Add option '--long-idle' for server

Restore the default behavior handling timeout, make an option to enable
long idle connections.

Previously discussion:

https://github.com/shadowsocks/shadowsocks-libev/pull/2421

https://github.com/shadowsocks/shadowsocks-libev/issues/2427

README.md

@@ -446,6 +446,8 @@ you may refer to the man pages of the applications, respectively.
 
        [--no-delay]               Enable TCP_NODELAY.
 
+       [--long-idle]              Enable TCP long idle connections.
+
        [--executable <path>]      Path to the executable of ss-server.
                                   (only available in manager mode)
 

completions/bash/ss-server

@@ -1,7 +1,7 @@
 _ss_server()
 {
     local cur prev opts ciphers
-    opts='-s -p -l -k -m -a -f -t -c -n -i -b -u -U -6 -d -v -h --reuse-port --fast-open --acl --manager-address --mtu --mptcp --no-delay --key --plugin --plugin-opts --help'
+    opts='-s -p -l -k -m -a -f -t -c -n -i -b -u -U -6 -d -v -h --reuse-port --fast-open --acl --manager-address --mtu --mptcp --no-delay --long-idle --key --plugin --plugin-opts --help'
     ciphers='rc4-md5 aes-128-gcm aes-192-gcm aes-256-gcm aes-128-cfb aes-192-cfb aes-256-cfb aes-128-ctr aes-192-ctr aes-256-ctr camellia-128-cfb camellia-192-cfb camellia-256-cfb bf-cfb chacha20-ietf-poly1305 salsa20 chacha20 chacha20-ietf'
     COMPREPLY=()
     cur=${COMP_WORDS[COMP_CWORD]}

completions/zsh/_ss-server

@@ -28,6 +28,7 @@ _arguments "-h::" \
            "--mtu::" \
            "--mptcp::" \
            "--no-delay::" \
+           "--long-idle::" \
            "--key:key in base64:" \
            "--plugin:plugin name:" \
            "--plugin-opts:plugin options:" \

doc/ss-server.asciidoc

@@ -117,6 +117,10 @@ Only available with Linux kernel > 3.9.0.
 --no-delay::
 Enable TCP_NODELAY.
 
+--long-idle::
+Enable TCP long idle connections.
+If enable, the connected TCP connections would not be destroyed after timeout.
+
 --acl <acl_config>::
 Enable ACL (Access Control List) and specify config file.
 

src/common.h

@@ -62,6 +62,7 @@ enum {
     GETOPT_VAL_REUSE_PORT,
     GETOPT_VAL_FAST_OPEN,
     GETOPT_VAL_NODELAY,
+    GETOPT_VAL_LONGIDLE,
     GETOPT_VAL_ACL,
     GETOPT_VAL_MTU,
     GETOPT_VAL_MPTCP,

src/server.c

@@ -120,6 +120,7 @@ static int mode      = TCP_ONLY;
 static int ipv6first = 0;
 int fast_open        = 0;
 static int no_delay  = 0;
+static int long_idle = 0;
 static int ret_val   = 0;
 
 #ifdef HAVE_SETRLIMIT
@@ -704,6 +705,11 @@ server_recv_cb(EV_P_ ev_io *w, int revents)
     if (server->stage == STAGE_STREAM) {
         remote = server->remote;
         buf    = remote->buf;
+
+        if (!long_idle) {
+            // Only timer the watcher if a valid connection is established
+            ev_timer_again(EV_A_ & server->recv_ctx->watcher);
+        }
     }
 
     ssize_t r = recv(server->fd, buf->data, SOCKET_BUF_SIZE, 0);
@@ -1107,6 +1113,11 @@ remote_recv_cb(EV_P_ ev_io *w, int revents)
         return;
     }
 
+    if (long_idle)
+        ev_timer_stop(EV_A_ & server->recv_ctx->watcher);
+    else
+        ev_timer_again(EV_A_ & server->recv_ctx->watcher);
+
     ssize_t r = recv(remote->fd, server->buf->data, SOCKET_BUF_SIZE, 0);
 
     if (r == 0) {
@@ -1229,9 +1240,6 @@ remote_send_cb(EV_P_ ev_io *w, int revents)
         int r = getpeername(remote->fd, (struct sockaddr *)&addr, &len);
 
         if (r == 0) {
-            // connection connected, stop the request timeout timer
-            ev_timer_stop(EV_A_ & server->recv_ctx->watcher);
-
             remote_send_ctx->connected = 1;
 
             if (remote->buf->len == 0) {
@@ -1391,10 +1399,12 @@ new_server(int fd, listen_ctx_t *listener)
     int request_timeout = min(MAX_REQUEST_TIMEOUT, listener->timeout)
                           + rand() % MAX_REQUEST_TIMEOUT;
 
+    int repeat_interval = long_idle ? 0 : listener->timeout;
+
     ev_io_init(&server->recv_ctx->io, server_recv_cb, fd, EV_READ);
     ev_io_init(&server->send_ctx->io, server_send_cb, fd, EV_WRITE);
     ev_timer_init(&server->recv_ctx->watcher, server_timeout_cb,
-                  request_timeout, 0);
+                  request_timeout, repeat_interval);
 
     cork_dllist_add(&connections, &server->entries);
 
@@ -1571,6 +1581,7 @@ main(int argc, char **argv)
         { "fast-open",       no_argument,       NULL, GETOPT_VAL_FAST_OPEN   },
         { "reuse-port",      no_argument,       NULL, GETOPT_VAL_REUSE_PORT  },
         { "no-delay",        no_argument,       NULL, GETOPT_VAL_NODELAY     },
+        { "long-idle",       no_argument,       NULL, GETOPT_VAL_LONGIDLE    },
         { "acl",             required_argument, NULL, GETOPT_VAL_ACL         },
         { "manager-address", required_argument, NULL,
           GETOPT_VAL_MANAGER_ADDRESS },
@@ -1600,6 +1611,10 @@ main(int argc, char **argv)
             no_delay = 1;
             LOGI("enable TCP no-delay");
             break;
+        case GETOPT_VAL_LONGIDLE:
+            long_idle = 1;
+            LOGI("enable TCP long idle connections");
+            break;
         case GETOPT_VAL_ACL:
             LOGI("initializing acl...");
             acl = !init_acl(optarg);

src/utils.c

@@ -406,6 +406,10 @@ usage()
 #ifndef MODULE_MANAGER
     printf(
         "       [--no-delay]               Enable TCP_NODELAY.\n");
+#ifdef MODULE_REMOTE
+    printf(
+        "       [--long-idle]              Enable TCP long idle connections.\n");
+#endif
     printf(
         "       [--key <key_in_base64>]    Key of your remote server.\n");
 #endif