refactor(commands2/cat) readability

core/commands2/cat.go

 package commands
 
 import (
+	"errors"
 	"io"
 
 	cmds "github.com/jbenet/go-ipfs/commands"
+	core "github.com/jbenet/go-ipfs/core"
 	uio "github.com/jbenet/go-ipfs/unixfs/io"
 )
 
@@ -14,26 +16,41 @@ var catCmd = &cmds.Command{
 	Help: "TODO",
 	Run: func(res cmds.Response, req cmds.Request) {
 		node := req.Context().Node
+		paths := make([]string, 0, len(req.Arguments()))
 		readers := make([]io.Reader, 0, len(req.Arguments()))
 
 		for _, arg := range req.Arguments() {
-			path := arg.(string)
-			dagnode, err := node.Resolver.ResolvePath(path)
-			if err != nil {
-				res.SetError(err, cmds.ErrNormal)
+			path, ok := arg.(string)
+			if !ok {
+				res.SetError(errors.New("cast error"), cmds.ErrNormal)
 				return
 			}
+			paths = append(paths, path)
+		}
 
-			read, err := uio.NewDagReader(dagnode, node.DAG)
+		readers, err := cat(node, paths)
 		if err != nil {
 			res.SetError(err, cmds.ErrNormal)
 			return
 		}
 
-			readers = append(readers, read)
-		}
-
 		reader := io.MultiReader(readers...)
 		res.SetOutput(reader)
 	},
 }
+
+func cat(node *core.IpfsNode, paths []string) ([]io.Reader, error) {
+	readers := make([]io.Reader, 0, len(paths))
+	for _, path := range paths {
+		dagnode, err := node.Resolver.ResolvePath(path)
+		if err != nil {
+			return nil, err
+		}
+		read, err := uio.NewDagReader(dagnode, node.DAG)
+		if err != nil {
+			return nil, err
+		}
+		readers = append(readers, read)
+	}
+	return readers, nil
+}