PubNub POSIX C++ SDK 4.15.0

Get Code: Source​

Hello World​

We recommend you use the Makefiles as a starting point in your own projects (whether they are based on Make or some other build tool / system or IDE).

Makefiles​

  • The Makefile to build for POSIX C++ is available at posix.mk. Please take a look at README for general info about the repo layout & contents.

  • The Makefile for Posix C++ with SSL/TLS (via OpenSSL) is available at posix_openssl.mk in the repo. See /openssl/README.md for info on how to build with OpenSSL on POSIX C++ and other OpenSSL related data.

Including the Header​

To include the PubNub POSIX C++ headers into your app, you must include pubnub.hpp:

#include "pubnub.hpp"
#include <iostream>

Once the header has been included, its easy to make calls to the PubNub service via the POSIX C++ API. The PubNub POSIX C++ API is flexible, supporting many different calling patterns. As such, before we dive in to actual coding samples, its important to go over the different types of calling patterns provided by the PubNub POSIX C++ client's futures support.

C++ Calling Patterns: Futures​

pubnub::futres

The pubnub::futres class name is a portmanteau, blending C++ future with enum pubnub_res. It was purposely not named pubnub::future to avoid namespacing conflicts.

Both POSIX and Windows C++ SDKs use the pubnub::futres class, based on the std::future class (introduced in C++ 11) which provides a way to track the outcome of an operation asynchronously. Every operation that the SDK initiates with PubNub returns a futures object. This object allows to track the progress and completion of the operation via the status identifiers.

Using Futures Synchronously​

There are several ways to use futures synchronously:

  • Single await() or get()
  • Separated start_await() and end_await()
  • Your own last_result() loop
Single await() or get()​

The pubnub::futres::await() method, similar to the pubnub_await() function from the C sync interface, is used to await the outcome of a transaction/operation. Since its function is the same as std::future<>::get(), we provide a synonym, and you can call pubnub::futres::get() with the same effect.

pubnub::context pb("demo", "demo");
pubnub::futres f = pb.publish("hello_world", "\"Here I am!\"");
if (PNR_OK == f.await()) {
    std::cout << "Published OK" << std::endl;
}
pubnub::futres f = pb.publish("hello_world", "\"Stuck in the middle\"");
if (PNR_OK == f.get()) {
    std::cout << "Published OK (again)" << std::endl;
}
Separated start_await() and end_await()​

You don't have to await at once. You can start the await, and finish later. This is useful if you are working with more than one context, so you start an operation on one context, then start the await on that context, proceed to start an operation on another context and then end the started await.

pubnub::context pb("demo", "demo");
pubnub::context pbsub("demo", "demo");
pbsub.subscribe("hello_world").await();  // connect
pubnub::futres fsub = pbsub.subscribe("hello_world");
fsub.start_await();
pubnub::futres f = pb.publish("hello_world", "\"with you!\"");
if (PNR_OK == f.await()) {
    std::cout << "Published OK" << std::endl;
}
if (PNR_OK == fsub.end_await()) {
    std::cout << "Received messages:" << std::endl;
    for (auto &&msg : pbsub.get_all()) {
        std::cout << msg << std::endl;
    }
}
Your own last_result() loop​

You don't have to use the await() functions. You can call last_result() in a loop and perform other operations. If you aren't doing other operations, this pattern won't be that useful for you -- in that case, just call await().

pubnub::context pb("demo", "demo");
pubnub::futres f = pb.publish("hello_world", "\"Waiting for Godot\"");
for (;;) {
    pubnub_res result = f.last_result();
    if (result() == PNR_STARTED) {
        // Do something while we wait
        play_some_tetris();
    }
    else if (PNR_OK == f.get()) {
        std::cout << "Published OK" << std::endl;
    }
}

Using Futures Asynchronously​

All asynchronous logic is built upon pubnub::futres::then() (similar to what is available in some future libraries, and proposed for addition to C++17). There are several ways to use futures asynchronously:

  • Using futures with a callback
  • Using futures with a lambda
  • Using futures with a function object
Using futures with a callback​

By providing a free function or a static class method, you'll be using the C++ client similarly to that of the C callback interface.

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.

static void on_publish(pubnub::context &pb, pubnub_res result)
{
    if (PNR_OK == result) {
          std::cout << "Published OK" << std::endl;
      }
}

int main(int argc, char *argv[])
{
    pubnub::context pb("demo", "demo");
    pubnub::futres f = pb.publish("hello_world", "\"Don't call us\"");
    f.then(on_publish);
    return 0;
}
Using futures with a lambda​

Instead of a function, you can also pass a lambda to pubnub::futres::then:

pubnub::context pb("demo", "demo");
pubnub::futres f = pb.publish("hello_world", "\"Lambda\"");
f.then([=](pubnub::context &pb, pubnub_res result) {
    if (PNR_OK == result) {
        std::cout << "Published OK" << std::endl;
    }
    pubnub::futres f2 = pb.publish("hello_world", "\"the ultimate\"");
    f2.then([=](pubnub::context &pb, pubnub_res result) {
        if (PNR_OK == result) {
            std::cout << "Published OK (nested)" << std::endl;
        }
    });
});
Using futures with a function object​

You can pass a callable object to pubnub::futres::then() - that is, an object of a class with an overloaded function call operator:

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.

class bean_counter {
    int beans;
    public:
        bean_counter() : beans(0) {}
        void operator()(pubnub::context &pb, pubnub_res result) {
            if (PNR_OK == result) {
                ++beans;
            }
                  std::cout << "Published " << beans << " beans" << std::endl;
        }
};

int main(int argc, char *argv[])
{
    pubnub::context pb("demo", "demo");
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Since std::function<> is a generic function object, if you have one, just pass it to pubnub::futres::then:

void planet_express(std::function<void(pubnub::context&,pubnub_res)> parcel)
{
    pubnub::context pb("demo", "demo");
    pubnub::futres f = pb.publish("hello_world", "\"Deliver\"");
    f.then(parcel);
}

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.

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"
#include <stdio.h>
int main()
{
    pubnub_t *ctx = pubnub_alloc();
    if (NULL == ctx) {
        puts("Couldn't allocate a Pubnub context");
        return -1;
    }
    /* Do something with ctx...
        and then: */
    pubnub_free(ctx);
    return 0
}

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 canceling 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 POSIX, you likely are, then:

  1. If at all possible, use a single context from only one thread - the one that created it.
  2. If this 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.
Threads and contexts

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).

Transaction and Operation​

The Posix C++ SDK operates as a set of transactions. A transaction is initiated by the client SDK and is defined as a single message exchange between the SDK and PubNub service. Every interaction that the client SDK initiates with PubNub is sequenced as a series of transactions which ultimately results in a PubNub service-specific operation.

Status and Events​

The SDK provides a set of status and event identifiers which can help developers interact with the library. The status identifier codes are returned as part of the SDK's API invocation. These are used by the developer to check for status of transactions or for detecting normal / abnormal conditions in an API call. Some of the commonly used status codes are as follows

  • PNR_OK: Success, the transaction finished successfully
  • PNR_STARTED: The previously initiated transaction has started.
  • PNR_IN_PROGRESS: Indicates that the previous transaction with PubNub service is still in progress.

Refer to the API docs for a complete list of status identifiers supported by the library.

Events refer to the PubNub REST operations which are initiated by the client SDK. The most common example of events are subscribe and publish. A client subscribing for a channel is a subscribe event and a client publishing a message on a channel is a publish event.

Some of the common event identifiers are as follows:

  • PBTT_SUBSCRIBE: Subscriber operation
  • PBTT_PUBLISH: Publish operation

Refer to the API docs for a complete list of operations supported by the SDK.

Calling Patterns​

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

Sync​

The sync interface 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_callback()
  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.

Hello World Sample Code​

Now that we delved into the inner workings of it all, lets get started with a simple, complete example using all the possible futures calling patterns to init, then publish and subscribe:

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.

// Sync version
#include "pubnub.hpp"
#include <iostream>
const std::string channel("hello_world");

void hello_world() {
  enum pubnub_res res;
  enum pubnub_res res2;

  pubnub::context pn("", "demo");
  pubnub::context pn2("demo", "demo");
  std::string uuid("myUniqueUUID");
  pn.set_uuid(uuid);

  int loop = 0;
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// Lambdas version
#include "pubnub.hpp"

#include <iostream>

const std::string channel("hello_world");

void publish() {
  pubnub_res res;

  pubnub::context pn("demo", "demo");
  res = pn.publish(channel, "\"Hello from PubNub Docs!\"").await();

  if (PNR_OK == res || PNR_PUBLISH_FAILED == res) {
    std::cout << pn.last_publish_result() << std::endl;
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// Functions version
#include "pubnub.hpp"
#include <iostream>

const std::string channel("hello_world");
static bool done = false;
static bool first = true;

static void on_publish(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res || PNR_PUBLISH_FAILED == res) {
    std::cout << pn.last_publish_result() << std::endl;
  }
}

void on_subscribe(pubnub::context &pn, pubnub_res res) {
show all 44 lines

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 Posix C++ instance.

secret_key

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::context pn("my_pubkey", "my_subkey");
std::string uuid("myUniqueUUID");
pn.set_uuid(uuid);

Time​

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

// Sync
void time(pubnub::context &pn) {
  enum pubnub_res res;

  res = pn.time().await();

  if (PNR_OK == res) {
    std::cout << pn.get() << std::endl;
  } else {
    std::cout << "Request failed" << std::endl;
  }
}
// Lambdas
void time(pubnub::context &ipn) {
  ipn.time().then([=](pubnub::context &pn, pubnub_res res) {
      if (PNR_OK == res) {
        std::cout << pn.get() << std::endl;
      } else {
        std::cout << "Request failed" << std::endl;
      }
    });
}
// Functions
void on_time(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res) {
    std::cout << pn.get() << std::endl;
  } else {
    std::cout << "Request failed" << std::endl;
  }
}

void time(pubnub::context &pn) {
  pn.time().then(on_time);
}

Subscribe​

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

Retrieving messages

Typically, you will want two separate contexts for publish and subscribe anyway. If you are changing the set of channels you subscribe to, you should first call leave() on the old set.

The subscribe() interface is essentially a transaction to start listening on the channel for arrival of next message. This has to be followed by a call to the method get() or get_all( ) 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.

// Sync
void subscribe(pubnub::context &pn) {
  enum pubnub_res res;

  for (;;) {
    res = pn.subscribe("my_channel").await();

    if (PNR_OK == res) {
      std::vector<std::string> msg = pn.get_all();

      for (std::vector<std::string>::iterator it = msg.begin(); it != msg.end(); ++it) {
       std::cout << *it << std::endl;
      }
    } else {
      std::cout << "Request failed" << std::endl;
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// Lambdas
void subscribe(pubnub::context &ipn) {
  ipn.subscribe("my_channel").then([=](pubnub::context &pn, pubnub_res res) {
    auto msg = pn.get_all();

    if (PNR_OK == res) {
      for (auto &&m: msg) {
        std::cout << m << std::endl;
      }

    } else {
      std::cout << "Request failed" << std::endl;
    }
  });
}
// Functions
void on_subscribe(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res) {
    std::vector<std::string> msg = pn.get_all();

    for (std::vector<std::string>::iterator it = msg.begin(); it != msg.end(); ++it) {
      std::cout << *it << std::endl;
    }
  } else {
    std::cout << "Request failed" << std::endl;
  }
}

void subscribe(pubnub::context &pn) {
  pn.subscribe("my_channel").then(on_subscribe);
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Publish​

Publish a message to a channel:

// Sync
void publish(pubnub::context &pn) {
  enum pubnub_res res;

  res = pn.publish("my_channel", "\"Hello from the PubNub C++ SDK!\"").await();

  if (PNR_OK == res) {
    std::cout << pn.last_publish_result() << std::endl;
  } else {
    std::cout << "Publish request failed" << std::endl;
  }
}
// Lambdas
void publish(pubnub::context &pn) {
  pn.publish("my_channel", "\"Hello from the PubNub C++ SDK!\"").
    then([=](pubnub::context &pn, pubnub_res res) {
      if (PNR_OK == res) {
        std::cout << pn.last_publish_result() << std::endl;
      } else {
        std::cout << "Publish request failed" << std::endl;
      }
    });
}
// Functions
static void on_publish(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res) {
    std::cout << pn.last_publish_result() << std::endl;
  } else {
    std::cout << "Publish request failed" << std::endl;
  }
}

void publish(pubnub::context &pn) {
  pn.publish("my_channel", "\"Hello from the PubNub C++ SDK!\"").then(on_publish);
}

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
void here_now(pubnub::context &pn) {
  enum pubnub_res res;

  res = pn.here_now("my_channel").await();

  if (PNR_OK == res) {
    std::cout << pn.get() << std::endl;
  } else {
    std::cout << "Here Now request failed" << std::endl;
  }
}
// Lambdas
void here_now(pubnub::context &pn) {
  pn.here_now("my_channel").then([=](pubnub::context &pn, pubnub_res res) {
      if (PNR_OK == res) {
        std::cout << pn.get() << std::endl;
      } else {
        std::cout << "Here Now request failed" << std::endl;
      }
    });
}
// Functions
void on_here_now(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res) {
    std::cout << pn.get() << std::endl;
  } else {
    std::cout << "Here Now request failed" << std::endl;
  }
}

void here_now(pubnub::context &pn) {
  pn.here_now("my_channel").then(on_here_now);
}

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
void presence(pubnub::context &pn) {
  enum pubnub_res res;
  bool done = false;

  while (!done) {
    res = pn.subscribe("my_channel-pnpres").await();

    if (PNR_OK == res) {
      std::vector<std::string> msg = pn.get_all();

      for (std::vector<std::string>::iterator it = msg.begin(); it != msg.end(); ++it) {
        std::cout << *it << std::endl;
      }

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// Lambdas
void presence(pubnub::context &ipn) {
  bool done = false;

  while (!done) {
    ipn.subscribe("my_channel-pnpres").then([&](pubnub::context &pn, pubnub_res res) {
      auto msg = pn.get_all();

      if (PNR_OK == res) {
        for (auto &&m: msg) {
          std::cout << m << std::endl;
        }

        if (msg.size() > 0) {
          done = true;
show all 22 lines
// Functions
void on_presence(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res) {
    std::vector<std::string> msg = pn.get_all();

    for (std::vector<std::string>::iterator it = msg.begin(); it != msg.end(); ++it) {
      std::cout << *it << std::endl;
    }

    if (msg.size() > 0) {
      done = true;
    }
  } else {
    std::cout << "Error" << std::endl;
  }
show all 22 lines

History​

Retrieve published messages from archival storage:

Requires Message Persistence

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

// Sync
void history(pubnub::context &pn) {
  enum pubnub_res res;

  res = pn.history("history_channel", 100).await();;

  if (PNR_OK == res) {
    std::vector<std::string> msg = pn.get_all();

    for (std::vector<std::string>::iterator it = msg.begin(); it != msg.end(); ++it) {
      std::cout << *it << std::endl;
    }
  } else {
    std::cout << "History request failed" << std::endl;
  }
show all 16 lines
// Lambdas
void history(pubnub::context &ipn) {
  ipn.history("history_channel").then([=](pubnub::context &pn, pubnub_res res) {
    auto msg = pn.get_all();

    if (PNR_OK == res) {
      for (auto &&m: msg) {
        std::cout << m << std::endl;
      }
    } else {
      std::cout << "Request failed" << std::endl;
    }
  });
}
// Functions
void on_history(pubnub::context &pn, pubnub_res res) {
  if (PNR_OK == res) {
    std::vector<std::string> msg = pn.get_all();

    for (std::vector<std::string>::iterator it = msg.begin(); it != msg.end(); ++it) {
      std::cout << *it << std::endl;
    }
  } else {
    std::cout << "History request failed" << std::endl;
  }
}

void history(pubnub::context &pn) {
  pn.history("history_channel", 100).then(on_history);
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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 - i.e., 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 cancel().
    4. Wait for the cancellation to finish (here you can call pubnub_await(), unless you want to do other stuff while you wait).
auto futr = ctx.subscribe( "my_channel");
/* If we don't set non-blocking I/O, we can't get out of a blocked read */
ctx.set_blocking_io(pubnub::blocking);
/* Can't use await() here, it will block */
auto pbresult = PNR_STARTED;
while (PNR_STARTED == pbresult) {
    pbresult = futr.last_result();
    /* Somehow decide we want to quit / unsubscribe */
    if (should_stop()) {
        ctx.cancel();
        /* 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 = futr.await();
        break;
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