[IO-818] NullInputStream breaks InputStream's read method contract

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.13.0
• Fix Version/s: 2.16.0
• Component/s: Streams/Writers

Environment

JDK 17.0

Apache commons-io-2.13.0, but it looks like this apply to 2.15.0 too.

• Assignee: Unassigned
• Reporter: X Liu
• Created: 27/Oct/23 17:08
• Updated: 27/Dec/23 14:20
• Resolved: 27/Dec/23 14:19

Description

A java.io.InputStream instance's read(...) method will always return -1 after it reaches its end.

 
However, after a NullInputStream instance reaches its end, if you call its read(...) method again, you'll get IOException with message Read after end of file. It's document says the read(...) method should return -1 if the end of file has been reached and throwEofException is set to false. However, its code doesn't check throwEofException flag before it throws the IOException:

public int read() throws IOException {
    if (eof) {
       throw new IOException("Read after end of file");
    }
    ....
}

I'm not sure whether its read method should strictly follow what InputStream does, i.e., always return -1 after it reaches end, or should it check throwEofException flag before it throws an IOException.

Following is a snippet that can reproduce this problem:

import org.apache.commons.io.input.NullInputStream;

import java.io.ByteArrayInputStream;
import java.io.InputStream;

public class InputStreamTest {

    private static void testOneStream(InputStream inputStream) throws Exception {
        final byte[] buffer = new byte[4096];
        int readLen;
        while ((readLen = inputStream.read(buffer)) != -1) {
            // do nothing
        }
        readLen = inputStream.read(buffer);
        if (readLen != -1) {
            throw new Exception("Failed to read after reaching the end of the stream.");
        }
    }

    public static void main(String[] args) {
        try { // Test ByteArrayInputStream
            final InputStream byteArrayInputStream = new ByteArrayInputStream(new byte[1024]);
            testOneStream(byteArrayInputStream);
            System.out.println("ByteArrayInputStream succeeded.");
        } catch (Exception e) {
            System.out.println("ByteArrayInputStream failed");
        }
        try { //Test NullInputStream
            final InputStream nullInputStream = new NullInputStream(1024, true, false);
            testOneStream(nullInputStream);
            System.out.println("NullInputStream succeeded.");
        } catch (Exception e) {
            System.out.println("NullInputStream failed");
        }
    }
}