PubNub FreeRTOS SDK 4.15.0

Get Code: Source​

Hello World​

There is no installation of this SDK. Just clone the Git(hub) repo, or download a ZIP or tarball of a release from https://github.com/pubnub/c-core/releases It has the code and example Visual Studio solutions to get you started, using the FreeRTOS Windows simulator. Please take a look at README.md in the root of the repo for general info about the repo layout & contents.

Solution for FreeRTOS+TCP (without SSL/TLS support) is at /freertos/samples/Pubnub.sln in the repo. Also, check /freertos/README.md for info on how to build on Windows. Solution should work with Visual Studio 2010 or newer.

Use the solution and its projects as a starting point in your own projects (whether they are based on Visual Studio or some other build tool / system or IDE).

Code Sample​

Required UUID

Always set the UUID to uniquely identify the user or device that connects to PubNub. This UUID should be persisted, and should remain unchanged for the lifetime of the user or the device. If you don't set the UUID, you won't be able to connect to PubNub.

#include "pubnub_alloc.h"

int memory_allocation_sample()
{
    pubnub_t *ctx = pubnub_alloc();
    if (NULL == ctx) {
        return -1;
    }
    /* Do something with ctx...
        and then: */
    pubnub_free(ctx);
    return 0
}

FreeRTOS+TCP remarks​

Pubnub SDK for FreeRTOS+TCP doesn't initialize the TCP/IP stack. It is expected that the user will initialize TCP/IP stack before the first call to any Pubnub SDK function. Other than that, there are no other special requirements for the usage of this SDK. You don't have to create a special task to use the SDK, or call some function in your task before you use the SDK, or anything like that.

FreeRTOS and its FreeRTOS+TCP stack are configurable. Pubnub SDK will adapt to the configuration that the user selects as much as possible, but, not all configurations are supported. Foremost, since TCP is required, you can't only build UDP.

Memory Allocation​

This client uses dynamic memory allocation for the PubNub contexts, but the usage is the same as for any other Pubnub C client - always use pubnub_alloc() to create a context (and check its return value) and always use pubnub_free() to dispose of a context.

Timers​

We only provide one timer - the (total) transaction timer. In general, it is started when a transaction is started and stopped when a transaction is finished. If it expires, the transaction will be cancelled. Keep in mind that this cancelling is local, so, for example, if you already published a message, but, for some reason, the HTTP response didn't arrive in time, this canceling will not revoke the publish - it will just stop the wait for response.

If the transaction timer expires, the outcome of the transaction will be timeout - different than when you cancel a transaction yourself.

The actual duration of the timer is at least as long as you set it. It could be significantly higher, depending on various platform issues. But, in general, it will be close to what you set.

You should set the timer after initializing the context and before starting a transaction. The duration you set will be used for all subsequent transactions, regardless of their type (i.e. for publish and subscribe and all other).

Thread safety​

C-core supports thread-safe operation, though, for performance, you may think about not using it. To use thread-safety support, define the preprocessor symbol PUBNUB_THREADSAFE (just define it, the value does not matter).

Thread-safe usage​

Thread safety is internal. Just because you can access the PubNub context through the PubNub C-core SDK API from different threads safely, doesn't mean you're off the hook for your own data that is related to a context. For example, if you're using the callback interface and signalling an event from it to other (worker) thread(s), you have to synchronise that data transfer yourself.

If you compiled thread-safety support in, you are free to access the same context from different threads, pretty much in any way you wish. However, there are some advised guidelines you should follow:

  • If you're using the sync blocking interface, threads that come to wait on the context may wait a long time, so try to avoid it (also, re-think your whole need for a thread-safe C-core)
  • If you're using the sync non-blocking interface by calling pubnub_await, things are pretty much the same as for sync blocking interface
  • If you're using the sync non-blocking interface and avoid pubnub_await, waiting threads will not block so long, but, pretty much the only useful thing you can do is cancel a transaction from another thread.
  • Using the sync interface, it's perfectly fine to call pubnub_await or pubnub_last_result in different threads, but, you probably shouldn't do that, as it will make debugging harder.
  • If you're using the callback interface, it's perfectly fine to call Functions from your callback, but, you should avoid doing that, except for some helper functions. Following this guideline will make your debugging, thus life, a lot easier

Thread-unsafe usage​

If you compile without thread-safety support, obviously, you will have an SDK which is not thread safe - that is, it is not safe to use a single context from more than one thread at the same time. So, if you're using such SDK configuration in a multithreaded code, which, on FreeRTOS, you likely are, then:

  1. If at all possible, use a single context from only one thread - the one that created it
  2. If 1. is not possible, provide some synchronization yourself, for example, using pthread condition variables, or just mutexes, or some higher abstraction, like message queues
  3. As a special case, if you're using the callback interface, you can start a transaction in one thread and then don't touch the context from that thread any more - use it only in the callback. This is safe.
Context usage

Keep in mind that it is perfectly safe to use different contexts from different threads at the same time. To each (thread) its own (context).

Calling Patterns​

This SDK provides sync and callback (notification) interfaces for retrieving the outcome of a Pubnub request/transaction/operation.

Sync​

The sync interface in general works like this:

  1. Start a transaction (say, publish - using pubnub_publish()).
  2. Either pubnub_await() the outcome or use your own loop in which you check if (PNR_STARTED != pubnub_last_result()).
  3. Handle the outcome as you wish.

This is illustrated in the Hello World example below (which is the same for any platform that supports sync interface).

Callback​

The callback interface is somewhat more flexible, uses less CPU resources, but is, in general, a little harder to use. One way to use it is to emulate the sync interface:

  1. Create a callback function (my_callback) per the prototype required by pubnub_register_callback().
  2. In my_callback(), use a condition variable to signal that outcome was received.
  3. Set the callback via pubnub_register_callbac().
  4. Start a transaction (say, publish - using pubnub_publish()).
  5. Wait on the condition variable (the same one used in my_callback).
  6. Handle the outcome as you wish.

This is illustrated in the Hello World example below, using pthreads condition variable. Obviously, on platforms that don't support pthreads you will use some similar API (for example, SetEvent/WaitForSingleObject on Windows).

There are other ways to use the callback interface, like the state machine or similar, where the callback will handle the outcome of a transaction but will also start the next Pubnub transaction, or do other stuff that it needs to do. This is application specific, so we don't provide an example here.

Calling Pattern Examples​

Sync Code Sample​

Required UUID

Always set the UUID to uniquely identify the user or device that connects to PubNub. This UUID should be persisted, and should remain unchanged for the lifetime of the user or the device. If you don't set the UUID, you won't be able to connect to PubNub.

#include "pubnub_sync.h"
int sync_sample()
{
    enum pubnub_res pbresult;
    pubnub_t *ctx = pubnub_alloc();
    if (NULL == ctx) {
        return -1;
    }
    pubnub_init(ctx, "demo", "demo");
    pubnub_set_uuid(ctx, "myUniqueUUID");
    /* Initial Subscribe on the "hello_world" channel */
    pubnub_subscribe(ctx, "hello_world", NULL);
    pbresult = pubnub_await(ctx);
    if (pbresult != PNR_OK) {
        pubnub_free(ctx);
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Callback Code Sample​

#include "pubnub_callback.h"

enum MyUserState {
    musIdle,
};
struct MyUserData {
    enum MyUserState state;
};
static struct MyUserData m_user_data;

void example_callback(pubnub_t *pb, enum pubnub_trans trans, enum pubnub_res result, void *user_data)
{
    struct MyUserData *my_user_data = user_data;
    switch (my_user_data->state) {
    case musIdle:
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Copy and paste examples​

In addition to the Hello World sample code, we also provide some copy and paste snippets of common API functions:

Init​

Instantiate a new Pubnub instance. Only the subscribe_key is mandatory. Also include publish_key if you intend to publish from this instance, and the secret_key if you wish to perform Access Manager administrative operations from this FreeRTOS instance.

Secure your secretKey

It is not a best practice to include the secret key in client-side code for security reasons.

When you init with secret_key, you get root permissions for the Access Manager. With this feature you don't have to grant access to your servers to access channel data. The servers get all access on all channels.

Required UUID

Always set the UUID to uniquely identify the user or device that connects to PubNub. This UUID should be persisted, and should remain unchanged for the lifetime of the user or the device. If you don't set the UUID, you won't be able to connect to PubNub.

pubnub_init(ctx, /*publish key*/"demo", /*subscribe key*/"demo");
pubnub_set_uuid(ctx, "myUniqueUUID");

Time​

Call pubnub_time() to verify the client connectivity to the origin:

// Sync
pubnub_time(ctx);
pbresult = pubnub_await(ctx);
if (PNR_OK == pbresult) {
    char const *gotten_time = pubnub_get(ctx);
}
// Callback
void some_function(pubnub_t *ctx)
{
    pubnub_time(ctx);
}

void example_callback(pubnub_t *pb, enum pubnub_trans trans, enum pubnub_res result, void *user_data)
{
    if (PNR_OK == result) {
        char const *gotten_time = pubnub_get(pb);
    }
}

Subscribe​

Subscribe (listen on) a channel (it's async!):

Message retrieval

Typically, you will want two separate contexts for publish and subscribe. When changing the active set of subscribed channels, first call pubnub_leave() on the old set. The pubnub_subscribe() interface is essentially a transaction to start listening on the channel for arrival of next message. This has to be followed by pubnub_get()call to retrieve the actual message, once the subscribe transaction completes successfully. This needs to be performed every time it is desired to retrieve a message from the channel.

pubnub_t *ctx = pubnub_alloc();

if (NULL == ctx) {
    return -1;
}
pubnub_init(ctx, "demo", "demo");
pubnub_subscribe(ctx, "hello_world", NULL);
pbresult = pubnub_await(ctx);
if (pbresult != PNR_OK) {
    printf("Failed to subscribe, error %d\n", pbresult);
    pubnub_free(ctx);
    return -1;
}
else {
    char const *msg = pubnub_get(ctx);
show all 22 lines

Publish​

Publish a message to a channel:

pubnub_t *ctx = pubnub_alloc();
if (NULL == ctx) {
    return -1;
}
pubnub_init(ctx, "demo", "demo");
pubnub_publish(ctx, "hello_world", "\"Hello from Pubnub C-core docs!\"");
pbresult = pubnub_await(ctx);
if (pbresult != PNR_OK) {
    pubnub_free(ctx);
    return -1;
}

Here Now​

Get occupancy of who's here now on the channel by UUID:

Requires Presence add-on

This method requires that the Presence add-on is enabled for your key in the Admin Portal. Read the support page on enabling add-on features on your keys.

// Sync
char const *chan = "my_channel";
char const *msg;
enum pubnub_res res;

res = pubnub_here_now(pn, chan, NULL);
if (res != PNR_STARTED) {
  return -1;
}

res = pubnub_await(pn);
if (res == PNR_STARTED) {
  return -1;
}

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//callback
int start_here_now(pubnub_t *pn) {
  char const *chan = "my_channel";
  if (PNR_STARTERD != pubnub_here_now(pn, chan, NULL)) {
    return -1;
  }
  return 0;
}
int receive_here_now(pubnub_t *pn, enum pubnub_res res) {
  char const *msg;
  if (res == PNR_STARTED) {
    return -1;
  }

  if (PNR_OK == res) {
show all 23 lines

Presence​

Subscribe to real-time Presence events, such as join, leave, and timeout, by UUID. Setting the presence attribute to a callback will subscribe to presents events on my_channel:

Requires Presence add-on

This method requires that the Presence add-on is enabled for your key in the Admin Portal. Read the support page on enabling add-on features on your keys.

// Sync
char *presence_channel = malloc(strlen(channel) + strlen(PUBNUB_PRESENCE_SUFFIX) + 1);
strcpy(presence_channel, channel);
strcat(presence_channel, PUBNUB_PRESENCE_SUFFIX);
pubnub_subscribe(ctx, presence_channel, NULL);
pbresult = pubnub_await(ctx);
if (PNR_OK == pbresult) {
    char const *presence_event = pubnub_get(ctx);
    while (presnce_event != NULL) {
        presence_event = pubnub_get(ctx);
    }
}
// Callback
void some_function(pubnub_t *ctx)
{
    char *presence_channel = malloc(strlen(channel) + strlen(PUBNUB_PRESENCE_SUFFIX) + 1);
    strcpy(presence_channel, channel);
    strcat(presence_channel, PUBNUB_PRESENCE_SUFFIX);
    pubnub_subscribe(ctx, presence_channel, NULL);
}

void example_callback(pubnub_t *pb, enum pubnub_trans trans, enum pubnub_res result, void *user_data)
{
    if (PNR_OK == result) {
        char const *presence_event = pubnub_get(pb);
        while (presence_event != NULL) {
            presence_event = pubnub_get(pb);
show all 18 lines

History​

Retrieve published messages from archival storage:

Requires Presence add-on

This method requires that the Presence add-on is enabled for your key in the Admin Portal. Read the support page on enabling add-on features on your keys.

// Sync
enum pubnub_res res;
const char *msg;

pubnub_history(pn, "history_channel", 10, false);
res = pubnub_await(pn);
if (PNR_OK == res) {
  for (;;) {
    msg = pubnub_get(pn);
    if (NULL == msg) {
      break;
    }
    // Print out, on Window simulator, `puts(msg)` should work
  }
} else {
show all 16 lines
// Callback
void start_get_last_10_messages(pubnub_t *pn) {
  enum pubnub_res res;
  const char *msg;

  pubnub_history(pn, "history_channel", 10, false);
}

void receive_last_10_messages(pubnub_t *pn, enum pubnub_res res) {

  if (PNR_OK == res) {
    for (;;) {
      msg = pubnub_get(pn);
      if (NULL == msg) {
        break;
show all 23 lines

Unsubscribe​

Stop subscribing (listening) to a channel.

To unsubscribe, you need to cancel a subscribe transaction.

  • If you configured SDK to be thread-safe, you can cancel at any time, but, the cancelling may actually fail - that is, your thread may wait for another thread to finish working with the context, and by the time your cancel request gets processed, the transaction may finish.

  • If you configured SDK to not be thread-safe, the only safe way to do it is to use the sync interface and:

    1. Set the context to use non-blocking I/O
    2. Wait for the outcome in a loop, checking for pubnub_last_result() - rather than calling pubnub_await()
    3. If a condition occurs that prompts you to unsubscribe, call pubnub_cancel()
    4. Wait for the cancellation to finish (here you can call pubnub_await(), unless you want to do other stuff while you wait)
pbresult = pubnub_subscribe(ctx, "my_channel", NULL);
/* If we don't set non-blocking I/O, we can't get out of a blocked read */
pubnub_set_non_blocking_io(ctx);
/* Can't use pubnub_await() here, it will block */
while (PNR_STARTED == pbresult) {
    pbresult = pubnub_last_result(ctx);
    /* Somehow decide we want to quit / unsubscribe */
    if (should_stop()) {
        pubnub_cancel(ctx);
        /* If we don't have anything else to do, it's OK to await now,
        but you could again have a loop "against" pubnub_last_result()
        */
        pbresult = pubnub_await(ctx);
        break;
    }
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