CFreeRTOSFreeRTOSWindows CmbedPosix CFreeRTOS Configuration API Reference for Realtime Apps

FreeRTOS complete API reference for building Realtime Applications on PubNub, including basic usage and sample code.

This documents the preprocessor definitions (macros) which are configuration options of C-core, which are kept in the pubnub_config.h header file. This header file is different for each platform. For some platforms, the definitions that "don't make sense" may be omitted from the header file.

Any definitions that you may find in pubnub_config.h, that are not listed here, should not be changed by the user.

Maximum number of PubNub contexts that can be used at the same time. It is used only if the contexts are statically allocated. The default on hosted platforms (POSIX, Windows…) is to use dynamically allocated contexts, so this is ignored. This is selected by linking in the "context allocation module" that you wish to use (static or dynamic).

A context is used to publish messages or subscribe to (get) them.

Each context can consume (for our purposes) a significant amount of memory, so don't put some number that is never going to be achieved here.

A typical configuration may consist of a single pubnub context for channel subscription and another pubnub context that will periodically publish messages about device status (with timeout lower than message generation frequency). This only needs two contexts.

Another typical setup may have a single subscription context and maintain a pool of contexts for each publish call triggered by an external event (e.g. a button push). This would need N+1 contexts, N being the number of external events.

Of course, there is nothing wrong with having just one context, but you can't publish and subscribe at the same time on the same context. This isn't as bad as it sounds, but may be a source of headaches (lost messages, etc).

Size, in octets, of the HTTP buffer. This is a major component of the memory size of the whole Pubnub context, but it is also an upper bound on URL-encoded form of published message, so if you need to construct big messages, you may need to raise this. So, if you need to publish only messages of up to 2Kb size, you don't need more than, say 2500 PUBNUB_BUF_MAXLEN. But, if you need to publish messages larger than 2Kb size, you would need a bigger buffer.

It is designed to be "settable" from the compiler options, with the value in the header being the default. But, it's perfectly fine to not set it in the compiler options but change its ("default") value in here.

Set to false (0) to use a static buffer and then set its size via PUBNUB_REPLY_MAXLEN. Set to true (anything !=0) to use a dynamic buffer, that is, dynamically try to allocate as much memory as needed for the buffer.

Default on hosted platforms (Windows, POSIX…) is to use dynamic reply buffer. But, be warned, this can be a lot of data, megabytes, even. If you don't really have that much memory to spare, you may be better of with the static reply butt. OTOH, if the reply is too long for your statically allocated buffer, your transaction will, effectively, fail. So, this is a trade-off that is specific to your application.

This is only significant if PUBNUB_DYNAMIC_REPLY_BUFFER is true. In that case it defines the size, in octets, of the reply buffer. It will hold the whole (HTTP) body of the reply, not the (HTTP) headers.

Replies of API calls longer than this will be discarded and an error will be reported. Specifically, this may cause lost messages returned by subscribe if too many too large messages got queued on the Pubnub server.

This is the string of the DNS hostname of the Pubnub network. In general, you should not change this. Also, if thus configured (see PUBNUB_ORIGIN_SETTABLE), you can change the origin at runtime.

But, in the case that you do need to change it at compile time, but not at runtime and want to save some RAM in the context, it's OK to change this macro.

If true (!=0), user will be able to change the origin at runtime. This incurs a small "memory penalty", of keeping the runtime origin in the context. This is the default, as the "penalty" is small.

If false (==0), user will not be able to change the origin at runtime. Use this if you need to squeeze the RAM memory footprint of C-core.

Duration of the transaction timeout set during context initialization, in milliseconds. Timeout duration in the context can be changed by the user after initialization (at runtime).

This is only used if timers support is used, which is the default on hosted platforms (POSIX, Windows…).

The size of the stack (in kilobytes) for the "polling" thread, when using the callback interface. We don't need much, so, if you want to conserve memory, you can try small values. It's hard to say what is the minimum, as it depends on the OS functions we call, but, you probably shouldn't try less than 64 KB.

Set to 0 to use the default stack size.

This is ignored when using the sync interface.

Set to true (!=0) to enable the proxy support. This is the default on hosted platforms (Windows, POSIX…). To actually use your proxy, you need to set proxy parameters (host, port, protocol….) with the appropriate C-core APIs.

Set to false (==0) to disable the proxy support. This can provide for significant code savings, which may be important if you wish the cut down the code/flash footprint.

Keep in mind that, depending on how you build C-core, this may not be enough. That is, you might also need to not compile and link the proxy modules. This is illustrated in the sample makefiles.

The maximum length (in characters) of the host name of the proxy that will be saved in the Pubnub context. Set this according to your proxy (or your "possible future proxies"). It's one "proxy hostname" per context, so, don't put kilobytes here "just in case", unless you know you can spare RAM.

Set to true (!=0) to use only the Publish and Subscribe transactions. Set to false to use all the available Pubnub transactions - this is the default on hosted (POSIX, Windows…) platforms.

This can provide for significant code size savings, if you don’t need anything more than publish and subscribes, which may be important if you wish the cut down the code/flash footprint.

Keep in mind that this is not "fully self contained". If you try to compile modules that are not needed when PUBNUB_ONLY_PUBSUB is true, you’ll get a warning. If you actually link them, you will only save the code memory if your linker discards modules that are not used - in general, that is what linkers do, but it depends on your linker and the options you pass to it.

This is designed to be set via compiler options, with the value in the header file being the default. But, there is nothing wrong with setting it in the header itself.

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).

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 very 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.

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.


#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
}

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).

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 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 pubnub 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

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.
 
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).

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

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).

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 very application specific, so we don't provide an example here.

This function is used for initializing the PubNub Client API context. This function must be called before attempting to utilize any API functionality in order to establish account level credentials such as publish_key and subscribe_key.
To Initialize Pubnub you can use the following method(s) in the FreeRTOS SDK:
  1. ParameterTypeRequiredDescription
    ppubnub_t*YesPointer to the Context to initialize (use pubnub_alloc() to obtain it)
    publish_keychar *YesPointer to the string of the key to use when publishing messages.
    subscribe_keychar *YesPointer to the string of the key to use when subscribing to messages
pubnub_t *ctx = pubnub_alloc();
if (NULL == ctx) {
    return -1;
}
pubnub_init(ctx, "demo", "demo");

pubnub_set_ssl_options(ctx, true, true, true);
It returns the Pubnub instance for invoking PubNub APIs like pubnub_publish(), pubnub_subscribe(), pubnub_history(), pubnub_here_now(), etc.
  1. pubnub_init(ctx, /*publish key*/"demo", /*subscribe key*/"demo");
  2. In the case where a client will only read messages and never publish to a channel, you can simply omit the publish_key when initializing the client:
    pubnub_init(ctx, "", "demo");
  3. Set a custom UUID to identify your users.
    pubnub_t *pn = pubnub_alloc();
    pubnub_init(pn, "myPublishKey", "mySubscribeKey");
    pubnub_set_uuid(pn, "myUniqueUUID");
  4. This examples demonstrates how to enable PubNub Transport Layer Encryption with SSL. Just initialize the client with 2nd set to true. The hard work is done, now the PubNub API takes care of the rest. Just subscribe and publish as usual and you are good to go.

    pubnub_t *ctx = pubnub_alloc();
    if (NULL == ctx) {
        return -1;
    }
    pubnub_init(ctx, "demo", "demo");
    
    pubnub_set_ssl_options(ctx, true, true, true);
    
These functions are used to set/get a user ID on the fly.
To set/get UUID you can use the following method(s) in FreeRTOS SDK
  1. ParameterTypeRequiredDescription
    ppubnub_t*YesPointer to pubnub context
    uuidconst char*YesPointer to uuid string
  2. ParameterTypeRequiredDescription
    ppubnub_t*YesPointer to pubnub client context.
    After pubnub_init(), it will return NULL until you change it to non-NULL via pubnub_set_uuid().
pubnub_t *ctx = pubnub_alloc();
if (NULL == ctx) {
    puts("Couldn't allocate a Pubnub context");
    return -1;
}
pubnub_init(ctx, "myPublishKey", "mySubscribeKey");
pubnub_set_uuid(ctx, "myUniqueUUID");
printf("UUID is %s", pubnub_uuid_get(ctx));
  1. Get UUID returns the following output:
    TypeDescription
    char const*UUID for context. Null if not set.
  1. pubnub_t *ctx = pubnub_alloc();
    if (NULL == ctx) {
        puts("Couldn't allocate a Pubnub context");
        return -1;
    }
    
    struct Pubnub_UUID uuid;
    char random_uuid;
    if (0 == pubnub_generate_uuid_v4_random(&uuid)) {
        random_uuid = pubnub_uuid_to_string(&uuid).uuid;
        pubnub_init(ctx, "myPublishKey", "mySubscribeKey"); 
        pubnub_set_uuid(ctx, random_uuid);
    }
    
    pubnub_free(ctx);
Setter and getter for users auth key.
  1. ParameterTypeRequiredDescription
    ppubnub_t*YesPointer to pubnub client context
    authconst char*OptionalPointer to auth string. NULL to unset
  2. ParameterTypeRequiredDescription
    ppubnub_t*YesPointer to pubnub client context
pubnub_t *ctx = pubnub_alloc();
if (NULL == ctx) {
    return -1;
}
pubnub_init(ctx, "demo", "demo");
pubnub_set_auth(ctx, "my_new_authkey");
pubnub_t *ctx = pubnub_alloc();
if (NULL == ctx) {
    puts("Couldn't allocate a Pubnub context");
    return -1;
}
pubnub_init(ctx, "demo", "demo");
pubnub_set_auth(ctx, "my_auth_key");
printf("Auth Key is %s", pubnub_auth_get(ctx));
Get Auth key returns the current authentication key.

Sets the origin to be used for the context p. If setting of the origin is not enabled, this will fail. It may also fail if it detects an invalid origin, but NULL is not an invalid origin - it resets the origin to default.

To set the origin for a Pubnub context use:
  1. ParameterTypeRequiredDescription
    ppubnub_t *YesPubnub context to set origin for
    Originchar const*OptionalThe origin to use for context p. If NULL, the default origin will be set

To set the origin to the European data center explicitly:

pubnub_origin_set(pn, "ps.pndsn.com");
TypeDescription
int0: success, -1: fail