Java simple code: java.net.SocketException: Unexpected end of file from server

Question

I wrote some simple code in Java, the method should connect to the website and return the BufferedReader.

private BufferedReader getConnection(String url_a)          


        

Answer 1

Summary

This exception is encountered when you are expecting a response, but the socket has been abruptly closed.

Detailed Explanation

Java's HTTPClient, found here, throws a SocketException with message "Unexpected end of file from server" in a very specific circumstance.

After making a request, HTTPClient gets an InputStream tied to the socket associated with the request. It then polls that InputStream repeatedly until it either:

1. Finds the string "HTTP/1."
2. The end of the InputStream is reached before 8 characters are read
3. Finds a string other than "HTTP/1."

In case of number 2, HTTPClient will throw this SocketException if any of the following are true:

• The HTTP method is CONNECT
• The HTTP method is POST and the client is set to streaming mode

Why would this happen

This indicates that the TCP socket has been closed before the server was able to send a response. This could happen for any number of reasons, but some possibilities are:

• Network connection was lost
• The server decided to close the connection
• Something in between the client and the server (nginx, router, etc) terminated the request

_{Note: When Nginx reloads its config, it forcefully closes any in-flight HTTP Keep-Alive connections (even POSTs), causing this exact error.}