To complete the message digest computation, call one of the
* digest methods on the associated message
* digest after your calls to one of this digest input stream's
* {@link #read() read} methods.
*
*
It is possible to turn this stream on or off (see
* {@link #on(boolean) on}). When it is on, a call to one of the
* read methods
* results in an update on the message digest. But when it is off,
* the message digest is not updated. The default is for the stream
* to be on.
*
*
Note that digest objects can compute only one digest (see
* {@link MessageDigest}),
* so that in order to compute intermediate digests, a caller should
* retain a handle onto the digest object, and clone it for each
* digest to be computed, leaving the orginal digest untouched.
*
* @see MessageDigest
*
* @see DigestOutputStream
*
* @author Benjamin Renaud
*/
public class DigestInputStream extends FilterInputStream {
/* NOTE: This should be made a generic UpdaterInputStream */
/* Are we on or off? */
private boolean on = true;
/**
* The message digest associated with this stream.
*/
protected MessageDigest digest;
/**
* Creates a digest input stream, using the specified input stream
* and message digest.
*
* @param stream the input stream.
*
* @param digest the message digest to associate with this stream.
*/
public DigestInputStream(InputStream stream, MessageDigest digest) {
super(stream);
setMessageDigest(digest);
}
/**
* Returns the message digest associated with this stream.
*
* @return the message digest associated with this stream.
* @see #setMessageDigest(java.security.MessageDigest)
*/
public MessageDigest getMessageDigest() {
return digest;
}
/**
* Associates the specified message digest with this stream.
*
* @param digest the message digest to be associated with this stream.
* @see #getMessageDigest()
*/
public void setMessageDigest(MessageDigest digest) {
this.digest = digest;
}
/**
* Reads a byte, and updates the message digest (if the digest
* function is on). That is, this method reads a byte from the
* input stream, blocking until the byte is actually read. If the
* digest function is on (see {@link #on(boolean) on}), this method
* will then call update on the message digest associated
* with this stream, passing it the byte read.
*
* @return the byte read.
*
* @exception IOException if an I/O error occurs.
*
* @see MessageDigest#update(byte)
*/
public int read() throws IOException {
int ch = in.read();
if (on && ch != -1) {
digest.update((byte)ch);
}
return ch;
}
/**
* Reads into a byte array, and updates the message digest (if the
* digest function is on). That is, this method reads up to
* len bytes from the input stream into the array
* b, starting at offset off. This method
* blocks until the data is actually
* read. If the digest function is on (see
* {@link #on(boolean) on}), this method will then call update
* on the message digest associated with this stream, passing it
* the data.
*
* @param b the array into which the data is read.
*
* @param off the starting offset into b of where the
* data should be placed.
*
* @param len the maximum number of bytes to be read from the input
* stream into b, starting at offset off.
*
* @return the actual number of bytes read. This is less than
* len if the end of the stream is reached prior to
* reading len bytes. -1 is returned if no bytes were
* read because the end of the stream had already been reached when
* the call was made.
*
* @exception IOException if an I/O error occurs.
*
* @see MessageDigest#update(byte[], int, int)
*/
public int read(byte[] b, int off, int len) throws IOException {
int result = in.read(b, off, len);
if (on && result != -1) {
digest.update(b, off, result);
}
return result;
}
/**
* Turns the digest function on or off. The default is on. When
* it is on, a call to one of the read methods results in an
* update on the message digest. But when it is off, the message
* digest is not updated.
*
* @param on true to turn the digest function on, false to turn
* it off.
*/
public void on(boolean on) {
this.on = on;
}
/**
* Prints a string representation of this digest input stream and
* its associated message digest object.
*/
public String toString() {
return "[Digest Input Stream] " + digest.toString();
}
}