Understanding and Troubleshooting net::ERR_HTTP2_PROTOCOL_ERROR

The net::ERR_HTTP2_PROTOCOL_ERROR is an error that occurs when there’s a problem with the HTTP/2 protocol used for communication between a client (usually a web browser) and a server. This tutorial will delve into the possible causes of this error, how to identify them, and potential solutions.

Introduction to HTTP/2

HTTP/2 is an improvement over its predecessor, HTTP/1.1, offering better performance, especially in scenarios where multiple resources are requested from the same domain. It achieves this through features like header compression, multiplexing (allowing multiple requests and responses to be sent concurrently over a single connection), and server push.

Causes of net::ERR_HTTP2_PROTOCOL_ERROR

The net::ERR_HTTP2_PROTOCOL_ERROR can arise due to various reasons related to both the client and server sides. Some common causes include:

1. Server Configuration Issues: The server might be configured in such a way that it cuts off connections if the data throughput falls below a certain threshold, often as a measure against slow HTTP denial-of-service (DoS) attacks.
2. Resource Starvation: When a client requests multiple large resources simultaneously, the bandwidth allocated to each request might become too low, triggering server settings designed to prevent slow drip attacks.
3. Browser Quirks and Bugs: Sometimes, the issue could be due to bugs or quirks in how the browser implements HTTP/2.

Identifying the Cause

To troubleshoot the net::ERR_HTTP2_PROTOCOL_ERROR, follow these steps:

1. Check Server Logs: Look for entries related to connection closures or throughput limits.
2. Use Browser Tools: Utilize the browser’s network log export feature (e.g., Chrome’s chrome://net-export/) and import the logs into a viewer like https://netlog-viewer.appspot.com/ to analyze the communication flow and identify potential reset streams (RST_STREAM).
3. Test Scenarios: Try reproducing the error with different numbers of concurrent requests or by adjusting server settings.

Solutions

Based on the identified cause, solutions may include:

1. Adjusting Server Settings: For servers like IIS, setting minBytesPerSecond to a lower value (or even 0) can prevent connection closures due to low throughput.
2. Optimizing Resource Loading: Implement techniques like code splitting, lazy loading, or using a content delivery network (CDN) to reduce the number of concurrent requests and their sizes.
3. Updating Browser or Server Software: Ensure that both the client’s browser and the server software are up-to-date, as newer versions might include fixes for known issues.

Example: Adjusting minBytesPerSecond in IIS

To adjust minBytesPerSecond in IIS:

• Open the Configuration Editor.
• Navigate to system.applicationHost/webLimits.
• Find the minBytesPerSecond setting and change its value to 0 or a lower threshold suitable for your application.

<configuration>
    <system.applicationHost>
        <webLimits minBytesPerSecond="0" />
    </system.applicationHost>
</configuration>

Conclusion

The net::ERR_HTTP2_PROTOCOL_ERROR can stem from various issues related to HTTP/2 protocol implementation and server or client configurations. By understanding the possible causes, using the right tools for analysis, and applying appropriate fixes, developers can troubleshoot and resolve this error, ensuring smoother communication between clients and servers.