invalid event envelope. Error causes: unexpected end of file. If Context is null

Environment

How do you use Sentry? SaaS and Self Hosted.

Which SDK and version? latest.

Steps to Reproduce

Only happens with the caching feature.

run the snippet

using System;
using System.Globalization;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Sentry;
using Sentry.Infrastructure;

SentrySdk.Init(o =>
{
    o.Dsn = "https://[e-mail]/5428537";
    o.Debug = true;
    o.DiagnosticLogger = new TraceDiagnosticLogger(SentryLevel.Debug); //only used for revealing the data on the IDE.
    o.CacheDirectoryPath = "D:/bob";
});


SentrySdk.ConfigureScope(scope =>
{
    scope.Contexts["MyCoolContext"] = null;
    scope.Contexts["MyCoolContext2"] = null;
});
SentrySdk.CaptureMessage("Hello Wôrld");
await Task.Delay(1000);

Expected Result

An event sent to Sentry.

Actual Result

  Error: Sentry rejected the envelope 3e2862cff51d43b3860e4513ef522764. Status code: BadRequest. Error detail: invalid event envelope. Error causes: unexpected end of file.
  Debug: Failed envelope '3e2862cff51d43b3860e4513ef522764' has payload:
{"sdk":{"name":"Sentry","version":"3.12.0-alpha.1"},"event_id":"3e2862cff51d43b3860e4513ef522764"}
{"type":"event","length":1965}
{"modules":{"System.Private.CoreLib":"5.0.0.0","Sentry.Samples.Console.Basic":"9.8.7.0","System.Runtime":"5.0.0.0","Sentry":"3.12.0.0","System.Net.Primitives":"5.0.0.0","System.IO.Compression":"5.0.0.0","System.Private.Uri":"5.0.0.0","System.Diagnostics.Process":"5.0.0.0","System.ComponentModel.Primitives":"5.0.0.0","Microsoft.Win32.Primitives":"5.0.0.0","System.Runtime.InteropServices":"5.0.0.0","System.Threading":"5.0.0.0","System.Diagnostics.TraceSource":"5.0.0.0","System.Net.Http":"5.0.0.0","System.Diagnostics.Tracing":"5.0.0.0","System.Diagnostics.DiagnosticSource":"5.0.0.0","System.Net.Security":"5.0.0.0","System.Security.Cryptography.X509Certificates":"5.0.0.0","System.Collections":"5.0.0.0","System.Collections.Concurrent":"5.0.0.0","System.Security.Cryptography.Algorithms":"5.0.0.0","System.Security.Cryptography.Primitives":"5.0.0.0","System.Memory":"5.0.0.0","System.IO.FileSystem":"5.0.0.0","System.Linq":"5.0.0.0","System.Threading.Thread":"5.0.0.0","System.Diagnostics.StackTrace":"5.0.0.0"},"event_id":"3e2862cff51d43b3860e4513ef522764","timestamp":"2021-11-19T21:00:13.8001629+00:00","logentry":{"message":"Hello W\u00F4rld"},"platform":"csharp","release":"Sentry.Samples.Console.Basic@9.8.7","level":"info","request":{},"contexts":{"app":{"type":"app","app_start_time":"2021-11-19T21:00:12.4422617+00:00"},"device":{"type":"device","timezone":"E. South America Standard Time","timezone_display_name":"(UTC-03:00) Brasilia","boot_time":"2021-11-17T17:50:47.9937672+00:00"},"runtime":{"type":"runtime","name":".NET","version":"5.0.10","raw_description":".NET 5.0.10"},"Current Culture":{"Name":"en-US","DisplayName":"English (United States)","Calendar":"GregorianCalendar"},"os":{"type":"os","raw_description":"Microsoft Windows 10.0.22000"}},"user":{},"environment":"debug","sdk":{"packages":[{"name":"nuget:Sentry","version":"3.12.0-alpha.1"}],"name":"sentry.dotnet","version":"3.12.0-alpha.1"}}

[mattjohnsonpint]

It would appear that the null entries are removed from the context section of the payload when caching is enabled, and the length header is not updated.

We should ensure first that the length header is always correct, but also we should decide whether to either send null context info always or never. It shouldn’t vary based on caching.

[mattjohnsonpint]

Also I’ll just add that it would have been a better design to encapsulate the ConcurrentDictionary rather than extending from it. Contexts : IDictionary<string, object> would have allowed us to filter out nulls when data was being added, rather than afterwards. It would have also hidden the concurrentness, which is an implementation detail. But changing it now would be a breaking change, so perhaps for the future.