fix: set the canonical url manually for subpath customers that are no…

…t setting x-fern-host (#1610)

packages/ui/docs-bundle/src/middleware.ts

@@ -3,8 +3,8 @@ import { getPageRoute, getPageRouteMatch, getPageRoutePath } from "@/server/page
 import { rewritePosthog } from "@/server/rewritePosthog";
 import { getXFernHostEdge } from "@/server/xfernhost/edge";
 import type { FernUser } from "@fern-ui/fern-docs-auth";
-import { getAuthEdgeConfig } from "@fern-ui/fern-docs-edge-config";
-import { COOKIE_FERN_TOKEN } from "@fern-ui/fern-docs-utils";
+import { getAuthEdgeConfig, getCanonicalHost } from "@fern-ui/fern-docs-edge-config";
+import { COOKIE_FERN_TOKEN, HEADER_X_FERN_HOST } from "@fern-ui/fern-docs-utils";
 import { removeTrailingSlash } from "next/dist/shared/lib/router/utils/remove-trailing-slash";
 import { NextRequest, NextResponse, type NextMiddleware } from "next/server";
 import urlJoin from "url-join";
@@ -15,10 +15,18 @@ const API_FERN_DOCS_PATTERN = /^(?!\/api\/fern-docs\/).*(\/api\/fern-docs\/)/;
 const CHANGELOG_PATTERN = /\.(rss|atom)$/;
 
 export const middleware: NextMiddleware = async (request) => {
-    const xFernHost = getXFernHostEdge(request);
+    let xFernHost = getXFernHostEdge(request);
     const nextUrl = request.nextUrl.clone();
     const headers = new Headers(request.headers);
 
+    // for legacy docs customers that use subpath routing and don't set x-fern-host,
+    // we use edge config to determine the true canonical host
+    const canonicalHost = await getCanonicalHost(xFernHost);
+    if (canonicalHost !== xFernHost) {
+        xFernHost = canonicalHost;
+        headers.set(HEADER_X_FERN_HOST, xFernHost);
+    }
+
     /**
      * Do not rewrite 404 and 500 pages
      */

packages/ui/fern-docs-edge-config/src/getCanonicalHost.ts

@@ -0,0 +1,7 @@
+import { get } from "@vercel/edge-config";
+
+export async function getCanonicalHost(host: string): Promise<string> {
+    const config = await get<Record<string, string>>("canonical-host");
+    const canonicalHost = config?.[host];
+    return canonicalHost ?? host;
+}

packages/ui/fern-docs-edge-config/src/index.ts

@@ -1,4 +1,5 @@
 export * from "./getAuthEdgeConfig";
+export * from "./getCanonicalHost";
 export * from "./getCustomerAnalytics";
 export * from "./getFeatureFlags";
 export * from "./getInkeepSettings";