import java.io.*;


/**
 * An input stream for reading both byte-stream data and
 * character-stream that is terminated using the HTTP end-of-line
 * characters ('\r\n')
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 0.0
 */
public class HttpInputStream extends DataInputStream
{
    private static final int  INITIAL_BUFFER_SIZE =  256;
    public  static final byte CR   = (byte)'\r'; //13;
    public  static final byte LF   = (byte)'\n'; //10;
    public  static final byte NULL = (byte)'\0'; // 0;

    private byte[] buffer;
    private int    currentSize;    

    /**
     * Explicit Value Constructor
     *
     * @param is    The underlying InputStream
     */
    public HttpInputStream(InputStream is)
    {
       super(is);
    }


    /**
     * Add a byte to the current line buffer (increasing the
     * size of the line buffer if necessary)
     *
     * @Param b  The byte to add
     */
    private void addToLineBuffer(byte b)
    {
       byte[]   temp;       

       buffer[currentSize] = b;
       currentSize++;
       
       if (currentSize == buffer.length)
       {
          temp = new byte[buffer.length*2];
          System.arraycopy(buffer, 0, temp, 0, buffer.length);
          buffer = temp;
       }
    }
    

    /**
     * Reads the input stream, one line at a time. 
     * Lines are terminated either by '\r\n' or by end-of-stream.
     *
     * @return    A String containing the line
     */
    public String readHttpLine() throws IOException 
    {
       byte     previous;
       byte[]   b;       
       int      status, stringLength;
       String   result;

       // This method will read a byte at a time.  It would be much
       // more efficient to read multiple bytes at a time into a buffer
       // but this is much simpler.
       b           = new byte[1];       

       buffer      = new byte[INITIAL_BUFFER_SIZE];
       currentSize = 0; 
       
       status      = -1;       
       previous    = NULL;
       
       while (status < 0)
       {
          try
          {
             readFully(b); // Blocks until a byte is available
             if ((b[0] == LF) && (previous == CR))
             {
                status = 1;
             }
             else
             {
                previous = b[0];
                addToLineBuffer(b[0]);
             }
          }
          catch (EOFException eofe)
          {
             status = 0;
          }
       }

       if (status == 0) stringLength = currentSize;     // Terminated by EOS
       else             stringLength = currentSize - 1; // Remove the CR

       try
       {
          // Use the HTTP "standard" character set
          result = new String(buffer, 0, stringLength, "ISO-8859-1");
       }
       catch (UnsupportedEncodingException uee)
       {
          // Use the default character set
          result = new String(buffer, 0, stringLength);
       }
       
       return result;       
    }
}