Serializing to and from a C# POCO using System.Text.Json

CompressionUtils.cs

using System;
using System.IO;
using System.IO.Compression;
using System.Text.Json;

namespace CodatIngestion
{
    public static class CompressionUtils
    {
        public static byte[] ToJsonSerializedGzipBytes<T>(T value, JsonSerializerOptions jsonOpts)
        {
            if (value is null)
            {
                return null;
            }

            if (jsonOpts is null)
            {
                throw new NullReferenceException(nameof(jsonOpts));
            }
            
            var jsonUtf8Bytes = JsonSerializer.SerializeToUtf8Bytes(value, jsonOpts);
            using (var dest = new MemoryStream())
            using (var gz = new GZipStream(dest, CompressionMode.Compress))
            {
                gz.Write(jsonUtf8Bytes, 0, jsonUtf8Bytes.Length);
                gz.Close();
                return dest.ToArray();
            }
        }
        
        public static T FromJsonSerializedGzipBytes<T>(byte[] jsonSerializedGzipBytes, JsonSerializerOptions jsonOpts)
        {
            if (jsonSerializedGzipBytes is null || jsonSerializedGzipBytes.Length == 0)
            {
                return default;
            }

            if (jsonOpts is null)
            {
                throw new NullReferenceException(nameof(jsonOpts));
            }
            
            using (var compressed = new MemoryStream(jsonSerializedGzipBytes))
            using (var gz = new GZipStream(compressed, CompressionMode.Decompress))
            using (var dest = new MemoryStream())
            {
                gz.CopyTo(dest);
                var jsonBytes = dest.ToArray();
                var jsonReader = new Utf8JsonReader(jsonBytes);
                var deserialized = JsonSerializer.Deserialize<T>(ref jsonReader, jsonOpts);
                return deserialized;
            }
        }
    }
}

Usage.cs

var deserializedJson = CompressionUtils.FromJsonSerializedGzipBytes<T>(gzippedPayload, jsonOpts);
var serialized = CompressionUtils.ToJsonSerializedGzipBytes(deserializedJson, jsonOpts);
var samePayload = serialized.SequenceEqual(payload.GzipJson);   // true