Add Cloudflare Pages middleware to handle trailing slash redirects

functions/README.md

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+# Cloudflare Pages Functions
+
+This directory contains Cloudflare Pages Functions that enhance the functionality of the docs site.
+
+## Middleware
+
+### `_middleware.js` - Trailing Slash Redirect Handler
+
+This middleware addresses a known Cloudflare Pages issue where URLs without trailing slashes don't match redirect rules in the `_redirects` file.
+
+**Problem it solves:**
+- `/wandb/config` → 404 (doesn't match redirect rule)
+- `/wandb/config/` → redirects correctly
+
+**How it works:**
+1. Intercepts requests to URLs without trailing slashes
+2. Checks if adding a slash would match a redirect rule
+3. If yes, redirects to the URL with a trailing slash
+4. The browser then follows the actual redirect rule
+
+**Example:**
+- User visits: `/wandb/config`
+- Middleware redirects to: `/wandb/config/`
+- _redirects rule redirects to: `/ref/python/sdk/functions/init/`
+
+This is a temporary solution until the migration off Cloudflare Pages is completed.

functions/_middleware.js

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+/**
+ * Cloudflare Pages middleware to handle trailing slash redirects
+ * 
+ * This middleware addresses the known Cloudflare Pages issue where URLs without
+ * trailing slashes don't match redirect rules that include trailing slashes.
+ */
+
+export async function onRequest(context) {
+  const { request, env, next } = context;
+  const url = new URL(request.url);
+
+  // Only process GET and HEAD requests
+  if (request.method !== 'GET' && request.method !== 'HEAD') {
+    return next();
+  }
+
+  // Skip if the path already has a trailing slash
+  if (url.pathname.endsWith('/')) {
+    return next();
+  }
+
+  // Skip if the path has a file extension
+  const hasFileExtension = /\.[a-zA-Z0-9]+$/.test(url.pathname);
+  if (hasFileExtension) {
+    return next();
+  }
+
+  // Skip certain system paths
+  const skipPaths = ['/robots.txt', '/sitemap.xml', '/_redirects', '/favicon.ico'];
+  if (skipPaths.includes(url.pathname)) {
+    return next();
+  }
+
+  // Skip paths with dots that might not be file extensions
+  // but could be version numbers or other valid path segments
+  // Only skip if the dot is followed by common file extensions
+  const commonExtensions = /\.(html|htm|css|js|json|xml|txt|pdf|jpg|jpeg|png|gif|svg|ico|woff|woff2|ttf|eot)$/i;
+  if (commonExtensions.test(url.pathname)) {
+    return next();
+  }
+
+  // Create URL with trailing slash, preserving query and hash
+  const urlWithSlash = new URL(request.url);
+  urlWithSlash.pathname = url.pathname + '/';
+
+  // Create a new request with the trailing slash
+  const requestWithSlash = new Request(urlWithSlash.toString(), {
+    method: request.method,
+    headers: request.headers,
+    redirect: 'manual' // Important: don't follow redirects
+  });
+
+  try {
+    // Fetch with the trailing slash URL
+    const response = await env.ASSETS.fetch(requestWithSlash);
+
+    // If we get a redirect response (301, 302, etc.), redirect to URL with slash
+    if (response.status >= 301 && response.status <= 308) {
+      // The path with trailing slash matches a redirect rule
+      // Redirect the browser to the URL with slash, which will then trigger the actual redirect
+      // Preserve query parameters and hash
+      const redirectUrl = new URL(request.url);
+      redirectUrl.pathname = url.pathname + '/';
+
+      return new Response(null, {
+        status: 301,
+        headers: {
+          'Location': redirectUrl.pathname + redirectUrl.search + redirectUrl.hash,
+          'Cache-Control': 'public, max-age=3600'
+        }
+      });
+    }
+
+    // If the response is successful (200), it means the trailing slash version exists
+    // In this case, we should also redirect to maintain consistency
+    if (response.status === 200) {
+      const redirectUrl = new URL(request.url);
+      redirectUrl.pathname = url.pathname + '/';
+
+      return new Response(null, {
+        status: 301,
+        headers: {
+          'Location': redirectUrl.pathname + redirectUrl.search + redirectUrl.hash,
+          'Cache-Control': 'public, max-age=3600'
+        }
+      });
+    }
+  } catch (error) {
+    // Log error but continue with original request
+    console.error('Trailing slash middleware error:', error);
+  }
+
+  // No redirect found, continue with the original request
+  return next();
+}