Replace recursive approach with iterative approach for readPacket()

[cxmcc]

Possible benefits:

• Less expensive function calls and stack space.
• Probably make it easier for compression implementation since the loop gonna work on the same buffer (uncompressed payload).

[arnehormann]

we don't need the copy without the recursion - data stays valid and appending copies it anyway

[cxmcc]

good point! just added a commit to remove that.

[julienschmidt]

This makes the common case (non splitted packets) a lot more expensive and destroys our current "zero allocations" approach.

[arnehormann]

@julienschmidt is you critique still valid if the append above is removed and this if becomes

if pktLen >= maxPacketSize {
  payload = append(payload, data...)
  continue
}
return data, nil

[arnehormann]

and (handwaving) the correct variable is returned every time... (not data if it should be payload)

[cxmcc]

@julienschmidt I understood what you mean.

It's doing payload = append(nil, data) for common cases. (I thought golang will do payload=data for append(nil...) but obviously not.)

We can still disable the buffer copying for common case by doing what @arnehormann suggested.

[cxmcc]

@julienschmidt the logic after the new patch, for the common cases (non-splitting), will not invoke any allocation (like old approach); for large packets, avoids recursive calls and copying twice.

[julienschmidt]

Maybe // zero allocations for non-split packets ?

I'm not a native speaker, but to me Zero-allocation sound like allocating a zero

[julienschmidt]

The new approach looks fine to me 👍

[cxmcc]

thanks @julienschmidt, amended suggestions to previous commits.

[julienschmidt]

LGTM now, final review by @arnehormann

[arnehormann]

what happens when the packet length of the last packet is exactly maxPacketSize? Is that possible?
I'll look it up now, but if you know, please chime in...

[julienschmidt]

what happens when the packet length of the last packet is exactly maxPacketSize? Is that possible?

No, a packet length of maxPacketSize marks a split packet

[arnehormann]

Thanks

[arnehormann]

LGTM before and still does...