adns is a resolver library for C (and C++) programs. In contrast with the existing interfaces, gethostbyname et al and libresolv, it has the following features:
- It is reasonably easy to use for simple programs which just want to translate names to addresses, look up MX records, etc.
- It can be used in an asynchronous, non-blocking, manner. Many queries can be handled simultaneously.
- Responses are decoded automatically into a natural representation for a C program - there is no need to deal with DNS packet formats.
- Sanity checking (eg, name syntax checking, reverse/forward correspondence, CNAME pointing to CNAME) is performed automatically.
- Time-to-live, CNAME and other similar information is returned in an easy-to-use form, without getting in the way.
- There is no global state in the library; resolver state is an opaque data structure which the client creates explicitly. A program can have several instances of the resolver.
- Errors are reported to the application in a way that distinguishes the various causes of failure properly.
- Understands conventional resolv.conf, but this can overridden by environment variables.
- Flexibility. For example, the application can tell adns to: ignore environment variables (for setuid programs), disable sanity checks eg to return arbitrary data, override or ignore resolv.conf in favour of supplied configuration, etc.
- Believed to be correct ! For example, will correctly back off to TCP in case of long replies or queries, or to other nameservers if several are available. It has sensible handling of bad responses etc.
The library is available as 32-bit and 64-bit:
- If you are compiling a 32-bit program, no special compiler options are needed.
- If you are compiling a 64-bit program, you have to compile and link your application with "cc -q64" or "gcc -maix64".