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adns is a DNS resolver library and a collection of utilities that use the
library. The adns library 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 hostname
syntax sanity checks 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.
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