port_posix: use IPv4+IPv6 sockets to check for a free port.

This allows the port picker to function across dual-stack and
IPv4/IPv6-only environments.

For a port to be considered available, the kernel must support at least
one of (IPv6, IPv4), and the port must be available on each supported
family.

Also use the bool type where feasible.

This is based on http://cl/97155408 (for those who can read it.)

test/core/util/port_posix.c

@@ -39,6 +39,7 @@
 
 #include <errno.h>
 #include <netinet/in.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/socket.h>
@@ -50,6 +51,8 @@
 #include <grpc/support/string_util.h>
 
 #include "src/core/lib/http/httpcli.h"
+#include "src/core/lib/iomgr/resolve_address.h"
+#include "src/core/lib/iomgr/sockaddr_utils.h"
 #include "src/core/lib/support/env.h"
 #include "test/core/util/port_server_client.h"
 
@@ -115,55 +118,68 @@ static void chose_port(int port) {
   chosen_ports[num_chosen_ports - 1] = port;
 }
 
-static int is_port_available(int *port, int is_tcp) {
-  const int proto = is_tcp ? IPPROTO_TCP : 0;
-  const int fd = socket(AF_INET, is_tcp ? SOCK_STREAM : SOCK_DGRAM, proto);
-  int one = 1;
-  struct sockaddr_in addr;
-  socklen_t alen = sizeof(addr);
-  int actual_port;
-
+static bool is_port_available(int *port, bool is_tcp) {
   GPR_ASSERT(*port >= 0);
   GPR_ASSERT(*port <= 65535);
-  if (fd < 0) {
-    gpr_log(GPR_ERROR, "socket() failed: %s", strerror(errno));
-    return 0;
-  }
 
-  /* Reuseaddr lets us start up a server immediately after it exits */
-  if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) {
-    gpr_log(GPR_ERROR, "setsockopt() failed: %s", strerror(errno));
-    close(fd);
-    return 0;
-  }
+  /* For a port to be considered available, the kernel must support
+     at least one of (IPv6, IPv4), and the port must be available
+     on each supported family. */
+  bool got_socket = false;
+  for (int is_ipv6 = 1; is_ipv6 >= 0; is_ipv6--) {
+    const int fd = socket(is_ipv6 ? AF_INET6 : AF_INET,
+                          is_tcp ? SOCK_STREAM : SOCK_DGRAM,
+                          is_tcp ? IPPROTO_TCP : 0);
+    if (fd >= 0) {
+      got_socket = true;
+    } else {
+      continue;
+    }
 
-  /* Try binding to port */
-  addr.sin_family = AF_INET;
-  addr.sin_addr.s_addr = INADDR_ANY;
-  addr.sin_port = htons((uint16_t)*port);
-  if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
-    gpr_log(GPR_DEBUG, "bind(port=%d) failed: %s", *port, strerror(errno));
-    close(fd);
-    return 0;
-  }
+    /* Reuseaddr lets us start up a server immediately after it exits */
+    const int one = 1;
+    if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)) < 0) {
+      gpr_log(GPR_ERROR, "setsockopt() failed: %s", strerror(errno));
+      close(fd);
+      return false;
+    }
+
+    /* Try binding to port */
+    grpc_resolved_address addr;
+    if (is_ipv6) {
+      grpc_sockaddr_make_wildcard6(*port, &addr);  /* [::]:port */
+    } else {
+      grpc_sockaddr_make_wildcard4(*port, &addr);  /* 0.0.0.0:port */
+    }
+    if (bind(fd, (struct sockaddr *)addr.addr, (socklen_t)addr.len) < 0) {
+      gpr_log(GPR_DEBUG, "bind(port=%d) failed: %s", *port, strerror(errno));
+      close(fd);
+      return false;
+    }
+
+    /* Get the bound port number */
+    if (getsockname(fd, (struct sockaddr *)addr.addr,
+                    (socklen_t *)&addr.len) < 0) {
+      gpr_log(GPR_ERROR, "getsockname() failed: %s", strerror(errno));
+      close(fd);
+      return false;
+    }
+    GPR_ASSERT(addr.len <= sizeof(addr.addr));
+    const int actual_port = grpc_sockaddr_get_port(&addr);
+    GPR_ASSERT(actual_port > 0);
+    if (*port == 0) {
+      *port = actual_port;
+    } else {
+      GPR_ASSERT(*port == actual_port);
+    }
 
-  /* Get the bound port number */
-  if (getsockname(fd, (struct sockaddr *)&addr, &alen) < 0) {
-    gpr_log(GPR_ERROR, "getsockname() failed: %s", strerror(errno));
     close(fd);
-    return 0;
   }
-  GPR_ASSERT(alen <= sizeof(addr));
-  actual_port = ntohs(addr.sin_port);
-  GPR_ASSERT(actual_port > 0);
-  if (*port == 0) {
-    *port = actual_port;
-  } else {
-    GPR_ASSERT(*port == actual_port);
+  if (!got_socket) {
+    gpr_log(GPR_ERROR, "socket() failed: %s", strerror(errno));
+    return false;
   }
-
-  close(fd);
-  return 1;
+  return true;
 }
 
 int grpc_pick_unused_port(void) {
@@ -180,7 +196,7 @@ int grpc_pick_unused_port(void) {
      UDP ports and they are scarcer. */
 
   /* Type of port to first pick in next iteration */
-  int is_tcp = 1;
+  bool is_tcp = true;
   int trial = 0;
 
   char *env = gpr_getenv("GRPC_TEST_PORT_SERVER");