Hello, This sounds very usable, especially since we could advertise multiple services.
It would be great if someone is able to make a proof-of-concept for this to test the practical limits on Android. Paul. On Thu, Oct 9, 2014 at 6:38 PM, Michael Rogers <[email protected]> wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > On 08/10/14 15:42, Nathan of Guardian wrote: > > Great to hear... btw, I just realized we can use the WifiDirect > > service discovery capability to send much longer data than the > > current SSID/name method allows: > > > http://developer.android.com/training/connect-devices-wirelessly/nsd-wifi-direct.html > > > > > > > Not sure what the limits are, but it doesn't require you to > > connect or join to be able to broadcast/listen for this info. > > Looks promising! I've found some scraps of information about limits: > > RFC 1035 section 3.2.1: > The length of the RDATA in a DNS resource record is an unsigned 16-bit > integer. > > Section 3.3: > A character-string may be up to 256 bytes, including one byte to > specify the length. > > Section 3.3.14: > A TXT record's RDATA consists of one or more character-strings. > > RFC 4408 section 3.1.3: > A single DNS TXT record can be comprised of more than one string. The > maximum length of each string is 255 bytes (this is consistent with > the above). > > Section 3.1.4: > The total record size SHOULD be kept below 512 bytes to prevent > clients from falling back to TCP. Records that don't fit within a > single UDP packet MAY be ignored. (This applies to SPF, but we should > bear in mind that similar limits may apply to Wi-Fi Direct for similar > reasons.) > > I would speculate that each entry in the WifiP2pServiceInfo's string > map is being translated into a character-string and RDATA consists of > the concatenated character-strings. If we use single-character keys > for the map, we can put up to 253 bytes of base64 (189 bytes of data) > in each value. > > We may run into compatibility problems if we try to encode more than > one max-length value in a single record... let's experiment with as > many device combinations as possible. > > Cheers, > Michael > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.12 (GNU/Linux) > > iQEcBAEBCAAGBQJUNkJ6AAoJEBEET9GfxSfM+VkH/3QzoBPzDyLBm1T7Gwv2DGY5 > ifaN9g1+vVN2bFQHy4zIxeByfPPSJ9bipqBb+qGfrKyOarAoQK+wkZeYEESUiIxa > kXK3Qv2u3lL5T8pA3iBhT5wNtY2QAHSM7TEm+gnagF/Mjm0GkCFSUJUxRGm2RJUq > 1+UZAFqNU2LeUMPySU9CckAijLniTW5h4RibLmlRkn3xB+dcBaY3O3H0cjloXzIT > r+PlnzwS4XGgcQWimt/Iul/UOv91dkcFwlFkVJjwIJSb4OZ1l3N/PM1FsZ8vNP3R > uoq5joM2MOWlov+50cZmC9xUyRuS/9aC7Z0alvAIX0JFK1vNmvhJW6FC+EmmC8w= > =QnJG > -----END PGP SIGNATURE----- >
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