fix(GraphQL): fix restoreStatus query with query variables (#6414)

Fixes GRAPHQL-642.

For this restoreStatus query using variable
```
query restoreStatus($restoreId: Int!) {
	restoreStatus(restoreId: $restoreId) {
		status
		errors
	}
}
```
was giving this panic
```
panic: interface conversion: interface {} is json.Number, not int64.
```
Whereas the expected result should be
```
{
  "data": {
    "restoreStatus": {
      "status": "UNKNOWN",
      "errors": []
    }
  },
  "extensions": {}
}
```
This PR fixes this panic, Now `resolveStatus` with or without variable works fine.

graphql/admin/restore_status.go

@@ -19,6 +19,7 @@ package admin
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 
 	"github.com/dgraph-io/dgraph/graphql/resolve"
 	"github.com/dgraph-io/dgraph/graphql/schema"
@@ -40,9 +41,25 @@ func unknownStatus(q schema.Query, err error) *resolve.Resolved {
 	}
 }
 
+func getRestoreStatusInput(q schema.Query) (int64, error) {
+	restoreId := q.ArgValue("restoreId")
+	switch v := restoreId.(type) {
+	case int64:
+		return v, nil
+	case json.Number:
+		return v.Int64()
+	default:
+		return -1, fmt.Errorf("Invalid value of restoreId")
+	}
+
+}
+
 func resolveRestoreStatus(ctx context.Context, q schema.Query) *resolve.Resolved {
-	restoreId := int(q.ArgValue("restoreId").(int64))
-	status, err := worker.ProcessRestoreStatus(ctx, restoreId)
+	restoreId, err := getRestoreStatusInput(q)
+	if err != nil {
+		return unknownStatus(q, err)
+	}
+	status, err := worker.ProcessRestoreStatus(ctx, int(restoreId))
 	if err != nil {
 		return unknownStatus(q, err)
 	}

graphql/admin/restore_status_test.go

@@ -0,0 +1,38 @@
+package admin
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"github.com/dgraph-io/dgraph/graphql/schema"
+	"github.com/dgraph-io/dgraph/graphql/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRestoreStatus(t *testing.T) {
+	gqlSchema := test.LoadSchema(t, graphqlAdminSchema)
+	Query := `query restoreStatus($restoreId: Int!) {
+					restoreStatus(restoreId: $restoreId) {
+						status
+						errors
+					}
+				}`
+	variables := `{"restoreId": 2 }`
+	vars := make(map[string]interface{})
+	d := json.NewDecoder(strings.NewReader(variables))
+	d.UseNumber()
+	err := d.Decode(&vars)
+	require.NoError(t, err)
+
+	op, err := gqlSchema.Operation(
+		&schema.Request{
+			Query:     Query,
+			Variables: vars,
+		})
+	require.NoError(t, err)
+	gqlQuery := test.GetQuery(t, op)
+	v, err := getRestoreStatusInput(gqlQuery)
+	require.NoError(t, err)
+	require.IsType(t, int64(2), v, nil)
+}