How to support zero copy when decode the message ?

[runzhiwang]

What language does this apply to?

proto3, java

Describe the problem you are trying to solve.

My request is similar to https://groups.google.com/g/protobuf/c/ZaDigptdcHM

Currently, when read ByteString.readBytes, the order is InputStream -> StreamDecoder.buffer with 4kB size -> copy StreamDecoder.buffer to byte array on heap. Can we change the order to InputStream -> byte array on heap directly ? Besides, instead use byte array on heap, can we use byte array off-heap ?

As the image shows, arraycopy in StreamDecoder.readBytesSlowPath really cost too much CPU. I want to improve it by avoid arraycopy. If there is other suggestions, I would appreciate it, thank you very much.

[deannagarcia]

As explained in the comment you linked, unfortunately it is impossible to return the byte array directly because it must be copied to guarantee immutability.