If you're new to Mesos

See the getting started page for more information about downloading, building, and deploying Mesos.

If you'd like to get involved or you're looking for support

See our community page for more details.

RecordIO Data Format


RecordIO is the name for a set of binary data exchange formats. The basic idea is to divide the data into individual chunks, called ‘records’, and then to prepend to every record its length in bytes, followed by the data.

Since there is no formal specification of the RecordIO format, there tend to be slight incompatibilities between RecordIO implementations. Common differences include, for example, a magic value at the beginning of the stream to indicate the stream format, encoding the record length using fixed-size fields with native integers or extra fields to suppord compressed record content.

Therefore, when using a third-party library, one needs to verify that the implementation matches the RecordIO format used by Mesos, as described below.

Mesos RecordIO Format

The BNF grammar for a RecordIO-encoded streaming response is:

    records         = *record

    record          = record-size LF record-data

    record-size     = 1*DIGIT
    record-data     = record-size(OCTET)

record-size should be interpreted as an unsigned 64-bit integer (uint64).

For example, a stream may look like:

{"type": "SUBSCRIBED","subscribed": {"framework_id": {"value":"12220-3440-12532-2345"},"heartbeat_interval_seconds":15.0}20\n

In pseudo-code, this could be parsed with something like the following:

  while (true) {
    do {
      lengthBytes = readline()
    } while (lengthBytes.length < 1)

    messageLength = parseInt(lengthBytes);
    messageBytes = read(messageLength);

Network intermediaries (e.g., proxies) are free to change the chunk boundaries; this should not have any effect on the recipient application.

Streaming HTTP requests

Within Mesos, RecordIO is used as data format for API endpoints that support streaming responses. The implementation expects the client to be aware of the following non-standard HTTP header fields when using such endpoints:

The Message-Accept header must be set by clients that request a streaming response from the server by setting the Accept header to application/recordio. It specifies which media types the client accepts encoded in the RecordIO stream, and its content must have the same format as the standard HTTP Accept header.

The Message-Content-Type is set by the server when streaming the response to an API call. It specifies the content type of the data encoded in the RecordIO stream and has the same format as the standard HTTP Content-Type header.

Currently, the only supported MIME types for both header fields are application/json and application/x-protobuf.