feat(adapter): add fetch adapter; (#6371)

lib/helpers/trackStream.js

@@ -0,0 +1,56 @@
+
+export const streamChunk = function* (chunk, chunkSize) {
+  let len = chunk.byteLength;
+
+  if (!chunkSize || len < chunkSize) {
+    yield chunk;
+    return;
+  }
+
+  let pos = 0;
+  let end;
+
+  while (pos < len) {
+    end = pos + chunkSize;
+    yield chunk.slice(pos, end);
+    pos = end;
+  }
+}
+
+const encoder = new TextEncoder();
+
+export const readBytes = async function* (iterable, chunkSize) {
+  for await (const chunk of iterable) {
+    yield* streamChunk(ArrayBuffer.isView(chunk) ? chunk : (await encoder.encode(String(chunk))), chunkSize);
+  }
+}
+
+export const trackStream = (stream, chunkSize, onProgress, onFinish) => {
+  const iterator = readBytes(stream, chunkSize);
+
+  let bytes = 0;
+
+  return new ReadableStream({
+    type: 'bytes',
+
+    async pull(controller) {
+      const {done, value} = await iterator.next();
+
+      if (done) {
+        controller.close();
+        onFinish();
+        return;
+      }
+
+      let len = value.byteLength;
+      onProgress && onProgress(bytes += len);
+      controller.enqueue(new Uint8Array(value));
+    },
+    cancel(reason) {
+      onFinish(reason);
+      return iterator.return();
+    }
+  }, {
+    highWaterMark: 2
+  })
+}