Re: [hybi] frame length encoding

[gustav trede <[e-mail]>]

On 20 August 2010 21:08, John Tamplin <[e-mail]> wrote:

> From the discussions related to my previous proposal, it seems like how we
> encode the length is the remaining contentious issue (at least there were no
> other comments on the rest of the 4 issues I outlined).  It is hard to get a
> sense of who prefers what to what extent.  Also, in a comment not intended
> as a serious proposal I mentioned a 1/2/8 option, I had a couple of people
> reply to me privately that they liked the idea.  So, I thought I would ask
> for a "show of hands" about three possibilities.  If you feel strongly for
> or against a particular option, please reply and say so.  If you are fine
> with any of the three, then there is no need to reply.
>
> A sample code snippet (not suggesting this is optimal for any of the cases)
> is included to make sure what is intended is clear.
>
> Option 1
> ========
> Use 7 bits in the frame header, and if the value is 0-126, that is the
> length.  If the value is 127, the next 8 bytes are a 63-bit length (the high
> bit must be zero).
>
> long long len = readByte();
> if (len == 127) {
>   len = readLongLong();
> }
>
Strong negative feeling against option 1


> Option 2
> ========
> Use 7 bits in the frame header, and if the value is 0-125, that is the
> length.  If the value is 126, then the next 2 bytes are a 16-bit length.  If
> the value is 127, the next 8 bytes are a 63-bit length (the high bit must be
> zero).
>
> long long len = readByte();
> switch (len) {
>   case 126:
>     len = readUnsignedShort();
>     break;
>   case 127:
>     len = readLongLong();
>     break;
> }
>
Strong positive feeling for option 2.


>
> Option 3
> ========
> Use 8 bits in the frame header (assigning RSV2 in the most recent proposal
> to be part of the length field).  If the high bit is set in that byte, shift
> the current length seven bits and read the next byte.  Leading 0x80 bytes
> are disallowed, and at most 9 length bytes may be included
>
> int byte = readByte();
> if (byte == 0x80) // fail
> long long len = byte;
> for (int i = 1; (byte & 0x80) && i < 9; ++i) {
>   byte = readByte();
>   len = (len << 7) | (byte & 0x7f);
> }
> if (byte & 0x80) // fail
>
>
>
> I would be willing to live with any of the three personally.  My preference
> is roughly even for #1 or #2 over #3 because #3 uses one of our reserved
> bits (reducing expansion options) and has error states which must be
> checked.  Also, most of the lengths don't buy you much in terms of reducing
> overhead, as the overall frame is much longer than the header at that point
> anyway.
>
> --
> John A. Tamplin
> Software Engineer (GWT), Google
>
> _______________________________________________
> hybi mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/hybi
>
>