add function to handle redirection of xsl schemas

.netlify/functions/edge-functions/xml-proxy.ts

@@ -0,0 +1,59 @@
+// Netlify helpfully redirects www.* request to the non-www version. This breaks resolving XSLs for our schemas if strict CORS is used.
+// the entries in _redirects don't solve this since it happens at the edge, instead rewrite the request to not use a 301 redirect
+
+export default async (request: Request) => {
+  const url = new URL(request.url);
+  const path = url.pathname;
+
+  let upstream: string | null = null;
+
+  if (path.startsWith("/xml-stylesheet/")) {
+    const rest = path.slice("/xml-stylesheet/".length);
+    upstream =
+      "https://raw.githubusercontent.com/OpenMS/OpenMS/develop/share/OpenMS/XSL/" +
+      rest;
+  } else if (path.startsWith("/xml-schema/")) {
+    const rest = path.slice("/xml-schema/".length);
+    upstream =
+      "https://raw.githubusercontent.com/OpenMS/OpenMS/develop/share/OpenMS/SCHEMAS/" +
+      rest;
+  }
+
+  if (!upstream) {
+    return;
+  }
+
+  const upstreamRes = await fetch(upstream, {
+    headers: { "User-Agent": "openms-netlify-edge" },
+  });
+
+  if (!upstreamRes.ok) {
+    return new Response(`Upstream error: ${upstreamRes.status}`, {
+      status: upstreamRes.status,
+      headers: {
+        "Access-Control-Allow-Origin": "*",
+        "Vary": "Origin",
+      },
+    });
+  }
+
+  const headers = new Headers(upstreamRes.headers);
+
+  headers.set("Access-Control-Allow-Origin", "*");
+  headers.set("Vary", "Origin");
+  headers.set("Access-Control-Allow-Methods", "GET, HEAD, OPTIONS");
+  if (path.startsWith("/xml-stylesheet/")) {
+    headers.set("Content-Type", "text/xsl; charset=utf-8");
+  } else if (path.endsWith(".xsd")) {
+    headers.set("Content-Type", "application/xml; charset=utf-8");
+  }
+
+  return new Response(upstreamRes.body, {
+    status: 200,
+    headers,
+  });
+};
+
+export const config = {
+  path: ["/xml-stylesheet/*", "/xml-schema/*"],
+};