Re: Re: Introducing TLS

The specification counts bits from left to right, so if the 16th host
(the 15th bit starting with 0-based numbers) is TLS-capable, that
would be described as:

 tls=0001,

Whereas if the first host (0th bit) and the 14th host (13th bit) were
TLS capable, that would be described as:

 tls=8002,

That is, the hexademical representation is purely a nibble-per-nibble
translation of each 4 bytes, starting from left to right, with
0000=0x0, 0001=0x1, 0010=0x2, 0011=0x3, etc... This method is
preferred because when the number is unwrapped to the bits, you can
easily index through the bits in the same order as the ip:port list.

Trailing 0s in both hexademical and byte[] form can be discarded.

My previous email was confusing though in that it could be construed
to mean only 2 chars could be listed.  Thanks for that clarification.

Sam

On 6/12/07, [email protected] <[email protected]> wrote:
> Quoting Sam Berlin <[email protected]> from ml.gnutella.dev-forum:
> :  The X-Alt header is changed so that "tls=##" is written prior to any of
> :the
> :  locations are listed.  '##' is the hexademical representation of the
> :byte[]
> :  that describes which of the following alternate locations can accept
> :TLS.
>
> This specification is confusing.  It looks like one cannot send more
> than 8 addresses in X-Alt.
>
> '##' does not stand for 2 hex chars, but rather a complete bit array
> in big-endian format, where bit 0 represents the first address,
> bit 1 the second address, etc..
>
> So in a list of 17 hosts where only the 16th (i.e. the last but not least)
> host can support TLS, this is bit #15 (numbering starts at 0), you would say:
>
>        tls=8000,
>
> at the beginning of the X-Alt field, where indeed only the bit #15 is set.
>
> Thanks for clarifying the specs accordingly.
>
> Raphael
>
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