Bad file descriptor?{resolved}

[Dillinger4]

Does anyone know what this might mean? I am trying to calculate a message digest for a stream but a java.io.Exception: Bad file descriptor keeps getting thrown.

[CornedBee]

What kind of stream?

[Dillinger4]

DigestInputStream.

[CornedBee]

Wrapped around what? A SocketInputStream?

The message sounds a bit like a cryptic way of saying "network connection lost", or maybe "no data currently available".

[Dillinger4]

I was able to get things to work but im not quite sure if the output produced from the code is correct. Run this on a directory and see what you get.

 import java.security.*; 
 import java.io.*;
  
 class Digest{

  FileInputStream fis;
  private MessageDigest md; 
  private DigestInputStream dis; 
  private BufferedOutputStream bis; 
  private byte[] digest;
  private File[] files;
  private int bytesread;
  private byte[] buffer;  
  
  public Digest(File[] files){
   this.files = files; 
  }  

  public void calDigest() throws IOException, NoSuchAlgorithmException{

    for(int i = 0; i < files.length; i++){
     md = MessageDigest.getInstance("SHA"); 
     fis = new FileInputStream(files[i]);  
     dis = new DigestInputStream(fis, md);
     buffer = new byte[(byte)files[i].length()];
     while((bytesread = dis.read(buffer)) != -1)  
     digest = dis.getMessageDigest().digest();
     System.out.println(files[i].getName() + ": " + digest);     
     System.out.println();
    
   }   
  }
 }

 public class DigestTest{
    public static void main(String[] args){
     
   File dir = new File(args[0]);
     if(args.length == 0){
       System.out.println("Usage: You must specify arguemets!");  
       System.exit(0); 
     }
     if(!dir.isDirectory()){
       System.out.println("Usage: You must specify a directory!");  
       System.exit(0); 
     }
     
    File[] files = dir.listFiles(); 
    Digest digest = new Digest(files);
    try{  
    digest.calDigest();
    }catch(IOException e){
        System.err.println(e);
    }
    catch(NoSuchAlgorithmException nsa){
      System.err.println(nsa);
      } 
    }
  }

[CornedBee]

You can't just pass a byte array to println, but aside from that it seems to be working. I have no means to check the digest though, but why should it be wrong?
I adjusted the code slightly, but I still get IOExceptions when the thing tries to digest a directory.

import java.security.*;
import java.io.*;

class Digest{

	FileInputStream fis;
	private MessageDigest md;
	private DigestInputStream dis;
	private BufferedOutputStream bis;
	private byte[] digest;
	private File[] files;
	private int bytesread;
	private byte[] buffer;

	public Digest(File[] files){
		this.files = files;
	}

	public void calDigest() throws IOException, NoSuchAlgorithmException{
		buffer = new byte[1024];
		for(int i = 0; i < files.length; i++){
			md = MessageDigest.getInstance("SHA");
			fis = new FileInputStream(files[i]);
			dis = new DigestInputStream(fis, md);
			while((bytesread = dis.read(buffer)) != -1)
			digest = dis.getMessageDigest().digest();
			System.out.println(files[i].getName() + ": ");
			writeDigest();
			System.out.println();
			System.out.flush();
		}
	}

	private void writeDigest() {
		int l = digest.length;
		for(int i = 0; i < l; ++i) {
			try {
			System.out.print(Integer.toHexString(digest[i]).substring(0,2) + " ");
			} catch(Exception e) {
			}
		}
	}
}

public class DigestTest{
	public static void main(String[] args){
	 
		if(args.length == 0){
			System.out.println("Usage: You must specify arguments!");  
			System.exit(0); 
		}
		File dir = new File(args[0]);
		if(!dir.isDirectory()){
			System.out.println("Usage: You must specify a directory!");  
			System.exit(0); 
		}
		
		File[] files = dir.listFiles(); 
		Digest digest = new Digest(files);
		try{  
			digest.calDigest();
		}catch(IOException e){
			System.err.println(e);
		}catch(NoSuchAlgorithmException nsa){
			System.err.println(nsa);
		} 
	}
}

[Dillinger4]

I forgot a byte[] array cannot be passed. The writeDigest() method was exactly what was needed. Thanks. Yeah i didnt account for directories within directories but thats ok. Thanks for the help.

[CornedBee]

BTW you need to refine writeDigest. Currently it just skips bytes where the most significant nibble is 0 (anything from 00 to 0F). This is because they are converted to the strings '' to 'F' and substring throws a StringIndexOutOfBoundsException.

[Dillinger4]

Im not too sure if i follow your use of substring. I used a StringBuffer instead and it seems to work pretty good.

private void writeDigest(String file) {
  StringBuffer sb = new StringBuffer(file);
  sb.append(":");
  for(int i = 0; i < digest.length; ++i) {
     sb.append(digest[i] + " "); 
  }	
   System.out.println(sb);
}

Thanks for the help.