Implement Phase 2 asset storage pipeline

server/src/assets/streaming.js

@@ -0,0 +1,66 @@
+const { Readable } = require("node:stream");
+const { pipeline } = require("node:stream/promises");
+const { AssetError } = require("./errors");
+
+function readableBody(body) {
+  if (body && typeof body.pipe === "function") return body;
+  if (Buffer.isBuffer(body) || body instanceof Uint8Array) {
+    return Readable.from([body]);
+  }
+  if (body && typeof body.getReader === "function") {
+    return Readable.fromWeb(body);
+  }
+  throw new AssetError(
+    "STORAGE_INCONSISTENCY",
+    "Stored asset bytes could not be streamed",
+    { statusCode: 503 },
+  );
+}
+
+function validateDescriptor(descriptor) {
+  if (
+    typeof descriptor.contentType !== "string" ||
+    !Number.isSafeInteger(descriptor.contentLength) ||
+    descriptor.contentLength < 0
+  ) {
+    throw new AssetError(
+      "STORAGE_INCONSISTENCY",
+      "Stored asset metadata is incomplete",
+      { statusCode: 503 },
+    );
+  }
+}
+
+function setCommonHeaders(response, descriptor) {
+  response.set("Content-Type", descriptor.contentType);
+  response.set("Content-Length", String(descriptor.contentLength));
+  response.set("X-Content-Type-Options", "nosniff");
+}
+
+async function storedBody(assetService, descriptor) {
+  const stored = await assetService.readStoredObject(descriptor);
+  return readableBody(stored.body);
+}
+
+async function sendImmutableMedia(assetService, response, descriptor) {
+  validateDescriptor(descriptor);
+  const body = await storedBody(assetService, descriptor);
+  setCommonHeaders(response, descriptor);
+  response.set("Cache-Control", "public, max-age=31536000, immutable");
+  response.set("ETag", `"${descriptor.hash}"`);
+  await pipeline(body, response);
+}
+
+async function sendOriginal(assetService, response, descriptor) {
+  validateDescriptor(descriptor);
+  const body = await storedBody(assetService, descriptor);
+  response.attachment(descriptor.asset.original_filename);
+  setCommonHeaders(response, descriptor);
+  response.set("Cache-Control", "private, no-store");
+  await pipeline(body, response);
+}
+
+module.exports = {
+  sendImmutableMedia,
+  sendOriginal,
+};