Enable TCP_NODELAY for the control socket

It is better to disable Nagle's algorithm to avoid unnecessary latency
for control messages. (I'm not sure this has any impact for a local TCP
socket though.)

app/src/server.c

@@ -659,6 +659,14 @@ sc_server_connect_to(struct sc_server *server, struct sc_server_info *info) {
         }
     }
 
+    if (control_socket != SC_SOCKET_NONE) {
+        // Disable Nagle's algorithm for the control socket
+        // (it only impacts the sending side, so it is useless to set it
+        // for the other sockets)
+        bool ok = net_set_tcp_nodelay(control_socket, true);
+        (void) ok; // error already logged
+    }
+
     // we don't need the adb tunnel anymore
     sc_adb_tunnel_close(tunnel, &server->intr, serial,
                         server->device_socket_name);

app/src/util/net.c

@@ -15,6 +15,7 @@
 # include <sys/types.h>
 # include <sys/socket.h>
 # include <netinet/in.h>
+# include <netinet/tcp.h>
 # include <arpa/inet.h>
 # include <unistd.h>
 # include <fcntl.h>
@@ -273,6 +274,22 @@ net_close(sc_socket socket) {
 #endif
 }
 
+bool
+net_set_tcp_nodelay(sc_socket socket, bool tcp_nodelay) {
+    sc_raw_socket raw_sock = unwrap(socket);
+
+    int value = tcp_nodelay ? 1 : 0;
+    int ret = setsockopt(raw_sock, IPPROTO_TCP, TCP_NODELAY,
+                         (const void *) &value, sizeof(value));
+    if (ret == -1) {
+        net_perror("setsockopt(TCP_NODELAY)");
+        return false;
+    }
+
+    assert(ret == 0);
+    return true;
+}
+
 bool
 net_parse_ipv4(const char *s, uint32_t *ipv4) {
     struct in_addr addr;

app/src/util/net.h

@@ -67,6 +67,10 @@ net_interrupt(sc_socket socket);
 bool
 net_close(sc_socket socket);
 
+// Disable Nagle's algorithm (if tcp_nodelay is true)
+bool
+net_set_tcp_nodelay(sc_socket socket, bool tcp_nodelay);
+
 /**
  * Parse `ip` "xxx.xxx.xxx.xxx" to an IPv4 host representation
  */