---
source_url: https://www.pubnub.com/docs/sdks/freertos/api-reference/storage-and-playback
title: Message Persistence API for FreeRTOS SDK
updated_at: 2026-05-28T08:24:17.462Z
sdk_name: PubNub FreeRTOS SDK
---

> Documentation Index
> For a curated overview of PubNub documentation, see: https://www.pubnub.com/docs/llms.txt
> For the full list of all documentation pages, see: https://www.pubnub.com/docs/llms-full.txt


# Message Persistence API for FreeRTOS SDK

PubNub FreeRTOS SDK

Message Persistence gives you real-time access to the history of messages published to PubNub. Each message is timestamped to the nearest 10 nanoseconds and stored across multiple availability zones in several geographic locations. You can encrypt stored messages with AES-256 so they are not readable on PubNub’s network. For details, see [Message Persistence](https://www.pubnub.com/docs/general/storage).

You control how long messages are stored through your account’s retention policy. Options include: 1 day, 7 days, 30 days, 3 months, 6 months, 1 year, or Unlimited.

You can retrieve the following:

* Messages
* Message reactions
* Files (using the File Sharing API)

## History

:::warning Requires Message Persistence
Enable Message Persistence for your key in the [Admin Portal](https://admin.pubnub.com/). See how to [enable add-on features](https://support.pubnub.com/hc/en-us/articles/360051974791-How-do-I-enable-add-on-features-for-my-keys-).
:::

Fetch historical messages for a channel. Use `count` to limit how many messages are returned.

### Method(s)

To run `History` you can use the following method(s) in the FreeRTOS SDK:

```c
enum pubnub_res pubnub_history (pubnub_t *p, const char *channel, const char *channel_group, unsigned count)
```

| Parameter | Type | Required | Default | Description |
| --- | --- | --- | --- | --- |
| p | pubnub_t* | Yes |  | Pointer to PubNub client context. Can't be NULL. |
| channel | const | Yes |  | The `string` with the `channel` name to fetch the `history` |
| count | unsigned | Yes |  | Maximum number of messages to get. If there are less than this available on the `channel`, you'll get less, but you can't get more. |
| include_token | bool | Yes |  | If `true`, include the [timetoken](https://www.pubnub.com/docs/sdks/freertos/api-reference/misc#time) for every `message`. default: `false` |

### Sample code

Retrieve the last 100 messages on a channel:

```c
// 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 {
}

// 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;
      }
    // Print out, on Window simulator, `puts(msg)` should work
    }
  } else {
     return -1;
  }
  return 0;
}
```

### Rest response from server

An array is returned on success. The `pubnub_history()` function returns a list of up to 100 messages, the timetoken of the first (oldest) message and the timetoken of the last (newest) message in the resulting set of messages. The output below demonstrates the format for a `pubnub_history()` response:

```javascript
[
    ["message1", "message2", "message3",... ],
    "Start Time Token",
    "End Time Token"
]
```

## Message counts

### Message count per channel structure

Contains channel name (as char memory block, *aka* `Pascal string`) and message count for messages received on the channel. The message counts are the number of messages published on one or more channels since a given time.

Used to store information retrieved by `pubnub_message_counts()` transaction.

### Declaration

`struct pubnub_chan_msg_count {pubnub_chamebl_t channel; size_t message_count; };`

### Members

| Members | Type | Description |
| --- | --- | --- |
| `channel` | pubnub_chamebl_t | Channel name as a char memory block (aka `Pascal string`) |
| `message_count` | size_t | Number of messages for the channel |

### Count channels in message count response

Returns the number of members (key->value pairs) of JSON object `channels` in the response to a `message count` transaction.

### Declaration

`int pubnub_get_chan_msg_counts_size(pubnub_t* pb);`

### Parameters

| Parameter | Description |
| --- | --- |
| `pb` *Type: pubnub_t* | The Pubnub context in which to parse the response |

### Sample code

```c
int n  = pubnub_get_chan_msg_counts_size(pb);
printf("There are %d channels in the message counts response\n", n);
```

### Returns

| Type | Value | Description |
| --- | --- | --- |
| `int` | -1 | Error (transaction still in progress or other) |
|  | >= 0 | The number of members of the `channels` JSON object) |

### Message counts transaction

Starts the transaction `pubnub_message_counts` on the context `@p` pb for the list of channels `@p` channel for messages counts starting from `@p` timeoken which can be a single timetoken, or list of comma-separated timetokens (corresponding to the `channel` list).

:::note Unlimited message retention
For keys with unlimited message retention enabled, this transaction considers only messages published in the last 30 days.
:::

### Declaration

`enum pubnub_res pubnub_message_counts(pubnub_t* pb, char const* channel, char const* timetoken);`

### Parameters

| Parameter | Description |
| --- | --- |
| `pb` *Type: pubnub_t* | The Pubnub context to use for transaction |
| `channel` *Type: char const* | The string with the channel name (or comma-delimited list of channel names) to subscribe for. |
| `timetoken` *Type: char const* | A single token OR a comma-separated list of tokens. If single, will be used for all channels. If a list, has to have the same number of elements as `@p` channel and each will be used for its channel, in-order. |

### Sample code

```c
/** Obtain message count for
        channel 'one' since 15517035062228243 and
        channel 'two' since 15517035052228243. */
pbres = pubnub_message_counts(pb, "one,two", "15517035062228243,15517035052228243");
```

### Returns

| Type | Value | Description |
| --- | --- | --- |
| `enum pubnub_res` | PNR_STARTED | Started |
|  | PNR_OK | Finished with a success (can only happen in the sync interface) |
|  | other | Failed, Indicates the type of error |

### Example: single token for all channels

```c
/** Obtain message count for channels
        'one' and 'two' since 15517035062228243 */
pbres = pubnub_message_counts(pb, "one,two", "15517035062228243");
```

### Read all channel message counts

On input, `@p` `io_count` is the number of allocated `counters per channel` (array dimension of `@p` `chan_msg_counters`). On output(`@p` `io_count`), number of counters per channel written. If there are more channel message counters in the answer than there are in the allocated array (`can't fit all`), that will not be considered an error, they will simply not be written to `@p` `chan_msg_counters`. To see how much elements there are (and allocate accordingly), use `pubnub_get_chan_msg_counts_size()`.

This is an alternative to `pubnub_get_message_counts()`, useful for `exploratory` usage, as one can get all the channel message counters that are in the report, without keeping track of what were the requested channels.

:::note Unlimited message retention
For keys with unlimited message retention enabled, this transaction considers only messages published in the last 30 days.
:::

### Declaration

`int pubnub_get_chan_msg_counts(pubnub_t* pb, size_t* io_count, struct pubnub_chan_msg_count* chan_msg_counters);`

### Parameters

| Parameter | Description |
| --- | --- |
| `pb` *Type: pubnub_t* | The Pubnub context to use for transaction |
| `io_count` *Type: size_t* | On input, the number of allocated `counters per channel` (array dimension of `@p` `chan_msg_counters`). On output, number of counters per channel written to `@p` `chan_msg_counters`. |
| `chan_msg_counters` *Type: struct pubnub_chan_msg_count* | An array of channel message counters, allocated by the caller, filled in by this function. |

### Sample code

```c
struct pubnub_chan_msg_count chan_msg_count[CHAN_COUNT];
size_t count = CHAN_COUNT;
int rslt = pubnub_get_chan_msg_counts(pb, &count, chan_msg_count);
if (0 == rslt) {
    size_t i;
    for (i = 0; i < count; ++i) {
        printf("  Channel    = '%.*s'\n", (int)chan_msg_count[i].channel.size, chan_msg_count[i].channel.ptr);
        printf("  Message count  = %z'\n", chan_msg_count[i].message_count);
    }
}
```

### Returns

| Type | Value | Description |
| --- | --- | --- |
| `int` | 0 | Success (even if there are more channel message counts than is possible to write to `@p` `chan_msg_counters`) |
|  | -1 | Error, messages not read (transaction still in progress, format error...) |

### Example: Make sure we have room for all the channel message counters

```c
int n  = pubnub_get_chan_msg_counts_size(pb);
if (n > 0) {
    struct pubnub_chan_msg_count *pchmsc = malloc(n * sizeof *pchmsc);
    if (pchmsc != NULL) {
        size_t count = n;
        int rslt = pubnub_get_chan_msg_counts(pb, &count, pchmsc);
        if (0 == rslt) {
            printf("Got %z counters, should be the same as %d\n", count, n);
        }
        free(pchmsc);
    }
}
```

### Read counters for channels

Reads message counters for the given channels (in `@p` channel) from the PubNub response to `pubnub_message_counts()`.

Array dimension for `@p` `o_count` is the number of channels from the comma-separated channel list `@p` channel and it (`@p` `o_count` array) is allocated by the caller.

Message counts order in `@p` `o_count` is corresponding to channel order in `@p` channel list respectively, even if the answer itself has the channels in a different order. If a requested channel is not found in the PubNub response, the message counter in the respective `@p` `o_count` array member has a negative value.

If there is a channel name in the answer, not to be found in requested `@p` channel list, that is not considered an error.

This is an alternative to `pubnub_get_chan_msg_count()`, useful if we already `maintain` the list of channels and just want to get the message counters.

:::note Unlimited message retention
For keys with unlimited message retention enabled, this transaction considers only messages published in the last 30 days.
:::

### Declaration

`int pubnub_get_message_counts(pubnub_t* pb, char const*channel, int* o_count);`

### Parameters

| Parameter | Description |
| --- | --- |
| `pb` *Type: pubnub_t* | The Pubnub context to use for transaction |
| `channel` *Type: char const* | A comma-separated list of channels to read message counters from |
| `o_count` *Type: int* | An array of message counters, allocated by the caller, filled in by this function. |

### Sample code

```c
int msg_count[2];
int rslt = pubnub_get_message_counts(pb, "one,two", msg_count);
if (0 == rslt) {
    printf("message counts: one -> %d, two -> %d\n", msg_count[0], msg_count[1]);
}
```

### Returns

| Type | Value | Description |
| --- | --- | --- |
| `int` | 0 | Success (even if there are channel message counts int `@p` channel that are not there in the response or vice-versa) |
|  | -1 | Error, messages not read (transaction still in progress, format error...) |

## Terms in this document

* **Message** - A unit of data transmitted between clients or between a client and a server in PubNub, containing information such as text, binary data, or structured data formats like JSON. Messages are sent over channels and can be tracked for delivery and read status.
* **PubNub** - PubNub is a real-time messaging platform that provides APIs and SDKs for building scalable applications. It handles the complex infrastructure of real-time communication, including: Message delivery and persistence, Presence detection, Access control, Push notifications, File sharing, Serverless processing with Functions and Events & Actions, Analytics and monitoring with BizOps Workspace, AI-powered insights with Illuminate.