dynsub

The dynsub example is a PoC for a C-based JSON printer of arbitrary data. It assumes that topic discovery is enabled, but doesn’t require it.

Running the example

Pass the name of a topic to dynsub and it waits for a writer of that topic to show up. When it finds one in the DCPSPublication topic, it tries to subscribe and print the received samples as JSON.

For example: Start the HelloworldPublisher in one shell:

# bin/HelloworldPublisher
=== [Publisher]  Waiting for a reader to be discovered ...

In another shell start dynsub:

# bin/dynsub HelloWorldData_Msg
{"userID":1,"message":"Hello World"}
{"userID":1}

The second line is the “invalid sample” generated because of the termination of the publisher. In Cyclone DDS, only the key fields are valid, and therefore printed.

Instead of the HelloWorldData_Msg, the small publisher program “variouspub” can publish a number of different types. Pass it the name of the type to publish. For example:

# bin/variouspub B

This publishes samples at 1Hz until killed.

Source code

dynsub.c
  1// Copyright(c) 2022 to 2023 ZettaScale Technology and others
  2//
  3// This program and the accompanying materials are made available under the
  4// terms of the Eclipse Public License v. 2.0 which is available at
  5// http://www.eclipse.org/legal/epl-2.0, or the Eclipse Distribution License
  6// v. 1.0 which is available at
  7// http://www.eclipse.org/org/documents/edl-v10.php.
  8//
  9// SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 10
 11#include <stdio.h>
 12#include <string.h>
 13#include <stdlib.h>
 14#include <assert.h>
 15#include <locale.h>
 16
 17#include "dds/dds.h"
 18#include "dynsub.h"
 19
 20// Interpreting the data of an arbitrary topic requires interpreting the type object that describes the data.
 21// The type object type is defined by the XTypes specification (https://www.omg.org/spec/DDS-XTypes/) and it
 22// comes in two forms: MinimalTypeObject and CompleteTypeObject.  Only the latter includes field names, so
 23// that's what need.
 24//
 25// Cyclone DDS includes a copy of the IDL as well as the corresponding type definitions in C as generated by
 26// IDLC.  So instead of including yet another copy, we simply refer to those.  These files are not (yet?)
 27// part of the stable API of Cyclone DDS and so the updates to Cyclone may change the locations or the names
 28// of the relevant header files.
 29//
 30// The API uses `dds_typeobj_t` and `dds_typeinfo_t` that are opaque types but really amount to the
 31// corresponding XTypes objects: DDS_XTypes_TypeObject and DDS_XTypes_TypeInformation.  Rather than casting
 32// pointers like we do here, they should be defined in a slightly different way so that they are not really
 33// opaque.  For now, this'll have to do.
 34#include "dds/ddsi/ddsi_xt_typeinfo.h"
 35
 36// For convenience, the DDS participant is global
 37static dds_entity_t participant;
 38
 39
 40// Helper function to wait for a DCPSPublication/DCPSSubscription to show up with the desired topic name,
 41// then calls dds_find_topic to create a topic for that data writer's/reader's type up the retrieves the
 42// type object.
 43static dds_return_t get_topic_and_typeobj (const char *topic_name, dds_duration_t timeout, dds_entity_t *topic, DDS_XTypes_TypeObject **xtypeobj)
 44{
 45  const dds_entity_t waitset = dds_create_waitset (participant);
 46  const dds_entity_t dcpspublication_reader = dds_create_reader (participant, DDS_BUILTIN_TOPIC_DCPSPUBLICATION, NULL, NULL);
 47  const dds_entity_t dcpspublication_readcond = dds_create_readcondition (dcpspublication_reader, DDS_ANY_STATE);
 48  const dds_entity_t dcpssubscription_reader = dds_create_reader (participant, DDS_BUILTIN_TOPIC_DCPSSUBSCRIPTION, NULL, NULL);
 49  const dds_entity_t dcpssubscription_readcond = dds_create_readcondition (dcpssubscription_reader, DDS_ANY_STATE);
 50  (void) dds_waitset_attach (waitset, dcpspublication_readcond, dcpspublication_reader);
 51  (void) dds_waitset_attach (waitset, dcpssubscription_readcond, dcpssubscription_reader);
 52  const dds_time_t abstimeout = (timeout == DDS_INFINITY) ? DDS_NEVER : dds_time () + timeout;
 53  dds_return_t ret = DDS_RETCODE_OK;
 54  *xtypeobj = NULL;
 55  struct ppc ppc;
 56  ppc_init (&ppc);
 57  dds_attach_t triggered_reader_x;
 58  while (*xtypeobj == NULL && dds_waitset_wait_until (waitset, &triggered_reader_x, 1, abstimeout) > 0)
 59  {
 60    void *epraw = NULL;
 61    dds_sample_info_t si;
 62    dds_entity_t triggered_reader = (dds_entity_t) triggered_reader_x;
 63    if (dds_take (triggered_reader, &epraw, &si, 1, 1) <= 0)
 64      continue;
 65    dds_builtintopic_endpoint_t *ep = epraw;
 66    const dds_typeinfo_t *typeinfo = NULL;
 67    // We are only interested in DCPSPublications where the topic name matches and that carry type information
 68    // (a non-XTypes capable DDS would not provide type information) because without that information there is
 69    // no way we can do anything interesting with it.
 70    if (strcmp (ep->topic_name, topic_name) == 0 && dds_builtintopic_get_endpoint_type_info (ep, &typeinfo) == 0 && typeinfo)
 71    {
 72      // Using dds_find_topic allows us to "clone" the topic definition including the topic QoS, but it does
 73      // require that topic discovery is enabled in the configuration.  The advantage of using dds_find_topic
 74      // is that it creates a topic with the same name, type *and QoS*.  That distinction only matters if
 75      // topic is discovery is enabled and/or if the topic has a durability kind of of transient or persistent:
 76      // - using a different topic QoS might result in an incompatible QoS notification if topic discovery is
 77      //   enabled (everything would still work).
 78      // - transient/persistent data behaviour is defined in terms of the topic QoS actually really matters
 79      //
 80      // So we try to use dds_find_topic, and if that fails, try to go the other route using the writer's QoS
 81      // as an approximation of the topic QoS.
 82      if ((*topic = dds_find_topic (DDS_FIND_SCOPE_GLOBAL, participant, ep->topic_name, typeinfo, DDS_SECS (2))) < 0)
 83      {
 84        fprintf (stderr, "dds_find_topic: %s ... continuing on the assumption that topic discovery is disabled\n", dds_strretcode (*topic));
 85        dds_topic_descriptor_t *descriptor;
 86        if ((ret = dds_create_topic_descriptor(DDS_FIND_SCOPE_GLOBAL, participant, typeinfo, DDS_SECS (10), &descriptor)) < 0)
 87        {
 88          fprintf (stderr, "dds_create_topic_descriptor: %s\n", dds_strretcode (ret));
 89          dds_return_loan (triggered_reader, &epraw, 1);
 90          goto error;
 91        }
 92        if ((*topic = dds_create_topic (participant, descriptor, ep->topic_name, ep->qos, NULL)) < 0)
 93        {
 94          fprintf (stderr, "dds_create_topic_descriptor: %s (be sure to enable topic discovery in the configuration)\n", dds_strretcode (*topic));
 95          dds_delete_topic_descriptor (descriptor);
 96          dds_return_loan (triggered_reader, &epraw, 1);
 97          goto error;
 98        }
 99        dds_delete_topic_descriptor (descriptor);
100      }
101      // The topic suffices for creating a reader, but we also need the TypeObject to make sense of the data
102      if ((*xtypeobj = load_type_with_deps (participant, typeinfo, &ppc)) == NULL)
103      {
104        fprintf (stderr, "loading type with all dependencies failed\n");
105        dds_return_loan (triggered_reader, &epraw, 1);
106        goto error;
107      }
108      if (load_type_with_deps_min (participant, typeinfo, &ppc) == NULL)
109      {
110        fprintf (stderr, "loading minimal type with all dependencies failed\n");
111        dds_return_loan (triggered_reader, &epraw, 1);
112        goto error;
113      }
114    }
115    dds_return_loan (triggered_reader, &epraw, 1);
116  }
117  if (*xtypeobj)
118  {
119    // If we got the type object, populate the type cache
120    size_t align, size;
121    build_typecache_to (&(*xtypeobj)->_u.complete, &align, &size);
122    fflush (stdout);
123    struct typeinfo templ = { .key = { .key = (uintptr_t) *xtypeobj } } , *info;
124    if ((info = type_cache_lookup (&templ)) != NULL)
125    {
126      assert (info->release == NULL);
127      info->release = *xtypeobj;
128    }
129    else
130    {
131      // not sure whether this is at all possible
132      info = malloc (sizeof (*info));
133      assert (info);
134      *info = (struct typeinfo){ .key = { .key = (uintptr_t) *xtypeobj }, .typeobj = &(*xtypeobj)->_u.complete, .release = *xtypeobj, .align = align, .size = size };
135      type_cache_add (info);
136    }
137  }
138error:
139  dds_delete (dcpspublication_reader);
140  dds_delete (dcpssubscription_reader);
141  dds_delete (waitset);
142  return (*xtypeobj != NULL) ? DDS_RETCODE_OK : DDS_RETCODE_TIMEOUT;
143}
144
145int main (int argc, char **argv)
146{
147  dds_return_t ret = 0;
148  dds_entity_t topic = 0;
149
150  // for printf("%ls")
151  setlocale (LC_CTYPE, "");
152
153  if (argc != 2)
154  {
155    fprintf (stderr, "usage: %s topicname\n", argv[0]);
156    return 2;
157  }
158
159  participant = dds_create_participant (DDS_DOMAIN_DEFAULT, NULL, NULL);
160  if (participant < 0)
161  {
162    fprintf (stderr, "dds_create_participant: %s\n", dds_strretcode (participant));
163    return 1;
164  }
165
166  // The one magic step: get a topic and type object ...
167  DDS_XTypes_TypeObject *xtypeobj;
168  type_cache_init ();
169  if ((ret = get_topic_and_typeobj (argv[1], DDS_SECS (10), &topic, &xtypeobj)) < 0)
170  {
171    fprintf (stderr, "get_topic_and_typeobj: %s\n", dds_strretcode (ret));
172    goto error;
173  }
174  // ... given those, we can create a reader just like we do normally ...
175  const dds_entity_t reader = dds_create_reader (participant, topic, NULL, NULL);
176  // ... and create a waitset that allows us to wait for any incoming data ...
177  const dds_entity_t waitset = dds_create_waitset (participant);
178  const dds_entity_t readcond = dds_create_readcondition (reader, DDS_ANY_STATE);
179  (void) dds_waitset_attach (waitset, readcond, 0);
180  while (1)
181  {
182    (void) dds_waitset_wait (waitset, NULL, 0, DDS_INFINITY);
183    void *raw = NULL;
184    dds_sample_info_t si;
185    if ((ret = dds_take (reader, &raw, &si, 1, 1)) < 0)
186      goto error;
187    else if (ret != 0)
188    {
189      // ... that we then print
190      print_sample (si.valid_data, raw, &xtypeobj->_u.complete);
191      if ((ret = dds_return_loan (reader, &raw, 1)) < 0)
192        goto error;
193    }
194  }
195
196 error:
197  type_cache_free ();
198  dds_delete (participant);
199  return ret < 0;
200}
variouspub_types.idl
 1struct A {
 2  @key
 3  string name;
 4  string message;
 5  unsigned long count;
 6};
 7
 8struct T {
 9  short s;
10  long l;
11};
12
13struct B {
14  A a;
15  sequence<T> ts;
16};
17
18struct C {
19  B b;
20  @key
21  short k;
22};
23
24module M1 {
25  @appendable
26  struct O {
27    @optional long x;
28  };
29};
30
31struct D {
32  wstring ws;
33  wchar wc;
34  unsigned long count;
35};
variouspub.c
  1#include <stdio.h>
  2#include <string.h>
  3#include <stdlib.h>
  4#include <signal.h>
  5#include <assert.h>
  6
  7#include "dds/dds.h"
  8#include "variouspub_types.h"
  9
 10static void *samples_a[] = {
 11  &(A){ "Mariken",   "Wie sidi, vrient?", 0 },
 12  &(A){ "Die duvel", "Een meester vol consten,", 0 },
 13  &(A){ "Die duvel", "Nieuwers af falende, wes ic besta.", 0 },
 14  &(A){ "Mariken",   "'t Comt mi alleleens met wien dat ick ga,", 0 },
 15  &(A){ "Mariken",   "Also lief gae ic metten quaetsten als metten besten.", 0 },
 16  NULL
 17};
 18
 19static void *samples_b[] = {
 20  &(B){ {"Die duvel", "Wildi u liefde te mi werts vesten,", 0},
 21        { ._length = 2, ._maximum = 2, ._release = false,
 22          ._buffer = (T[]){ {2,3},{5,7} } } },
 23  &(B){ {"Die duvel", "Ick sal u consten leeren sonder ghelijcke,", 0},
 24        { ._length = 3, ._maximum = 3, ._release = false,
 25          ._buffer = (T[]){ {11,13},{17,19},{23,29} } } },
 26  &(B){ {"Die duvel", "Die seven vrie consten: rethorijcke, musijcke,", 0},
 27        { ._length = 5, ._maximum = 5, ._release = false,
 28          ._buffer = (T[]){ {31,37},{41,43},{47,52},{59,61},{67,71} } } },
 29  &(B){ {"Die duvel", "Logica, gramatica ende geometrie,", 0},
 30        { ._length = 7, ._maximum = 7, ._release = false,
 31          ._buffer = (T[]){ {73,79},{83,89},{97,101},{103,107},{109,113},
 32                            {127,131},{137,139} } } },
 33  &(B){ {"Die duvel", "Aristmatica ende alkenie,", 0},
 34        { ._length = 11, ._maximum = 11, ._release = false,
 35          ._buffer = (T[]){ {149,151},{157,163},{167,173},{179,181},
 36                            {191,193},{197, 199},{211,223},{227,229},
 37                            {233,239},{241,251},{257,263} } } },
 38  NULL
 39};
 40
 41static void *samples_c[] = {
 42  &(C){ { {"Die duvel", "Dwelc al consten sijn seer curable.", 0},
 43          { ._length = 13, ._maximum = 13, ._release = false,
 44            ._buffer = (T[]){ {269,271},{277,281},{283,293},{307,311},
 45                              {313,317},{331,337},{347,349},{353,359},
 46                              {367,373},{379,383},{389,397},{401,409},
 47                              {419,421} } } },
 48        8936 },
 49  &(C){ { {"Die duvel", "Noyt vrouwe en leefde op eerde so able", 0},
 50          { ._length = 17, ._maximum = 17, ._release = false,
 51            ._buffer = (T[]){ {431,433},{439,443},{449,457},{461,463},
 52                              {467,479},{487,491},{499,503},{509,521},
 53                              {523,541},{547,557},{563,569},{571,577},
 54                              {587,593},{599,601},{607,613},{617,619},
 55                              {631,641} } } },
 56        18088 },
 57  &(C){ { {"Die duvel", "Als ic u maken sal.", 0},
 58          { ._length = 19, ._maximum = 19, ._release = false,
 59            ._buffer = (T[]){ {643,647},{653,659},{661,673},{677,683},
 60                              {691,701},{709,719},{727,733},{739,743},
 61                              {751,757},{761,769},{773,787},{797,809},
 62                              {811,821},{823,827},{829,839},{853,857},
 63                              {859,863},{877,881},{883,887} } } },
 64        29172 },
 65  &(C){ { {"Mariken",  "So moetti wel zijn een constich man.", 0},
 66          { ._length = 23, ._maximum = 23, ._release = false,
 67            ._buffer = (T[]){ {907,911},{919,929},{937,941},{947,953},
 68                              {967,971},{977,983},{991,997},{1009,1013},
 69                              {1019,1021},{1031,1033},{1039,1049},{1051,1061},
 70                              {1063,1069},{1087,1091},{1093,1097},{1103,1109},
 71                              {1117,1123},{1129,1151},{1153,1163},{1171,1181},
 72                              {1187,1193},{1201,1213},{1217,1223} } } },
 73        16022 },
 74  &(C){ { {"Mariken",  "Wie sidi dan?", 0},
 75          { ._length = 29, ._maximum = 29, ._release = false,
 76            ._buffer = (T[]){ {1229,1231},{1237,1249},{1259,1277},{1279,1283},
 77                              {1289,1291},{1297,1301},{1303,1307},{1319,1321},
 78                              {1327,1361},{1367,1373},{1381,1399},{1409,1423},
 79                              {1427,1429},{1433,1439},{1447,1451},{1453,1459},
 80                              {1471,1481},{1483,1487},{1489,1493},{1499,1511},
 81                              {1523,1531},{1543,1549},{1553,1559},{1567,1571},
 82                              {1579,1583},{1597,1601},{1607,1609},{1613,1619},
 83                              {1621,1627} } } },
 84        17880 },
 85  NULL
 86};
 87
 88static int32_t long_4 = 4;
 89static void *samples_M1_O[] = {
 90  &(M1_O){ .x = NULL },
 91  &(M1_O){ .x = &long_4 },
 92  NULL
 93};
 94
 95static void *samples_d[] = {
 96  &(D){ L"😀 Een Kruyck gaat soo langh te water tot datse barst.", 0x2206, 0 },
 97  &(D){ L"🙃 Men treckt een Boogh soo lang tot datse stucken knarst.", 0x2207, 0 },
 98  &(D){ L"😊 De Steel-kunst doet zyn Meester de dood vaak verwerven.", 0x22a5, 0 },
 99  NULL
100};
101
102static struct tpentry {
103  const char *name;
104  const dds_topic_descriptor_t *descr;
105  void **samples;
106  size_t count_offset;
107} tptab[] = {
108  { "A", &A_desc, samples_a, offsetof (A, count) },
109  { "B", &B_desc, samples_b, offsetof (B, a.count) },
110  { "C", &C_desc, samples_c, offsetof (C, b.a.count) },
111  { "M1::O", &M1_O_desc, samples_M1_O, SIZE_MAX },
112  { "D", &D_desc, samples_d, offsetof (D, count) },
113  { NULL, NULL, NULL, 0 }
114};
115
116static void usage (const char *argv0)
117{
118  fprintf (stderr, "usage: %s {", argv0);
119  const char *sep = "";
120  for (struct tpentry *tpentry = &tptab[0]; tpentry->name; tpentry++)
121  {
122    fprintf (stderr, "%s%s", sep, tpentry->name);
123    sep = "|";
124  }
125  fprintf (stderr, "}\n");
126  exit (2);
127}
128
129static volatile sig_atomic_t interrupted;
130
131static void sigint (int sig)
132{
133  (void) sig;
134  interrupted = 1;
135}
136
137int main (int argc, char **argv)
138{
139  if (argc != 2)
140    usage (argv[0]);
141  struct tpentry *tpentry;
142  for (tpentry = &tptab[0]; tpentry->name; tpentry++)
143    if (strcmp (tpentry->name, argv[1]) == 0)
144      break;
145  if (tpentry->name == NULL)
146    usage (argv[0]);
147
148  const dds_entity_t participant = dds_create_participant (DDS_DOMAIN_DEFAULT, NULL, NULL);
149  if (participant < 0)
150  {
151    fprintf (stderr, "dds_create_participant: %s\n", dds_strretcode (participant));
152    return 1;
153  }
154
155  const dds_entity_t topic = dds_create_topic (participant, tpentry->descr, tpentry->name, NULL, NULL);
156  const dds_entity_t writer = dds_create_writer (participant, topic, NULL, NULL);
157  uint32_t sample_idx = 0;
158  uint32_t count = 0;
159  signal (SIGINT, sigint);
160  while (!interrupted)
161  {
162    dds_return_t ret = 0;
163    void *sample = tpentry->samples[sample_idx];
164    uint32_t * const countp =
165      (tpentry->count_offset != SIZE_MAX)
166      ? (uint32_t *) ((unsigned char *) sample + tpentry->count_offset)
167      : 0;
168    if (countp)
169      *countp = count++;
170    if ((ret = dds_write (writer, sample)) < 0)
171    {
172      fprintf (stderr, "dds_write: %s\n", dds_strretcode (ret));
173      dds_delete (participant);
174      return 1;
175    }
176    if (tpentry->samples[++sample_idx] == NULL)
177    {
178      sample_idx = 0;
179    }
180    dds_sleepfor (DDS_SECS (1));
181  }
182
183  dds_delete (participant);
184  return 0;
185}