Observed during investigation of
https://github.com/ARMmbed/mbed-os/issues/4246 - DNS queries sent
the entire buffer, not just the bit filled in.
Inefficient, especially for 6LoWPAN, and a security hole - the trailing
data could be previously-used heap.
nsapi_error_t - enum of errors or 0 for NSAPI_ERROR_OK
nsapi_size_t - unsigned size of data that could be sent
nsapi_size_or_error_t - either a non-negative size or negative error
Replace Comodo and OpenDNS IPv4 servers with Google and DNS.WATCH IPv6
servers, so IPv6-only devices (eg 6LoWPAN) have a default.
3 IPv4 resolvers should be plenty - existing code doesn't remember which
one last worked, so if early list entries were unreachable performance
would be consistently bad anyway. Replacing two entries avoids
increasing image size and RAM consumption.
On an IPv6-only or IPv4-only system, the sendto() for the wrong type of
address should fail immediately - change loop to move on to the next
server for any sendto() error.
Kevin Bracey
Martin Kojtal
Christopher Haster
Bartek Szatkowski