What kind of format we need to return for supergraphsdl .I am getting errro throw new Error("Expected ".concat((0, _inspect.default)(schema), " to be a GraphQL schema."));

[Revanth-guduru-balaji]

GATEWAY.js######

const { ApolloServer } = require('apollo-server')
const { ApolloGateway } = require('@apollo/gateway')
const { get,post } = require('httpie')

async function getSupergraph() {
const res = await get(http://localhost:4007/graph)
console.log(res.data);
return {
supergraphSdl: res.data
}
}

async function startServer() {
const gateway = new ApolloGateway({
experimental_pollInterval: 30000,
async experimental_updateSupergraphSdl() {
return getSupergraph()
},
__exposeQueryPlanExperimental: false,
})

const server = new ApolloServer({
gateway,
engine: false,
subscriptions: false,
})

server.listen().then(({ url }) => {
console.log(🚀 Server ready at ${url})
})
}

startServer().catch((err) => {
console.error(err)
process.exit(1)
})
################
########Graph-api.js########

const express = require('express')
const app = express()
const port = 4007
const { readFileSync } = require('fs');
const supergraphSdl = readFileSync('./supergraph.graphql');

app.use(express.json());

app.get('/', (req, res) => {
res.end('Hello World!');
});

app.get("/graph", (req, res) => {
console.log(supergraphSdl.toString());
res.end(supergraphSdl);
});

app.listen(port, () => {
console.log(🚀Super graphAPI listening at http://localhost:${port})
});
##################
#########supergraph.graphql########

schema
@core(feature: "https://specs.apollo.dev/core/v0.2"),
@core(feature: "https://specs.apollo.dev/join/v0.1", for: EXECUTION)
{
query: Query
mutation: Mutation
}

directive @core(as: String, feature: String!, for: core__Purpose) repeatable on SCHEMA

directive @join__field(graph: join__Graph, provides: join__FieldSet, requires: join__FieldSet) on FIELD_DEFINITION

directive @join__graph(name: String!, url: String!) on ENUM_VALUE

directive @join__owner(graph: join__Graph!) on INTERFACE | OBJECT

directive @join__type(graph: join__Graph!, key: join__FieldSet) repeatable on INTERFACE | OBJECT

type AddStudentResponse {
code: Int!
message: String!
student: Student
success: Boolean!
}

type Mutation {
addStudent(gender: String!, name: String!): AddStudentResponse! @join__field(graph: STUDENTS)
}

type Query {
studentDetails: [Student!]! @join__field(graph: STUDENTS)
studentDetailsbyId(id: ID!): Student! @join__field(graph: STUDENTS)
}

type Student
@join__owner(graph: STUDENTS)
@join__type(graph: STUDENTS, key: "id")
{
gender: String @join__field(graph: STUDENTS)
id: ID @join__field(graph: STUDENTS)
name: String @join__field(graph: STUDENTS)
}

enum core__Purpose {
"""
EXECUTION features provide metadata necessary to for operation execution.
"""
EXECUTION

"""
SECURITY features provide metadata necessary to securely resolve fields.
"""
SECURITY
}

scalar join__FieldSet

enum join__Graph {
STUDENTS @join__graph(name: "students" url: "http://localhost:4004/")
}