BundlerDownload OOM on Android during local development

[AndreiCalazans]

Description

Created a PR with a reproducible here.

We are facing this OOM on Android emluators due to our large bundles. While we can reduce the size of the bundles this seems to keep cropping back up as it grows again or when the emulator gets bottlenecked by other memory usages. We were able to fix the problem by patching the BundleDownloader with a bit of help from LLM and we want to start this dicussion if this is something that could land on React Native Core or if there is another solution to this problem other than reducing bundle size.

07-16 07:33:48.691  9900 10089 E AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher

07-16 07:33:48.691  9900 10089 E AndroidRuntime: Process: com.<REDACTED>.android.development, PID: 9900

07-16 07:33:48.691  9900 10089 E AndroidRuntime: java.lang.OutOfMemoryError: Failed to allocate a 8208 byte allocation with 1982936 free bytes and 1936KB until OOM, target footprint 201326592, growth limit 201326592; giving up on allocation because <1% of heap free after GC.

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.Segment.<init>(Segment.kt:62)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.SegmentPool.take(SegmentPool.kt:90)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.Buffer.writableSegment$okio(Buffer.kt:1485)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.InputStreamSource.read(JvmOkio.kt:91)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.AsyncTimeout$source$1.read(AsyncTimeout.kt:128)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.RealBufferedSource.read(RealBufferedSource.kt:192)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okhttp3.internal.http1.Http1ExchangeCodec$AbstractSource.read(Http1ExchangeCodec.kt:339)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okhttp3.internal.http1.Http1ExchangeCodec$ChunkedSource.read(Http1ExchangeCodec.kt:420)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okhttp3.internal.connection.Exchange$ResponseBodySource.read(Exchange.kt:281)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.RealBufferedSource.read(RealBufferedSource.kt:192)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at com.facebook.react.devsupport.MultipartStreamReader.readAllParts(MultipartStreamReader.java:136)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at com.facebook.react.devsupport.BundleDownloader.processMultipartResponse(BundleDownloader.java:178)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at com.facebook.react.devsupport.BundleDownloader.-$$Nest$mprocessMultipartResponse(Unknown Source:0)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at

Patch that fixes on 0.77.2:

We were able to fix it by patching the BundleDownloader and MultipartStreamReader on version 0.77.2 which was still the Java version. I didn't want to put any effort towards migrating this to Kotlin unless RN Core team says this is ok to land in RN Core.

M packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/BundleDownloader.java
@@ -177,42 +177,25 @@ public class BundleDownloader {
         bodyReader.readAllParts(
             new MultipartStreamReader.ChunkListener() {
               @Override
-              public void onChunkComplete(
-                  Map<String, String> headers, Buffer body, boolean isLastChunk)
+              public void onChunkComplete(Map<String, String> headers, BufferedSource body, boolean isLastChunk)
                   throws IOException {
-                // This will get executed for every chunk of the multipart response. The last chunk
-                // (isLastChunk = true) will be the JS bundle, the other ones will be progress
-                // events
-                // encoded as JSON.
-                if (isLastChunk) {
-                  // The http status code for each separate chunk is in the X-Http-Status header.
+                if (isLastChunk || "application/javascript".equals(headers.get("Content-Type"))) {
                   int status = response.code();
                   if (headers.containsKey("X-Http-Status")) {
                     status = Integer.parseInt(headers.get("X-Http-Status"));
                   }
                   processBundleResult(
                       url, status, Headers.of(headers), body, outputFile, bundleInfo, callback);
-                } else {
-                  if (!headers.containsKey("Content-Type")
-                      || !headers.get("Content-Type").equals("application/json")) {
-                    return;
-                  }
-
+                } else if ("application/json".equals(headers.get("Content-Type"))) {
                   try {
-                    JSONObject progress = new JSONObject(body.readUtf8());
-                    String status =
-                        progress.has("status") ? progress.getString("status") : "Bundling";
-                    Integer done = null;
-                    if (progress.has("done")) {
-                      done = progress.getInt("done");
-                    }
-                    Integer total = null;
-                    if (progress.has("total")) {
-                      total = progress.getInt("total");
-                    }
+                    String progressText = body.readUtf8(); // safe because progress is small
+                    JSONObject progress = new JSONObject(progressText);
+                    String status = progress.optString("status", "Bundling");
+                    Integer done = progress.has("done") ? progress.getInt("done") : null;
+                    Integer total = progress.has("total") ? progress.getInt("total") : null;
                     callback.onProgress(status, done, total);
                   } catch (JSONException e) {
-                    FLog.e(ReactConstants.TAG, "Error parsing progress JSON. " + e.toString());
+                    FLog.e(ReactConstants.TAG, "Error parsing progress JSON: " + e);
                   }
                 }
               }
@@ -237,51 +220,41 @@ public class BundleDownloader {
   }
 
   private void processBundleResult(
-      String url,
-      int statusCode,
-      Headers headers,
-      BufferedSource body,
-      File outputFile,
-      BundleInfo bundleInfo,
-      DevBundleDownloadListener callback)
-      throws IOException {
-    // Check for server errors. If the server error has the expected form, fail with more info.
-    if (statusCode != 200) {
-      String bodyString = body.readUtf8();
-      DebugServerException debugServerException = DebugServerException.parse(url, bodyString);
-      if (debugServerException != null) {
-        callback.onFailure(debugServerException);
-      } else {
-        StringBuilder sb = new StringBuilder();
-        sb.append("The development server returned response error code: ")
-            .append(statusCode)
-            .append("\n\n")
-            .append("URL: ")
-            .append(url)
-            .append("\n\n")
-            .append("Body:\n")
-            .append(bodyString);
-        callback.onFailure(new DebugServerException(sb.toString()));
-      }
-      return;
-    }
-
-    if (bundleInfo != null) {
-      populateBundleInfo(url, headers, bundleInfo);
+    String url,
+    int statusCode,
+    Headers headers,
+    BufferedSource body,
+    File outputFile,
+    BundleInfo bundleInfo,
+    DevBundleDownloadListener callback
+) throws IOException {
+  if (statusCode != 200) {
+    String errorText = body.readUtf8(); // read small error body into memory
+    DebugServerException exception = DebugServerException.parse(url, errorText);
+    if (exception != null) {
+      callback.onFailure(exception);
+    } else {
+      callback.onFailure(new DebugServerException("Server error: " + errorText));
     }
+    return;
+  }
 
-    File tmpFile = new File(outputFile.getPath() + ".tmp");
+  if (bundleInfo != null) {
+    populateBundleInfo(url, headers, bundleInfo);
+  }
 
-    if (storePlainJSInFile(body, tmpFile)) {
-      // If we have received a new bundle from the server, move it to its final destination.
-      if (!tmpFile.renameTo(outputFile)) {
-        throw new IOException("Couldn't rename " + tmpFile + " to " + outputFile);
-      }
-    }
+  File tmpFile = new File(outputFile.getPath() + ".tmp");
+  try (Sink output = Okio.sink(tmpFile)) {
+    body.readAll(output); // stream to disk
+  }
 
-    callback.onSuccess();
+  if (!tmpFile.renameTo(outputFile)) {
+    throw new IOException("Failed to move temp file to final location");
   }
 
+  callback.onSuccess();
+}
+
   private static boolean storePlainJSInFile(BufferedSource body, File outputFile)
       throws IOException {
     Sink output = null;
M packages/react-native/ReactAndroid/src/main/java/com/facebook/react/devsupport/MultipartStreamReader.java
@@ -7,6 +7,7 @@
 
 package com.facebook.react.devsupport;
 
+import java.io.EOFException;
 import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
@@ -16,151 +17,93 @@ import okio.ByteString;
 
 /** Utility class to parse the body of a response of type multipart/mixed. */
 public class MultipartStreamReader {
-  // Standard line separator for HTTP.
-  private static final String CRLF = "\r\n";
 
-  private final BufferedSource mSource;
-  private final String mBoundary;
-  private long mLastProgressEvent;
+  private static final String CRLF = "\r\n";
+  private final BufferedSource source;
+  private final String boundary;
 
   public interface ChunkListener {
-    /** Invoked when a chunk of a multipart response is fully downloaded. */
-    void onChunkComplete(Map<String, String> headers, Buffer body, boolean isLastChunk)
-        throws IOException;
-
-    /** Invoked as bytes of the current chunk are read. */
+    void onChunkComplete(Map<String, String> headers, BufferedSource body, boolean isLastChunk) throws IOException;
     void onChunkProgress(Map<String, String> headers, long loaded, long total) throws IOException;
   }
 
   public MultipartStreamReader(BufferedSource source, String boundary) {
-    mSource = source;
-    mBoundary = boundary;
+    this.source = source;
+    this.boundary = boundary;
   }
 
-  private Map<String, String> parseHeaders(Buffer data) {
-    Map<String, String> headers = new HashMap<>();
-
-    String text = data.readUtf8();
-    String[] lines = text.split(CRLF);
-    for (String line : lines) {
-      int indexOfSeparator = line.indexOf(":");
-      if (indexOfSeparator == -1) {
-        continue;
+  public boolean readAllParts(final ChunkListener listener) throws IOException {
+    final String boundaryMarker = "--" + boundary;
+    final String closingMarker = boundaryMarker + "--";
+
+    int partCount = 0;
+    Map<String, String> headers = null;
+    Buffer chunkBuffer = null;
+
+    while (!source.exhausted()) {
+      String line;
+      try {
+        line = source.readUtf8LineStrict();
+      } catch (EOFException eof) {
+        // emit last part if boundary was missing
+        if (headers != null && chunkBuffer != null) {
+          listener.onChunkComplete(headers, chunkBuffer, true);
+        }
+        return true;
       }
 
-      String key = line.substring(0, indexOfSeparator).trim();
-      String value = line.substring(indexOfSeparator + 1).trim();
-      headers.put(key, value);
-    }
+      if (line == null || !line.startsWith("--")) continue;
+      if (!line.equals(boundaryMarker) && !line.equals(closingMarker)) continue;
 
-    return headers;
-  }
-
-  private void emitChunk(Buffer chunk, boolean done, ChunkListener listener) throws IOException {
-    ByteString marker = ByteString.encodeUtf8(CRLF + CRLF);
-    long indexOfMarker = chunk.indexOf(marker);
-    if (indexOfMarker == -1) {
-      listener.onChunkComplete(null, chunk, done);
-    } else {
-      Buffer headers = new Buffer();
-      Buffer body = new Buffer();
-      chunk.read(headers, indexOfMarker);
-      chunk.skip(marker.size());
-      chunk.readAll(body);
-      listener.onChunkComplete(parseHeaders(headers), body, done);
-    }
-  }
-
-  private void emitProgress(
-      Map<String, String> headers, long contentLength, boolean isFinal, ChunkListener listener)
-      throws IOException {
-    if (headers == null || listener == null) {
-      return;
-    }
-
-    long currentTime = System.currentTimeMillis();
-    if (currentTime - mLastProgressEvent > 16 || isFinal) {
-      mLastProgressEvent = currentTime;
-      long headersContentLength =
-          headers.get("Content-Length") != null ? Long.parseLong(headers.get("Content-Length")) : 0;
-      listener.onChunkProgress(headers, contentLength, headersContentLength);
-    }
-  }
+      // ✅ Emit previous part before starting a new one
+      if (headers != null && chunkBuffer != null) {
+        boolean isLast = line.equals(closingMarker);
+        listener.onChunkComplete(headers, chunkBuffer, isLast);
+        headers = null;
+        chunkBuffer = null;
+        partCount++;
+      }
 
-  /**
-   * Reads all parts of the multipart response and execute the listener for each chunk received.
-   *
-   * @param listener Listener invoked when chunks are received.
-   * @return If the read was successful
-   */
-  public boolean readAllParts(ChunkListener listener) throws IOException {
-    ByteString delimiter = ByteString.encodeUtf8(CRLF + "--" + mBoundary + CRLF);
-    ByteString closeDelimiter = ByteString.encodeUtf8(CRLF + "--" + mBoundary + "--" + CRLF);
-    ByteString headersDelimiter = ByteString.encodeUtf8(CRLF + CRLF);
-
-    int bufferLen = 4 * 1024;
-    long chunkStart = 0;
-    long bytesSeen = 0;
-    Buffer content = new Buffer();
-    Map<String, String> currentHeaders = null;
-    long currentHeadersLength = 0;
-
-    while (true) {
-      boolean isCloseDelimiter = false;
-
-      // Search only a subset of chunk that we haven't seen before + few bytes
-      // to allow for the edge case when the delimiter is cut by read call.
-      long searchStart = Math.max(bytesSeen - closeDelimiter.size(), chunkStart);
-      long indexOfDelimiter = content.indexOf(delimiter, searchStart);
-      if (indexOfDelimiter == -1) {
-        isCloseDelimiter = true;
-        indexOfDelimiter = content.indexOf(closeDelimiter, searchStart);
+      if (line.equals(closingMarker)) {
+        return true;
       }
 
-      if (indexOfDelimiter == -1) {
-        bytesSeen = content.size();
-
-        if (currentHeaders == null) {
-          long indexOfHeaders = content.indexOf(headersDelimiter, searchStart);
-          if (indexOfHeaders >= 0) {
-            mSource.read(content, indexOfHeaders);
-            Buffer headers = new Buffer();
-            content.copyTo(headers, searchStart, indexOfHeaders - searchStart);
-            currentHeadersLength = headers.size() + headersDelimiter.size();
-            currentHeaders = parseHeaders(headers);
-          }
-        } else {
-          emitProgress(currentHeaders, content.size() - currentHeadersLength, false, listener);
+      headers = new HashMap<>();
+      while (true) {
+        String headerLine = source.readUtf8LineStrict();
+        if (headerLine.isEmpty()) break;
+        int index = headerLine.indexOf(':');
+        if (index != -1) {
+          headers.put(headerLine.substring(0, index).trim(), headerLine.substring(index + 1).trim());
         }
+      }
 
-        long bytesRead = mSource.read(content, bufferLen);
-        if (bytesRead <= 0) {
-          return false;
+      chunkBuffer = new Buffer();
+      while (!source.exhausted()) {
+        source.request(1);
+        String maybeBoundary;
+        try {
+          maybeBoundary = source.readUtf8LineStrict();
+        } catch (EOFException eof) {
+          listener.onChunkComplete(headers, chunkBuffer, true);
+          return true;
         }
-        continue;
-      }
 
-      long chunkEnd = indexOfDelimiter;
-      long length = chunkEnd - chunkStart;
-
-      // Ignore preamble
-      if (chunkStart > 0) {
-        Buffer chunk = new Buffer();
-        content.skip(chunkStart);
-        content.read(chunk, length);
-        emitProgress(currentHeaders, chunk.size() - currentHeadersLength, true, listener);
-        emitChunk(chunk, isCloseDelimiter, listener);
-        currentHeaders = null;
-        currentHeadersLength = 0;
-      } else {
-        content.skip(chunkEnd);
-      }
+        if (maybeBoundary.equals(boundaryMarker) || maybeBoundary.equals(closingMarker)) {
+          // boundary found: backtrack to outer loop to emit and re-parse
+          source.buffer().writeUtf8(maybeBoundary).writeUtf8("\n");
+          break;
+        }
 
-      if (isCloseDelimiter) {
-        return true;
+        chunkBuffer.writeUtf8(maybeBoundary).writeUtf8("\n");
       }
+    }
 
-      bytesSeen = chunkStart = delimiter.size();
+    // last fallback
+    if (headers != null && chunkBuffer != null) {
+      listener.onChunkComplete(headers, chunkBuffer, true);
     }
+
+    return true;
   }
 }

Steps to reproduce

1. Open RNTester in development on Android
2. Let Metro load
3. Observe the app crashes.

React Native Version

0.80.2 and previous

Affected Platforms

Runtime - Android

Output of npx @react-native-community/cli info

info Fetching system and libraries information...
System:
  OS: macOS 15.5
  CPU: (12) arm64 Apple M2 Pro
  Memory: 326.69 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.17.1
    path: ~/versions/node/v22.17.1/bin/node
  Yarn:
    version: 1.22.22
    path: ~/versions/node/v22.17.1/bin/yarn
  npm:
    version: 10.9.2
    path: ~/versions/node/v22.17.1/bin/npm
  Watchman:
    version: 2025.06.30.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.15.2
    path: /Users/andreicalazans/.local/share/mise/installs/ruby/3.2.1/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.5
      - iOS 18.5
      - macOS 15.5
      - tvOS 18.5
      - visionOS 2.5
      - watchOS 11.5
  Android SDK:
    API Levels:
      - "30"
      - "31"
      - "33"
      - "34"
      - "35"
      - "36"
    Build Tools:
      - 30.0.3
      - 33.0.0
      - 33.0.1
      - 34.0.0
      - 35.0.0
      - 36.0.0
    System Images:
      - android-30 | Google Play ARM 64 v8a
      - android-32 | Google Play ARM 64 v8a
      - android-34 | Google APIs ARM 64 v8a
      - android-34 | Google Play ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2022.3 AI-223.8836.35.2231.11005911
  Xcode:
    version: 16.4/16F6
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.2
    path: /Users/andreicalazans/.local/share/mise/installs/java/17.0.2/bin/javac
  Ruby:
    version: 3.2.1
    path: /Users/andreicalazans/.local/share/mise/installs/ruby/3.2.1/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 19.1.0
    wanted: 19.1.0
  react-native: Not Found
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

07-16 07:33:48.691  9900 10089 E AndroidRuntime: FATAL EXCEPTION: OkHttp Dispatcher

07-16 07:33:48.691  9900 10089 E AndroidRuntime: Process: com.<REDACTED>.android.development, PID: 9900

07-16 07:33:48.691  9900 10089 E AndroidRuntime: java.lang.OutOfMemoryError: Failed to allocate a 8208 byte allocation with 1982936 free bytes and 1936KB until OOM, target footprint 201326592, growth limit 201326592; giving up on allocation because <1% of heap free after GC.

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.Segment.<init>(Segment.kt:62)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.SegmentPool.take(SegmentPool.kt:90)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.Buffer.writableSegment$okio(Buffer.kt:1485)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.InputStreamSource.read(JvmOkio.kt:91)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.AsyncTimeout$source$1.read(AsyncTimeout.kt:128)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.RealBufferedSource.read(RealBufferedSource.kt:192)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okhttp3.internal.http1.Http1ExchangeCodec$AbstractSource.read(Http1ExchangeCodec.kt:339)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okhttp3.internal.http1.Http1ExchangeCodec$ChunkedSource.read(Http1ExchangeCodec.kt:420)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okhttp3.internal.connection.Exchange$ResponseBodySource.read(Exchange.kt:281)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at okio.RealBufferedSource.read(RealBufferedSource.kt:192)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at com.facebook.react.devsupport.MultipartStreamReader.readAllParts(MultipartStreamReader.java:136)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at com.facebook.react.devsupport.BundleDownloader.processMultipartResponse(BundleDownloader.java:178)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at com.facebook.react.devsupport.BundleDownloader.-$$Nest$mprocessMultipartResponse(Unknown Source:0)

07-16 07:33:48.691  9900 10089 E AndroidRuntime: at

MANDATORY Reproducer

#52797

Screenshots and Videos

No response

[react-native-bot]

Warning

Missing reproducer: We could not detect a reproducible example in your issue report. Reproducers are mandatory and we can accept only one of those as a valid reproducer:

• For majority of bugs: send us a Pull Request with the RNTesterPlayground.js edited to reproduce your bug.
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• If your bug is build/upgrade related: a project using our Reproducer Template

You can read more about about it on our website: How to report a bug.

[cortinico]

cc @robhogan as this is related to Metro integration

[react-native-bot]

This issue is waiting for author's feedback since 24 days. Please provide the requested feedback or this will be closed in 7 days.

[react-native-bot]

This issue is waiting for author's feedback since 24 days. Please provide the requested feedback or this will be closed in 7 days.