1This is ares, an asynchronous resolver library. It is intended for 2applications which need to perform DNS queries without blocking, or 3need to perform multiple DNS queries in parallel. The primary 4examples of such applications are servers which communicate with 5multiple clients and programs with graphical user interfaces. 6 7This library implementation is not especially portable to crufty old 8systems like SunOS 4. It assumes a compiler which can handle ANSI C 9syntax, a system malloc which properly handles realloc(NULL, foo) and 10free(NULL), and a reasonably up-to-date <arpa/nameser.h>. 11 12I have attempted to preserve the externally visible behavior of the 13BIND resolver in nearly all respects. The API of the library is, of 14course, very different from the synchronous BIND API; instead of 15invoking a function like res_send() and getting a return value back 16indicating the number of bytes in the response, you invoke a function 17like ares_send() and give it a callback function to invoke when the 18response arrives. You then have to select() on the file descriptors 19indicated by ares_fds(), with a timeout given by ares_timeout(). You 20call ares_process() when select() returns. 21 22Some features are missing from the current version of ares, relative 23to the BIND resolver: 24 25 * There is no IPV6 support. 26 * There is no hostname verification. 27 * There is no logging of unexpected events. 28 * There is no debugging-oriented logging. 29 * There is no YP support. 30 31libares requires an ANSI compiler to compile and use. To build the 32library, just run "./configure" and "make". To install it, run "make 33install". Run "./configure --help" to see a list of options you can 34provide to configure to change how the library builds. libares has no 35data files, so you can move the include file and library around freely 36without leaving behind any dependencies on old paths. Building the 37library will also build the "adig" program, a little toy for trying 38out the library. It doesn't get installed. 39 40libares is distributed at athena-dist.mit.edu:pub/ATHENA/ares. Please 41send bug reports and comments to ghudson@mit.edu. 42