add fetch() shim to proxy cross-origin requests through server

src/shims/globals.js

@@ -115,6 +115,144 @@ function installWindowOpen() {
   };
 }
 
+function arrayBufferToBase64(buf) {
+  const bytes = new Uint8Array(buf);
+  let binary = "";
+  const chunk = 8192;
+
+  for (let i = 0; i < bytes.length; i += chunk) {
+    binary += String.fromCharCode.apply(null, bytes.subarray(i, i + chunk));
+  }
+
+  return btoa(binary);
+}
+
+function base64ToArrayBuffer(base64) {
+  const binary = atob(base64);
+  const bytes = new Uint8Array(binary.length);
+
+  for (let i = 0; i < binary.length; i++) {
+    bytes[i] = binary.charCodeAt(i);
+  }
+
+  return bytes.buffer;
+}
+
+function isSameOrigin(url) {
+  if (
+    !url ||
+    url.startsWith("/") ||
+    url.startsWith("./") ||
+    url.startsWith("../")
+  ) {
+    return true;
+  }
+
+  if (url.startsWith("data:") || url.startsWith("blob:")) {
+    return true;
+  }
+
+  try {
+    const parsed = new URL(url, window.location.origin);
+    return parsed.origin === window.location.origin;
+  } catch {
+    return true;
+  }
+}
+
+function installFetchShim() {
+  const originalFetch = window.fetch.bind(window);
+  window.__originalFetch = originalFetch;
+
+  window.fetch = async function (input, init) {
+    let url;
+
+    if (typeof input === "string") {
+      url = input;
+    } else if (input instanceof URL) {
+      url = input.href;
+    } else if (input instanceof Request) {
+      url = input.url;
+    } else {
+      url = String(input);
+    }
+
+    if (isSameOrigin(url)) {
+      return originalFetch(input, init);
+    }
+
+    // Cross-origin  -  route through server proxy
+    const method = (
+      init?.method || (input instanceof Request ? input.method : "GET")
+    ).toUpperCase();
+    const headers = {};
+
+    if (init?.headers) {
+      const h =
+        init.headers instanceof Headers
+          ? init.headers
+          : new Headers(init.headers);
+      h.forEach((val, key) => {
+        headers[key] = val;
+      });
+    } else if (input instanceof Request) {
+      input.headers.forEach((val, key) => {
+        headers[key] = val;
+      });
+    }
+
+    // Mimic the real Obsidian desktop app headers for cross-origin requests
+    if (!headers["user-agent"] && !headers["User-Agent"]) {
+      headers["user-agent"] = navigator.userAgent;
+    }
+    if (!headers["origin"] && !headers["Origin"]) {
+      headers["origin"] = "app://obsidian.md";
+    }
+
+    let body = null;
+    let binary = false;
+
+    if (init?.body && method !== "GET" && method !== "HEAD") {
+      if (typeof init.body === "string") {
+        body = init.body;
+      } else if (init.body instanceof ArrayBuffer) {
+        body = arrayBufferToBase64(init.body);
+        binary = true;
+      } else if (init.body instanceof Uint8Array) {
+        body = arrayBufferToBase64(init.body.buffer);
+        binary = true;
+      } else if (typeof init.body === "object") {
+        body = JSON.stringify(init.body);
+      } else {
+        body = String(init.body);
+      }
+    }
+
+    console.log("[shim:fetch] Proxying cross-origin:", method, url);
+
+    const proxyRes = await originalFetch("/api/proxy", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ url, method, headers, body, binary }),
+    });
+
+    if (!proxyRes.ok) {
+      const err = await proxyRes
+        .json()
+        .catch(() => ({ error: "Proxy request failed" }));
+      throw new TypeError(err.error || "Failed to fetch");
+    }
+
+    const result = await proxyRes.json();
+    const respBody = base64ToArrayBuffer(result.body);
+
+    return new Response(respBody, {
+      status: result.status,
+      headers: result.headers,
+    });
+  };
+}
+
 function installContextMenuFix() {
   // hacky fix to prevent browser from showing context menu while allowing obsidian context menu
   window.addEventListener(
@@ -130,6 +268,7 @@ function installContextMenuFix() {
 export function installGlobals() {
   installProcess();
   installBuffer();
+  installFetchShim();
   installWindowClose();
   installWindowOpen();
   installContextMenuFix();