pool: Gen extra nonce before initialize.

This modifies the new client logic to create the extra nonce before to
creating the client and using it during initialization.  Constructors
should generally handle everything that can error prior to creating the
object since it is wasteful to create an object only to immediately
throw it away when there is an error.

pool/client.go

@@ -150,39 +150,30 @@ type Client struct {
 	wg          sync.WaitGroup
 }
 
-// generateExtraNonce1 generates a random 4-byte extraNonce1
-// for the client.
-func (c *Client) generateExtraNonce1() error {
-	id := make([]byte, 4)
-	_, err := rand.Read(id)
-	if err != nil {
-		return err
-	}
-	c.extraNonce1 = hex.EncodeToString(id)
-	return nil
-}
-
 // NewClient creates client connection instance.
 func NewClient(ctx context.Context, conn net.Conn, addr *net.TCPAddr, cCfg *ClientConfig) (*Client, error) {
-	ctx, cancel := context.WithCancel(ctx)
-	c := &Client{
-		addr:     addr,
-		cfg:      cCfg,
-		conn:     conn,
-		ctx:      ctx,
-		cancel:   cancel,
-		ch:       make(chan Message),
-		readCh:   make(chan readPayload),
-		encoder:  json.NewEncoder(conn),
-		reader:   bufio.NewReaderSize(conn, maxMessageSize),
-		hashRate: ZeroRat,
-	}
-	err := c.generateExtraNonce1()
+	// Generate a random 4-byte value to use as extraNonce1 for the client.
+	var extraNonce1 [4]byte
+	_, err := rand.Read(extraNonce1[:])
 	if err != nil {
 		return nil, err
 	}
 
-	return c, nil
+	ctx, cancel := context.WithCancel(ctx)
+	c := Client{
+		addr:        addr,
+		cfg:         cCfg,
+		conn:        conn,
+		ctx:         ctx,
+		cancel:      cancel,
+		ch:          make(chan Message),
+		extraNonce1: hex.EncodeToString(extraNonce1[:]),
+		readCh:      make(chan readPayload),
+		encoder:     json.NewEncoder(conn),
+		reader:      bufio.NewReaderSize(conn, maxMessageSize),
+		hashRate:    ZeroRat,
+	}
+	return &c, nil
 }
 
 // shutdown terminates all client processes and established connections.