s4: Implement UDP echo server example

This is a simple UDP-based echo server. It is mainly intended as an
example on how to do server service tasks in s4.

source4/echo_server/echo_server.c

@@ -0,0 +1,345 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   Echo server service example
+
+   Copyright (C) 2010 Kai Blin  <kai@samba.org>
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "includes.h"
+#include "echo_server/echo_server.h"
+/* Get at the config file settings */
+#include "param/param.h"
+/* This defines task_server_terminate */
+#include "smbd/process_model.h"
+/* We get load_interfaces from here */
+#include "socket/netif.h"
+/* NTSTATUS-related stuff */
+#include "libcli/util/ntstatus.h"
+/* tsocket-related functions */
+#include "lib/tsocket/tsocket.h"
+
+/* Structure to hold an echo server socket */
+struct echo_socket {
+	/* This can come handy for the task struct in there */
+	struct echo_server *echo;
+	struct tsocket_address *local_address;
+};
+
+/* Structure to hold udp socket */
+struct echo_udp_socket {
+	struct echo_socket *echo_socket;
+	struct tdgram_context *dgram;
+	struct tevent_queue *send_queue;
+};
+
+/*
+ * Main processing function.
+ *
+ * This is the start of the package processing.
+ * In the echo server it doesn't do much, but for more complicated servers,
+ * your code goes here (or at least is called from here.
+ */
+static NTSTATUS echo_process(struct echo_server *echo,
+			     TALLOC_CTX *mem_ctx,
+			     DATA_BLOB *in,
+			     DATA_BLOB *out)
+{
+	uint8_t *buf = talloc_memdup(mem_ctx, in->data, in->length);
+	NT_STATUS_HAVE_NO_MEMORY(buf);
+
+	out->data = buf;
+	out->length = in->length;
+
+	return NT_STATUS_OK;
+}
+
+/* Structure keeping track of a single UDP echo server call */
+struct echo_udp_call {
+	/* The UDP packet came from here, our reply goes there as well */
+	struct tsocket_address *src;
+	DATA_BLOB in;
+	DATA_BLOB out;
+};
+
+/** Prototype of the send callback */
+static void echo_udp_call_sendto_done(struct tevent_req *subreq);
+
+/* Callback to receive UDP packets */
+static void echo_udp_call_loop(struct tevent_req *subreq)
+{
+	/*
+	 * Our socket structure is the callback data. Get it in a
+	 * type-safe way
+	 */
+	struct echo_udp_socket *sock = tevent_req_callback_data(subreq,
+				       struct echo_udp_socket);
+	struct echo_udp_call *call;
+	uint8_t *buf;
+	ssize_t len;
+	NTSTATUS status;
+	int sys_errno;
+
+	call = talloc(sock, struct echo_udp_call);
+	if (call == NULL) {
+		goto done;
+	}
+
+	len = tdgram_recvfrom_recv(subreq, &sys_errno, call, &buf, &call->src);
+	TALLOC_FREE(subreq);
+	if (len == -1) {
+		TALLOC_FREE(call);
+		goto done;
+	}
+
+	call->in.data = buf;
+	call->in.length = len;
+
+	DEBUG(10, ("Received echo UDP packet of %lu bytes from %s\n",
+		  (long)len, tsocket_address_string(call->src, call)));
+
+	/* Handle the data coming in and compute the reply */
+	status = echo_process(sock->echo_socket->echo, call,
+			      &call->in, &call->out);
+	if (!NT_STATUS_IS_OK(status)) {
+		TALLOC_FREE(call);
+		DEBUG(0, ("echo_process returned %s\n",
+			  nt_errstr(status)));
+		goto done;
+	}
+
+	/* I said the task struct would come in handy. */
+	subreq = tdgram_sendto_queue_send(call,
+				sock->echo_socket->echo->task->event_ctx,
+				sock->dgram,
+				sock->send_queue,
+				call->out.data,
+				call->out.length,
+				call->src);
+	if (subreq == NULL) {
+		TALLOC_FREE(call);
+		goto done;
+	}
+
+	tevent_req_set_callback(subreq, echo_udp_call_sendto_done, call);
+
+done:
+	/* Now loop for the next incoming UDP packet, the async way */
+	subreq = tdgram_recvfrom_send(sock,
+				sock->echo_socket->echo->task->event_ctx,
+				sock->dgram);
+	if (subreq == NULL) {
+		task_server_terminate(sock->echo_socket->echo->task,
+				      "no memory for tdgram_recvfrom_send",
+				      true);
+		return;
+	}
+	tevent_req_set_callback(subreq, echo_udp_call_loop, sock);
+}
+
+/* Callback to send UDP replies */
+static void echo_udp_call_sendto_done(struct tevent_req *subreq)
+{
+	struct echo_udp_call *call = tevent_req_callback_data(subreq,
+				     struct echo_udp_call);
+	ssize_t ret;
+	int sys_errno;
+
+	ret = tdgram_sendto_queue_recv(subreq, &sys_errno);
+
+	/*
+	 * We don't actually care about the error, just get on with our life.
+	 * We already set a new echo_udp_call_loop callback already, so we're
+	 * almost done, just some memory to free.
+	 */
+	TALLOC_FREE(call);
+}
+
+/* Start listening on a given address */
+static NTSTATUS echo_add_socket(struct echo_server *echo,
+				const struct model_ops *ops,
+				const char *name,
+				const char *address,
+				uint16_t port)
+{
+	struct echo_socket *echo_socket;
+	struct echo_udp_socket *echo_udp_socket;
+	struct tevent_req *udpsubreq;
+	NTSTATUS status;
+	int ret;
+
+	echo_socket = talloc(echo, struct echo_socket);
+	NT_STATUS_HAVE_NO_MEMORY(echo_socket);
+
+	echo_socket->echo = echo;
+
+	/*
+	 * Initialize the tsocket_address.
+	 * The nifty part is the "ip" string. This tells tsocket to autodetect
+	 * ipv4 or ipv6 based on the IP address string passed.
+	 */
+	ret = tsocket_address_inet_from_strings(echo_socket, "ip",
+						address, port,
+						&echo_socket->local_address);
+	if (ret != 0) {
+		status = map_nt_error_from_unix(errno);
+		return status;
+	}
+
+	/* Now set up the udp socket */
+	echo_udp_socket = talloc(echo_socket, struct echo_udp_socket);
+	NT_STATUS_HAVE_NO_MEMORY(echo_udp_socket);
+
+	echo_udp_socket->echo_socket = echo_socket;
+
+	ret = tdgram_inet_udp_socket(echo_socket->local_address,
+				     NULL,
+				     echo_udp_socket,
+				     &echo_udp_socket->dgram);
+	if (ret != 0) {
+		status = map_nt_error_from_unix(errno);
+		DEBUG(0, ("Failed to bind to %s:%u UDP - %s\n",
+			  address, port, nt_errstr(status)));
+		return status;
+	}
+
+	/*
+	 * We set up a send queue so we can have multiple UDP packets in flight
+	 */
+	echo_udp_socket->send_queue = tevent_queue_create(echo_udp_socket,
+							"echo_udp_send_queue");
+	NT_STATUS_HAVE_NO_MEMORY(echo_udp_socket->send_queue);
+
+	/*
+	 * To handle the UDP requests, set up a new tevent request as a
+	 * subrequest of the current one.
+	 */
+	udpsubreq = tdgram_recvfrom_send(echo_udp_socket,
+					 echo->task->event_ctx,
+					 echo_udp_socket->dgram);
+	NT_STATUS_HAVE_NO_MEMORY(udpsubreq);
+	tevent_req_set_callback(udpsubreq, echo_udp_call_loop, echo_udp_socket);
+
+	return NT_STATUS_OK;
+}
+
+/* Set up the listening sockets */
+static NTSTATUS echo_startup_interfaces(struct echo_server *echo,
+					struct loadparm_context *lp_ctx,
+					struct interface *ifaces)
+{
+	const struct model_ops *model_ops;
+	int num_interfaces;
+	TALLOC_CTX *tmp_ctx = talloc_new(echo);
+	NTSTATUS status;
+	int i;
+
+	/*
+	 * Samba allows subtask to set their own process model.
+	 * Available models currently are:
+	 * - onefork  (forks exactly one child process)
+	 * - prefork  (keep a couple of child processes around)
+	 * - single   (only run a single process)
+	 * - standard (fork one subprocess per incoming connection)
+	 * - thread   (use threads instead of forks)
+	 *
+	 * For the echo server, the "single" process model works fine,
+	 * you probably don't want to use the thread model unless you really
+	 * know what you're doing.
+	 */
+
+	model_ops = process_model_startup("single");
+	if (model_ops == NULL) {
+		DEBUG(0, ("Can't find 'single' proces model_ops\n"));
+		return NT_STATUS_INTERNAL_ERROR;
+	}
+
+	num_interfaces = iface_count(ifaces);
+
+	for(i=0; i<num_interfaces; i++) {
+		const char *address = talloc_strdup(tmp_ctx, iface_n_ip(ifaces, i));
+
+		status = echo_add_socket(echo, model_ops, "echo", address, ECHO_SERVICE_PORT);
+		NT_STATUS_NOT_OK_RETURN(status);
+	}
+
+	TALLOC_FREE(tmp_ctx);
+	return NT_STATUS_OK;
+}
+
+
+/* Do the basic task initialization, check if the task should run */
+
+static void echo_task_init(struct task_server *task)
+{
+	struct interface *ifaces;
+	struct echo_server *echo;
+	NTSTATUS status;
+
+	/*
+	 * For the purpose of the example, let's only start the server in DC
+	 * and standalone modes, and not as a member server.
+	 */
+	switch(lpcfg_server_role(task->lp_ctx)) {
+	case ROLE_STANDALONE:
+		/* Yes, we want to run the echo server */
+		break;
+	case ROLE_DOMAIN_MEMBER:
+		task_server_terminate(task, "echo: Not starting echo server " \
+				      "for domain members", false);
+		return;
+	case ROLE_DOMAIN_CONTROLLER:
+		/* Yes, we want to run the echo server */
+		break;
+	}
+
+	load_interfaces(task, lpcfg_interfaces(task->lp_ctx), &ifaces);
+
+	if (iface_count(ifaces) == 0) {
+		task_server_terminate(task,
+				      "echo: No network interfaces configured",
+				      false);
+		return;
+	}
+
+	task_server_set_title(task, "task[echo]");
+
+	echo = talloc_zero(task, struct echo_server);
+	if (echo == NULL) {
+		task_server_terminate(task, "echo: Out of memory", true);
+		return;
+	}
+
+	echo->task = task;
+
+	status = echo_startup_interfaces(echo, task->lp_ctx, ifaces);
+	if (!NT_STATUS_IS_OK(status)) {
+		task_server_terminate(task, "echo: Failed to set up interfaces",
+				      true);
+		return;
+	}
+}
+
+/*
+ * Register this server service with the main samba process.
+ *
+ * This is the function you need to put into the wscript_build file as
+ * init_function. All the real work happens in "echo_task_init" above.
+ */
+NTSTATUS server_service_echo_init(void)
+{
+	return register_server_service("echo", echo_task_init);
+}

source4/echo_server/echo_server.h

@@ -0,0 +1,33 @@
+/*
+   Unix SMB/CIFS implementation.
+
+   Echo structures, server service example
+
+   Copyright (C) 2010 Kai Blin  <kai@samba.org>
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef __ECHO_SERVER_H__
+#define __ECHO_SERVER_H__
+
+struct task_server;
+
+struct echo_server {
+        struct task_server *task;
+};
+
+#define ECHO_SERVICE_PORT 7
+
+#endif /*__ECHO_SERVER_H__*/

source4/echo_server/wscript_build

@@ -0,0 +1,9 @@
+#!/usr/bin/env python
+
+bld.SAMBA_MODULE('ECHO',
+        source='echo_server.c',
+        subsystem='service',
+        init_function='server_service_echo_init',
+        deps='samba-hostconfig LIBTSOCKET LIBSAMBA_TSOCKET',
+        local_include=False
+        )

source4/wscript_build

@@ -58,6 +58,7 @@ bld.RECURSE('../lib/zlib')
 bld.RECURSE('lib')
 bld.RECURSE('lib/com')
 bld.RECURSE('dns_server')
+bld.RECURSE('echo_server')
 bld.RECURSE('smb_server')
 bld.RECURSE('rpc_server')
 bld.RECURSE('ldap_server')