r35395: server supports port=0

src/brpc/server.cpp

@@ -646,6 +646,15 @@ struct RevertServerStatus {
     }
 };
 
+static int get_port_from_fd(int fd) {
+    struct sockaddr_in addr;
+    socklen_t size = sizeof(addr);
+    if (getsockname(fd, (struct sockaddr*)&addr, &size) < 0) {
+        return -1;
+    }
+    return ntohs(addr.sin_port);
+}
+
 int Server::StartInternal(const butil::ip_t& ip,
                           const PortRange& port_range,
                           const ServerOptions *opt) {
@@ -877,6 +886,15 @@ int Server::StartInternal(const butil::ip_t& ip,
             }
             return -1;
         }
+        if (_listen_addr.port == 0) {
+            // port=0 makes kernel dynamically select a port from
+            // https://en.wikipedia.org/wiki/Ephemeral_port
+            _listen_addr.port = get_port_from_fd(sockfd);
+            if (_listen_addr.port <= 0) {
+                LOG(ERROR) << "Fail to get port from fd=" << sockfd;
+                return -1;
+            }
+        }
         if (_am == NULL) {
             _am = BuildAcceptor();
             if (NULL == _am) {
@@ -906,6 +924,12 @@ int Server::StartInternal(const butil::ip_t& ip,
                        << " is same with port=" << _listen_addr.port << " to Start()";
             return -1;
         }
+        if (_options.internal_port == 0) {
+            LOG(ERROR) << "ServerOptions.internal_port cannot be 0, which"
+                " allocates a dynamic and probabaly unfiltered port,"
+                " against the purpose of \"being internal\".";
+            return -1;
+        }
         butil::EndPoint internal_point = _listen_addr;
         internal_point.port = _options.internal_port;
         butil::fd_guard sockfd(tcp_listen(internal_point, FLAGS_reuse_addr));

src/brpc/server.h

@@ -409,28 +409,25 @@ public:
     Server(ProfilerLinker = ProfilerLinker());
     ~Server();
 
-    // Start this server. Use default options if `opt' is NULL.
-    // This function can be called multiple times if the server is completely
-    // stopped by Stop() and Join().
+    // A set of functions to start this server.
     // Returns 0 on success, -1 otherwise and errno is set appropriately.
+    // Notes:
+    // * Default options are taken if `opt' is NULL.
+    // * A server can be started more than once if the server is completely
+    //   stopped by Stop() and Join().
+    // * port can be 0, which makes kernel to choose a port dynamically.
     
-    // Start on a single address "0.0.0.0:8000".
+    // Start on an address in form of "0.0.0.0:8000".
     int Start(const char* ip_port_str, const ServerOptions* opt);
-
+    int Start(const butil::EndPoint& ip_port, const ServerOptions* opt);
     // Start on IP_ANY:port.
     int Start(int port, const ServerOptions* opt);
-    
-    // Start on ip:port enclosed in butil::EndPoint which is defined in
-    // src/butil/endpoint.h
-    int Start(const butil::EndPoint& ip_port, const ServerOptions* opt);
-
-    // Start on `ip_str' + any useable port in `port_range'
-    int Start(const char* ip_str, PortRange port_range,
-              const ServerOptions *opt);
+    // Start on `ip_str' + any useable port in `range'
+    int Start(const char* ip_str, PortRange range, const ServerOptions *opt);
 
-    // NOTE: Stop() is paired with Join() to stop a server with minimum lost
-    // of requests. The point of separating them is that you can Stop() 
-    // multiple servers before Join()-ing them, the total time to Join is 
+    // NOTE: Stop() is paired with Join() to stop a server without losing
+    // requests. The point of separating them is that you can Stop() multiple
+    // servers before Join() them, in which case the total time to Join is
     // time of the slowest Join(). Otherwise you have to Join() them one by
     // one, in which case the total time is sum of all Join().
 

test/brpc_server_unittest.cpp

@@ -164,6 +164,13 @@ TEST_F(ServerTest, sanity) {
         // accept hostname as well.
         ASSERT_EQ(0, server.Start("localhost:8613", NULL));
     }
+    {
+        brpc::Server server;
+        ASSERT_EQ(0, server.Start("localhost:0", NULL));
+        // port should be replaced with the actually used one.
+        ASSERT_NE(0, server.listen_address().port);
+    }
+
     {
         brpc::Server server;
         ASSERT_EQ(-1, server.Start(99999, NULL));