Group members send and receive messages within the group.
App admin sends messages
The app admin can send messages from the backend, or impersonate other users to send messages. In the latter case, even if the app admin or sender is not a group member, the messages will still be delivered.
App admin simulates system messages
The app admin can simulate system notification by sending messages from the backend. These messages are delivered as system notification to specified online group members, and the app admin’s custom messages that are received on the app can be handled in special ways.
SEQ Mechanism of Group Messages
Chat maintains a message SEQ for each group, which starts from an initial value of 1. Every time an ordinary message is sent in the group chat, the Chat backend uses the current SEQ value as the SEQ of the message and then increases the SEQ by 1.
Group ID and SEQ together constitute the unique identifier of a message.
Caution:
Chat generates incremental SEQs only for roamable messages.
Group message types
Message Type
Description
Text message
The message content is plain text.
Image message
The message content includes the URL, dimensions, and size of the image.
Emoji message
Emoji messages are customized by developers.
Audio message
Audio data must include the duration in seconds.
Location message
The message content contains the caption, longitude, and latitude of the location.
File message
The message content includes the URL, size, and format of the file. There are no file format restrictions, and the maximum supported file size is 100 MB.
Short video message
The message content includes the URL, duration, size, and format of the short video file. The maximum file size supported is 100 MB.
Custom
Message types that are customized by developers, such as red packet and rock-paper-scissor.
System notification
This type of message is divided into built-in system notification messages and system notification messages customized by developers.
Group messaging capabilities
Type
Feature Description
Application Scenario
Send ordinary group messages
Group members can send messages through the Chat SDK APIs. By calling RESTful APIs, app admins can send messages in any group without joining the group.
Group members send messages in the group, and app admins can send messages in any group.
Send group system notifications
By calling RESTful APIs, app admins can send system notifications in any group without joining the group. These system notifications are only received by online group members and do not possess roaming capabilities.
App admins push time-sensitive notifications to all or a subset of online group members.
Offline push of group messages
Supported by Apple, Huawei, Xiaomi, OPPO, vivo, and Meizu mobile phones
Offline push of group messages
Group members receive online group messages
Group members can receive online group messages through the Chat SDK.
Online group members receive group messages in real time.
Group members receive offline messages or historical messages
Group members can query historical messages through the Chat SDK.
Group members receive offline messages when they go back online, and group members can view group historical messages.
App backend obtains group messages
App admins can download all messages generated during a certain time period through RESTful APIs. App admins can also obtain the chat history of any group through RESTful APIs. The app backend can obtain group messages through webhook after messages are sent in the group.
Apps back up message history regularly. Apps need to quickly obtain the message history of specific groups. Apps need to obtain group messages in real time.
Delete messages
Historical messages can be deleted through RESTful APIs to ensure that they will not be further propagated.
Delete malicious information in a group.
Group messages include user profile
Group messages can contain the sender nickname, profile photo, group profile, user-level custom fields, and member-level custom fields.
Display sender information such as the nickname and profile photo.
Group message sending control
You can control group message sending by muting and pre-send group message webhook.
Prevent a group member from sending messages, prevent all group members from sending messages, and filter or modify messages at the app backend.
Group message receiving control
You can set different message receiving options for individual groups: receive and notify, receive without notifying, and block messages. When receive without notifying is selected, iOS devices will disable APNs push.
A user blocks messages from a group.
Group message frequency control
Control the sending frequency of group messages. The default value is 40 messages per second. Group system messages sent by the app admin through RESTful APIs are not subject to frequency control. For more information, see the message priority and frequency control described below.
Prevent spam messages.
Caution:
If the sender nickname and profile photo need to be included, import the information in these two fields to user profiles in Chat.
If custom fields need to be included, configure custom fields in the console and submit a ticket to add the corresponding fields to messages.
Group Message Sending Control
The sending of group messages can be controlled through the following methods:
Control Method
Description
Mute group members
Prevent a group member from sending messages for a certain period of time. This feature is effective within a single group. If the muted user leaves the group and joins again, the user remains muted until the mute time expires.
Group message pre-send webhook
Before a message is delivered to group members, Chat checks with the app backend for permission. If not allowed, the message will not be delivered.
After receiving a webhook, the app backend can modify the message content and return it to Chat, which will deliver the modified message. For more information, see Before Group Message Is Sent.After invoking a webhook, Chat will deliver the message directly if it does not receive a response in two seconds, without retrying.
Message Priority and Frequency Control
Group message priority
Group messages are divided into three levels by priority. If a group exceeds the message frequency cap, the backend delivers high-priority messages first. Therefore, select appropriate priorities according to the importance of messages.
The following lists the priorities from high to low:
Priority
Recommended Message Type
High
Red packet and gift message
Normal
Plain text message
Low
Like message
Group message frequency control
Number-based frequency control
Note:
Number-based frequency control limits the maximum number of messages sent by all client APIs per second in a single group. The default value is 40 messages per second. When the number of sent messages exceeds the limit, the backend will first deliver higher-priority messages, with messages with the same priority delivered randomly.
A message that has been restricted by frequency control is not delivered or stored in the message history, but a success response will be returned to the sender. Before Group Message Is Sent webhook is triggered, but After Group Message Is Sent webhook is not triggered.
Priority-based frequency control
Priority-based frequency control limits the maximum number of messages with a certain priority sent per second in a single group. A message sending request must first pass the number-based frequency control check before it enters the priority-based frequency control processing.
All messages are subject to the frequency limit of 40 messages per second. You can set three levels of priority. Messages with High priority are the top-priority messages, which are not likely to be restricted. However, if the number of high-priority messages sent in a second exceeds 40, high-priority messages will also be discarded.
Processing of Offline Group Messages
Offline group messages are processed as follows:
1. User A calls sendMessage to send messages to group C when user B is offline.
1.1 Group C is added to the recent contacts of user B, with up to 100 messages cached.
1.2 The system updates the group message information, including the latest group message seq.
1.3 Messages are stored on the roaming server for 7 days.
2. User B calls the login API to log in to Chat.
3. The SDK automatically pulls the seq information of all group messages, including the latest message seq and unread message count.
4. The SDK automatically pulls recent contacts and triggers the OnNewMessage API.
5. Users are notified through the OnRefresh API when group message synchronization is completed.
6. Users call getMessage, and the SDK automatically pulls the messages from the roaming server.
