react-native: `Fetch` no longer returns all rows of the same-name response headers after RN Upgrade

I am having this issue on v.0.57.

I found a workaround for this issue, but I’m not sure of any additional implications of it. Inspired by comments on a ReadableNativeArray issue, if you add the following lines to MainApplication.java, the duplicate headers are properly parsed:

ReadableNativeArray.setUseNativeAccessor(true);
ReadableNativeMap.setUseNativeAccessor(true);

I created a repo to reproduce the issue using 0.55.4: https://github.com/patricksmith/rn-headers. You can see the workaround in this commit: https://github.com/patricksmith/rn-headers/commit/e666aa814bf36616d73e015bef75654fc315ec10. I can’t find any documentation on what setUseNativeAccessor is doing, so it may have additional unintended repercussions.

Our app was also affected by this when trying to update to 0.55.4. It breaks use case of reading cookies from responses as there’s often more than one set-cookie headers in one response.

I’ve also just ran into this problem. It seems to be an issue with the WritableMap that collects the response headers in the translateHeaders() method in com.facebook.react.modules.network.NetworkingModule. The code checks to see if the key exists in the map, but for some reason it returns false. Debugging the code, it calls hasKey() on ReadableNativeMap. This drops down to the local map since mUseNativeAccessor is false, and the local map is empty.

Facing the same issue, spent the morning trying to debug why on iOS we had 3 cookies and on Android only 1 cookie and the problem happens when there are more headers with the same name, on Android it takes only the last one ignoring the others.

An easy way to reproduce, using an express server

    app.get('/test', noCache, (req, res) => {
      res.cookie('mattia1', 'hello');
      res.cookie('mattia2', 'world');
      res.sendStatus(200);
    });

Then on the app

fetch({
  url: 'http://localhost:3000/test'
}).then(res => {
  console.log(res.headers);
})

On Android you get mattia2=world; Path=/ On iOS you get mattia1=hello; Path=/, mattia2=world; Path=/

Only if you control the server the workaround is to not send 2 headers of the same type

In this case with cookies you have to manually set the header with

// doesnt work
// res.cookie('mattia1', 'hello');
// res.cookie('mattia2', 'world');
// works
res.set('Set-Cookie', 'mattia1=hello; Path=/, mattia2=world; Path=/');

We were affected by this issue after upgrading our Android app from RN 0.53.3 to RN 0.54.4, and I see that it’s still an issue in RN 0.55.4. We’re using an API that returns multiple Link headers and we’re now only receiving one of those headers in our app.

Same issue affect our app when moving from RN 0.52 The server we are connecting to returns Basic & Digest authentication headers but in the Android app we only get the Basic authentication header returned. The same servers work OK on iOS

I’m seeing the same thing happening since upgrading from RN 0.52 to 0.54.

Headers being returned by some servers we use have the same fields spread across multiple lines. Since 0.54 it is not possible to talk to these devices any more using RN on Android! RN on iOS is fine.

This is still an issue on RN v0.57.0-rc.3

Also have same issue after upgrading RN version 0.53 to 0.55. fetch() is not returning body returned by the server. When I downgraded to RN version 0.53, it works well. Please give the solution.