aeron-io/aeron · error · InvalidMessage

Terminated prematurely

Error message

Terminated prematurely

What it means

DecodingState.incrementOffset advances the CBOR decode cursor and checks it against the buffer limit. If the increment would move the offset past the limit, the buffer is exhausted mid-message and InvalidMessage('Terminated prematurely') is thrown — the CBOR payload ended before the decoder expected it to.

Solutions

1. Verify the buffer slice passed to the decoder covers the full record (use the encoded header's captureLength/length fields).
2. Check that the event log wasn't truncated by the capture-length cap when writing.
3. Add a remaining-bytes check before parsing variable-length fields.
4. Re-capture with a larger capture length if records are being cut off.

Example fix

// before
decoder.decode(buffer, offset, buffer.capacity()); // limit beyond actual data
// after
final int limit = offset + CommonEventEncoder.encodedLength(captureLength);
if (limit > buffer.capacity()) throw new IllegalArgumentException("buffer too small");
decoder.decode(buffer, offset, limit);

if (limit - offset < minimumExpectedRecordLength)
{
    throw new IllegalArgumentException("buffer slice too small for record");
}

try
{
    cborDecoder.decode(buffer, offset, limit);
}
catch (final InvalidMessage ex)
{
    LOGGER.warn("truncated CBOR record at " + offset + ": " + ex.getMessage());
}

When it happens

Trigger: Any parse step (parseMessage, parseString, parseLong, parseBoolean, parseEntry, parseNumber) consuming more bytes than remain — e.g. a declared string/byte-array length larger than the actual remaining buffer, or a truncated capture buffer.

Common situations: Truncated event-log fragments passed to the decoder; a log header claiming more bytes than the buffer holds; off-by-one in slicing the buffer around the log record.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• Invalid value type
• Invalid value length
• Invalid key length
• Expected timestamp
• Expected boolean

AI-assisted analysis of aeron-io/aeron@6d60124e15 (2026-09-12). Data as JSON: /api/errors/ba50b1b7ba152622. Report an issue: GitHub.

Appendix: source

Thrown at aeron-client/src/main/java/io/aeron/logging/DecodingState.java:51

    {
        this.buffer = buffer;
        this.offset = initialOffset;
        this.length = length;
        this.limit = offset + length;
        this.terminated = false;
    }

    void reset()
    {
        wrap(null, 0, 0);
    }

    void incrementOffset(final int increment)
    {
        this.offset += increment;
        if (this.limit < this.offset)
        {
            throw new InvalidMessage("Terminated prematurely");
        }
    }

    int remaining()
    {
        return this.limit - this.offset;
    }

    void ensureRemaining(final int count)
    {
        if (this.remaining() < count)
        {
            throw new InvalidMessage("Terminated prematurely");
        }
    }

    int offset()
    {

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