ASCIIBytesToPrintString converts the buffer b to the closest ASCII string equivalent, substituting '*' for unprintable characters.
CtIsZero returns true iff the buffer b is all 0x00, doing the check in constant time.
EnsureAddrIPPort returns nil iff the address is a raw IP + Port combination.
ExplicitBzero explicitly clears out the buffer b, by filling it with 0x00 bytes.
GetExternalIPv4Address attempts to guess an external IPv4 address by interface enumeration.
MkDataDir creates a data directory of appropriate (paranoid) permissions if it does not exist, and validates that existing directories have the intended permissions if it does exist.