microsoft/aspire · error · InvalidOperationException

Tracked browser protocol frame ended unexpectedly.

Error message

Tracked browser protocol frame ended unexpectedly.

What it means

While parsing a CDP frame header, the parser reads the value for each property name. If the JSON stream ends right after a property name (no value token follows), the frame is truncated and this InvalidOperationException is thrown. It indicates the tracked browser's frame ended mid-object.

Solutions

1. Verify frame-length framing so only complete frames are handed to the parser
2. Log the raw payload via DescribeFrame to confirm truncation
3. Check browser process health - a crash can truncate the last frame
4. Buffer and reassemble partial reads before parsing
5. Catch the exception and re-establish the browser connection

Example fix

// before
var header = BrowserLogsCdpProtocol.ParseMessageHeader(partialBuffer);
// after
if (!frameReader.TryReadCompleteFrame(out var frame))
{
    pendingBuffer = frame; // wait for more data
    return;
}
var header = BrowserLogsCdpProtocol.ParseMessageHeader(frame);

// Only parse frames known to be complete per the framing protocol
if (!TryReadCompleteFrame(ref buffer, out var frame))
{
    return; // wait for remainder
}

When it happens

Trigger: ParseMessageHeader encounters a property name token but Utf8JsonReader.Read() returns false - i.e. the payload ends immediately after a key like {"id": or a final dangling key, typically a truncated or partial frame.

Common situations: Socket/stream read returned a partial frame, buffer boundary split a JSON object mid-key, the browser process crashed or was killed mid-write, or network disconnect during DevTools message delivery.

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.

Related errors

• Tracked browser protocol event method was not a string.
• Tracked browser protocol frame was malformed.
• Tracked browser protocol response id was not an integer.
• Browser debug connection closed by the remote endpoint with…
• Chromium profile metadata in

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/c51a2e452fb5b1e3. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Browsers/BrowserLogsCdpProtocol.cs:89

        string? method = null;
        string? sessionId = null;

        while (reader.Read())
        {
            if (reader.TokenType == JsonTokenType.EndObject)
            {
                break;
            }

            if (reader.TokenType != JsonTokenType.PropertyName)
            {
                throw new InvalidOperationException("Tracked browser protocol frame was malformed.");
            }

            var propertyName = reader.GetString();
            if (!reader.Read())
            {
                throw new InvalidOperationException("Tracked browser protocol frame ended unexpectedly.");
            }

            switch (propertyName)
            {
                case "id":
                    if (!reader.TryGetInt64(out var parsedId))
                    {
                        throw new InvalidOperationException("Tracked browser protocol response id was not an integer.");
                    }

                    id = parsedId;
                    break;
                case "method":
                    method = reader.TokenType == JsonTokenType.String
                        ? reader.GetString()
                        : throw new InvalidOperationException("Tracked browser protocol event method was not a string.");
                    break;
                case "sessionId":

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