sharding: refactor proposers

Former-commit-id: 27b5dfe6a36681e873a11887690428e255df1d97 [formerly 6394a809217dc1450fdfb1d6de7f91153afd6eaf]
Former-commit-id: 57f44262b2223ddefa48558d0b4e9cfa6b85d00c

sharding/node/node.go

@@ -112,6 +112,7 @@ func (n *shardingNode) registerShardingServices() error {
 	clientType := n.ctx.GlobalString(utils.ClientType.Name)
 
 	err := n.Register(func(ctx *node.ServiceContext) (node.Service, error) {
+		// TODO(terenc3t): handle case when we just want to start an observer node.
 		if clientType == "notary" {
 			return notary.NewNotary(n.ctx)
 		}

sharding/proposer/proposer.go

@@ -0,0 +1,29 @@
+package proposer
+
+import (
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/sharding/node"
+	"github.com/ethereum/go-ethereum/swarm/api/client"
+	cli "gopkg.in/urfave/cli.v1"
+)
+
+// Proposer holds functionality required to run a collation proposer
+// in a sharded system. Must satisfy the Service interface defined in
+// sharding/service.go.
+type Proposer struct {
+	client client.Client
+}
+
+// NewProposer creates a struct instance. It is initialized and
+// registered as a service upon start of a sharding node.
+// Has access to the public methods of this node.
+func NewProposer(ctx *cli.Context, node node.Node) *Proposer {
+	return &Proposer{}
+}
+
+// Start the main entry point for proposing collations.
+func (p *Proposer) Start() error {
+	log.Info("Starting proposer client")
+	// TODO: Propose collations.
+	return nil
+}

sharding/proposer/proposer_client.go

@@ -1,38 +0,0 @@
-package proposer
-
-import (
-	"github.com/ethereum/go-ethereum/log"
-	"github.com/ethereum/go-ethereum/sharding/client"
-	cli "gopkg.in/urfave/cli.v1"
-)
-
-// Proposer holds functionality required to run a collation proposer
-// in a sharded system.
-type Proposer interface {
-	Start() error
-}
-
-type proposer struct {
-	client client.Client
-}
-
-// NewProposer creates a struct instance.
-func NewProposer(ctx *cli.Context) Proposer {
-	return &proposer{
-		client: client.NewClient(ctx),
-	}
-}
-
-// Start the main entry point for proposing collations.
-func (p *proposer) Start() error {
-	log.Info("Starting proposer client")
-	err := p.client.Start()
-	if err != nil {
-		return err
-	}
-	defer p.client.Close()
-
-	// TODO: Propose collations.
-
-	return nil
-}