DNSClient: own requests, and cancel them on timeout

Fixes crashes where a request times-out, but then is completed by
UDN sometime afterwards, with a free-d object. Have the DNS::Client own
requests, and be able to retrieve the udns_query to cancel them, in 
the timeout case.

Fixes a couple of Sentry reports.

simgear/io/DNSClient.cxx

@@ -61,6 +61,10 @@ public:
 
     struct dns_ctx * ctx;
     static size_t instanceCounter;
+
+    using RequestVec = std::vector<Request_ptr>;
+
+    RequestVec _activeRequests;
 };
 
 size_t Client::ClientPrivate::instanceCounter = 0;
@@ -78,6 +82,11 @@ Request::~Request()
 {
 }
 
+void Request::cancel()
+{
+    _cancelled = true;
+}
+
 bool Request::isTimeout() const
 {
     return (time(NULL) - _start) > _timeout_secs;
@@ -114,6 +123,7 @@ static void dnscbSRV(struct dns_ctx *ctx, struct dns_rr_srv *result, void *data)
 {
     SRVRequest * r = static_cast<SRVRequest*>(data);
     if (result) {
+        if (!r->isCancelled()) {
             r->cname = result->dnssrv_cname;
             r->qname = result->dnssrv_qname;
             r->ttl = result->dnssrv_ttl;
@@ -126,6 +136,7 @@ static void dnscbSRV(struct dns_ctx *ctx, struct dns_rr_srv *result, void *data)
                 srv->target = result->dnssrv_srv[i].name;
             }
             std::sort(r->entries.begin(), r->entries.end(), sortSRV);
+        }
         free(result);
     }
     r->setComplete();
@@ -134,11 +145,16 @@ static void dnscbSRV(struct dns_ctx *ctx, struct dns_rr_srv *result, void *data)
 void SRVRequest::submit( Client * client )
 {
     // if service is defined, pass service and protocol
-    if (!dns_submit_srv(client->d->ctx, getDn().c_str(), _service.empty() ? NULL : _service.c_str(), _service.empty() ? NULL : _protocol.c_str(), 0, dnscbSRV, this )) {
+    auto q = dns_submit_srv(client->d->ctx, getDn().c_str(), _service.empty() ? NULL : _service.c_str(),
+                            _service.empty() ? NULL : _protocol.c_str(),
+                            0, dnscbSRV, this);
+
+    if (!q) {
         SG_LOG(SG_IO, SG_ALERT, "Can't submit dns request for " << getDn());
         return;
     }
     _start = time(NULL);
+    _query = q;
 }
 
 TXTRequest::TXTRequest( const std::string & dn ) :
@@ -151,6 +167,7 @@ static void dnscbTXT(struct dns_ctx *ctx, struct dns_rr_txt *result, void *data)
 {
     TXTRequest * r = static_cast<TXTRequest*>(data);
     if (result) {
+        if (!r->isCancelled()) {
             r->cname = result->dnstxt_cname;
             r->qname = result->dnstxt_qname;
             r->ttl = result->dnstxt_ttl;
@@ -168,6 +185,7 @@ static void dnscbTXT(struct dns_ctx *ctx, struct dns_rr_txt *result, void *data)
                     r->attributes[tokens[0]] = tokens[1];
                 }
             }
+        }
         free(result);
     }
     r->setComplete();
@@ -176,11 +194,13 @@ static void dnscbTXT(struct dns_ctx *ctx, struct dns_rr_txt *result, void *data)
 void TXTRequest::submit( Client * client )
 {
     // protocol and service an already encoded in DN so pass in NULL for both
-    if (!dns_submit_txt(client->d->ctx, getDn().c_str(), DNS_C_IN, 0, dnscbTXT, this )) {
+    auto q = dns_submit_txt(client->d->ctx, getDn().c_str(), DNS_C_IN, 0, dnscbTXT, this);
+    if (!q) {
         SG_LOG(SG_IO, SG_ALERT, "Can't submit dns request for " << getDn());
         return;
     }
     _start = time(NULL);
+    _query = q;
 }
 
 
@@ -195,6 +215,7 @@ static void dnscbNAPTR(struct dns_ctx *ctx, struct dns_rr_naptr *result, void *d
 {
     NAPTRRequest * r = static_cast<NAPTRRequest*>(data);
     if (result) {
+        if (!r->isCancelled()) {
             r->cname = result->dnsnaptr_cname;
             r->qname = result->dnsnaptr_qname;
             r->ttl = result->dnsnaptr_ttl;
@@ -216,6 +237,7 @@ static void dnscbNAPTR(struct dns_ctx *ctx, struct dns_rr_naptr *result, void *d
                 naptr->replacement = result->dnsnaptr_naptr[i].replacement;
             }
             std::sort(r->entries.begin(), r->entries.end(), sortNAPTR);
+        }
         free(result);
     }
     r->setComplete();
@@ -223,11 +245,13 @@ static void dnscbNAPTR(struct dns_ctx *ctx, struct dns_rr_naptr *result, void *d
 
 void NAPTRRequest::submit( Client * client )
 {
-    if (!dns_submit_naptr(client->d->ctx, getDn().c_str(), 0, dnscbNAPTR, this )) {
+    auto q = dns_submit_naptr(client->d->ctx, getDn().c_str(), 0, dnscbNAPTR, this);
+    if (!q) {
         SG_LOG(SG_IO, SG_ALERT, "Can't submit dns request for " << getDn());
         return;
     }
     _start = time(NULL);
+    _query = q;
 }
 
 
@@ -242,6 +266,7 @@ Client::Client() :
 
 void Client::makeRequest(const Request_ptr& r)
 {
+    d->_activeRequests.push_back(r);
     r->submit(this);
 }
 
@@ -252,6 +277,19 @@ void Client::update(int waitTimeout)
         return;
 
     dns_ioevent(d->ctx, now);
+
+    // drop our owning ref to completed requests,
+    // and cancel any which timed out
+    auto it = std::remove_if(d->_activeRequests.begin(), d->_activeRequests.end(),
+                             [this](const Request_ptr& r) {
+                                 if (r->isTimeout()) {
+                                     dns_cancel(d->ctx, reinterpret_cast<struct dns_query*>(r->_query));
+                                     return true;
+                                 }
+
+                                 return r->isComplete();
+                             });
+    d->_activeRequests.erase(it, d->_activeRequests.end());
 }
 
 } // of namespace DNS

simgear/io/DNSClient.hxx

@@ -40,28 +40,38 @@ namespace DNS
 {
 
 class Client;
+
+using UDNSQueryPtr = void*;
+
 class Request : public SGReferenced
 {
 public:
     Request( const std::string & dn );
     virtual ~Request();
-    std::string getDn() const { return _dn; }
+    const std::string& getDn() const { return _dn; }
     int getType() const { return _type; }
     bool isComplete() const { return _complete; }
     bool isTimeout() const;
     void setComplete( bool b = true ) { _complete = b; }
+    bool isCancelled() const { return _cancelled; }
 
     virtual void submit( Client * client) = 0;
 
+    void cancel();
+
     std::string cname;
     std::string qname;
     unsigned ttl;
 protected:
+    friend class Client;
+
+    UDNSQueryPtr _query = nullptr;
     std::string _dn;
     int _type;
     bool _complete;
     time_t _timeout_secs;
     time_t _start;
+    bool _cancelled = false;
 };
 typedef SGSharedPtr<Request> Request_ptr;
 
@@ -69,7 +79,7 @@ class NAPTRRequest : public Request
 {
 public:
     NAPTRRequest( const std::string & dn );
-    virtual void submit( Client * client );
+    void submit(Client* client) override;
 
     struct NAPTR : SGReferenced {
         int order;
@@ -92,7 +102,7 @@ class SRVRequest : public Request
 public:
     SRVRequest( const std::string & dn );
     SRVRequest( const std::string & dn, const string & service, const string & protocol );
-    virtual void submit( Client * client );
+    void submit(Client* client) override;
 
     struct SRV : SGReferenced {
       int priority;
@@ -112,7 +122,7 @@ class TXTRequest : public Request
 {
 public:
     TXTRequest( const std::string & dn );
-    virtual void submit( Client * client );
+    void submit(Client* client) override;
 
     typedef std::vector<string> TXT_list;
     typedef std::map<std::string,std::string> TXT_Attribute_map;