Store channel metadata

The Signaling storage service enables you to store and share contextual channel data in your game, such as props, announcements, member lists, and relationship chains. When channel metadata is set, updated, or deleted, the SDK triggers a storage event notification. Other users in the channel receive this notification within 100ms and use the information according to your business logic.

Understand the tech

Use channel metadata to store and share channel level information such as room attributes, group announcements, and auction item price updates. A set of channel metadata for a specific channel facilitates business-level data storage and real-time notifications. Each channel has only one set of channel metadata, but each set may contain multiple metadata items. For relevant restrictions, refer to the API usage restrictions. Each metadata item has key, value, and revision properties.

Channel metadata is stored permanently in the Signaling database. The data persists even after a channel is destroyed. You must explicitly delete it to remove it from the database. This feature impacts your storage billing. Refer to Pricing for details.

The storage service is available for both message channels and stream channels. Use the channelType parameter in the storage event to determine the channel type.

Prerequisites

Ensure that you have:

Integrated the Signaling SDK in your project.
Implemented the framework functionality from the SDK quickstart page.
Enabled storage in Storage configuration.

Implement channel metadata storage

The section shows you how to implement channel metadata storage in your Signaling game.

Set channel metadata

To create a new metadata item for the channel, or to update the value of an existing item, call SetChannelMetadataAsync. This method creates a new item in the channel metadata if the specified key does not exist, or overwrites the associated value if a metadata item with the specified key already exists.

The following example saves a set of metadata items for a message channel named channel1. Signaling adds timestamp and authorUid information to each metadata item it stores.

var metadata = new RtmMetadata();
var apple = new MetadataItem()
            {
                key = "Apple",
                value = "100",
            };
var banana = new MetadataItem()
            {
                key = "Banana",
                value = "200",
            };
metadata.metadataItems = new MetadataItem[] { apple, banana };
metadata.metadataItemsSize = 2;
var metadataOptions = new MetadataOptions()
            {
                recordUserId = true,
                recordTs = true
            };
var lockName = "";

var (status,response) = await rtmClient.GetStorage().SetChannelMetadataAsync("channel1", RTM_CHANNEL_TYPE.MESSAGE, metadata, metadataOptions, lockName);
if (status.Error)
{
    Debug.Log(string.Format("{0} is failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Set Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
}
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Signaling triggers an OnStorageEvent notification of event type UPDATE within 100 ms to inform other channel members.

Get channel metadata

To retrieve all metadata items associated with a specific channel, call GetChannelMetadataAsync by specifying the channel name and the channel type. Refer to the following example:

var (status,respones) = await rtmClient.GetStorage().GetChannelMetadataAsync("channel_name", RTM_CHANNEL_TYPE.MESSAGE);
if (status.Error)
{
    Debug.Log(string.Format("{0} is failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Get Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
    var data =  response.data;
    if (data.metadataItemsSize != 0)
    {
        Debug.Log(string.Format("Channel Metadata Major Revision is :{0} ! ", data.majorRevision));
        for ( int i =0; i < data.metadataItemsSize; i++)
        {
            Debug.Log(string.Format("The {0}'th iterms Key is:{1}, Value is {2} ! ", i, data.metadataItems[i].key, data.metadataItems[i].value));
        }
    }
}
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Signaling SDK returns the following data structure:

{
    majorRevision: 734874892,
    metadata:{
        {   key:"Quantity",
            value:"20",
            revision:734874888,
            updateTs:1688978391900,
            authorUid:"Tony"
        },
        {
            key:"Announcement",
            value:"Welcome to our Shop!",
            revision:734874333,
            updated:1688978391800,
            authorUid:"Tomas"
        },
        {
            key:"T-shirt",
            value:"100",
            revision:734874222,
            updated:168897839100,
            authorUid:"Adam"
        }
    }
}
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Update channel metadata

To modify existing metadata items for a specified channel, call UpdateChannelMetadataAsync. If the metadata item does not exist, an error is returned. This method is useful for business use-cases that require permission control on creating new metadata items. For example, consider the following use-cases:

In an e-commerce auction, only administrators or product owners are authorized to list new products and set new attributes, while bidders may only modify price attributes.
In a gaming environment, only the administrator may define permissions as room properties.

The following example updates the value of a metadata item:

var metadata = new RtmMetadata();
var apple = new MetadataItem()
{
    key = "Apple",
    value = "120",
};
var banana = new MetadataItem()
{
    key = "Banana",
    value = "220",
};
metadata.metadataItems = new MetadataItem[] { apple, banana };
metadata.metadataItemsSize = 2;

var options = new MetadataOptions()
{
    recordUserId = true,
    recordTs = true
};

var lockName = "";

var (status, response) = await rtmClient.GetStorage().UpdateChannelMetadataAsync(
    "channel_name",
    RTM_CHANNEL_TYPE.MESSAGE,
    metadata, 
    options,
    lockName
);

if (status.Error)
{
    Debug.LogError(string.Format("{0} failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Update Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
}
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Signaling triggers an OnStorageEvent notification of event type UPDATE within 100 ms to inform other channel members.

Delete channel metadata

To delete metadata items that are no longer required, call RemoveChannelMetadataAsync. Refer to the following sample code:

var metadata = new RtmMetadata();
var metadataItem = new MetadataItem()
            {
                key = "Apple",
            };
metadata.metadataItems = new MetadataItem[] { metadataItem };
metadata.metadataItemsSize = 1;
var options = new MetadataOptions() { };

var (status,response) = await rtmClient.GetStorage().RemoveChannelMetadataAsync("channel_name", RTM_CHANNEL_TYPE.MESSAGE, options, "");
if (status.Error)
{
    Debug.Log(string.Format("{0} is failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Remove Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
}
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Setting the value for a metadata item that is being deleted has no effect.

Signaling triggers an OnStorageEvent notification of event type UPDATE within 100 ms to inform other channel members.

To delete the entire set of metadata for a channel, do not specify any metadata items when calling RemoveChannelMetadataAsync. Refer to the following sample code:

var metadata = new RtmMetadata();
var options = new MetadataOptions() { };

var (status,response) = await rtmClient.GetStorage().RemoveChannelMetadataAsync("channel_name", RTM_CHANNEL_TYPE.MESSAGE, options,"");
if (status.Error)
{
    Debug.Log(string.Format("{0} is failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Remove Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
}
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info

Once channel metadata is deleted, it cannot be recovered. If you need data restoration, back up the metadata before deleting it.

Receive storage event notifications

A storage event notification returns the StorageEvent data structure, which includes the RTM_STORAGE_EVENT_TYPE parameter.

To receive storage event notifications, implement an event listener. See event listeners for details. In addition, set the withMetadata parameter to true when subscribing to or joining a channel.

Event notification mode

Currently, Signaling only supports the full data update mode. This means that when user or channel metadata is updated, the data field in the event notification contains all the attribute data of the user or the channel.

Additional storage features

To help resolve issues arising from concurrent updates to storage, Signaling offers version control and locking features.

Version control

The Compare and Set (CAS) version control feature in channel metadata storage provides two independent version control parameters. Set one or more of these values according to the needs of your business use-case:

majorRevision property in the RtmMetadata class: Enable version number verification of the entire set of channel metadata.
revision property of a MetadataItem: Enable version number verification of a single metadata item.

When setting channel metadata, or a single channel metadata item, use the revision attribute to enable or disable version control as follows:

To disable CAS verification, use the default value of -1 for the revision parameter. If the channel metadata or channel metadata item already exists, the value is overwritten. If it does not exist, the SDK creates a metadata item and updates the value.
To enable CAS verification, set the majorRevision or the revision parameter to a positive integer. If the channel metadata or channel metadata item already exists, the SDK updates the corresponding value after successfully verifying the revision number. If the specified revision number does not match the latest revision number in the database, the SDK returns an error code.

The following sample shows how to use majorRevision and revision to update channel metadata and a metadata item:

var metadata = new RtmMetadata();
metadata.majorRevision = 174298270 ;
var apple = new MetadataItem()
            {
                key = "Apple",
                value = "120",
                revision = 174298200,
            };
var banana = new MetadataItem()
            {
                key = "Banana",
                value = "220",
                revision = 174298100,
            };
metadata.metadataItems = new MetadataItem[] { apple, banana };
metadata.metadataItemsSize = 2;
var options = new MetadataOptions()
            {
                recordUserId = true,
                recordTs = true
            };

var lockName = "lockName";

var (status,response) = await rtmClient.GetStorage().UpdateChannelMetadataAsync("channel_name", RTM_CHANNEL_TYPE.MESSAGE, data, options, lockName);
if (status.Error)
{
    Debug.Log(string.Format("{0} is failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Remove Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
}
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In the above example, CAS verification for channel metadata and metadata items is enabled by setting majorRevision and revision parameters to positive integers. Upon receiving the update call request, Signaling first verifies the provided major revision number against the latest value in the database. If there's a mismatch, it returns an error; if the values match, Signaling verifies the revision number for each metadata item using a similar logic.

info

When using version control, monitor OnStorageEvent notifications to retrieve updated values for majorRevision and revision to ensure that the latest revision values are used for subsequent operations.

Following are some sample use-cases where version control is useful:

In the bidding use-case, if multiple users bid on a product at the same time, the first bidder succeeds, while others receive an error. Users obtain the latest price information to update their bids.
In the red envelope grabbing use-case, the red envelope may only be grabbed once. The first user succeeds, while the rest receive an error.

Locks

Locks enable users to gain exclusive access to critical resources, resolving contention issues with shared resources. For instance, consider a use-case where only one administrator is allowed in a channel at a time, and only the administrator can manage channel metadata by setting, deleting, and modifying it.

Compared to CAS, which controls the version of channel metadata, locks offer a higher level of control. They determine whether a user has the authority to call the SetChannelMetadataAsync, UpdateChannelMetadataAsync, and RemoveChannelMetadataAsync interfaces. Without acquiring the lock, a user cannot perform operations on channel metadata.

The following code demonstrates using a lock to update channel metadata. The user calling UpdateChannelMetadataAsync must acquire the lock first for the call to succeed.

var metadata = new RtmMetadata();
var apple = new MetadataItem()
{
    key = "Apple",
    value = "120",
};
var banana = new MetadataItem()
{
    key = "Banana",
    value = "220",
};
metadata.metadataItems = new MetadataItem[] { apple, banana };
metadata.metadataItemsSize = 2;

var options = new MetadataOptions()
{
    recordUserId = true,
    recordTs = true
};

var lockName = "lockName";

var (status, response) = await rtmClient.GetStorage().UpdateChannelMetadataAsync(
    "channel_name",
    RTM_CHANNEL_TYPE.MESSAGE,
    metadata, 
    options,
    lockName
);

if (status.Error)
{
    Debug.LogError(string.Format("{0} failed, ErrorCode: {1}, due to: {2}", status.Operation, status.ErrorCode, status.Reason));
}
else
{
    Debug.Log(string.Format("Update Channel :{0} metadata success! Channel Type is :{1}! ", response.ChannelName, response.ChannelType));
}
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For more information on setting, acquiring, releasing, revoking, and removing locks, see Locks.

Reference

This section contains content that completes the information on this page, or points you to documentation that explains other aspects to this product.

API reference

Metadata