put the evdns documentation into the header file. pathetic start of evdns manpage. a little bit

more testing and debug output for the DNS regression test.   add a BSD copyright to evdns.h with
appropriate explanations.


svn:r239

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+.\"
+.\" Copyright (c) 2006 Niels Provos <provos@citi.umich.edu>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\"
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
+.\" AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+.\" THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+.\" EXEMPLARY, OR CONSEQUENTIAL  DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+.\" PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+.\" OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+.\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+.\" ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"
+.Dd October 7, 2006
+.Dt EVDNS 3
+.Os
+.Sh NAME
+.Nm evdns_init
+.Nm evdns_shutdown
+.Nm evdns_err_to_string
+.Nm evdns_nameserver_add
+.Nm evdns_count_nameservers
+.Nm evdns_clear_nameservers_and_suspend
+.Nm evdns_resume
+.Nm evdns_nameserver_ip_add
+.Nm evdns_resolve_ipv4
+.Nm evdns_resolve_reverse
+.Nm evdns_resolv_conf_parse
+.Nm evdns_config_windows_nameservers
+.Nm evdns_search_clear
+.Nm evdns_search_add
+.Nm evdns_search_ndots_set
+.Nm evdns_set_log_fn
+.Nd asynchronous functions for DNS resolution.
+.Sh SYNOPSIS
+.Fd #include <sys/time.h>
+.Fd #include <event.h>
+.Fd #include <evdns.h>
+.Ft int
+.Fn evdns_init
+.Ft void
+.Fn evdns_shutdown "int fail_requests"
+.Ft "const char *"
+.Fn evdns_err_to_string "int err"
+.Ft int
+.Fn evdns_nameserver_add "unsigned long int address"
+.Ft int
+.Fn evdns_count_nameservers
+.Ft int
+.Fn evdns_clear_nameservers_and_suspend
+.Ft int
+.Fn evdns_resume
+.Ft int
+.Fn evdns_nameserver_ip_add(const char *ip_as_string);
+.Ft int
+.Fn evdns_resolve_ipv4 "const char *name" "int flags" "evdns_callback_type callback" "void *ptr"
+.Ft int
+.Fn evdns_resolve_reverse "struct in_addr *in" "int flags" "evdns_callback_type callback" "void *ptr"
+.Ft int
+.Fn evdns_resolv_conf_parse "int flags" "const char *"
+.Ft void
+.Fn evdns_search_clear
+.Ft void
+.Fn evdns_search_add "const char *domain"
+.Ft void
+.Fn evdns_search_ndots_set "const int ndots"
+.Ft void
+.Fn evdns_set_log_fn "evdns_debug_log_fn_type fn"
+.Ft int
+.Fn evdns_config_windows_nameservers
+.Sh DESCRIPTION
+Welcome, gentle reader
+.Pp
+Async DNS lookups are really a whole lot harder than they should be,
+mostly stemming from the fact that the libc resolver has never been
+very good at them. Before you use this library you should see if libc
+can do the job for you with the modern async call getaddrinfo_a
+(see http://www.imperialviolet.org/page25.html#e498). Otherwise,
+please continue.
+.Pp
+This code is based on libevent and you must call event_init before
+any of the APIs in this file. You must also seed the OpenSSL random
+source if you are using OpenSSL for ids (see below).
+.Pp
+This library is designed to be included and shipped with your source
+code. You statically link with it. You should also test for the
+existence of strtok_r and define HAVE_STRTOK_R if you have it.
+.Pp
+The DNS protocol requires a good source of id numbers and these
+numbers should be unpredictable for spoofing reasons. There are
+three methods for generating them here and you must define exactly
+one of them. In increasing order of preference:
+.Pp
+DNS_USE_GETTIMEOFDAY_FOR_ID:
+  Using the bottom 16 bits of the usec result from gettimeofday. This
+  is a pretty poor solution but should work anywhere.
+DNS_USE_CPU_CLOCK_FOR_ID:
+  Using the bottom 16 bits of the nsec result from the CPU's time
+  counter. This is better, but may not work everywhere. Requires
+  POSIX realtime support and you'll need to link against -lrt on
+  glibc systems at least.
+DNS_USE_OPENSSL_FOR_ID:
+  Uses the OpenSSL RAND_bytes call to generate the data. You must
+  have seeded the pool before making any calls to this library.
+.Pp
+The library keeps track of the state of nameservers and will avoid
+them when they go down. Otherwise it will round robin between them.
+.Pp
+Quick start guide:
+  #include "evdns.h"
+  void callback(int result, char type, int count, int ttl,
+	 void *addresses, void *arg);
+  evdns_resolv_conf_parse(DNS_OPTIONS_ALL, "/etc/resolv.conf");
+  evdns_resolve("www.hostname.com", 0, callback, NULL);
+.Pp
+When the lookup is complete the callback function is called. The
+first argument will be one of the DNS_ERR_* defines in evdns.h.
+Hopefully it will be DNS_ERR_NONE, in which case type will be
+DNS_IPv4_A, count will be the number of IP addresses, ttl is the time
+which the data can be cached for (in seconds), addresses will point
+to an array of uint32_t's and arg will be whatever you passed to
+evdns_resolve.
+.Pp
+Searching:
+.Pp
+In order for this library to be a good replacement for glibc's resolver it
+supports searching. This involves setting a list of default domains, in
+which names will be queried for. The number of dots in the query name
+determines the order in which this list is used.
+.Pp
+Searching appears to be a single lookup from the point of view of the API,
+although many DNS queries may be generated from a single call to
+evdns_resolve. Searching can also drastically slow down the resolution
+of names.
+.Pp
+To disable searching:
+  1. Never set it up. If you never call evdns_resolv_conf_parse or
+  evdns_search_add then no searching will occur.
+.Pp
+  2. If you do call evdns_resolv_conf_parse then don't pass
+  DNS_OPTION_SEARCH (or DNS_OPTIONS_ALL, which implies it).
+.Pp
+  3. When calling evdns_resolve, pass the DNS_QUERY_NO_SEARCH flag.
+.Pp
+The order of searches depends on the number of dots in the name. If the
+number is greater than the ndots setting then the names is first tried
+globally. Otherwise each search domain is appended in turn.
+.Pp
+The ndots setting can either be set from a resolv.conf, or by calling
+evdns_search_ndots_set.
+.Pp
+For example, with ndots set to 1 (the default) and a search domain list of
+["myhome.net"]:
+ Query: www
+ Order: www.myhome.net, www.
+.Pp
+ Query: www.abc
+ Order: www.abc., www.abc.myhome.net
+.Pp
+API reference:
+.Pp
+int evdns_nameserver_add(unsigned long int address)
+  Add a nameserver. The address should be an IP address in
+  network byte order. The type of address is chosen so that
+  it matches in_addr.s_addr.
+  Returns non-zero on error.
+.Pp
+int evdns_nameserver_ip_add(const char *ip_as_string)
+  This wraps the above function by parsing a string as an IP
+  address and adds it as a nameserver.
+  Returns non-zero on error
+.Pp
+int evdns_resolve(const char *name, int flags,
+	      evdns_callback_type callback,
+	      void *ptr)
+  Resolve a name. The name parameter should be a DNS name.
+  The flags parameter should be 0, or DNS_QUERY_NO_SEARCH
+  which disables searching for this query. (see defn of
+  searching above).
+.Pp
+  The callback argument is a function which is called when
+  this query completes and ptr is an argument which is passed
+  to that callback function.
+.Pp
+  Returns non-zero on error
+.Pp
+void evdns_search_clear()
+  Clears the list of search domains
+.Pp
+void evdns_search_add(const char *domain)
+  Add a domain to the list of search domains
+.Pp
+void evdns_search_ndots_set(int ndots)
+  Set the number of dots which, when found in a name, causes
+  the first query to be without any search domain.
+.Pp
+int evdns_count_nameservers(void)
+  Return the number of configured nameservers (not necessarily the
+  number of running nameservers).  This is useful for double-checking
+  whether our calls to the various nameserver configuration functions
+  have been successful.
+.Pp
+int evdns_clear_nameservers_and_suspend(void)
+  Remove all currently configured nameservers, and suspend all pending
+  resolves.  Resolves will not necessarily be re-attempted until
+  evdns_resume() is called.
+.Pp
+int evdns_resume(void)
+  Re-attempt resolves left in limbo after an earlier call to
+  evdns_clear_nameservers_and_suspend().
+.Pp
+int evdns_config_windows_nameservers(void)
+  Attempt to configure a set of nameservers based on platform settings on
+  a win32 host.  Preferentially tries to use GetNetworkParams; if that fails,
+  looks in the registry.  Returns 0 on success, nonzero on failure.
+.Pp
+int evdns_resolv_conf_parse(int flags, const char *filename)
+  Parse a resolv.conf like file from the given filename.
+.Pp
+  See the man page for resolv.conf for the format of this file.
+  The flags argument determines what information is parsed from
+  this file:
+    DNS_OPTION_SEARCH - domain, search and ndots options
+    DNS_OPTION_NAMESERVERS - nameserver lines
+    DNS_OPTION_MISC - timeout and attempts options
+    DNS_OPTIONS_ALL - all of the above
+  The following directives are not parsed from the file:
+    sortlist, rotate, no-check-names, inet6, debug
+.Pp
+  Returns non-zero on error:
+   0 no errors
+   1 failed to open file
+   2 failed to stat file
+   3 file too large
+   4 out of memory
+   5 short read from file
+.Pp
+Internals:
+.Pp
+Requests are kept in two queues. The first is the inflight queue. In
+this queue requests have an allocated transaction id and nameserver.
+They will soon be transmitted if they haven't already been.
+.Pp
+The second is the waiting queue. The size of the inflight ring is
+limited and all other requests wait in waiting queue for space. This
+bounds the number of concurrent requests so that we don't flood the
+nameserver. Several algorithms require a full walk of the inflight
+queue and so bounding its size keeps thing going nicely under huge
+(many thousands of requests) loads.
+.Pp
+If a nameserver loses too many requests it is considered down and we
+try not to use it. After a while we send a probe to that nameserver
+(a lookup for google.com) and, if it replies, we consider it working
+again. If the nameserver fails a probe we wait longer to try again
+with the next probe.
+.Sh SEE ALSO
+.Xr event 3 ,
+.Xr gethostbyname 3 ,
+.Xr resolv.conf 5
+.Sh HISTORY
+The
+.Nm evdns
+API was developed by Adam Langley on top of the
+.Nm libevent
+API.
+The code was integrate into
+.Nm Tor
+by Nick Mathewson and finally put into
+.Nm libevent
+itself by Niels Provos.
+.Sh AUTHORS
+The
+.Nm evdns
+API and code was written by Adam Langley with significant
+contributions by Nick Mathewson.
+.Sh BUGS
+This documentation is neither complete nor authoritative.
+If you are in doubt about the usage of this API then
+check the source code to find out how it works, write
+up the missing piece of documentation and send it to
+me for inclusion in this man page.