custom DownloadHandlerScript not working properly, even though DownloadHandlerBuffer does

We have a custom DownloadHandlerScript; I've reduced it here to the simplest example. It's been working fine for us for over a year. The problem is, when we create a request to download some addresses on https://ifps.io, the download handler never even gets any callbacks— it fails with errors like
Curl error 23: Failed writing body (0 != 4096).

This only happens for some addresses on https://ifps.io . Please email me at josh@spatial.io or mike@spatial.io for a specific address that can repro this.

Using Unity 2020.1.17f1, and reproducing this in editor on a mac (as well as on other platforms).

Code (CSharp):

1. public class SampleDownloadHandler : DownloadHandlerScript, System.IDisposable
2.     {
3.         public NativeArray<byte> buffer
4.         {
5.             get;
6.             private set;
7.         }
8.  
9.         private int _writeIndex = 0;
10.  
11.         protected override void ReceiveContentLengthHeader(ulong contentLength)
12.         {
13.             buffer = new NativeArray<byte>((int)contentLength, Allocator.Persistent, NativeArrayOptions.UninitializedMemory);
14.         }
15.  
16.         protected override bool ReceiveData(byte[] data, int dataLength)
17.         {
18.             if (_writeIndex + dataLength > buffer.Length)
19.             {
20.                 return false;
21.             }
22.  
23.             NativeArray<byte>.Copy(data, 0, buffer, _writeIndex, dataLength);
24.             _writeIndex += dataLength;
25.  
26.             return _writeIndex < buffer.Length;
27.         }
28.  
29.         protected override byte[] GetData()
30.         {
31.             Log.Warning($"{nameof(GLTFDownloadHandler)}: using this may cause memory leaks");
32.             return buffer.ToArray();
33.         }
34.  
35.         protected override string GetText()
36.         {
37.             Log.Warning($"{nameof(GLTFDownloadHandler)}: using this may cause memory leaks");
38.             return buffer.GetText();
39.         }
40.  
41.     }

 

I see, thank you!
The problem was we were expecting to receive the call to ReceiveContentLengthHeader before receiving data, but never are receiving the content length header. We adjusted it to work without that expectation and it works fine now