1 /*
2  * nghttp2 - HTTP/2 C Library
3  *
4  * Copyright (c) 2016 Tatsuhiro Tsujikawa
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining
7  * a copy of this software and associated documentation files (the
8  * "Software"), to deal in the Software without restriction, including
9  * without limitation the rights to use, copy, modify, merge, publish,
10  * distribute, sublicense, and/or sell copies of the Software, and to
11  * permit persons to whom the Software is furnished to do so, subject to
12  * the following conditions:
13  *
14  * The above copyright notice and this permission notice shall be
15  * included in all copies or substantial portions of the Software.
16  *
17  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
18  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
19  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
20  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
21  * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
22  * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
23  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
24  */
25 #ifndef SHRPX_DNS_TRACKER_H
26 #define SHRPX_DNS_TRACKER_H
27 
28 #include "shrpx.h"
29 
30 #include <map>
31 
32 #include "shrpx_dual_dns_resolver.h"
33 
34 using namespace nghttp2;
35 
36 namespace shrpx {
37 
38 struct DNSQuery {
DNSQueryDNSQuery39   DNSQuery(StringRef host, CompleteCb cb)
40       : host(std::move(host)),
41         cb(std::move(cb)),
42         dlnext(nullptr),
43         dlprev(nullptr),
44         status(DNSResolverStatus::IDLE),
45         in_qlist(false) {}
46 
47   // Host name we lookup for.
48   StringRef host;
49   // Callback function called when name lookup finished.  This
50   // callback is not called if name lookup finishes within
51   // DNSTracker::resolve().
52   CompleteCb cb;
53   DNSQuery *dlnext, *dlprev;
54   DNSResolverStatus status;
55   // true if this object is in linked list ResolverEntry::qlist.
56   bool in_qlist;
57 };
58 
59 struct ResolverEntry {
60   // Host name this entry lookups for.
61   ImmutableString host;
62   // DNS resolver.  Only non-nullptr if status is
63   // DNSResolverStatus::RUNNING.
64   std::unique_ptr<DualDNSResolver> resolv;
65   // DNSQuery interested in this name lookup result.  The result is
66   // notified to them all.
67   DList<DNSQuery> qlist;
68   // Use the same enum with DNSResolverStatus
69   DNSResolverStatus status;
70   // result and its expiry time
71   Address result;
72   // time point when cached result expires.
73   ev_tstamp expiry;
74 };
75 
76 class DNSTracker {
77 public:
78   DNSTracker(struct ev_loop *loop);
79   ~DNSTracker();
80 
81   // Lookups host name described in |dnsq|.  If name lookup finishes
82   // within this function (either it came from /etc/hosts, host name
83   // is numeric, lookup result is cached, etc), it returns
84   // DNSResolverStatus::OK or DNSResolverStatus::ERROR.  If lookup is
85   // successful, DNSResolverStatus::OK is returned, and |result| is
86   // filled.  If lookup failed, DNSResolverStatus::ERROR is returned.
87   // If name lookup is being done background, it returns
88   // DNSResolverStatus::RUNNING.  Its completion is notified by
89   // calling dnsq->cb.
90   DNSResolverStatus resolve(Address *result, DNSQuery *dnsq);
91   // Cancels name lookup requested by |dnsq|.
92   void cancel(DNSQuery *dnsq);
93   // Removes expired entries from ents_.
94   void gc();
95   // Starts GC timer.
96   void start_gc_timer();
97 
98 private:
99   ResolverEntry make_entry(std::unique_ptr<DualDNSResolver> resolv,
100                            ImmutableString host, DNSResolverStatus status,
101                            const Address *result);
102 
103   void update_entry(ResolverEntry &ent, std::unique_ptr<DualDNSResolver> resolv,
104                     DNSResolverStatus status, const Address *result);
105 
106   void add_to_qlist(ResolverEntry &ent, DNSQuery *dnsq);
107 
108   std::map<StringRef, ResolverEntry> ents_;
109   // Periodically iterates ents_, and removes expired entries to avoid
110   // excessive use of memory.  Since only backend API can potentially
111   // increase memory consumption, interval could be very long.
112   ev_timer gc_timer_;
113   struct ev_loop *loop_;
114 };
115 
116 } // namespace shrpx
117 
118 #endif // SHRPX_DNS_TRACKER_H
119