aboutsummaryrefslogtreecommitdiffstats
path: root/src/mds-echo.c
blob: aa3c8b75e90565b12d5dd5eab331693664c6c355 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
/**
 * mds — A micro-display server
 * Copyright © 2014  Mattias Andrée (maandree@member.fsf.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 "mds-echo.h"

#include <libmdsserver/macros.h>
#include <libmdsserver/util.h>
#include <libmdsserver/mds-message.h>

#include <errno.h>
#include <inttypes.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#define reconnect_to_display() -1 /* TODO */



#define MDS_ECHO_VARS_VERSION  0



/**
 * This variable should declared by the actual server implementation.
 * It must be configured before `main` is invoked.
 * 
 * This tells the server-base how to behave
 */
server_characteristics_t server_characteristics =
  {
    .require_privileges = 0,
    .require_display = 1,
    .require_respawn_info = 0,
    .sanity_check_argc = 1
  };



/**
 * Value of the ‘Message ID’ header for the next message
 */
static int32_t message_id = 1;

/**
 * Buffer for received messages
 */
static mds_message_t received;

/**
 * Whether the server is connected to the display
 */
static int connected = 1;

/**
 * Buffer for message echoing
 */
static char* echo_buffer = NULL;

/**
 * The size allocated to `echo_buffer` divided by `sizeof(char)`
 */
static size_t echo_buffer_size = 0;



/**
 * This function will be invoked before `initialise_server` (if not re-exec:ing)
 * or before `unmarshal_server` (if re-exec:ing)
 * 
 * @return  Non-zero on error
 */
int __attribute__((const)) preinitialise_server(void)
{
  return 0;
}


/**
 * This function should initialise the server,
 * and it not invoked after a re-exec.
 * 
 * @return  Non-zero on error
 */
int initialise_server(void)
{
  const char* const message =
    "Command: intercept\n"
    "Message ID: 0\n"
    "Length: 14\n"
    "\n"
    "Command: echo\n";
  
  if (full_send(message, strlen(message)))
    return 1;
  mds_message_initialise(&received);
  return 0;
}


/**
 * This function will be invoked after `initialise_server` (if not re-exec:ing)
 * or after `unmarshal_server` (if re-exec:ing)
 * 
 * @return  Non-zero on error
 */
int postinitialise_server(void)
{
  if (connected)
    return 0;
  
  if (reconnect_to_display())
    {
      mds_message_destroy(&received);
      return 1;
    }
  connected = 1;
  return 0;
}


/**
 * Calculate the number of bytes that will be stored by `marshal_server`
 * 
 * On failure the program should `abort()` or exit by other means.
 * However it should not be possible for this function to fail.
 * 
 * @return  The number of bytes that will be stored by `marshal_server`
 */
size_t marshal_server_size(void)
{
  return 2 * sizeof(int) + sizeof(int32_t) + mds_message_marshal_size(&received);
}


/**
 * Marshal server implementation specific data into a buffer
 * 
 * @param   state_buf  The buffer for the marshalled data
 * @return             Non-zero on error
 */
int marshal_server(char* state_buf)
{
  buf_set_next(state_buf, int, MDS_ECHO_VARS_VERSION);
  buf_set_next(state_buf, int, connected);
  buf_set_next(state_buf, int32_t, message_id);
  mds_message_marshal(&received, state_buf);
  return 0;
}


/**
 * Unmarshal server implementation specific data and update the servers state accordingly
 * 
 * On critical failure the program should `abort()` or exit by other means.
 * That is, do not let `reexec_failure_recover` run successfully, if it unrecoverable
 * error has occurred or one severe enough that it is better to simply respawn.
 * 
 * @param   state_buf  The marshalled data that as not been read already
 * @return             Non-zero on error
 */
int unmarshal_server(char* state_buf)
{
  int r;
  /* buf_get_next(state_buf, int, MDS_ECHO_VARS_VERSION); */
  buf_next(state_buf, int, 1);
  buf_get_next(state_buf, int, connected);
  buf_get_next(state_buf, int32_t, message_id);
  r = mds_message_unmarshal(&received, state_buf);
  if (r)
    mds_message_destroy(&received);
  return r;
}


/**
 * Attempt to recover from a re-exec failure that has been
 * detected after the server successfully updated it execution image
 * 
 * @return  Non-zero on error
 */
int __attribute__((const)) reexec_failure_recover(void)
{
  return -1;
}


/**
 * Perform the server's mission
 * 
 * @return  Non-zero on error
 */
int master_loop(void)
{
  while (!reexecing && !terminating)
    {
      int r = mds_message_read(&received, socket_fd);
      if (r == 0)
	{
	  r = echo_message();
	  if (r == 0)
	    continue;
	}
      
      if (r == -2)
	{
	  eprint("corrupt message received, aborting.");
	  goto fail;
	}
      else if (errno == EINTR)
	continue;
      else if (errno != ECONNRESET)
	goto pfail;
      
      eprint("lost connection to server.");
      mds_message_destroy(&received);
      mds_message_initialise(&received);
      connected = 0;
      if (reconnect_to_display())
	goto fail;
      connected = 1;
    }
  
  mds_message_destroy(&received);
  free(echo_buffer);
  return 0;
 pfail:
  perror(*argv);
 fail:
  mds_message_destroy(&received);
  free(echo_buffer);
  return 1;
}


/**
 * Echo the received message payload
 * 
 * @return  Zero on success -1 on error or interruption,
 *          errno will be set accordingly
 */
int echo_message(void)
{
  const char* recv_client_id = NULL;
  const char* recv_message_id = NULL;
  const char* recv_length = NULL;
  size_t i, n;
  
#define __get_header(storage, header, skip)  \
  (startswith(received.headers[i], header))  \
    storage = received.headers[i] + skip * strlen(header)
  
  for (i = 0; i < received.header_count; i++)
    {
      if      __get_header(recv_client_id,  "Client ID: ",  1);
      else if __get_header(recv_message_id, "Message ID: ", 1);
      else if __get_header(recv_length,     "Length: ",     0);
      else
	continue;
      if (recv_client_id && recv_message_id && recv_length)
	break;
    }
  
#undef __get_header
  
  
  if ((recv_client_id == NULL) || (strequals(recv_client_id, "0:0")))
    {
      eprint("received message from anonymous sender, ignoring.");
      return 0;
    }
  else if (recv_message_id == NULL)
    {
      eprint("received message with ID, ignoring, master server is misbehaving.");
      return 0;
    }
  
  n = 1 + strlen("To: \nIn response to: \nMessage ID: \n\n");
  n += strlen(recv_client_id) + strlen(recv_message_id) + 3 * sizeof(int32_t);
  if (recv_length != NULL)
    n += strlen(recv_length) + 1;
  
  if ((echo_buffer_size < n) || (echo_buffer_size * 4 > n))
    {
      char* old_buffer = echo_buffer;
      if (xrealloc(echo_buffer, echo_buffer_size = n, char))
	{
	  free(old_buffer);
	  return -1;
	}
    }
  
  sprintf(echo_buffer, "To: %s\nIn response to: %s\nMessage ID: %" PRIi32 "\n%s%s\n",
	  recv_client_id, recv_message_id, message_id,
	  recv_length == NULL ? "" : recv_length,
	  recv_length == NULL ? "" : "\n");
  
  message_id = message_id == INT32_MAX ? 0 : (message_id + 1);
  
  if (full_send(echo_buffer, strlen(echo_buffer)))
    return 1;
  return full_send(received.payload, received.payload_size);
}


/**
 * Send a full message even if interrupted
 * 
 * @param   message  The message to send
 * @param   length   The length of the message
 * @return           Non-zero on success
 */
int full_send(const char* message, size_t length)
{
  size_t sent;
  
  while (length > 0)
    {
      sent = send_message(socket_fd, message, length);
      if (sent > length)
	{
	  eprint("Sent more of a message than exists in the message, aborting.");
	  return -1;
	}
      else if ((sent < length) && (errno != EINTR))
	{
	  perror(*argv);
	  return -1;
	}
      message += sent;
      length -= sent;
    }
  return 0;
}