE_RELAY message in go

Message_OFFLINE_RELAY.go

package webrelay

import (
	"context"
	"fmt"
	"github.com/OpenBazaar/openbazaar-go/core"
	"github.com/OpenBazaar/openbazaar-go/pb"
	"github.com/golang/protobuf/proto"

	"github.com/golang/protobuf/ptypes/any"
	ic "gx/ipfs/QmTW4SdgBWq9GjsBsHeUx8WuGxzhgzAf88UMH2w62PC8yK/go-libp2p-crypto"
	libp2p "gx/ipfs/QmTW4SdgBWq9GjsBsHeUx8WuGxzhgzAf88UMH2w62PC8yK/go-libp2p-crypto"
	peer "gx/ipfs/QmYVXrKrKHDC9FobgmcmshCDyWwdrfwfanNQN4oxJ9Fk3h/go-libp2p-peer"
)

func GenerateCipher(peerId string, k *ic.PubKey, m *pb.Message, n *core.OpenBazaarNode) ([]byte, error) {
	p, err := peer.IDB58Decode(peerId)
	if err != nil {
		return nil, err
	}

	skBytes, err := n.IpfsNode.PrivateKey
	if err != nil {
		return nil, err
	}

	// Use node's private key to sign contract information
	privateKey, err := ic.UnmarshalPrivateKey(skBytes)
	if err != nil {
		return nil, err
	}

	ser, err := proto.Marshal(m)
	if err != nil {
		return nil, err
	}

	sig, err := privateKey.Sign(ser)
	if err != nil {
		return nil, err
	}

	pkBytes, err := n.IpfsNode.PrivateKey.GetPublic().Bytes()
	if err != nil {
		return nil, err
	}

	env := pb.Envelope{Message: m, Pubkey: pkBytes, Signature: sig}
	messageBytes, merr := proto.Marshal(&env)
	if merr != nil {
		return nil, merr
	}

	ciphertext, cerr := n.EncryptMessage(p, k, messageBytes)
	if cerr != nil {
		return nil, cerr
	}

	return ciphertext, nil
}

func SendMessage(n *core.OpenBazaarNode, peerID string, k *libp2p.PubKey, message pb.Message) error {
	p, err := peer.IDB58Decode(peerID)
	if err != nil {
		return err
	}

	cipher, err := GenerateCipher(peerID, k, &message, n)
	if err != nil {
		return err
	}

	cm := pb.Message{
		MessageType: pb.Message_OFFLINE_RELAY,
		Payload:     &any.Any{Value: cipher},
	}
	go func() {
		ctx, cancel := context.WithCancel(context.Background())
		defer cancel()


		err = n.Service.SendMessage(ctx, p, &cm)
		if err != nil {
			if err := n.SendOfflineMessage(p, nil, &m); err != nil {
				return err
			}
		}
	}()

	return nil
}