setupRedirects.js

const { join } = require("path");
const { existsSync, readFileSync, writeFileSync } = require("fs-extra");
const { logTitle, logItem } = require("../helpers/logger");
const {
  CUSTOM_REDIRECTS_PATH,
  NEXT_IMAGE_FUNCTION_NAME,
} = require("../config");
const getSortedRedirects = require("../helpers/getSortedRedirects");
const getNetlifyRoutes = require("../helpers/getNetlifyRoutes");
const isRootCatchAllRedirect = require("../helpers/isRootCatchAllRedirect");
const isDynamicRoute = require("../helpers/isDynamicRoute");
const removeFileExtension = require("../helpers/removeFileExtension");

// Setup _redirects file that routes all requests to the appropriate location,
// such as one of the Netlify functions or one of the static files.
const setupRedirects = (publishPath) => {
  logTitle("🔀 Setting up redirects");

  // Collect custom redirects defined by the user
  const redirects = [];
  if (existsSync(CUSTOM_REDIRECTS_PATH)) {
    logItem("# Prepending custom redirects");
    redirects.push(readFileSync(CUSTOM_REDIRECTS_PATH, "utf8"));
  }

  // Collect redirects for NextJS pages
  const nextRedirects = [
    ...require("../pages/api/redirects"),
    ...require("../pages/getInitialProps/redirects"),
    ...require("../pages/getServerSideProps/redirects"),
    ...require("../pages/getStaticProps/redirects"),
    ...require("../pages/getStaticPropsWithFallback/redirects"),
    ...require("../pages/getStaticPropsWithRevalidate/redirects"),
    ...require("../pages/withoutProps/redirects"),
  ];

  // Add _redirect section heading
  redirects.push("# Next-on-Netlify Redirects");

  const staticRedirects = nextRedirects.filter(
    ({ route }) => !isDynamicRoute(removeFileExtension(route))
  );
  const dynamicRedirects = nextRedirects.filter(({ route }) =>
    isDynamicRoute(removeFileExtension(route))
  );

  // Add next/image redirect to our image function
  dynamicRedirects.push({
    route: "/_next/image*  url=:url w=:width q=:quality",
    target: `/.netlify/functions/${NEXT_IMAGE_FUNCTION_NAME}?url=:url&w=:width&q=:quality`,
  });

  const sortedStaticRedirects = getSortedRedirects(staticRedirects);
  const sortedDynamicRedirects = getSortedRedirects(dynamicRedirects);

  // Assemble redirects for each route
  [...sortedStaticRedirects, ...sortedDynamicRedirects].forEach(
    (nextRedirect) => {
      // One route may map to multiple Netlify routes: e.g., catch-all pages
      // require two Netlify routes in the _redirects file
      getNetlifyRoutes(nextRedirect.route).map((netlifyRoute) => {
        const {
          conditions = [],
          force = false,
          statusCode = "200",
          target,
        } = nextRedirect;
        const redirectPieces = [
          netlifyRoute,
          target,
          `${statusCode}${force ? "!" : ""}`,
          conditions.join("  "),
        ];
        const redirect = redirectPieces.join("  ").trim();
        logItem(redirect);
        redirects.push(redirect);
      });
    }
  );

  // This takes care of this issue: https://github.com/netlify/next-on-netlify/issues/43
  // where the page chunk for a root level catch-all is served incorrectly to the client.
  // NOTE: Netlify is also investigating this issue internally.
  const hasRootCatchAll = redirects.some(isRootCatchAllRedirect);
  if (hasRootCatchAll) {
    const rootCatchAllIndex = redirects.findIndex(isRootCatchAllRedirect);
    // Add general "no-op" redirect before the root catch-all redirect
    redirects.splice(rootCatchAllIndex, 0, "/_next/*  /_next/:splat  200");
  }

  // Write redirects to _redirects file
  writeFileSync(join(publishPath, "_redirects"), redirects.join("\n"));
};

module.exports = setupRedirects;