Ios swift – Using iOS compression library to decompress zlib compressed data keeps returning NSCocoaErrorDomain code=5377

I’m writing an iOS app that wants to read in a zlib compressed data file and uncompress it. This should be easy using the builtin compression library and zlib is one of the supported compression algorithms. Here is my code:
”’
import Compression

do {
   let data = try Data(contentsOf: URL(fileURLWithPath: filePath))
   print("read data of size (fileData.count) bytes")
   decompressedData = try (data as NSData).decompressed(using: .zlib) as Data
}
catch {
   print("Failed to decompress data: (error)")
}

”’

The decompression keeps failing with Error Domain=NSCocoaErrorDomain Code=5377.

I’ve verified that the file is correctly compressed using zlib compression. I can compress and uncompress the data file on both macos and linux using a python program that uses zlib compression. I can also do the same with zlib-flate. I correctly read the compressed file into a Data object and is 4581383 bytes.

Any suggestions as to why I can’t decompress the data?

Thanks,

Bobby