Playing with Sharp Objects.

For the longest time I’ve been looking for an automated way to extract DMARC reports, which come in gz format, within our Microsoft infrastructure. Power Automate does a nice job of grabbing the files and putting them in various places. The blocker in this was that Microsoft Power Automate does not have a step for extracting gz files, so I still had a manual step that was tied to a script running on a certain workstation. The answer was in this post using Power Apps.

https://medium.com/@vandanrohatgi/extract-gzip-files-with-power-automate-0387cf3ca0e3

However the C# code gave me a few error messages, and I am not familiar with C#. Enter ChatGPT. This is my working code:

using System;
using System.IO;
using System.IO.Compression;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json.Linq;

public class Script : ScriptBase
{
  public override async Task<HttpResponseMessage> ExecuteAsync()
  {
    // Read body
    string contentAsString = await this.Context.Request.Content
      .ReadAsStringAsync().ConfigureAwait(false);

    // Parse JSON
    JObject contentAsJson;
    try
    {
      contentAsJson = JObject.Parse(contentAsString);
    }
    catch (Exception ex)
    {
      return Error(HttpStatusCode.BadRequest, $"Invalid JSON: {ex.Message}");
    }

    // Extract base64 "file"
    string fileBase64 = contentAsJson.Value<string>("file");
    if (string.IsNullOrEmpty(fileBase64))
      return Error(HttpStatusCode.BadRequest, "Missing 'file' property.");

    // Base64 decode
    byte[] data;
    try
    {
      data = Convert.FromBase64String(fileBase64);
    }
    catch (FormatException ex)
    {
      return Error(HttpStatusCode.BadRequest, $"Invalid base64: {ex.Message}");
    }

    // GZip decompress
    string decompressedData;
    try
    {
      decompressedData = DecompressGzip(data);
    }
    catch (Exception ex)
    {
      return Error(HttpStatusCode.BadRequest, $"GZip decompress failed: {ex.Message}");
    }

    // Build OK response
    var payload = new JObject { ["gzipBody"] = decompressedData };
    var response = new HttpResponseMessage(HttpStatusCode.OK)
    {
      Content = CreateJsonContent(payload.ToString())
    };
    return response;
  }

  private static string DecompressGzip(byte[] compressedData)
  {
    using (var compressedStream = new MemoryStream(compressedData))
    using (var gzipStream = new GZipStream(compressedStream, CompressionMode.Decompress))
    using (var decompressedStream = new MemoryStream())
    {
      gzipStream.CopyTo(decompressedStream);
      return Encoding.UTF8.GetString(decompressedStream.ToArray());
    }
  }

  private HttpResponseMessage Error(HttpStatusCode status, string message)
  {
    var body = new JObject { ["error"] = message };
    var resp = new HttpResponseMessage(status)
    {
      Content = CreateJsonContent(body.ToString())
    };
    return resp;
  }
}

It’s a very simple method, and it doesn’t cost anything, although there seems to be a 750 flow limit per month.