zeroconf is a cross-platform library that wraps underlying ZeroConf/mDNS implementations such as Bonjour or Avahi, providing an easy and idiomatic way to both register and browse services.
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Fix size constant passed to avahi_address_snprint() #11
Problem: avahi_address_snprint() takes the size in bytes of the buffer being printed into as its second argument. This library was using std::mem::size_of_val() on a CString type to pass this argument; however, that will return the size of the CString type, which is not necessarily the size of the underlying array that the CString was generated from.
On 64-bit platforms the size of CString happens to be 16, which fits the string representation of most IPv4 addresses, but is lower than AVAHI_ADDRESS_STR_MAX which is defined to 40. This also means:
The avahi_address_to_string() function will probably not work with most IPv6 addresses at all
It won't even work with IPv4 addresses on 32-bit ARM platforms where the size of CString is smaller
I believe the correct solution is to pass the constant that was used to allocate the string buffer instead. I also added 2 tests, the IPv6 one fails using the previous code on 64-bit Ubuntu 20.04, but passes with the modified implementation of avahi_address_to_string().
windy1
commented
3 years ago
Problem:
avahi_address_snprint()takes the size in bytes of the buffer being printed into as its second argument. This library was usingstd::mem::size_of_val()on aCStringtype to pass this argument; however, that will return the size of theCStringtype, which is not necessarily the size of the underlying array that theCStringwas generated from.On 64-bit platforms the size of
CStringhappens to be 16, which fits the string representation of most IPv4 addresses, but is lower than AVAHI_ADDRESS_STR_MAX which is defined to 40. This also means:avahi_address_to_string()function will probably not work with most IPv6 addresses at allCStringis smallerI believe the correct solution is to pass the constant that was used to allocate the string buffer instead. I also added 2 tests, the IPv6 one fails using the previous code on 64-bit Ubuntu 20.04, but passes with the modified implementation of
avahi_address_to_string().