Introduce ares_dup(3) and new thoughts about API/ABI and how to move forwards.

Also discussed on the ml.

CHANGES

@@ -1,5 +1,39 @@
   Changelog for the c-ares project
 
+* Dec 3 2008 (Daniel Stenberg)
+
+  API changes:
+
+  I made sure the public ares_config struct looks like before and yet it
+  supports the ROTATE option thanks to c-ares now storing the "optmask"
+  internally. Thus we should be ABI compatible with the past release(s)
+  now. My efforts mentioned below should not break backwards ABI compliance.
+
+  Here's how I suggest we proceed with the API:
+
+  ares_init() will be primary "channel creator" function.
+
+  ares_init_options() will continue to work exactly like now and before. For
+  starters, it will be the (only) way to set the existing options.
+
+  ares_save_options() will continue to work like today, but will ONLY save
+  options that you can set today (including ARES_OPT_ROTATE actually) but new
+  options that we add may not be saved with this.
+
+  Instead we introduce:
+
+  ares_dup() that instead can make a new channel and clone the config used
+  from an existing channel. It will then clone all config options, including
+  future new things we add.
+
+  ares_set_*() style functions that set (new) config options. As a start we
+  simply add these for new functionality, but over time we can also introduce
+  them for existing "struct ares_options" so that we can eventually deprecate
+  the two ares_*_options() functions.
+
+  ares_get_*() style functions for extracting info from a channel handle that
+  should be used instead of ares_save_options().
+
 * Nov 26 2008 (Yang Tse)
 - Brad Spencer provided changes to allow buildconf to work on OS X.
 

Makefile.inc

@@ -18,5 +18,5 @@ MANPAGES= ares_destroy.3 ares_expand_name.3 ares_expand_string.3 ares_fds.3 \
  ares_parse_a_reply.3 ares_parse_ptr_reply.3 ares_process.3		    \
  ares_query.3 ares_search.3 ares_send.3 ares_strerror.3 ares_timeout.3	    \
  ares_version.3 ares_cancel.3 ares_parse_aaaa_reply.3 ares_getnameinfo.3    \
- ares_getsock.3 ares_parse_ns_reply.3 \
+ ares_getsock.3 ares_parse_ns_reply.3 ares_dup.3 \
  ares_destroy_options.3 ares_save_options.3 ares_gethostbyname_file.3

ares.h

@@ -1,7 +1,7 @@
 /* $Id$ */
 
 /* Copyright 1998 by the Massachusetts Institute of Technology.
- * Copyright (C) 2007 by Daniel Stenberg
+ * Copyright (C) 2007-2008 by Daniel Stenberg
  *
  * Permission to use, copy, modify, and distribute this
  * software and its documentation for any purpose and without
@@ -180,6 +180,26 @@ typedef void (*ares_sock_state_cb)(void *data,
 
 struct apattern;
 
+/* NOTE about the ares_options struct to users and developers.
+
+   This struct will remain looking like this. It will not be extended nor
+   shrunk in future releases, but all new options will be set by ares_set_*()
+   options instead of with the ares_init_options() function.
+
+   Eventually (in a galaxy far far away), all options will be settable by
+   ares_set_*() options and the ares_init_options() function will become
+   deprecated.
+
+   ares_save_options() is considered deprecated as of right now. Use ares_dup()
+   instead!
+
+   So, if new options are added they are not added to this struct. And they
+   are not "saved" with the ares_save_options() function but instead we
+   encourage the use of the ares_dup() function. Needless to say, if you add
+   config options to c-ares you need to make sure ares_dup() duplicates this
+   new option.
+
+ */
 struct ares_options {
   int flags;
   int timeout; /* in seconds or milliseconds, depending on options */
@@ -215,8 +235,10 @@ typedef void (*ares_nameinfo_callback)(void *arg, int status, int timeouts,
 int ares_init(ares_channel *channelptr);
 int ares_init_options(ares_channel *channelptr, struct ares_options *options,
                       int optmask);
-int ares_save_options(ares_channel channel, struct ares_options *options, int *optmask);
+int ares_save_options(ares_channel channel, struct ares_options *options,
+                      int *optmask);
 void ares_destroy_options(struct ares_options *options);
+int ares_dup(ares_channel *dest, ares_channel src);
 void ares_destroy(ares_channel channel);
 void ares_cancel(ares_channel channel);
 void ares_send(ares_channel channel, const unsigned char *qbuf, int qlen,

ares_dup.3

@@ -0,0 +1,43 @@
+.\" $Id$
+.\"
+.\" Copyright (C) 2007-2008 by Daniel Stenberg
+.\"
+.\" Permission to use, copy, modify, and distribute this
+.\" software and its documentation for any purpose and without
+.\" fee is hereby granted, provided that the above copyright
+.\" notice appear in all copies and that both that copyright
+.\" notice and this permission notice appear in supporting
+.\" documentation, and that the name of M.I.T. not be used in
+.\" advertising or publicity pertaining to distribution of the
+.\" software without specific, written prior permission.
+.\" M.I.T. makes no representations about the suitability of
+.\" this software for any purpose.  It is provided "as is"
+.\" without express or implied warranty.
+.\"
+.TH ARES_DUP 3 "2 Dec 2008"
+.SH NAME
+ares_dup \- Duplicate a resolver channel
+.SH SYNOPSIS
+.nf
+.B #include <ares.h>
+.PP
+.B int ares_dup(ares_channel *\fIchannel\fP, ares_channel \fIsource\fP)
+.fi
+.SH DESCRIPTION
+The \fBares_dup(3)\fP function duplicates an existing communications channel
+for name service lookups.  If it returns successfully, \fBares_dup(3)\fP will
+set the variable pointed to by \fIchannel\fP to a handle used to identify the
+name service channel.  The caller should invoke \fIares_destroy(3)\fP on the
+handle when the channel is no longer needed.
+
+The \fBares_dup_options\fP function also initializes a name service channel,
+with additional options set exactly as the \fIsource\fP channel has them
+configured.
+.SH SEE ALSO
+.BR ares_destroy(3),
+.BR ares_init(3)
+.SH AVAILABILITY
+ares_dup(3) was added in c-ares 1.6.0
+.SH AUTHOR
+Daniel Stenberg
+

ares_init.3

@@ -185,7 +185,8 @@ A configuration file could not be read.
 .B ARES_ENOMEM
 The process's available memory was exhausted.
 .SH SEE ALSO
-.BR ares_destroy (3)
+.BR ares_destroy(3),
+.BR ares_dup(3)
 .SH AUTHOR
 Greg Hudson, MIT Information Systems
 .br

ares_init.c

@@ -257,6 +257,39 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
   return ARES_SUCCESS;
 }
 
+/* ares_dup() duplicates a channel handle with all its options and returns a
+   new channel handle */
+int ares_dup(ares_channel *dest, ares_channel src)
+{
+  struct ares_options opts;
+  int rc;
+  int optmask;
+
+  *dest = NULL; /* in case of failure return NULL explicitly */
+
+  /* First get the options supported by the old ares_save_options() function,
+     which is most of them */
+  rc = ares_save_options(src, &opts, &optmask);
+  if(rc)
+    return rc;
+
+  /* Then create the new channel with those options */
+  rc = ares_init_options(dest, &opts, optmask);
+
+  /* destroy the options copy to not leak any memory */
+  ares_destroy_options(&opts);
+
+  if(rc)
+    return rc;
+
+  /* Now clone the options that ares_save_options() doesn't support. */
+
+  /* No such options available yet */
+
+  return ARES_SUCCESS; /* everything went fine */
+
+}
+
 /* Save options from initialized channel */
 int ares_save_options(ares_channel channel, struct ares_options *options,
                       int *optmask)

ares_save_options.3

@@ -24,9 +24,7 @@ ares_save_options \- Save configuration values obtained from initialized ares_ch
 .B void ares_save_options(ares_channel \fIchannel\fP, struct ares_options *\fIoptions\fP, int *\fIoptmask\fP)
 .fi
 .SH DESCRIPTION
-The
-.B ares_save_options
-function saves the channel data identified by
+The \fBares_save_options(3)\fP function saves the channel data identified by
 .IR channel ,
 into the options struct identified by
 .IR options ,
@@ -38,11 +36,18 @@ The resultant options and optmask are then able to be
 passed directly to ares_init_options.  When the options
 are no longer needed, ares_destroy_options should be called
 to free any associated memory.
-
-
+.SH NOTE
+Since c-ares 1.6.0 the ares_options struct has been "locked" meaning that it
+won't be extended to cover new funtions. This function will remain
+functioning, but it can only return config data that can be represented in
+this config struct, which may no longer be the complete set of config
+options. \fBares_dup(3)\fP will not have that restriction.
 .SH SEE ALSO
 .BR ares_destroy_options (3),
-.BR ares_init_options (3)
+.BR ares_init_options (3),
+.BR ares_dup (3)
+.SH AVAILABILITY
+ares_save_options(3) was added in c-ares 1.4.0
 .SH AUTHOR
 Brad House
 .br