elsa-workflows/elsa-core · error · JsonException

Failed to parse JsonDocument

Error message

Failed to parse JsonDocument

What it means

Thrown in ObsoleteConnectionJsonConverter.Read when the legacy connection JSON cannot be parsed into a JsonDocument. This converter handles the obsolete flat Connection format (source/target/sourcePort/targetPort strings), so the error indicates corrupt or non-object JSON in a legacy payload.

Solutions

1. Validate the legacy JSON with JsonDocument.Parse before deserialization to find the corrupt element.
2. Verify the source storage (file/DB) is not truncating the definition JSON.
3. Confirm the legacy connection is an object: {"source":"a","target":"b","sourcePort":"...","targetPort":"..."}.
4. If migrating, convert legacy definitions to the current format first, then deserialize.

Example fix

// before
var conn = JsonSerializer.Deserialize<ObsoleteConnection>(legacyJson); // throws on malformed json
// after
using var doc = JsonDocument.Parse(legacyJson); // pre-validate
var conn = JsonSerializer.Deserialize<ObsoleteConnection>(legacyJson);

using var doc = JsonDocument.Parse(legacyJson); // pre-validate before ObsoleteConnection deserialization

static bool CanParseJson(string json) { try { using var _ = JsonDocument.Parse(json); return true; } catch (JsonException) { return false; } }

try { var conn = JsonSerializer.Deserialize<ObsoleteConnection>(legacyJson); }
catch (JsonException ex)
{
    logger.LogError(ex, "Malformed legacy connection JSON during migration: {Message}", ex.Message);
}

When it happens

Trigger: Deserializing legacy workflow definitions whose connection JSON is malformed — truncated, wrong token type, or not a JSON object.

Common situations: Migrating old Elsa 2.x workflow definitions from storage where the JSON was corrupted; legacy export files edited by hand; partial reads of definition blobs.

Understand the failure class

Background: JSON parse error: "Unexpected token" / "not valid JSON" / "failed to parse" — what JSON parsers are really complaining about — this error's family across 45 libraries.

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to parse JsonDocument
• Failed to parse JsonDocument
• Cannot deserialize to .
• Failed to deserialize
• The binding to activity type

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/6c72eef8ff2d651f. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Workflows.Core/Activities/Flowchart/Serialization/ObsoleteConnectionJsonConverter.cs:28

[Obsolete("Use ConnectionJsonConverter instead.")]
public class ObsoleteConnectionJsonConverter : JsonConverter<ObsoleteConnection>
{
    private readonly IDictionary<string, IActivity> _activities;

    /// <inheritdoc />
    public override bool CanConvert(Type typeToConvert) => typeToConvert == typeof(ObsoleteConnection);

    /// <inheritdoc />
    public ObsoleteConnectionJsonConverter(IDictionary<string, IActivity> activities)
    {
        _activities = activities;
    }

    /// <inheritdoc />
    public override ObsoleteConnection Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (!JsonDocument.TryParseValue(ref reader, out var doc))
            throw new JsonException("Failed to parse JsonDocument");

        var sourceId = doc.RootElement.GetProperty("source").GetString()!;
        var targetId = doc.RootElement.GetProperty("target").GetString()!;
        var sourcePort = doc.RootElement.GetProperty("sourcePort").GetString()!;
        var targetPort = doc.RootElement.GetProperty("targetPort").GetString()!;

        var source = _activities.TryGetValue(sourceId, out var s) ? s : null!;
        var target = _activities.TryGetValue(targetId, out var t) ? t : null!;

        return new ObsoleteConnection(source, target, sourcePort, targetPort);
    }

    /// <inheritdoc />
    public override void Write(Utf8JsonWriter writer, ObsoleteConnection value, JsonSerializerOptions options)
    {
        var (activity, target, sourcePort, targetPort) = value;

        var model = new

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