Re-link peers by IP when dnsmgr changes the IP

Asterisk's dnsmgr currently takes a pointer to an ast_sockaddr and updates it
anytime an address resolves to something different. There are a couple of
issues with this. First, the ast_sockaddr is usually the address of an
ast_sockaddr inside a refcounted struct and we never bump the refcount of those
structs when using dnsmgr. This makes it possible that a refresh could happen
after the destructor for that object is called (despite ast_dnsmgr_release
being called in that destructor). Second, the module using dnsmgr cannot be
aware of an address changing without polling for it in the code. If an action
needs to be taken on address update (like re-linking a SIP peer in the
peers_by_ip table), then polling for this change negates many of the benefits
of having dnsmgr in the first place.

This patch adds a function to the dnsmgr API that calls an update callback
instead of blindly updating the address itself. It also moves calls to
ast_dnsmgr_release outside of the destructor functions and into cleanup
functions that are called when we no longer need the objects and increments the
refcount of the objects using dnsmgr since those objects are stored on the
ast_dnsmgr_entry struct. A helper function for returning the proper default SIP
port (non-tls vs tls) is also added and used.

This patch also incorporates changes from a patch posted by Timo Teräs to
ASTERISK-19106 for related dnsmgr issues.

(closes issue ASTERISK-19106)

Review: https://reviewboard.asterisk.org/r/1691/
........

Merged revisions 353371 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 353397 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@353418 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 27 insertions, 0 deletions

diff --git a/include/asterisk/dnsmgr.h b/include/asterisk/dnsmgr.h
index b62c2a14b..07d6268ba 100644
--- a/include/asterisk/dnsmgr.h
+++ b/include/asterisk/dnsmgr.h
@@ -37,6 +37,8 @@ extern "C" {
  */
 struct ast_dnsmgr_entry;
 
+typedef void (*dns_update_func)(struct ast_sockaddr *old_addr, struct ast_sockaddr *new_addr, void *data);
+
 /*!
  * \brief Allocate a new DNS manager entry
  *
@@ -105,6 +107,31 @@ void ast_dnsmgr_release(struct ast_dnsmgr_entry *entry);
 int ast_dnsmgr_lookup(const char *name, struct ast_sockaddr *result, struct ast_dnsmgr_entry **dnsmgr, const char *service);
 
 /*!
+ * \brief Allocate and initialize a DNS manager entry, with update callback
+ *
+ * \param name the hostname
+ * \param result The addr which is intended to be updated in the update callback when DNS manager calls it on refresh.
+ * The address family is used as an input parameter to filter the returned addresses.
+ * If it is 0, both IPv4 and IPv6 addresses can be returned.
+ * \param dnsmgr Where to store the allocate DNS manager entry
+ * \param service
+ * \param func The update callback function
+ * The update callback will be called when DNS manager detects that an IP address has been changed.
+ * Instead of updating the addr itself, DNS manager will call this callback function with the old
+ * and new addresses. It is the responsibility of the callback to perform any updates
+ * \param data A pointer to data that will be passed through to the callback function
+ *
+ * \note
+ * This function allocates a new DNS manager entry object, and fills it with
+ * the provided hostname and IP address.  This function _does_ force an initial
+ * lookup, so it may block for some period of time.
+ *
+ * \retval 0 success
+ * \retval non-zero failure
+ */
+int ast_dnsmgr_lookup_cb(const char *name, struct ast_sockaddr *result, struct ast_dnsmgr_entry **dnsmgr, const char *service, dns_update_func func, void *data);
+
+/*!
  * \brief Force a refresh of a dnsmgr entry
  *
  * \retval non-zero if the result is different than the previous result