Core: implement TCP_KEEPALIVE on Darwin

In earlier versions, macOS only supported setting TCP_KEEPALIVE in place of TCP_KEEPIDLE,
but macOS has supported TCP_KEEPINTVL and TCP_KEEPCNT since 10.8 in 2012.

Ref:
https://lists.apple.com/archives/macnetworkprog/2012/Jul/msg00005.html
2ff845c2e0/bsd/netinet/tcp.h (L215-L230)
8d741a5de7/bsd/netinet/tcp.h (L226-L241)

auto/os/darwin

@@ -118,3 +118,19 @@ ngx_feature_libs=
 ngx_feature_test="int32_t  lock = 0;
                   if (!OSAtomicCompareAndSwap32Barrier(0, 1, &lock)) return 1"
 . auto/feature
+
+
+# TCP keepalive
+
+ngx_feature="TCP_KEEPALIVE"
+ngx_feature_name="NGX_HAVE_KEEPALIVE_TUNABLE"
+ngx_feature_run=no
+ngx_feature_incs="#include <sys/socket.h>
+                  #include <netinet/in.h>
+                  #include <netinet/tcp.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="setsockopt(0, IPPROTO_TCP, TCP_KEEPALIVE, NULL, 0);
+                  setsockopt(0, IPPROTO_TCP, TCP_KEEPINTVL, NULL, 0);
+                  setsockopt(0, IPPROTO_TCP, TCP_KEEPCNT, NULL, 0)"
+. auto/feature

auto/unix

@@ -508,18 +508,20 @@ ngx_feature_test="setsockopt(0, IPPROTO_TCP, TCP_DEFER_ACCEPT, NULL, 0)"
 . auto/feature
 
 
-ngx_feature="TCP_KEEPIDLE"
-ngx_feature_name="NGX_HAVE_KEEPALIVE_TUNABLE"
-ngx_feature_run=no
-ngx_feature_incs="#include <sys/socket.h>
-                  #include <netinet/in.h>
-                  #include <netinet/tcp.h>"
-ngx_feature_path=
-ngx_feature_libs=
-ngx_feature_test="setsockopt(0, IPPROTO_TCP, TCP_KEEPIDLE, NULL, 0);
-                  setsockopt(0, IPPROTO_TCP, TCP_KEEPINTVL, NULL, 0);
-                  setsockopt(0, IPPROTO_TCP, TCP_KEEPCNT, NULL, 0)"
-. auto/feature
+if [ -z "$NGX_HAVE_KEEPALIVE_TUNABLE" ]; then
+    ngx_feature="TCP_KEEPIDLE"
+    ngx_feature_name="NGX_HAVE_KEEPALIVE_TUNABLE"
+    ngx_feature_run=no
+    ngx_feature_incs="#include <sys/socket.h>
+                      #include <netinet/in.h>
+                      #include <netinet/tcp.h>"
+    ngx_feature_path=
+    ngx_feature_libs=
+    ngx_feature_test="setsockopt(0, IPPROTO_TCP, TCP_KEEPIDLE, NULL, 0);
+                      setsockopt(0, IPPROTO_TCP, TCP_KEEPINTVL, NULL, 0);
+                      setsockopt(0, IPPROTO_TCP, TCP_KEEPCNT, NULL, 0)"
+    . auto/feature
+fi
 
 
 ngx_feature="TCP_FASTOPEN"

src/core/ngx_connection.c

@@ -772,6 +772,7 @@ ngx_configure_listening_sockets(ngx_cycle_t *cycle)
             value *= NGX_KEEPALIVE_FACTOR;
 #endif
 
+#ifdef TCP_KEEPIDLE
             if (setsockopt(ls[i].fd, IPPROTO_TCP, TCP_KEEPIDLE,
                            (const void *) &value, sizeof(int))
                 == -1)
@@ -780,6 +781,17 @@ ngx_configure_listening_sockets(ngx_cycle_t *cycle)
                               "setsockopt(TCP_KEEPIDLE, %d) %V failed, ignored",
                               value, &ls[i].addr_text);
             }
+#elif defined(TCP_KEEPALIVE)
+            /* The equivalent of TCP_KEEPIDLE on Darwin is TCP_KEEPALIVE. */
+            if (setsockopt(ls[i].fd, IPPROTO_TCP, TCP_KEEPALIVE,
+                           (const void *) &value, sizeof(int))
+                == -1)
+            {
+                ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_socket_errno,
+                              "setsockopt(TCP_KEEPALIVE, %d) %V failed, ignored",
+                              value, &ls[i].addr_text);
+            }
+#endif
         }
 
         if (ls[i].keepintvl) {