Is there a way to get message payloads to allocate extra memory?

[joerowell]

I have an application that reads multiple messages from a Kafka topic. Primarily, these messages are JSON files, which I then parse with the simdjson library. However, for maximum performance the simdjson library requires a string of n bytes to be stored in a buffer of around n + 64 bytes. This means that for any particular message I need to allocate a new buffer for each message and copy over the payload.

Is there a way to make librdkafka allocate extra memory per message when the message is received / taken from the consumer's queue? In particular, I want to have a way to specify that each message (with a payload of n bytes) should allocate n + 64 bytes of storage.