From ea38df2c2888c55feea7383af7f7913d2e6d2481 Mon Sep 17 00:00:00 2001
From: Arthur Passos <arthur.ti@outlook.com>
Date: Thu, 26 Jan 2023 13:54:12 -0300
Subject: [PATCH] add comments to the code

---
 src/Common/CaresPTRResolver.cpp | 32 +++++++++++++++++---------------
 src/Common/CaresPTRResolver.h   |  5 ++++-
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/src/Common/CaresPTRResolver.cpp b/src/Common/CaresPTRResolver.cpp
index 31edd3beb0d..600ddf44694 100644
--- a/src/Common/CaresPTRResolver.cpp
+++ b/src/Common/CaresPTRResolver.cpp
@@ -82,7 +82,7 @@ namespace DB
 
         resolve(ip, ptr_records);
 
-        if (!wait())
+        if (!wait_and_process())
         {
             cancel_requests();
             throw DB::Exception("Failed to complete reverse DNS query for IP " + ip, DB::ErrorCodes::DNS_ERROR);
@@ -99,7 +99,7 @@ namespace DB
 
         resolve_v6(ip, ptr_records);
 
-        if (!wait())
+        if (!wait_and_process())
         {
             cancel_requests();
             throw DB::Exception("Failed to complete reverse DNS query for IP " + ip, DB::ErrorCodes::DNS_ERROR);
@@ -125,7 +125,7 @@ namespace DB
         ares_gethostbyaddr(channel, reinterpret_cast<const void*>(&addr), sizeof(addr), AF_INET6, callback, &response);
     }
 
-    bool CaresPTRResolver::wait()
+    bool CaresPTRResolver::wait_and_process()
     {
         int sockets[ARES_GETSOCK_MAXNUM];
         pollfd pollfd[ARES_GETSOCK_MAXNUM];
@@ -140,17 +140,19 @@ namespace DB
             {
                 number_of_fds_ready = poll(readable_sockets.data(), static_cast<nfds_t>(readable_sockets.size()), static_cast<int>(timeout));
 
-                // will add comments/ improve readability soon
-                if (number_of_fds_ready < 0)
+                bool poll_error = number_of_fds_ready < 0;
+                bool is_poll_error_an_interrupt = poll_error && errno == EINTR;
+
+                /*
+                 * Retry in case of interrupts and return false in case of actual errors.
+                 * */
+                if (is_poll_error_an_interrupt)
                 {
-                    if (errno == EINTR)
-                    {
-                        continue;
-                    }
-                    else
-                    {
-                        return false;
-                    }
+                    continue;
+                }
+                else if (poll_error)
+                {
+                    return false;
                 }
             }
 
@@ -187,7 +189,7 @@ namespace DB
             if (ARES_GETSOCK_READABLE(sockets_bitmask, i))
             {
                 pollfd[i].fd = sockets[i];
-                pollfd[i].events = POLLRDNORM | POLLIN;
+                pollfd[i].events = C_ARES_POLL_EVENTS;
             }
 
             if (pollfd[i].events)
@@ -227,7 +229,7 @@ namespace DB
     {
         for (auto readable_socket : readable_sockets)
         {
-            auto fd = readable_socket.revents & (POLLRDNORM | POLLIN) ? readable_socket.fd : ARES_SOCKET_BAD;
+            auto fd = readable_socket.revents & C_ARES_POLL_EVENTS ? readable_socket.fd : ARES_SOCKET_BAD;
             ares_process_fd(channel, fd, ARES_SOCKET_BAD);
         }
     }
diff --git a/src/Common/CaresPTRResolver.h b/src/Common/CaresPTRResolver.h
index 436542f9fd0..454509ae43c 100644
--- a/src/Common/CaresPTRResolver.h
+++ b/src/Common/CaresPTRResolver.h
@@ -23,6 +23,9 @@ namespace DB
          * Allow only DNSPTRProvider to instantiate this class
          * */
         struct provider_token {};
+
+        static constexpr auto C_ARES_POLL_EVENTS = POLLRDNORM | POLLIN;
+
     public:
         explicit CaresPTRResolver(provider_token);
         ~CaresPTRResolver() override;
@@ -32,7 +35,7 @@ namespace DB
         std::unordered_set<std::string> resolve_v6(const std::string & ip) override;
 
     private:
-        bool wait();
+        bool wait_and_process();
 
         void cancel_requests();