wrapAppGetInitialPropsWithSentry.ts

import type App from 'next/app';

import { isBuild } from '../utils/isBuild';
import { withErrorInstrumentation, withTracedServerSideDataFetcher } from '../utils/wrapperUtils';

type AppGetInitialProps = (typeof App)['getInitialProps'];

/**
 * Create a wrapped version of the user's exported `getInitialProps` function in
 * a custom app ("_app.js").
 *
 * @param origAppGetInitialProps The user's `getInitialProps` function
 * @param parameterizedRoute The page's parameterized route
 * @returns A wrapped version of the function
 */
export function wrapAppGetInitialPropsWithSentry(origAppGetInitialProps: AppGetInitialProps): AppGetInitialProps {
  return new Proxy(origAppGetInitialProps, {
    apply: async (wrappingTarget, thisArg, args: Parameters<AppGetInitialProps>) => {
      if (isBuild()) {
        return wrappingTarget.apply(thisArg, args);
      }

      const [context] = args;
      const { req, res } = context.ctx;

      const errorWrappedAppGetInitialProps = withErrorInstrumentation(wrappingTarget);

      // Generally we can assume that `req` and `res` are always defined on the server:
      // https://nextjs.org/docs/api-reference/data-fetching/get-initial-props#context-object
      // This does not seem to be the case in dev mode. Because we have no clean way of associating the the data fetcher
      // span with each other when there are no req or res objects, we simply do not trace them at all here.
      if (req && res) {
        const tracedGetInitialProps = withTracedServerSideDataFetcher(errorWrappedAppGetInitialProps, req, res, {
          dataFetcherRouteName: '/_app',
          requestedRouteName: context.ctx.pathname,
          dataFetchingMethodName: 'getInitialProps',
        });

        const {
          data: appGetInitialProps,
          sentryTrace,
          baggage,
        }: {
          data?: unknown;
          sentryTrace?: string;
          baggage?: string;
        } = await tracedGetInitialProps.apply(thisArg, args);

        if (typeof appGetInitialProps === 'object' && appGetInitialProps !== null) {
          // Per definition, `pageProps` is not optional, however an increased amount of users doesn't seem to call
          // `App.getInitialProps(appContext)` in their custom `_app` pages which is required as per
          // https://nextjs.org/docs/advanced-features/custom-app - resulting in missing `pageProps`.
          // For this reason, we just handle the case where `pageProps` doesn't exist explicitly.
          if (!(appGetInitialProps as Record<string, unknown>).pageProps) {
            (appGetInitialProps as Record<string, unknown>).pageProps = {};
          }

          // The Next.js serializer throws on undefined values so we need to guard for it (#12102)
          if (sentryTrace) {
            (appGetInitialProps as { pageProps: Record<string, unknown> }).pageProps._sentryTraceData = sentryTrace;
          }

          // The Next.js serializer throws on undefined values so we need to guard for it (#12102)
          if (baggage) {
            (appGetInitialProps as { pageProps: Record<string, unknown> }).pageProps._sentryBaggage = baggage;
          }
        }

        return appGetInitialProps;
      } else {
        return errorWrappedAppGetInitialProps.apply(thisArg, args);
      }
    },
  });
}