Add optional support for RFC864, Character Generator Protocol

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

README.md

@@ -74,6 +74,7 @@ interface, reducing the need for a full blown firewall.
 Built-in optional inetd services:
 
 - echo RFC862
+- chargen RFC864
 - discard RFC863
 - time (rdate) RFC868
 
@@ -478,28 +479,30 @@ Compared to Finit v1.12 you must *explicitly deny* access from `eth0`!
 
 **Internal Services**
 
-The original `inetd` had a few standard services built-in:
+Like the original `inetd`, Finit has a few standard services built-in.
+They are realized as plugins to provide a simple means of testing the
+inetd functionality stand-alone.  But this also provides both a useful
+network testing/availability, as well as a rudimentary time server for
+`rdate` clients.
 
-- time
 - echo
 - chargen
 - discard
+- time
 
-Finit currently supports the `time`, `echo`, and `discard` services.
+For security reasons they are all disabled by default and have to be
-Both of which are realized as plugins to provide a simple means of
+enabled with both the `configure` script and a special `inetd` stanza in
-testing the inetd functionality stand-alone.  But this also provides
+the `finit.conf` or `finit.d/*.conf` like this:
-both a useful network testing/availability and a rudimentary time server
-for rdate clients.
-
-Internal inetd services are set up as follows:
 
 ```shell
-    inetd time/udp           wait [2345] internal
-    inetd time/tcp         nowait [2345] internal
     inetd echo/udp           wait [2345] internal
     inetd echo/tcp         nowait [2345] internal
+    inetd chargen/udp        wait [2345] internal
+    inetd chargen/tcp      nowait [2345] internal
     inetd discard/udp        wait [2345] internal
     inetd discard/tcp      nowait [2345] internal
+    inetd time/udp           wait [2345] internal
+    inetd time/tcp         nowait [2345] internal
 ```
 
 Then call `rdate` from a remote machine (or use localhost):
@@ -523,6 +526,13 @@ Or `echoping -d` to reach the discard service:
     echoping -duv <IP>
 ```
 
+Or `echoping -c` to reach the chargen service:
+
+```shell
+    echoping -cv  <IP>
+    echoping -cuv <IP>
+```
+
 If you use `time/udp` you must use the standard rdate implementation and
 then call it with `rdate -up` to connect using UDP.  Without the `-p`
 argument rdate will try to set the system clock.  Please note that rdate
@@ -565,6 +575,8 @@ For your convenience a set of *optional* plugins are available:
 
 * *echo.so*: RFC 862 plugin.  Start as inetd service, like time below.
 
+* *chargen.so*: RFC 864 plugin.  Start as inetd service, like time below.
+
 * *discard.so*: RFC 863 plugin.  Start as inetd service, like time below.
 
 * *hwclock.so*: Restore and save system clock from/to RTC on

configure.ac

@@ -56,6 +56,7 @@ enable_all_plugins=auto
 AC_PLUGIN([alsa-utils],    [no],  [Save and restore ALSA sound settings using alsactl])
 AC_PLUGIN([dbus],          [no],  [Setup and start system message bus, D-Bus])
 AC_PLUGIN([inetd-echo],    [no],  [Inetd plugin: echo server, RFC862])
+AC_PLUGIN([inetd-chargen], [no],  [Inetd plugin: character generator, RFC864])
 AC_PLUGIN([inetd-discard], [no],  [Inetd plugin: discard server, RFC862])
 AC_PLUGIN([inetd-time],    [no],  [Inetd plugin: time (rdate) server, RFC868])
 AC_PLUGIN([lost],          [no],  [Example HOOK_SVC_LOST plugin, very noisy as-is!])

plugins/Makefile.am

@@ -19,6 +19,10 @@ if BUILD_INETD_ECHO_PLUGIN
 libplug_la_SOURCES += echo.c
 endif
 
+if BUILD_INETD_CHARGEN_PLUGIN
+libplug_la_SOURCES += chargen.c
+endif
+
 if BUILD_INETD_DISCARD_PLUGIN
 libplug_la_SOURCES += discard.c
 endif
@@ -54,6 +58,10 @@ if BUILD_INETD_ECHO_PLUGIN
 pkglib_LTLIBRARIES += echo.la
 endif
 
+if BUILD_INETD_CHARGEN_PLUGIN
+pkglib_LTLIBRARIES += chargen.la
+endif
+
 if BUILD_INETD_DISCARD_PLUGIN
 pkglib_LTLIBRARIES += discard.la
 endif

plugins/chargen.c

@@ -0,0 +1,110 @@
+/* Optional inetd plugin for the Character Generator Protocol, RFC 864
+ *
+ * Copyright (c) 2016  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <arpa/inet.h>
+#include <unistd.h>		/* STDIN_FILENO */
+#include <sys/socket.h>
+
+#include "../plugin.h"
+
+#define PATTERN "!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~ "
+
+static char *generator(char *buf, size_t len)
+{
+	size_t num;
+	static size_t pos = 0;
+	const char pattern[] = PATTERN;
+
+	len = 72;
+	if (pos + len > sizeof(pattern)) {
+		num = sizeof(pattern) - pos;
+		len -= num;
+	} else {
+		num = 72;
+		len = 0;
+	}
+
+	strncpy(&buf[0], &pattern[pos], num--);
+	if (len++)
+		strncpy(&buf[num], pattern, len);
+	strcat(buf, "\r\n");
+
+	if (++pos >= sizeof(pattern) - 1)
+		pos = 0;
+
+	return buf;
+}
+
+static int recv_peer(int sd, char *buf, ssize_t len, struct sockaddr *sa, socklen_t *sa_len)
+{
+	len = recvfrom(sd, buf, len, MSG_DONTWAIT, sa, sa_len);
+	if (-1 == len)
+		return -1;	/* On error, close connection. */
+
+	return 0;
+} 
+
+static int send_peer(int sd, char *buf, ssize_t len, struct sockaddr *sa, socklen_t sa_len)
+{
+	char *pattern = generator(buf, len);
+
+	return sendto(sd, pattern, strlen(pattern), MSG_DONTWAIT, sa, sa_len);
+}
+
+static int cb(int type)
+{
+	int sd = STDIN_FILENO;
+	ssize_t len;
+	char buf[BUFSIZ];
+	struct sockaddr_storage sa;
+	socklen_t sa_len = sizeof(sa);
+
+	if (recv_peer(sd, buf, sizeof(buf), (struct sockaddr *)&sa, &sa_len))
+		return -1;
+
+	return send_peer(sd, buf, sizeof(buf), (struct sockaddr *)&sa, sa_len);
+}
+
+static plugin_t plugin = {
+	.name  = "chargen",	/* Must match the inetd /etc/services entry */
+	.inetd = {
+		.cmd = cb
+	},
+};
+
+PLUGIN_INIT(plugin_init)
+{
+	plugin_register(&plugin);
+}
+
+PLUGIN_EXIT(plugin_exit)
+{
+	plugin_unregister(&plugin);
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */