Connection.isValid(timeout) hangs indefinitely after network interruption during PGCopyOutputStream COPY #3957

import org.postgresql.copy.PGCopyOutputStream;
import org.postgresql.jdbc.PgConnection;

import java.nio.charset.StandardCharsets;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
import java.util.UUID;


public class PgjdbcCopyDemoStream {

    private static final String DB_URL = "jdbc:postgresql://localhost:5432/postgres";
    private static final String DB_USER = "postgres";
    private static final String DB_PASSWORD = "password";
    private static final String TABLE_NAME = "copy_test";

    public static void main(String[] args) throws Exception {
        try (Connection conn = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD)) {
            createTable(conn);
            copyData(conn);
        }
    }

    private static void createTable(Connection conn) throws Exception {
        try (Statement stmt = conn.createStatement()) {
            stmt.execute("DROP TABLE IF EXISTS " + TABLE_NAME);
            stmt.execute("CREATE TABLE " + TABLE_NAME + " (id SERIAL PRIMARY KEY, data TEXT)");
        }
    }

    private static void copyData(Connection conn) throws Exception {
        String copySql = "COPY " + TABLE_NAME + " (data) FROM STDIN WITH (FORMAT CSV)";

        try (PGCopyOutputStream copyOut = new PGCopyOutputStream(conn.unwrap(PgConnection.class), copySql)) {
            System.out.println("Start copying. Please interrupt network or restart PostgreSQL server.");
            // Interrupt network during this phase
            for (int i = 0; i < 500; i++) {
                copyOut.write((UUID.randomUUID() + "\n").getBytes(StandardCharsets.UTF_8));
                copyOut.flush();
                Thread.sleep(100);
            }
        } catch (Exception e) {
            System.err.println("COPY failed: " + e.getMessage());
            System.out.println("Check isValid(5)");
            // conn.isValid(5) should return false within 5 seconds, but hangs indefinitely
            System.out.println("isValid: " + conn.isValid(5));
        }
    }
}