Offline Chat

Unreliable connectivity shouldn't end conversations. Offline chat allows users to stay engaged in their chats, even when moving in and out of service.

What Is Offline Chat?

Offline chat lets users ‌write, queue, and access messages when disconnected from the internet. Queued messages are sent when the connection is restored. Its primary purpose is to prevent interruptions and preserve the flow of conversation.

This capability is standard across many social messaging apps, such as WhatsApp and Telegram. Developers can add it to in-app messaging by building it in-house or using chat APIs/SDKs.

Offline messages improve user experience by minimizing disruption and ensuring information isn't lost during connectivity drops. For example, if one of the sellers on your marketplace app has a blackout, they can still work in some capacity by reading stored messages and drafting replies to customers.

How Does Offline Chat Work?

Local Storage and Caching

When users compose messages without an internet connection, they're saved to local storage, like a database or file system. This storage is non-volatile, so data survives app restarts and device reboots.

Caching complements this by temporarily storing conversation state and drafts in memory. The cache syncs periodically with persistent storage, so queued messages remain available even if the app is closed or suspended.

Once connectivity returns, the app reads from its storage and automatically sends the pending messages.

Automatic Syncing on Reconnect

Automatic syncing ensures that offline activity is accounted for.

It's a near-real-time catch-up experience where messages appear in the order they were sent. This process runs in the background and usually doesn't require user input.

As the app sends queued messages upon reconnecting, it requests updates from the server to fetch new messages sent by others during the outage.

Some apps ask the user if they want to retry after several attempts. This uses less bandwidth,‌ saves the user's resources, and avoids duplicate uploads.

Timestamping and Message Ordering

Accurate timestamping keeps your users' messages in order and consistent across multiple devices.

The backend server assigns a timestamp to each message sent. This provides a single source of truth for message order, avoiding conflicts caused by local device clocks. The server then arranges messages chronologically before delivering them to all participants.

The messages are timestamped according to when they are sent to the server, not when the client queues them, which is more accurate from the receiver's point of view.

Delivery Receipts

When messages are composed offline, their status stays pending until the client syncs with the server. Once both users have connectivity, the server confirms delivery and updates each message's status.

On some platforms, if just the recipient is offline, the sender sees the message as "sent" (to the server), and the status updates to "received" (by the other party), once the recipient is online.

For instance, WhatsApp uses one grey checkmark for "sent" and two for "received"; when read, the checkmarks turn blue.

These updates often happen in quick succession, creating an experience where reconnected users see all pending messages transition from unsent to delivered.

Offline Chat Use Cases

Remote and Low-Connectivity Environments

Users in sectors like field work, logistics, and telehealth often work in areas with spotty or no internet connection. Offline chats allow these workers to communicate important updates, like status reports or patient notes, without fear of losing data.

Business Continuity and Reliability

Teams using collaboration platforms may face temporary network outages, especially when working remotely. Being able to send offline messages and (on some platforms) media files reduces the risk of information gaps or productivity jams, especially for organizations using chat for operational coordination.

Consumer-Facing Apps

In gaming, social media, and dating apps, users expect real-time communication but may frequently move in and out of service.

During these moments, queued messages keep conversations smooth once service returns, with the added benefit of making some short connectivity drops unnoticeable to consumers.

Customer Service and Support

Conversations being cut off when contacting support agents creates friction, particularly if the issue is urgent or beyond the scope of a chatbot.

Storing messages locally until they can be transmitted keeps customer data available for support teams to review and prepare replies, minimizing the delay between ticket creation and resolution.

Common Issues and How To Solve Them

Message Order Conflicts

When users send messages offline, there's no guarantee they'll stay in the right order once the connection is restored. Ordering messages on the client side can create inconsistency across devices, as well as conflicts with local device times.

You can solve this by letting the server handle message ordering. When a server receives a message, it assigns official timestamps and reorders the conversation accordingly. The client then automatically refreshes its local history to match.

Event streams or message queues like Kafka or RabbitMQ keep ordering consistent across multiple devices and users.

Duplicate and Lost Messages

Offline clients can create duplicates in message queues by initiating multiple send requests. Once they reconnect, the server can end up with multiple copies of the same message, or if the app crashes before syncing, none at all.

Duplicates clutter the conversation, while lost messages can frustrate your users.

The solution is to implement idempotency by assigning a unique ID to every message when the user presses send.

UUIDs and ULIDs are popular choices to accomplish this because they're globally unique, but teams can also use custom ID schemes for tighter control.

This lets the server identify duplicates and ignore them. Pairing this with retry logic (like an exponential backoff function) ensures that the app keeps trying to deliver unsent messages until it gets confirmation back, without flooding the server with extra requests.

Inconsistent Delivery Receipts

When users send messages offline, delivery and read receipts can't be confirmed until those messages reach the server. Without proper refreshing, the client may continue to display outdated indicators even after reconnecting.

To avoid this, your app should trigger a sync once reconnected. After the server confirms message delivery or read events, it overwrites the stale information on the client side.

Mobile apps have Reachability on iOS and ConnectivityManager on Android, which update your service on changes in network status, allowing the app to send and pull data from the server near-instantly after connecting.

Web apps typically require custom logic. If your app uses WebSockets, you can attempt reconnections and sync once they're established.

Data Storage, Security, and Compliance

Offline messages rely on temporarily storing messages on the user's device‌, which gives anyone handling the device access to queued data. The risk of compromised information is high if the device is lost, stolen, or infected with malware.

Encrypt data at rest using mobile platform tools like Keychain (iOS) and SQLCipher (Android) or the WebCrypto API for web apps. This way, even if a malicious party accesses the files, they'll be protected.

In-transit encryption reduces the risk of data tampering when the client syncs. Use TLS and WSS to prevent interception. Additionally, adding hashing and message signing ensures the server can verify that queued messages weren't altered before delivery.

These secure practices are essential for many compliance frameworks in highly regulated industries. For instance, while not a requirement under HIPAA, organizations that lack tamper protection and both in-transit and at-rest encryption must justify why they chose not to implement them.

Frequently Asked Questions