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Learn how to effectively resolve the HandshakeException that occurs due to connection termination during handshake while fetching data from an API in your Flutter application.
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How to Resolve HandshakeException During API Data Fetching in Flutter App?

In the world of mobile app development, fetching data from APIs is a fundamental task. However, developers often encounter challenges, including the notorious HandshakeException: Connection terminated during handshake. This article aims to guide Flutter developers in resolving this specific exception to ensure smooth API data fetching.

Understanding HandshakeException

Before jumping into solutions, it's essential to understand what a HandshakeException is. This exception usually occurs during the SSL/TLS handshake process, which is part of establishing a secure connection between your app and a server. During this handshake, if there's a failure or an abrupt connection termination, a HandshakeException is thrown.

Common Causes

Outdated SSL Certificate: One common cause is that the server’s SSL certificate might be outdated or not correctly configured.

Incorrect Clock Settings: If the device's clock settings are incorrect, they can cause SSL handshake problems because SSL certificates are time-sensitive.

Network Issues: Sometimes, unstable network connections can interrupt the handshake process.

Server Configuration: Misconfiguration on the server-side can also lead to handshake failures.

Potential Solutions

Update SSL Certificates: Ensure that the server’s SSL certificates are up to date and correctly configured. If you’re using third-party services, check their status page for any SSL-related issues.

Check Device Clock Settings: Ensure that the device clock settings are correctly synchronized. Incorrect time can disrupt the handshake process because SSL certificates have validity periods.

Use Secure HTTP (HTTPS): Make sure you're making requests over HTTPS rather than HTTP, as HTTPS ensures secure communication.

Configure SecurityContext: In Flutter, you can configure the SecurityContext to accept specific certificates. This involves creating a custom HttpClient with pre-installed certificates:

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Check Ciphers: Certain ciphers might not be supported by both client and server. Ensure that the server supports modern and commonly used ciphers.

Use Trusted Libraries: Sometimes, the problem can be within the libraries or the way they handle SSL handshakes. Depending on your project, you might want to use trusted libraries that manage this well.

Example Solution

Here is a step-by-step example to set up a custom HttpClient in Flutter:

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In this example, we override the HTTP settings globally, allowing self-signed certificates. While this is useful for development and testing, it's not recommended for production due to security risks.

Conclusion

Encountering a HandshakeException can be frustrating, but with the right approach and understanding, you can troubleshoot and resolve it effectively. Make sure to keep your SSL certificates updated, verify your device's clock settings, and configure the Flutter HttpClient correctly. By following these steps, you can ensure secure and reliable API data fetching in your Flutter applications.