Author Archive for frankdu

Best Practices of usinsg HttpClient in Android

by frankdu • January 18, 2013 • 0 Comments

The best practices of using HttpClient in Android? Must Check the following items:

How to display FPS (frame per second) number in Android

by frankdu • January 15, 2013 • 0 Comments

Well, check out this blog:

Window Backgrounds & UI Speed
http://android-developers.blogspot.com/2009/03/window-backgrounds-ui-speed.html

Deploy OAuth provider with mod_wsgi

by frankdu • July 10, 2011 • 0 Comments

Recently I deploy an OAuth provider with apache/mod_wsgi. Everything works fine on django dev server locally, but is broken onto apache server. After analyzing the logs, it shows that the HTTP header ‘Authroization’ is dropped by default.

To pass thru OAuth parameters to mod_wsgi applications, you need to use the WSGIPassAuthorization directive. An example is like below, at the same level of ServerName directive:

WSGIPassAuthorization On

1	WSGIPassAuthorization On

Bear in mind that the ‘Authorization’ header will be passed thru and renamed to ‘HTTP_AUTHORIZATION’. You need to do such modification if you use python-oauth2 like me. I plan to submit a patch, in order to contribute and learn about git as well, LOL.

References

Many profilers, and I need at least one

by frankdu • April 15, 2011 • 0 Comments

Performance improvement is an ongoing task, always. So a profiler is a good friend. For me, the very basic tool is timing and print functions, lol. Yes, they are. In one of language tool, it helps to identify the parsing phase takes 60~80% of the time. The granulatiry is coarse (not down to function level), but very useful. Later I introduced multithreading for parsing. It’s very useful to run one parsing thread on each CPU core.

This week, I tried 2 C++ profiler. ‘Very Sleepy’ and VS profiler. I like ‘Very Sleepy’. It helps to identify a hash table implementation in a runtime module. It is mostly from key collision, and we got significant performance improvement after tuning the codes.

For Java, last year I tried eclipse TPTP and yourkit. TPTP sucks. Yes, you wasted hours and lose patience before a running finished. Normally it takes 30+ seconds for each running. Maybe TPTP is not good at profiling a recursive-descedent parser. Then I tried yourkit and quickly identified which parser rule was causing the problem. After the fix, the time dropped from 1200seconds to ~4 seconds in doing 22 nested if-else-if-else statements. Pretty exciting profiling experience.

4 years ago we profiled a C# web app. I forgot which profiler we used. Finally we improved the performance by trade-off in UX/speed + more offline computing.

Haven’t got experience with profiler in other languages. But so many profilers, I need at least one.

Another Way of Javascript Method Overloading

by frankdu • April 8, 2011 • 0 Comments

In John Resig post, he presented a subtle method to support method overloading. It’s very useful when you have method overloading and each method behaves differently.

However, it adds overhead by wrap up existing methods inside a new function. For performance consideration, we check the length of arguments to execute different logics. It’s a more efficient and simple way to do the overloading. Examples:

// define class, which takes 0 or 1 argument
function Counter(x){	
	this.count = (arguments.length == 0 ? 0 : x);
}

// add a method. The 2nd argument has a default value, if not supplied
Counter.prototype.increase = function(quantity, times){
	times = (arguments.length &lt; 2 ? 1 : times);
	this.count += (quantity * times);	
}

// allow arbitrary number of arguments
Counter.prototype.add = function(x){
	if(arguments.length == 0){
		this.count += x;
	} else {
		for(var i=0; i&lt;arguments.length; i++){
			this.x += arguments[i];
		}
	}
}

// define class, which takes 0 or 1 argument

function Counter(x){

this.count = (arguments.length == 0 ? 0 : x);

}

// add a method. The 2nd argument has a default value, if not supplied

Counter.prototype.increase = function(quantity, times){

times = (arguments.length < 2 ? 1 : times);

this.count += (quantity * times);

}

// allow arbitrary number of arguments

Counter.prototype.add = function(x){

if(arguments.length == 0){

this.count += x;

} else {

for(var i=0; i<arguments.length; i++){

this.x += arguments[i];

}

Mercurial: How to ignore everything in a folder?

by frankdu • March 22, 2011 • 0 Comments

I have been looking for this for a while. It’s pretty simple. Let’s say you have project A, and want to ignore 2 folders: bin and output.

1. In your project folder, edit the file ‘.hgignore’, or create it if non-existing.
2. Add the following lines:

syntax: glob
output/**
syntax: glob
bin/**

syntax: glob

output/**

syntax: glob

bin/**

That’s it. You are all set.

Implement Unsigned Right Shift (>>>) if the Operator is Unsupported

by frankdu • March 11, 2011 • 0 Comments

If you are Java/Javascript/AS3 developer, you know what the >>> operator does.

It is called unsigned right shift, or logical right shift. Check the definition in wikipedia.

However, C# and C++ don’t have such operator for signed integers, though it is available for unsigned integers. Here is one of my implementation. Hope it helps if you looking for such code:

int unsignedRightShift(int num, int offset){		
	// 1. Convention to check negative offset
	// 2. Check num == 0 to avoid different representation of positive/negative zero 
	if (offset < 0 || num == 0) {
		return 0;
	} else if (offset == 0) {
		return num;
	} else if (num < 0) {
		// Don't use 0x80000000, because some platform (.NET) treat it as long but not integer.
		// Use left shift to get the desired bit pattern. This number can be cached for performance
		return ((num >> 1) ^ (1 << 31)) >> (offset - 1);
	} else {
		return num >> offset;
	}
}

int unsignedRightShift(int num, int offset){

// 1. Convention to check negative offset

// 2. Check num == 0 to avoid different representation of positive/negative zero

if (offset < 0 || num == 0) {

return 0;

} else if (offset == 0) {

return num;

} else if (num < 0) {

// Don't use 0x80000000, because some platform (.NET) treat it as long but not integer.

// Use left shift to get the desired bit pattern. This number can be cached for performance

return ((num >> 1) ^ (1 << 31)) >> (offset - 1);

} else {

return num >> offset;

}

Get the real client IP address, when you use a reverse proxy

by frankdu • February 11, 2011 • 0 Comments

Let’s say you are running ASP.NET, PHP, JSP, or Python web. If the code is visited via reverse proxy, then the client IP address is the proxy IP with regular detecting routue. To fix the issue, let’s first take a look at 3 HTTP headers added by proxies:

X-Forwarded-For
The IP address(s) of the client. If there are multiple proxies, you see multiple IP addresses, separated by comma. For example:

X-Forwarded-For: client1, proxy1, proxy2

X-Forwarded-Host
The original host requested by the client in the Host HTTP request header.

X-Forwarded-Server
The hostname of the proxy server.

———————————————

The Solution:

It’s pretty straightforward. The flow is:

Check if there is X-Forwarded-For in http headers.
If yes, get the string, and split it by comma. Then get the first piece.
If no, fall back on regular way of reading IP address.

That’s it.

Base64 Encoding in Android 2.1 or Earlier

by frankdu • January 27, 2011 • 3 Comments

Base64 is common used. Now Google added a utility class android.util.Base64. Unfortunately it is only available in Android 2.2 and later.

So, you need just a little bit work to use it with Android 2.1 or ealier. Yes, just copy and past the source of Base64 into your project. Make sure to preserve the Apache 2.0 license section, in order to conform to the license. The source code is provided at the end of this post, for your reference.

My disclaimer: I am not responsible for any result in doing the practice described hereby. Read the license if you need.

Now let’s see example usage:

import android.util.Base64;

public class Test {
    public static void main(String[] args) {
        String data = "this is a message by frank.";
        String encoded = Base64.encodeToString(data.getBytes(), Base64.DEFAULT);
        System.out.println("Encoded: " + encoded);

        String decoded = new String(Base64.decode(encoded, Base64.DEFAULT));
        System.out.println("Decoded: " + decoded);
    }
}

import android.util.Base64;

public class Test {

public static void main(String[] args) {

String data = "this is a message by frank.";

String encoded = Base64.encodeToString(data.getBytes(), Base64.DEFAULT);

System.out.println("Encoded: " + encoded);

String decoded = new String(Base64.decode(encoded, Base64.DEFAULT));

System.out.println("Decoded: " + decoded);

}

The output is:

Encoded: dGhpcyBpcyBhIG1lc3NhZ2UgYnkgZnJhbmsu

Decoded: this is a message by frank.

Let’s try decode the message in python:

import base64
print base64.b64decode('dGhpcyBpcyBhIG1lc3NhZ2UgYnkgZnJhbmsu')

1 2	import base64 print base64.b64decode('dGhpcyBpcyBhIG1lc3NhZ2UgYnkgZnJhbmsu')

You will get the same input message htere. Now you are ready to send your data to anywhere, like app engine, you know!

The android.util.Base64 source

package android.util;
/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */



import java.io.UnsupportedEncodingException;

/**
 * Utilities for encoding and decoding the Base64 representation of
 * binary data.  See RFCs <a
 * href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a
 * href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.
 */
public class Base64 {
    /**
     * Default values for encoder/decoder flags.
     */
    public static final int DEFAULT = 0;

    /**
     * Encoder flag bit to omit the padding '=' characters at the end
     * of the output (if any).
     */
    public static final int NO_PADDING = 1;

    /**
     * Encoder flag bit to omit all line terminators (i.e., the output
     * will be on one long line).
     */
    public static final int NO_WRAP = 2;

    /**
     * Encoder flag bit to indicate lines should be terminated with a
     * CRLF pair instead of just an LF.  Has no effect if {@code
     * NO_WRAP} is specified as well.
     */
    public static final int CRLF = 4;

    /**
     * Encoder/decoder flag bit to indicate using the "URL and
     * filename safe" variant of Base64 (see RFC 3548 section 4) where
     * {@code -} and {@code _} are used in place of {@code +} and
     * {@code /}.
     */
    public static final int URL_SAFE = 8;

    /**
     * Flag to pass to {@link Base64OutputStream} to indicate that it
     * should not close the output stream it is wrapping when it
     * itself is closed.
     */
    public static final int NO_CLOSE = 16;

    //  --------------------------------------------------------
    //  shared code
    //  --------------------------------------------------------

    /* package */ static abstract class Coder {
        public byte[] output;
        public int op;

        /**
         * Encode/decode another block of input data.  this.output is
         * provided by the caller, and must be big enough to hold all
         * the coded data.  On exit, this.opwill be set to the length
         * of the coded data.
         *
         * @param finish true if this is the final call to process for
         *        this object.  Will finalize the coder state and
         *        include any final bytes in the output.
         *
         * @return true if the input so far is good; false if some
         *         error has been detected in the input stream..
         */
        public abstract boolean process(byte[] input, int offset, int len, boolean finish);

        /**
         * @return the maximum number of bytes a call to process()
         * could produce for the given number of input bytes.  This may
         * be an overestimate.
         */
        public abstract int maxOutputSize(int len);
    }

    //  --------------------------------------------------------
    //  decoding
    //  --------------------------------------------------------

    /**
     * Decode the Base64-encoded data in input and return the data in
     * a new byte array.
     *
     * <p>The padding '=' characters at the end are considered optional, but
     * if any are present, there must be the correct number of them.
     *
     * @param str    the input String to decode, which is converted to
     *               bytes using the default charset
     * @param flags  controls certain features of the decoded output.
     *               Pass {@code DEFAULT} to decode standard Base64.
     *
     * @throws IllegalArgumentException if the input contains
     * incorrect padding
     */
    public static byte[] decode(String str, int flags) {
        return decode(str.getBytes(), flags);
    }

    /**
     * Decode the Base64-encoded data in input and return the data in
     * a new byte array.
     *
     * <p>The padding '=' characters at the end are considered optional, but
     * if any are present, there must be the correct number of them.
     *
     * @param input the input array to decode
     * @param flags  controls certain features of the decoded output.
     *               Pass {@code DEFAULT} to decode standard Base64.
     *
     * @throws IllegalArgumentException if the input contains
     * incorrect padding
     */
    public static byte[] decode(byte[] input, int flags) {
        return decode(input, 0, input.length, flags);
    }

    /**
     * Decode the Base64-encoded data in input and return the data in
     * a new byte array.
     *
     * <p>The padding '=' characters at the end are considered optional, but
     * if any are present, there must be the correct number of them.
     *
     * @param input  the data to decode
     * @param offset the position within the input array at which to start
     * @param len    the number of bytes of input to decode
     * @param flags  controls certain features of the decoded output.
     *               Pass {@code DEFAULT} to decode standard Base64.
     *
     * @throws IllegalArgumentException if the input contains
     * incorrect padding
     */
    public static byte[] decode(byte[] input, int offset, int len, int flags) {
        // Allocate space for the most data the input could represent.
        // (It could contain less if it contains whitespace, etc.)
        Decoder decoder = new Decoder(flags, new byte[len*3/4]);

        if (!decoder.process(input, offset, len, true)) {
            throw new IllegalArgumentException("bad base-64");
        }

        // Maybe we got lucky and allocated exactly enough output space.
        if (decoder.op == decoder.output.length) {
            return decoder.output;
        }

        // Need to shorten the array, so allocate a new one of the
        // right size and copy.
        byte[] temp = new byte[decoder.op];
        System.arraycopy(decoder.output, 0, temp, 0, decoder.op);
        return temp;
    }

    /* package */ static class Decoder extends Coder {
        /**
         * Lookup table for turning bytes into their position in the
         * Base64 alphabet.
         */
        private static final int DECODE[] = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        };

        /**
         * Decode lookup table for the "web safe" variant (RFC 3548
         * sec. 4) where - and _ replace + and /.
         */
        private static final int DECODE_WEBSAFE[] = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63,
            -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
            41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        };

        /** Non-data values in the DECODE arrays. */
        private static final int SKIP = -1;
        private static final int EQUALS = -2;

        /**
         * States 0-3 are reading through the next input tuple.
         * State 4 is having read one '=' and expecting exactly
         * one more.
         * State 5 is expecting no more data or padding characters
         * in the input.
         * State 6 is the error state; an error has been detected
         * in the input and no future input can "fix" it.
         */
        private int state;   // state number (0 to 6)
        private int value;

        final private int[] alphabet;

        public Decoder(int flags, byte[] output) {
            this.output = output;

            alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
            state = 0;
            value = 0;
        }

        /**
         * @return an overestimate for the number of bytes {@code
         * len} bytes could decode to.
         */
        public int maxOutputSize(int len) {
            return len * 3/4 + 10;
        }

        /**
         * Decode another block of input data.
         *
         * @return true if the state machine is still healthy.  false if
         *         bad base-64 data has been detected in the input stream.
         */
        public boolean process(byte[] input, int offset, int len, boolean finish) {
            if (this.state == 6) return false;

            int p = offset;
            len += offset;

            // Using local variables makes the decoder about 12%
            // faster than if we manipulate the member variables in
            // the loop.  (Even alphabet makes a measurable
            // difference, which is somewhat surprising to me since
            // the member variable is final.)
            int state = this.state;
            int value = this.value;
            int op = 0;
            final byte[] output = this.output;
            final int[] alphabet = this.alphabet;

            while (p < len) {
                // Try the fast path:  we're starting a new tuple and the
                // next four bytes of the input stream are all data
                // bytes.  This corresponds to going through states
                // 0-1-2-3-0.  We expect to use this method for most of
                // the data.
                //
                // If any of the next four bytes of input are non-data
                // (whitespace, etc.), value will end up negative.  (All
                // the non-data values in decode are small negative
                // numbers, so shifting any of them up and or'ing them
                // together will result in a value with its top bit set.)
                //
                // You can remove this whole block and the output should
                // be the same, just slower.
                if (state == 0) {
                    while (p+4 <= len &&
                           (value = ((alphabet[input[p] & 0xff] << 18) |
                                     (alphabet[input[p+1] & 0xff] << 12) |
                                     (alphabet[input[p+2] & 0xff] << 6) |
                                     (alphabet[input[p+3] & 0xff]))) >= 0) {
                        output[op+2] = (byte) value;
                        output[op+1] = (byte) (value >> 8);
                        output[op] = (byte) (value >> 16);
                        op += 3;
                        p += 4;
                    }
                    if (p >= len) break;
                }

                // The fast path isn't available -- either we've read a
                // partial tuple, or the next four input bytes aren't all
                // data, or whatever.  Fall back to the slower state
                // machine implementation.

                int d = alphabet[input[p++] & 0xff];

                switch (state) {
                case 0:
                    if (d >= 0) {
                        value = d;
                        ++state;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 1:
                    if (d >= 0) {
                        value = (value << 6) | d;
                        ++state;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 2:
                    if (d >= 0) {
                        value = (value << 6) | d;
                        ++state;
                    } else if (d == EQUALS) {
                        // Emit the last (partial) output tuple;
                        // expect exactly one more padding character.
                        output[op++] = (byte) (value >> 4);
                        state = 4;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 3:
                    if (d >= 0) {
                        // Emit the output triple and return to state 0.
                        value = (value << 6) | d;
                        output[op+2] = (byte) value;
                        output[op+1] = (byte) (value >> 8);
                        output[op] = (byte) (value >> 16);
                        op += 3;
                        state = 0;
                    } else if (d == EQUALS) {
                        // Emit the last (partial) output tuple;
                        // expect no further data or padding characters.
                        output[op+1] = (byte) (value >> 2);
                        output[op] = (byte) (value >> 10);
                        op += 2;
                        state = 5;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 4:
                    if (d == EQUALS) {
                        ++state;
                    } else if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;

                case 5:
                    if (d != SKIP) {
                        this.state = 6;
                        return false;
                    }
                    break;
                }
            }

            if (!finish) {
                // We're out of input, but a future call could provide
                // more.
                this.state = state;
                this.value = value;
                this.op = op;
                return true;
            }

            // Done reading input.  Now figure out where we are left in
            // the state machine and finish up.

            switch (state) {
            case 0:
                // Output length is a multiple of three.  Fine.
                break;
            case 1:
                // Read one extra input byte, which isn't enough to
                // make another output byte.  Illegal.
                this.state = 6;
                return false;
            case 2:
                // Read two extra input bytes, enough to emit 1 more
                // output byte.  Fine.
                output[op++] = (byte) (value >> 4);
                break;
            case 3:
                // Read three extra input bytes, enough to emit 2 more
                // output bytes.  Fine.
                output[op++] = (byte) (value >> 10);
                output[op++] = (byte) (value >> 2);
                break;
            case 4:
                // Read one padding '=' when we expected 2.  Illegal.
                this.state = 6;
                return false;
            case 5:
                // Read all the padding '='s we expected and no more.
                // Fine.
                break;
            }

            this.state = state;
            this.op = op;
            return true;
        }
    }

    //  --------------------------------------------------------
    //  encoding
    //  --------------------------------------------------------

    /**
     * Base64-encode the given data and return a newly allocated
     * String with the result.
     *
     * @param input  the data to encode
     * @param flags  controls certain features of the encoded output.
     *               Passing {@code DEFAULT} results in output that
     *               adheres to RFC 2045.
     */
    public static String encodeToString(byte[] input, int flags) {
        try {
            return new String(encode(input, flags), "US-ASCII");
        } catch (UnsupportedEncodingException e) {
            // US-ASCII is guaranteed to be available.
            throw new AssertionError(e);
        }
    }

    /**
     * Base64-encode the given data and return a newly allocated
     * String with the result.
     *
     * @param input  the data to encode
     * @param offset the position within the input array at which to
     *               start
     * @param len    the number of bytes of input to encode
     * @param flags  controls certain features of the encoded output.
     *               Passing {@code DEFAULT} results in output that
     *               adheres to RFC 2045.
     */
    public static String encodeToString(byte[] input, int offset, int len, int flags) {
        try {
            return new String(encode(input, offset, len, flags), "US-ASCII");
        } catch (UnsupportedEncodingException e) {
            // US-ASCII is guaranteed to be available.
            throw new AssertionError(e);
        }
    }

    /**
     * Base64-encode the given data and return a newly allocated
     * byte[] with the result.
     *
     * @param input  the data to encode
     * @param flags  controls certain features of the encoded output.
     *               Passing {@code DEFAULT} results in output that
     *               adheres to RFC 2045.
     */
    public static byte[] encode(byte[] input, int flags) {
        return encode(input, 0, input.length, flags);
    }

    /**
     * Base64-encode the given data and return a newly allocated
     * byte[] with the result.
     *
     * @param input  the data to encode
     * @param offset the position within the input array at which to
     *               start
     * @param len    the number of bytes of input to encode
     * @param flags  controls certain features of the encoded output.
     *               Passing {@code DEFAULT} results in output that
     *               adheres to RFC 2045.
     */
    public static byte[] encode(byte[] input, int offset, int len, int flags) {
        Encoder encoder = new Encoder(flags, null);

        // Compute the exact length of the array we will produce.
        int output_len = len / 3 * 4;

        // Account for the tail of the data and the padding bytes, if any.
        if (encoder.do_padding) {
            if (len % 3 > 0) {
                output_len += 4;
            }
        } else {
            switch (len % 3) {
                case 0: break;
                case 1: output_len += 2; break;
                case 2: output_len += 3; break;
            }
        }

        // Account for the newlines, if any.
        if (encoder.do_newline && len > 0) {
            output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *
                (encoder.do_cr ? 2 : 1);
        }

        encoder.output = new byte[output_len];
        encoder.process(input, offset, len, true);

        assert encoder.op == output_len;

        return encoder.output;
    }

    /* package */ static class Encoder extends Coder {
        /**
         * Emit a new line every this many output tuples.  Corresponds to
         * a 76-character line length (the maximum allowable according to
         * <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
         */
        public static final int LINE_GROUPS = 19;

        /**
         * Lookup table for turning Base64 alphabet positions (6 bits)
         * into output bytes.
         */
        private static final byte ENCODE[] = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',
        };

        /**
         * Lookup table for turning Base64 alphabet positions (6 bits)
         * into output bytes.
         */
        private static final byte ENCODE_WEBSAFE[] = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',
        };

        final private byte[] tail;
        /* package */ int tailLen;
        private int count;

        final public boolean do_padding;
        final public boolean do_newline;
        final public boolean do_cr;
        final private byte[] alphabet;

        public Encoder(int flags, byte[] output) {
            this.output = output;

            do_padding = (flags & NO_PADDING) == 0;
            do_newline = (flags & NO_WRAP) == 0;
            do_cr = (flags & CRLF) != 0;
            alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;

            tail = new byte[2];
            tailLen = 0;

            count = do_newline ? LINE_GROUPS : -1;
        }

        /**
         * @return an overestimate for the number of bytes {@code
         * len} bytes could encode to.
         */
        public int maxOutputSize(int len) {
            return len * 8/5 + 10;
        }

        public boolean process(byte[] input, int offset, int len, boolean finish) {
            // Using local variables makes the encoder about 9% faster.
            final byte[] alphabet = this.alphabet;
            final byte[] output = this.output;
            int op = 0;
            int count = this.count;

            int p = offset;
            len += offset;
            int v = -1;

            // First we need to concatenate the tail of the previous call
            // with any input bytes available now and see if we can empty
            // the tail.

            switch (tailLen) {
                case 0:
                    // There was no tail.
                    break;

                case 1:
                    if (p+2 <= len) {
                        // A 1-byte tail with at least 2 bytes of
                        // input available now.
                        v = ((tail[0] & 0xff) << 16) |
                            ((input[p++] & 0xff) << 8) |
                            (input[p++] & 0xff);
                        tailLen = 0;
                    };
                    break;

                case 2:
                    if (p+1 <= len) {
                        // A 2-byte tail with at least 1 byte of input.
                        v = ((tail[0] & 0xff) << 16) |
                            ((tail[1] & 0xff) << 8) |
                            (input[p++] & 0xff);
                        tailLen = 0;
                    }
                    break;
            }

            if (v != -1) {
                output[op++] = alphabet[(v >> 18) & 0x3f];
                output[op++] = alphabet[(v >> 12) & 0x3f];
                output[op++] = alphabet[(v >> 6) & 0x3f];
                output[op++] = alphabet[v & 0x3f];
                if (--count == 0) {
                    if (do_cr) output[op++] = 'r';
                    output[op++] = 'n';
                    count = LINE_GROUPS;
                }
            }

            // At this point either there is no tail, or there are fewer
            // than 3 bytes of input available.

            // The main loop, turning 3 input bytes into 4 output bytes on
            // each iteration.
            while (p+3 <= len) {
                v = ((input[p] & 0xff) << 16) |
                    ((input[p+1] & 0xff) << 8) |
                    (input[p+2] & 0xff);
                output[op] = alphabet[(v >> 18) & 0x3f];
                output[op+1] = alphabet[(v >> 12) & 0x3f];
                output[op+2] = alphabet[(v >> 6) & 0x3f];
                output[op+3] = alphabet[v & 0x3f];
                p += 3;
                op += 4;
                if (--count == 0) {
                    if (do_cr) output[op++] = 'r';
                    output[op++] = 'n';
                    count = LINE_GROUPS;
                }
            }

            if (finish) {
                // Finish up the tail of the input.  Note that we need to
                // consume any bytes in tail before any bytes
                // remaining in input; there should be at most two bytes
                // total.

                if (p-tailLen == len-1) {
                    int t = 0;
                    v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
                    tailLen -= t;
                    output[op++] = alphabet[(v >> 6) & 0x3f];
                    output[op++] = alphabet[v & 0x3f];
                    if (do_padding) {
                        output[op++] = '=';
                        output[op++] = '=';
                    }
                    if (do_newline) {
                        if (do_cr) output[op++] = 'r';
                        output[op++] = 'n';
                    }
                } else if (p-tailLen == len-2) {
                    int t = 0;
                    v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |
                        (((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
                    tailLen -= t;
                    output[op++] = alphabet[(v >> 12) & 0x3f];
                    output[op++] = alphabet[(v >> 6) & 0x3f];
                    output[op++] = alphabet[v & 0x3f];
                    if (do_padding) {
                        output[op++] = '=';
                    }
                    if (do_newline) {
                        if (do_cr) output[op++] = 'r';
                        output[op++] = 'n';
                    }
                } else if (do_newline && op > 0 && count != LINE_GROUPS) {
                    if (do_cr) output[op++] = 'r';
                    output[op++] = 'n';
                }

                assert tailLen == 0;
                assert p == len;
            } else {
                // Save the leftovers in tail to be consumed on the next
                // call to encodeInternal.

                if (p == len-1) {
                    tail[tailLen++] = input[p];
                } else if (p == len-2) {
                    tail[tailLen++] = input[p];
                    tail[tailLen++] = input[p+1];
                }
            }

            this.op = op;
            this.count = count;

            return true;
        }
    }

    private Base64() { }   // don't instantiate
}

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package android.util;

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

* http://www.apache.org/licenses/LICENSE-2.0

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

import java.io.UnsupportedEncodingException;

/**

* Utilities for encoding and decoding the Base64 representation of

* binary data. See RFCs <a

* href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a

* href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.

public class Base64 {

/**

* Default values for encoder/decoder flags.

public static final int DEFAULT = 0;

/**

* Encoder flag bit to omit the padding '=' characters at the end

* of the output (if any).

public static final int NO_PADDING = 1;

/**

* Encoder flag bit to omit all line terminators (i.e., the output

* will be on one long line).

public static final int NO_WRAP = 2;

/**

* Encoder flag bit to indicate lines should be terminated with a

* CRLF pair instead of just an LF. Has no effect if {@code

* NO_WRAP} is specified as well.

public static final int CRLF = 4;

/**

* Encoder/decoder flag bit to indicate using the "URL and

* filename safe" variant of Base64 (see RFC 3548 section 4) where

* {@code -} and {@code _} are used in place of {@code +} and

* {@code /}.

public static final int URL_SAFE = 8;

/**

* Flag to pass to {@link Base64OutputStream} to indicate that it

* should not close the output stream it is wrapping when it

* itself is closed.

public static final int NO_CLOSE = 16;

// --------------------------------------------------------

// shared code

// --------------------------------------------------------

/* package */ static abstract class Coder {

public byte[] output;

public int op;

/**

* Encode/decode another block of input data. this.output is

* provided by the caller, and must be big enough to hold all

* the coded data. On exit, this.opwill be set to the length

* of the coded data.

* @param finish true if this is the final call to process for

* this object. Will finalize the coder state and

* include any final bytes in the output.

* @return true if the input so far is good; false if some

* error has been detected in the input stream..

public abstract boolean process(byte[] input, int offset, int len, boolean finish);

/**

* @return the maximum number of bytes a call to process()

* could produce for the given number of input bytes. This may

* be an overestimate.

public abstract int maxOutputSize(int len);

}

// --------------------------------------------------------

// decoding

// --------------------------------------------------------

/**

* Decode the Base64-encoded data in input and return the data in

* a new byte array.

* <p>The padding '=' characters at the end are considered optional, but

* if any are present, there must be the correct number of them.

* @param str the input String to decode, which is converted to

* bytes using the default charset

* @param flags controls certain features of the decoded output.

* Pass {@code DEFAULT} to decode standard Base64.

* @throws IllegalArgumentException if the input contains

* incorrect padding

public static byte[] decode(String str, int flags) {

return decode(str.getBytes(), flags);

}

/**

* Decode the Base64-encoded data in input and return the data in

* a new byte array.

* <p>The padding '=' characters at the end are considered optional, but

* if any are present, there must be the correct number of them.

* @param input the input array to decode

* @param flags controls certain features of the decoded output.

* Pass {@code DEFAULT} to decode standard Base64.

* @throws IllegalArgumentException if the input contains

* incorrect padding

public static byte[] decode(byte[] input, int flags) {

return decode(input, 0, input.length, flags);

}

/**

* Decode the Base64-encoded data in input and return the data in

* a new byte array.

* <p>The padding '=' characters at the end are considered optional, but

* if any are present, there must be the correct number of them.

* @param input the data to decode

* @param offset the position within the input array at which to start

* @param len the number of bytes of input to decode

* @param flags controls certain features of the decoded output.

* Pass {@code DEFAULT} to decode standard Base64.

* @throws IllegalArgumentException if the input contains

* incorrect padding

public static byte[] decode(byte[] input, int offset, int len, int flags) {

// Allocate space for the most data the input could represent.

// (It could contain less if it contains whitespace, etc.)

Decoder decoder = new Decoder(flags, new byte[len*3/4]);

if (!decoder.process(input, offset, len, true)) {

throw new IllegalArgumentException("bad base-64");

}

// Maybe we got lucky and allocated exactly enough output space.

if (decoder.op == decoder.output.length) {

return decoder.output;

}

// Need to shorten the array, so allocate a new one of the

// right size and copy.

byte[] temp = new byte[decoder.op];

System.arraycopy(decoder.output, 0, temp, 0, decoder.op);

return temp;

}

/* package */ static class Decoder extends Coder {

/**

* Lookup table for turning bytes into their position in the

* Base64 alphabet.

private static final int DECODE[] = {

-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,

-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,

52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,

-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,

15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,

-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,

41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,

-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,

};

/**

* Decode lookup table for the "web safe" variant (RFC 3548

* sec. 4) where - and _ replace + and /.

private static final int DECODE_WEBSAFE[] = {

-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,

-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1,

52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -1, -1,

-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,

15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63,

-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,

41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,

-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,

};

/** Non-data values in the DECODE arrays. */

private static final int SKIP = -1;

private static final int EQUALS = -2;

/**

* States 0-3 are reading through the next input tuple.

* State 4 is having read one '=' and expecting exactly

* one more.

* State 5 is expecting no more data or padding characters

* in the input.

* State 6 is the error state; an error has been detected

* in the input and no future input can "fix" it.

private int state; // state number (0 to 6)

private int value;

final private int[] alphabet;

public Decoder(int flags, byte[] output) {

this.output = output;

alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;

state = 0;

value = 0;

}

/**

* @return an overestimate for the number of bytes {@code

* len} bytes could decode to.

public int maxOutputSize(int len) {

return len * 3/4 + 10;

}

/**

* Decode another block of input data.

* @return true if the state machine is still healthy. false if

* bad base-64 data has been detected in the input stream.

public boolean process(byte[] input, int offset, int len, boolean finish) {

if (this.state == 6) return false;

int p = offset;

len += offset;

// Using local variables makes the decoder about 12%

// faster than if we manipulate the member variables in

// the loop. (Even alphabet makes a measurable

// difference, which is somewhat surprising to me since

// the member variable is final.)

int state = this.state;

int value = this.value;

int op = 0;

final byte[] output = this.output;

final int[] alphabet = this.alphabet;

while (p < len) {

// Try the fast path: we're starting a new tuple and the

// next four bytes of the input stream are all data

// bytes. This corresponds to going through states

// 0-1-2-3-0. We expect to use this method for most of

// the data.

// If any of the next four bytes of input are non-data

// (whitespace, etc.), value will end up negative. (All

// the non-data values in decode are small negative

// numbers, so shifting any of them up and or'ing them

// together will result in a value with its top bit set.)

// You can remove this whole block and the output should

// be the same, just slower.

if (state == 0) {

while (p+4 <= len &&

(value = ((alphabet[input[p] & 0xff] << 18) |

(alphabet[input[p+1] & 0xff] << 12) |

(alphabet[input[p+2] & 0xff] << 6) |

(alphabet[input[p+3] & 0xff]))) >= 0) {

output[op+2] = (byte) value;

output[op+1] = (byte) (value >> 8);

output[op] = (byte) (value >> 16);

op += 3;

p += 4;

}

if (p >= len) break;

}

// The fast path isn't available -- either we've read a

// partial tuple, or the next four input bytes aren't all

// data, or whatever. Fall back to the slower state

// machine implementation.

int d = alphabet[input[p++] & 0xff];

switch (state) {

case 0:

if (d >= 0) {

value = d;

++state;

} else if (d != SKIP) {

this.state = 6;

return false;

}

break;

case 1:

if (d >= 0) {

value = (value << 6) | d;

++state;

} else if (d != SKIP) {

this.state = 6;

return false;

}

break;

case 2:

if (d >= 0) {

value = (value << 6) | d;

++state;

} else if (d == EQUALS) {

// Emit the last (partial) output tuple;

// expect exactly one more padding character.

output[op++] = (byte) (value >> 4);

state = 4;

} else if (d != SKIP) {

this.state = 6;

return false;

}

break;

case 3:

if (d >= 0) {

// Emit the output triple and return to state 0.

value = (value << 6) | d;

output[op+2] = (byte) value;

output[op+1] = (byte) (value >> 8);

output[op] = (byte) (value >> 16);

op += 3;

state = 0;

} else if (d == EQUALS) {

// Emit the last (partial) output tuple;

// expect no further data or padding characters.

output[op+1] = (byte) (value >> 2);

output[op] = (byte) (value >> 10);

op += 2;

state = 5;

} else if (d != SKIP) {

this.state = 6;

return false;

}

break;

case 4:

if (d == EQUALS) {

++state;

} else if (d != SKIP) {

this.state = 6;

return false;

}

break;

case 5:

if (d != SKIP) {

this.state = 6;

return false;

}

break;

}

if (!finish) {

// We're out of input, but a future call could provide

// more.

this.state = state;

this.value = value;

this.op = op;

return true;

}

// Done reading input. Now figure out where we are left in

// the state machine and finish up.

switch (state) {

case 0:

// Output length is a multiple of three. Fine.

break;

case 1:

// Read one extra input byte, which isn't enough to

// make another output byte. Illegal.

this.state = 6;

return false;

case 2:

// Read two extra input bytes, enough to emit 1 more

// output byte. Fine.

output[op++] = (byte) (value >> 4);

break;

case 3:

// Read three extra input bytes, enough to emit 2 more

// output bytes. Fine.

output[op++] = (byte) (value >> 10);

output[op++] = (byte) (value >> 2);

break;

case 4:

// Read one padding '=' when we expected 2. Illegal.

this.state = 6;

return false;

case 5:

// Read all the padding '='s we expected and no more.

// Fine.

break;

}

this.state = state;

this.op = op;

return true;

}

// --------------------------------------------------------

// encoding

// --------------------------------------------------------

/**

* Base64-encode the given data and return a newly allocated

* String with the result.

* @param input the data to encode

* @param flags controls certain features of the encoded output.

* Passing {@code DEFAULT} results in output that

* adheres to RFC 2045.

public static String encodeToString(byte[] input, int flags) {

try {

return new String(encode(input, flags), "US-ASCII");

} catch (UnsupportedEncodingException e) {

// US-ASCII is guaranteed to be available.

throw new AssertionError(e);

}

/**

* Base64-encode the given data and return a newly allocated

* String with the result.

* @param input the data to encode

* @param offset the position within the input array at which to

* start

* @param len the number of bytes of input to encode

* @param flags controls certain features of the encoded output.

* Passing {@code DEFAULT} results in output that

* adheres to RFC 2045.

public static String encodeToString(byte[] input, int offset, int len, int flags) {

try {

return new String(encode(input, offset, len, flags), "US-ASCII");

} catch (UnsupportedEncodingException e) {

// US-ASCII is guaranteed to be available.

throw new AssertionError(e);

}

/**

* Base64-encode the given data and return a newly allocated

* byte[] with the result.

* @param input the data to encode

* @param flags controls certain features of the encoded output.

* Passing {@code DEFAULT} results in output that

* adheres to RFC 2045.

public static byte[] encode(byte[] input, int flags) {

return encode(input, 0, input.length, flags);

}

/**

* Base64-encode the given data and return a newly allocated

* byte[] with the result.

* @param input the data to encode

* @param offset the position within the input array at which to

* start

* @param len the number of bytes of input to encode

* @param flags controls certain features of the encoded output.

* Passing {@code DEFAULT} results in output that

* adheres to RFC 2045.

public static byte[] encode(byte[] input, int offset, int len, int flags) {

Encoder encoder = new Encoder(flags, null);

// Compute the exact length of the array we will produce.

int output_len = len / 3 * 4;

// Account for the tail of the data and the padding bytes, if any.

if (encoder.do_padding) {

if (len % 3 > 0) {

output_len += 4;

}

} else {

switch (len % 3) {

case 0: break;

case 1: output_len += 2; break;

case 2: output_len += 3; break;

}

// Account for the newlines, if any.

if (encoder.do_newline && len > 0) {

output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *

(encoder.do_cr ? 2 : 1);

}

encoder.output = new byte[output_len];

encoder.process(input, offset, len, true);

assert encoder.op == output_len;

return encoder.output;

}

/* package */ static class Encoder extends Coder {

/**

* Emit a new line every this many output tuples. Corresponds to

* a 76-character line length (the maximum allowable according to

* <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).

public static final int LINE_GROUPS = 19;

/**

* Lookup table for turning Base64 alphabet positions (6 bits)

* into output bytes.

private static final byte ENCODE[] = {

'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',

'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',

'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',

'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/',

};

/**

* Lookup table for turning Base64 alphabet positions (6 bits)

* into output bytes.

private static final byte ENCODE_WEBSAFE[] = {

'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',

'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',

'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',

'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-', '_',

};

final private byte[] tail;

/* package */ int tailLen;

private int count;

final public boolean do_padding;

final public boolean do_newline;

final public boolean do_cr;

final private byte[] alphabet;

public Encoder(int flags, byte[] output) {

this.output = output;

do_padding = (flags & NO_PADDING) == 0;

do_newline = (flags & NO_WRAP) == 0;

do_cr = (flags & CRLF) != 0;

alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;

tail = new byte[2];

tailLen = 0;

count = do_newline ? LINE_GROUPS : -1;

}

/**

* @return an overestimate for the number of bytes {@code

* len} bytes could encode to.

public int maxOutputSize(int len) {

return len * 8/5 + 10;

}

public boolean process(byte[] input, int offset, int len, boolean finish) {

// Using local variables makes the encoder about 9% faster.

final byte[] alphabet = this.alphabet;

final byte[] output = this.output;

int op = 0;

int count = this.count;

int p = offset;

len += offset;

int v = -1;

// First we need to concatenate the tail of the previous call

// with any input bytes available now and see if we can empty

// the tail.

switch (tailLen) {

case 0:

// There was no tail.

break;

case 1:

if (p+2 <= len) {

// A 1-byte tail with at least 2 bytes of

// input available now.

v = ((tail[0] & 0xff) << 16) |

((input[p++] & 0xff) << 8) |

(input[p++] & 0xff);

tailLen = 0;

};

break;

case 2:

if (p+1 <= len) {

// A 2-byte tail with at least 1 byte of input.

v = ((tail[0] & 0xff) << 16) |

((tail[1] & 0xff) << 8) |

(input[p++] & 0xff);

tailLen = 0;

}

break;

}

if (v != -1) {

output[op++] = alphabet[(v >> 18) & 0x3f];

output[op++] = alphabet[(v >> 12) & 0x3f];

output[op++] = alphabet[(v >> 6) & 0x3f];

output[op++] = alphabet[v & 0x3f];

if (--count == 0) {

if (do_cr) output[op++] = 'r';

output[op++] = 'n';

count = LINE_GROUPS;

}

// At this point either there is no tail, or there are fewer

// than 3 bytes of input available.

// The main loop, turning 3 input bytes into 4 output bytes on

// each iteration.

while (p+3 <= len) {

v = ((input[p] & 0xff) << 16) |

((input[p+1] & 0xff) << 8) |

(input[p+2] & 0xff);

output[op] = alphabet[(v >> 18) & 0x3f];

output[op+1] = alphabet[(v >> 12) & 0x3f];

output[op+2] = alphabet[(v >> 6) & 0x3f];

output[op+3] = alphabet[v & 0x3f];

p += 3;

op += 4;

if (--count == 0) {

if (do_cr) output[op++] = 'r';

output[op++] = 'n';

count = LINE_GROUPS;

}

if (finish) {

// Finish up the tail of the input. Note that we need to

// consume any bytes in tail before any bytes

// remaining in input; there should be at most two bytes

// total.

if (p-tailLen == len-1) {

int t = 0;

v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;

tailLen -= t;

output[op++] = alphabet[(v >> 6) & 0x3f];

output[op++] = alphabet[v & 0x3f];

if (do_padding) {

output[op++] = '=';

}

if (do_newline) {

if (do_cr) output[op++] = 'r';

output[op++] = 'n';

}

} else if (p-tailLen == len-2) {

int t = 0;

v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |

(((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);

tailLen -= t;

output[op++] = alphabet[(v >> 12) & 0x3f];

output[op++] = alphabet[(v >> 6) & 0x3f];

output[op++] = alphabet[v & 0x3f];

if (do_padding) {

output[op++] = '=';

}

if (do_newline) {

if (do_cr) output[op++] = 'r';

output[op++] = 'n';

}

} else if (do_newline && op > 0 && count != LINE_GROUPS) {

if (do_cr) output[op++] = 'r';

output[op++] = 'n';

}

assert tailLen == 0;

assert p == len;

} else {

// Save the leftovers in tail to be consumed on the next

// call to encodeInternal.

if (p == len-1) {

tail[tailLen++] = input[p];

} else if (p == len-2) {

tail[tailLen++] = input[p];

tail[tailLen++] = input[p+1];

}

this.op = op;

this.count = count;

return true;

}

private Base64() { } // don't instantiate

}

Get the latitude and longitude from google map, which can be copied easily

by frankdu • January 22, 2011 • 1 Comment

1. Center the location of interest. You can use the yellow people marker to center it.
2. Copy and paste the following line to the address bar. Then press ENTER:

javascript:void(prompt(gApplication.getMap().getCenter()));

—- or —-

javascript:void(prompt(”,gApplication.getMap().getCenter()));

Resolve ambiguities in antlr v3

by frankdu • June 10, 2010 • 0 Comments

When there is ambiguities in writing antlr grammar, there are different ways to solve it.

1. Simply avoid them. This is the ideal way when it’s possible.

2. Turn on backtracking, which is most inefficient way.

3. Use left factoring.

4. Use syntax predicates.

For some samples, check it out at http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar

The format of sytnax predicate is close to semantic predicates. There are 3 types of them:

1. Validating semantic predicate, to place constraints on rules. For example
data : ( b += BYTE )+ {$b.size() <= 4}? ;
2. Gated semantic predicate, to turn on some alternatives under runtime condition. For example:
stat: ifState | {allowAssert}?=> assertStat ;
3. Disambiguating semantic predicate, to choose alternatives based on semantic context. For example:
stat: keyIf ID stat | keyCall ID ‘;’ ;
keyIf: {input.LT(1).getText().equals(“if”)}? ID ;
keyCall: {input.LT(1).getText().equals(“call”)}? ID ;

How to read cassandra source code by Ran

by frankdu • May 3, 2010 • 0 Comments

Here is a good article explaining how to read cassandra source codes:

Understanding Cassandra Code Base

http://prettyprint.me/2010/05/02/understanding-cassandra-code-base/

A simple thrift tutorial

by frankdu • April 7, 2010 • 0 Comments

Check it out at http://skorage.org/2009/03/08/simple-thrift-tutorial/

Let firefox use your Windows authentications automatically

by frankdu • April 6, 2010 • 0 Comments

In Firefox, visit:

about:config

Then set network.automatic-ntlm-auth.trusted-uris to your trusted domains, separated by comma.

A very nice presentation about agile software development

by frankdu • April 2, 2010 • 0 Comments

Some of my thoughts: Unit tests are very important in TDD. It enables you easily refactor code, adhere to customer requirements, and verify logics at earliest points. It also enables Continuously Integration to work brilliantly.

Lions, Tigers, and Bears: Scrum, XP, and Eclipse

View more presentations from kingargyle.

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