example schema loading utilities

schemaLoader.ts

import {
  getIntrospectionQuery,
  IntrospectionOptions,
  IntrospectionQuery,
  DocumentNode,
  BuildSchemaOptions,
  buildClientSchema,
  buildASTSchema,
  buildSchema
} from 'graphql';

import type { GraphQLSchemaValidationOptions } from 'graphql/type/schema';

export type SchemaConfig = {
  uri: string;
  introspectionOptions?: IntrospectionOptions;
  validationOptions?: GraphQLSchemaValidationOptions;
  requestOpts?: {
    method: 'post' | 'get',
    headers: { [name: string]: string }
  }
};

type IntrospectionSchemaResponse = {
  responseType: 'introspection',
  response: IntrospectionQuery
}

type ASTSchemaResponse = {
  responseType: 'ast',
  response: DocumentNode
}

type SDLSchemaResponse = {
  responseType: 'sdl',
  response: string
}

export type SchemaResponse = IntrospectionSchemaResponse | ASTSchemaResponse | SDLSchemaResponse

export type SchemaLoader = (config: SchemaConfig) => Promise<SchemaResponse | void>


export const defaultSchemaLoader: SchemaLoader = async (
  schemaConfig: SchemaConfig,
): Promise<SchemaResponse | void> => {
  const rawResult = await fetch(schemaConfig.uri, {
    method: schemaConfig?.requestOpts?.method ?? 'post',
    body: JSON.stringify({
      query: getIntrospectionQuery(schemaConfig.introspectionOptions),
      operationName: 'IntrospectionQuery',
    }),
    headers: {
      'Content-Type': 'application/json',
      credentials: 'omit',
      ...schemaConfig?.requestOpts?.headers
    },
  });

  const introspectionResponse: { data: IntrospectionQuery } = await rawResult.json();

  if (!introspectionResponse || !introspectionResponse.data) {
    throw Error(`error fetching introspection schema for ${schemaConfig.uri}`);
  }
  return { response: introspectionResponse.data, responseType: 'introspection' }
};


export function buildSchemaFromResponse(schema: SchemaResponse, buildSchemaOptions?: BuildSchemaOptions) {
  switch (schema.responseType) {
    case "introspection": {
      return buildClientSchema(schema.response, buildSchemaOptions)
    }
    case "ast": {
      return buildASTSchema(schema.response, buildSchemaOptions);
    }
    case "sdl": {
      return buildSchema(schema.response, buildSchemaOptions);
    }
  }
}