Understanding the java.net.SocketException: Connection Reset

Introduction

The java.net.SocketException: Connection reset is an error that occurs when a socket connection is abruptly terminated by the remote party. This exception is usually thrown by Java’s networking API, specifically when attempting to read from or write to a closed socket.

The Role of Socket.setSoTimeout()

When establishing a connection with another system using sockets, it is common to set a timeout value for the socket. This timeout value determines how long Java will wait for data to be received before throwing an exception.

In this case, the server had added the following line of code just prior to reading from the socket:

socket.setSoTimeout(10000);

This sets the socket’s timeout to 10 seconds. With this setting in place, if no data is received within 10 seconds, a SocketException: Connection reset will be thrown.

Possible Causes of java.net.SocketException: Connection Reset

There are several possible causes for this exception:

1. Deliberate Connection Termination by the Remote Party

In some cases, another party may deliberately terminate the connection. This could be due to various reasons such as a server-side shutdown or a client-side application error.

While this is rare and generally considered bad practice, it can occur in certain scenarios, such as when a commercial software product deliberately closes a connection.

2. Application Protocol Errors

More commonly, java.net.SocketException: Connection reset occurs due to an application protocol error. This happens when the remote party writes data to the socket without first closing or flushing it properly.

For example, if one system expects a specific format of data and receives something else, it may close the connection prematurely, resulting in this exception.

3. Closing a Socket with Unread Data

Another possible cause is that the socket was closed by the other end while there was still unread data in the receive buffer.

This can happen when an application writes to a socket but does not flush or close it properly before closing the connection.

4. Windows-Specific Issues

On Windows, java.net.SocketException: Connection reset is sometimes caused by network issues that occur on the sending end.

There’s a Microsoft knowledge base article available for more information on this specific issue.

5. Local Resources Reaching Thresholds

Finally, there’s also a possibility that local resources, such as network buffers or connection limits, might be reached. When these thresholds are exceeded, Java may throw an exception to prevent further issues.

Example Use Case: Flushing the Socket Before Reading

To avoid this issue, it is recommended to flush the socket before attempting to read from it:

socket.flush();
int bytesRead = socket.read(buffer);

However, be aware that flush() only ensures that any buffered data is written out of the socket’s output buffer. It does not guarantee that the data has been received by the remote party.

Conclusion

The java.net.SocketException: Connection reset error can occur due to a variety of reasons, including deliberate connection termination by the remote party, application protocol errors, closing a socket with unread data, Windows-specific issues, and local resources reaching thresholds.

By understanding these possible causes and taking steps to prevent them, such as flushing the socket before reading or setting an adequate timeout value, you can minimize the occurrence of this exception in your Java-based applications.

Last modified on 2023-10-16