Increase NOFILE limit for tox-bootstrapd

tox-bootstrapd can use around 600 TCP sockets during TCP server's normal
functioning. Many systems default to having a soft limit of 1024 open file
descriptors, which we are close to reaching, so it was suggested we bump that
limit to a higher number. iphy suggested increasing it to 32768.

.travis/tox-bootstrapd-docker

@@ -23,7 +23,7 @@ cat docker/Dockerfile
 sudo docker build -t tox-bootstrapd docker/
 sudo useradd --home-dir /var/lib/tox-bootstrapd --create-home --system --shell /sbin/nologin --comment "Account to run Tox's DHT bootstrap daemon" --user-group tox-bootstrapd
 sudo chmod 700 /var/lib/tox-bootstrapd
-sudo docker run -d --name tox-bootstrapd -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ -p 443:443 -p 3389:3389 -p 33445:33445 -p 33445:33445/udp tox-bootstrapd
+sudo docker run -d --name tox-bootstrapd -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ --ulimit nofile=32768:32768 -p 443:443 -p 3389:3389 -p 33445:33445 -p 33445:33445/udp tox-bootstrapd
 
 sudo ls -lbh /var/lib/tox-bootstrapd
 
@@ -59,6 +59,12 @@ if [ "`sudo docker inspect -f {{.State.Running}} tox-bootstrapd`" != "true" ]; t
   exit 1
 fi
 
+cat /proc/$(pidof tox-bootstrapd)/limits
+if ! cat /proc/$(pidof tox-bootstrapd)/limits | grep -P '^Max open files(\s+)32768(\s+)32768(\s+)files'; then
+  echo "Error: ulimit is not set to the expected value"
+  exit 1
+fi
+
 if ! python3 ../fun/bootstrap_node_info.py ipv4 localhost 33445 ; then
   echo "Error: Unable to get bootstrap node info"
   exit 1

other/bootstrap_daemon/README.md

@@ -219,7 +219,7 @@ sudo docker build -t tox-bootstrapd docker/
 sudo useradd --home-dir /var/lib/tox-bootstrapd --create-home --system --shell /sbin/nologin --comment "Account to run Tox's DHT bootstrap daemon" --user-group tox-bootstrapd
 sudo chmod 700 /var/lib/tox-bootstrapd
 
-sudo docker run -d --name tox-bootstrapd --restart always -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ -p 443:443 -p 3389:3389 -p 33445:33445 -p 33445:33445/udp tox-bootstrapd
+sudo docker run -d --name tox-bootstrapd --restart always -v /var/lib/tox-bootstrapd/:/var/lib/tox-bootstrapd/ --ulimit nofile=32768:32768 -p 443:443 -p 3389:3389 -p 33445:33445 -p 33445:33445/udp tox-bootstrapd
 ```
 
 We create a new user and protect its home directory in order to mount it in the Docker image, so that the kyepair the daemon uses would be stored on the host system, which makes it less likely that you would loose the keypair while playing with or updating the Docker container.

other/bootstrap_daemon/src/tox-bootstrapd.c

@@ -27,11 +27,14 @@
 #endif
 
 // system provided
+#include <sys/resource.h>
 #include <sys/stat.h>
-#include <signal.h> // for POSIX sigaction(2)
+#include <signal.h> // system header, rather than C, because we need it for POSIX sigaction(2)
 #include <unistd.h>
 
 // C
+#include <assert.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -424,6 +427,30 @@ int main(int argc, char *argv[])
 
         if (tcp_server != nullptr) {
             log_write(LOG_LEVEL_INFO, "Initialized Tox TCP server successfully.\n");
+
+            struct rlimit limit;
+
+            const rlim_t rlim_suggested = 32768;
+            const rlim_t rlim_min = 4096;
+
+            assert(rlim_suggested >= rlim_min);
+
+            if (!getrlimit(RLIMIT_NOFILE, &limit)) {
+                if (limit.rlim_cur < limit.rlim_max) {
+                    // Some systems have a hard limit of over 1000000 open file descriptors, so let's cap it at something reasonable
+                    // so that we don't set it to an unreasonably high number.
+                    limit.rlim_cur = limit.rlim_max > rlim_suggested ? rlim_suggested : limit.rlim_max;
+                    setrlimit(RLIMIT_NOFILE, &limit);
+                }
+            }
+
+            if (!getrlimit(RLIMIT_NOFILE, &limit) && limit.rlim_cur < rlim_min) {
+                log_write(LOG_LEVEL_WARNING,
+                          "Current limit on the number of files this process can open (%ju) is rather low for the proper functioning of the TCP server. "
+                          "Consider raising the limit to at least %ju or the recommended %ju. "
+                          "Continuing using the current limit (%ju).\n",
+                          (uintmax_t)limit.rlim_cur, (uintmax_t)rlim_min, (uintmax_t)rlim_suggested, (uintmax_t)limit.rlim_cur);
+            }
         } else {
             log_write(LOG_LEVEL_ERROR, "Couldn't initialize Tox TCP server. Exiting.\n");
             kill_onion_announce(onion_a);

other/bootstrap_daemon/tox-bootstrapd.service

@@ -11,6 +11,9 @@ WorkingDirectory=/var/lib/tox-bootstrapd
 ExecStart=/usr/local/bin/tox-bootstrapd --config /etc/tox-bootstrapd.conf
 User=tox-bootstrapd
 Group=tox-bootstrapd
+# TCP Server needs to be able to have lots of TCP sockets open.
+LimitNOFILE=32768
+# Uncomment to allow binding to ports < 1024, e.g. 443 (HTTPS) for TCP Server
 #CapabilityBoundingSet=CAP_NET_BIND_SERVICE
 
 [Install]

other/bootstrap_daemon/tox-bootstrapd.sh

@@ -1,4 +1,4 @@
-#! /bin/sh
+#! /bin/bash
 ### BEGIN INIT INFO
 # Provides:          tox-bootstrapd
 # Required-Start:    $remote_fs $syslog
@@ -22,6 +22,35 @@ SCRIPTNAME=/etc/init.d/$NAME
 USER=tox-bootstrapd
 GROUP=tox-bootstrapd
 
+# Set ulimit -n based on number of fds available.
+# This check is borrowed from Debian's tor package, with a few modifications.
+if [ -r /proc/sys/fs/file-max ]; then
+	system_max=$(cat /proc/sys/fs/file-max)
+	if [ "$system_max" -gt "80000" ] ; then
+		MAX_FILEDESCRIPTORS=32768
+	elif [ "$system_max" -gt "40000" ] ; then
+		MAX_FILEDESCRIPTORS=16384
+	elif [ "$system_max" -gt "20000" ] ; then
+		MAX_FILEDESCRIPTORS=8192
+	elif [ "$system_max" -gt "10000" ] ; then
+		MAX_FILEDESCRIPTORS=4096
+	else
+		MAX_FILEDESCRIPTORS=1024
+		cat << EOF
+
+Warning: Your system has very few file descriptors available in total.
+
+Maybe you should try raising that by adding 'fs.file-max=100000' to your
+/etc/sysctl.conf file.  Feel free to pick any number that you deem appropriate.
+Then run 'sysctl -p'.  See /proc/sys/fs/file-max for the current value, and
+file-nr in the same directory for how many of those are used at the moment.
+
+EOF
+	fi
+else
+	MAX_FILEDESCRIPTORS=32768
+fi
+
 # Exit if the package is not installed
 [ -x "$DAEMON" ] || exit 0
 
@@ -48,6 +77,8 @@ do_start()
 	fi
 	chown $USER:$GROUP $PIDDIR
 	start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test --chuid $USER > /dev/null || return 1
+	# TCP Server needs to be able to have lots of TCP sockets open.
+	ulimit -n $MAX_FILEDESCRIPTORS
 	start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --chuid $USER -- $DAEMON_ARGS || return 2
 }