cli: Support --tipset in chain get /pstate

cli/chain.go

@@ -422,6 +422,10 @@ var chainGetCmd = &cli.Command{
 			Name:  "verbose",
 			Value: false,
 		},
+		&cli.StringFlag{
+			Name:  "tipset",
+			Usage: "specify tipset for /pstate (pass comma separated array of cids)",
+		},
 	},
 	Description: `Get ipld node under a specified path:
 
@@ -462,11 +466,19 @@ var chainGetCmd = &cli.Command{
 		p := path.Clean(cctx.Args().First())
 		if strings.HasPrefix(p, "/pstate") {
 			p = p[len("/pstate"):]
-			head, err := api.ChainHead(ctx)
+
+			ts, err := LoadTipSet(ctx, cctx, api)
 			if err != nil {
 				return err
 			}
-			p = "/ipfs/" + head.ParentState().String() + p
+
+			if ts == nil {
+				ts, err = api.ChainHead(ctx)
+				if err != nil {
+					return err
+				}
+			}
+			p = "/ipfs/" + ts.ParentState().String() + p
 			if cctx.Bool("verbose") {
 				fmt.Println(p)
 			}