struct addrinfo* res = nullptr;
auto ret = getaddrinfo(name.c_str(), nullptr, &hints, &res);
- // We pick the first address returned for now
+ // We pick the first address returned for now.
+ // XXX This might trigger unwanted "changes detected "if the sort order varies
if (ret == 0) {
auto address = ComboAddress{res->ai_addr, res->ai_addrlen};
freeaddrinfo(res);
return answer;
}
+// do a id.server/CH/TXT query
std::string serverID()
{
auto buffer = resolve("id.server", QClass::CHAOS, QType::TXT);
bool pdns::RecResolve::refresh(time_t now)
{
- // The refrsh taks shol dnot take the lock for a long time, so we're working on a copy
+ // The refresh task should not take the lock for a long time, so we're working on a copy
ResolveData copy;
{
auto data = d_data.lock();
log->error(Logr::Error, "Name did not resolve", "name", Logging::Loggable(entry.first));
}
if (newAddress != entry.second.d_address) {
- log->info(Logr::Debug, "Name resolved to new address", "name", Logging::Loggable(entry.first),
+ log->info(Logr::Debug, "Name resolved to new address",
+ "name", Logging::Loggable(entry.first),
"address", Logging::Loggable(newAddress.toString()));
// An address changed
updated = true;
#include "iputils.hh"
#include "lock.hh"
+/************************************************************************************************
+The pdns::RecResove class implements a facility to use the system configured resolver. At the moment
+of writing, this can only be used to configure forwarding by name instead of IP.
+ ************************************************************************************************/
+
+/************************************************************************************************
+DESIGN CONSIDERATIONS
+
+- all names looked up with lookupAndRegister() will be entered into a table.
+
+- the names in the table will ber periodically checked by a refresh thread. Set the period (before
+ starting to use the system resolver) by calling pdbs::RecResolve::setInstanceParameters().
+
+- if *a* name resolves to a different result than stored, we will call the callback. Curently this is
+ used to call the equivalent of rec_control reload-zones
+
+- A manual rec_control reload-zones will *also* flush the existng table before doing the reload, so
+ we force a re-resolve all names. See
+ rec_channel_rec.cc:reloadZoneConfigurationWithSysResolveReset()
+
+**************************************************************************************************/
+
+/************************************************************************************************
+PRACTICAL CONSIDERATIONS/IMPLEMENTATION LIMITS
+
+- Currently the facility is *only* used by the forwarding code
+
+- We resolve with AI_ADDRCONFIG, the address families enabled will depend on the network config
+ of the machine
+
+- We pick the first adress that getaddrinfo() produced. Currently no handling of multiple addresses
+ and/or multiple address famailies.
+
+- There is a check to detect *some* cases of self-resolve. This is done by resolving
+ id.server/CH/TXT and comparing the result to the system-id set. Both false positives and false
+ negatives can occur.
+
+**************************************************************************************************/
namespace pdns
{
class RecResolve
public:
// Should be called before any getInstance() call is done
static void setInstanceParameters(std::string serverID, time_t ttl, const std::function<void()>& callback);
+ // Get "the" instance of the system resolver.
static RecResolve& getInstance();
RecResolve(time_t ttl = 60, const std::function<void()>& callback = nullptr);
~RecResolve();
+ // Lookup a name and register it in the names to be checked if not already there
ComboAddress lookupAndRegister(const std::string& name, time_t now);
+ // Lookup a name which must be already registered
ComboAddress lookup(const std::string& name);
+
+ // When an instance is created, it will runn a refresh thread, stop it wit this method
void stopRefresher();
+ // And restart it again
void startRefresher();
+ // Wipe one or all names
void wipe(const std::string& name = "");
- bool refresh(time_t now);
+ // Did we se a cahnage? Calling this functino will reset the flag.
bool changeDetected();
private:
+ bool refresh(time_t now);
struct AddressData
{
ComboAddress d_address;
LockGuarded<ResolveData> d_data;
const time_t d_ttl;
+ // This private class impements the refresher thread
class Refresher
{
public:
'default' : '0',
'help' : 'Set TTL of system resolver feature, 0 (default) is disabled',
'doc' : '''
-Sets TTL of the system resolver feature. This allows names to be used in the config in forwarding targets.
+Sets TTL in seconds of the system resolver feature.
+This allows names to be used in the config in forwarding targets.
+The TTL is used as a check interval to see if the names used in forwarding resolve to a different address than before.
+If that happens, the forward configuration is reloaded.
Make sure the recursor itself is not used by the system resolver! Default is 0 (not enabled).
+A suggested value is 60.
''',
'versionadded': '5.1.0'
},
projects / thirdparty / pdns.git / commitdiff
