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Category: Tech Blog

Here you can find my random notes on software design and development, software engineering, coding, and all other tech-related stuff.

Installing mod_xsendfile on OS X Lion

Published 2012/11/14 by Daoyuan Li

First download mod_xsendfile.c from https://tn123.org/mod_xsendfile/

Then compile and install it:

sudo apxs -cia mod_xsendfile.c

Add the following line to /etc/apache2/httpd.conf at the end of the first block of “Load” statements:

LoadModule xsendfile_module libexec/apache2/mod_xsendfile.so

At last, restart the apache server

sudo apachectl restart

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XBMC and OS X firewall permission popups

Published 2012/07/06 by Daoyuan Li

I installed XBMC on my Mac OS X Lion and every time I open up the program, a firewall permission dialog pops up. It didn’t help even if I added the XBMC in my firewall configurations. Popups still show up. This link solves the problem neatly — You can generate a certificate and sign the program by yourself. After that the frustrating dialog should appear only once (at most). In case the link becomes invalid, here’s a screenshot of the instructions. Click to see the large picture.

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Block unauthorized ssh login attempts (attacks)

Published 2012/06/30 by Daoyuan Li

My friends and I am working on a hobby project and  we need a Git server, so I set up one on my MacBook Pro. We access the repository via SSH. However when I checked the ssh log I found someone trying to get ssh access to my machine by guessing usernames. The log looks as follows:

Jun 29 21:06:52 doh1 sshd[19400]: Invalid user postgres from 190.181.132.70
Jun 29 21:06:52 doh1 sshd[19401]: input_userauth_request: invalid user postgres
Jun 29 21:06:52 doh1 sshd[19401]: Received disconnect from 190.181.132.70: 11: Bye Bye
Jun 29 21:06:54 doh1 sshd[19402]: reverse mapping checking getaddrinfo for wimax132-70.yota.com.ni [190.181.132.70] failed - POSSIBLE BREAK-IN ATTEMPT!
Jun 29 21:06:54 doh1 sshd[19403]: Received disconnect from 190.181.132.70: 11: Bye Bye
Jun 29 21:06:55 doh1 sshd[19405]: reverse mapping checking getaddrinfo for wimax132-70.yota.com.ni [190.181.132.70] failed - POSSIBLE BREAK-IN ATTEMPT!
Jun 29 21:06:55 doh1 sshd[19405]: Invalid user backup from 190.181.132.70
Jun 29 21:06:55 doh1 sshd[19406]: input_userauth_request: invalid user backup
Jun 29 21:06:56 doh1 sshd[19406]: Received disconnect from 190.181.132.70: 11: Bye Bye
Jun 29 21:06:57 doh1 sshd[19407]: reverse mapping checking getaddrinfo for wimax132-70.yota.com.ni [190.181.132.70] failed - POSSIBLE BREAK-IN ATTEMPT!

I first tried to use DenyHosts, however, there are still attempts from other IP addresses. Since there are three of us accessing the repository, I configured the hosts.allow and hosts.deny manually: deny all hosts other than the IP addresses I trust.

hosts.deny:

~$ cat /etc/hosts.deny 
sshd: ALL

hosts.allow:

~$ cat /etc/hosts.allow
sshd: [The IP addresses you allow to connect via SSH]
ALL: localhost

Now the log file should be quite…

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Migrating JComments to WordPress

Published 2012/04/28 by Daoyuan Li

I switched back to WordPress from Joomla! after I registered this new domain. After migrated all the posts to WordPress using FG Joomla to WordPress, I noticed the comments have not been transferred. After some digging I didn’t find satisfactory plugin to do that, so I wrote my own PHP script to fulfill this task. The code is also available from GitHub.
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Downgrade Preview in OS X Lion

Published 2012/04/23 by Daoyuan Li

I’ve had enough with the slow Preview application in Lion. After some digging I found this tutorial to downgrade the Preview in Lion to the Snow Leopard version. Basically you need to have a copy of both the Preview.app and /System/Library/PrivateFrameworks/MeshKit.framework from Snow Leopard. If you need to associate the default app to open pdf/png with the downgraded Preview, you have to delete the original Preview.app.

tar -pczf Preview.app.tar.gz /Applications/Preview.app
sudo rm -rf /Applications/Preview.app

Update: after installing OS X updates you need to remove the Preview.app again and put the SL Preview.app to /Applications/ directory.

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C a[i] vs i[a]

Published 2012/03/22 by Daoyuan Li

When following the MIT 6.828 open course, there’s one C source code discussing pointers in Exercise 4 of lab 1.

There’s one line of code in pointers.c:

3[a] = 302;

Looks weird at first sight; but TCPL says in Chapter 5.3:

In evaluating a[i], C converts it to *(a+i) immediately; the two forms are equivalent.

So: a[i] and i[a] are equvalent (if i is a constant). 🙂

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i386-jos-elf toolchain on OS X Lion

Published 2012/03/18 by Daoyuan Li

Yesterday friend and I decided to follow the MIT Operating System Engineering course together in order to get a deep understanding of OS’s. And today I started setting up the cross compling environment for the labs. At first I wanted to get the toolchain from macports, but unluckily it didn’t successfully build binutils on my Mac. As a result, I started building the toolchain from the source code, following the instructions at http://pdos.csail.mit.edu/6.828/2011/tools.html.

The programs you need for the toolchain include binutils, gcc, and gdb. For compiling gcc you also need GMP, MPFR, and MPC. The source codes are available at:

wget http://ftpmirror.gnu.org/binutils/binutils-2.21.1.tar.bz2
wget ftp://ftp.gmplib.org/pub/gmp-5.0.4/gmp-5.0.4.tar.bz2
wget http://www.mpfr.org/mpfr-current/mpfr-3.1.0.tar.bz2
wget http://www.multiprecision.org/mpc/download/mpc-0.8.2.tar.gz
wget http://ftpmirror.gnu.org/gcc/gcc-4.5.1/gcc-core-4.5.1.tar.bz2
wget http://ftpmirror.gnu.org/gdb/gdb-6.8a.tar.gz

Unzip them in a directory and build binutils, gcc, and gdb one by one.

$ tar jxvf binutils-2.21.1.tar.bz2
$ cd binutils-2.21.1
$ ./configure --target=i386-jos-elf --disable-nls && make && sudo make install

In order to build gcc, GMP, MPFR and MPC needs to be built first.

$ mkdir -p libs/install
$ mv gmp-5.0.4.tar.bz2 mpfr-3.1.0.tar.bz2 mpc-0.8.2.tar.gz libs/
$ tar jxvf gmp-5.0.4.tar.bz2
$ mkdir gmp-build; cd gmp-build
$ ../gmp-5.0.4/configure --prefix=$(cd ../install && pwd)
$ make && sudo make install
$ cd ..
$ tar jxvf mpfr-3.1.0.tar.bz2
$ mkdir mpfr-build; cd mpfr-build
$ ../mpfr-3.1.0/configure --prefix=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/ --with-gmp=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/
$ make && sudo make install
$ cd ..
$ tar zxvf mpc-0.8.2.tar.gz
$ mkdir mpc-build; cd mpc-build
$ ./configure --prefix=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/ --with-gmp=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/ --with-mpfr=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/
$ make ; sudo make install
$ cd ..
$ tar jxvf gcc-core-4.5.1.tar.bz2
$ mkdir gcc-build; cd gcc-build
$ ../gcc-4.5.1/configure --target=i386-jos-elf --disable-nls --without-headers --with-newlib --disable-threads --disable-shared --disable-libmudflap --disable-libssp --with-gmp=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/ --with-mpfr=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/ --with-mpc=/Users/daoyuanli/Downloads/i386-elf-gcc/libs/install/
$ make ; sudo make install

Note that it’s essential to build gcc in a directory different from the source code directory to avoid compiling errors.

Then make gdb:

$ tar zxvf gdb-6.8a.tar.gz
$ mkdir gdb-build; cd gdb-build
$ ../gdb-6.8/./configure --target=i386-jos-elf --program-prefix=i386-jos-elf- --disable-werror
$ make && sudo make install

QEMU is available in macports:

$ sudo port install qemu
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Port already in use issue of Arduino for Eclipse plugin

Published 2012/03/14 by Daoyuan Li

When uploading with avrdude the plugin give a error prompt saying “Port already in use” (while no other application is using the port). After clicking OK it actually uploads the program to Arduino board.

port_in_use

After reading issue #6 I check the librxtxSerial.jnilib in eclipse:

.cp$ file librxtxSerial.jnilib
librxtxSerial.jnilib: Mach-O universal binary with 4 architectures
librxtxSerial.jnilib (for architecture x86_64): Mach-O 64-bit bundle x86_64
librxtxSerial.jnilib (for architecture i386): Mach-O bundle i386
librxtxSerial.jnilib (for architecture ppc7400): Mach-O bundle ppc
librxtxSerial.jnilib (for architecture ppc64): Mach-O 64-bit bundle ppc64

While in my Arduino application the librxtxSerial.jnilib output is:

llibrxtxSerial.jnilib: Mach-O universal binary with 2 architectures
librxtxSerial.jnilib (for architecture i386): Mach-O bundle i386
librxtxSerial.jnilib (for architecture ppc): Mach-O bundle ppc

So I just copied the Arduino.app//Contents/Resources/Java/librxtxSerial.jnilib file to eclipse/configuration/org.eclipse.osgi/bundles/419/1/.cp/librxtxSerial.jnilib It works after restarting eclipse. No error prompts are shown.

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iCal crashes with iCal Reply Checker uninstalled

Published 2011/10/11 by Daoyuan Li

My iCal crashes everytime when someone sends me an invitation and I try either to accapt or decline it. After some investigation I found out it is the problem with “iCal Reply Checker” at http://www.nhoj.co.uk/icalreplychecker

After unstalled this app, it resets the Mail.scpt file to an empty file. To solve the problem: get another copy of Mail.scpt from another Mac, preferably from the same OS X version; and put it inside the folder: /Applications/iCal.app/Contents/Resources/Scripts

Lesson learnt: take care when trying amature software.

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Bug in Waspmote API v0.15

Published 2011/05/12 by Daoyuan Li

I found a bug in Waspmote API v0.15 when I was trying to set XBee link keys. The API failed to set the key as specified in the code. The bug lies in function gen_data()” in lines 4355-4403. Details below. However, it was corrected in v0.18.

/*
 Function: Generates the API frame to send to the XBee module
 Parameters:
 	data : The string that contains part ofthe API frame
 	param : The param to set
 Returns: Nothing
 Values: Stores in 'command' variable the API frame to send to the XBee module
*/
void WaspXBeeCore::gen_data(const char* data, uint8_t* param)
{
	uint8_t inc=0;
	uint8_t inc2=0;
		
	clearCommand();
	it=0;
	while(data[it] != '\0') {
		inc++;
		it++;
	}
	inc/=2;
	
	while(inc211) 
	{
		for(it=0;it<8;it++)
		{
			command[inc-9+it]=param[it];
		}
	}
	else if(inc==11)
	{
		for(it=0;it<3;it++)
		{
			command[inc-4+it]=param[it];
		}
	}
	else if(inc==10)
	{
		for(it=0;it<2;it++)
		{
			command[inc-3+it]=param[it];
		}
	}
	else command[inc-2]=param[0];
}

The function in v0.18 is as follows:

/*
 Function: Generates the API frame to send to the XBee module
 Parameters:
 	data : The string that contains part of the API frame
 	param : The param to set
 Returns: Nothing
 Values: Stores in 'command' variable the API frame to send to the XBee module
*/
void WaspXBeeCore::gen_data(const char* data, uint8_t* param)
{
    uint8_t    inc=0;
    uint8_t inc2=0;
		
    clearCommand();
    it=0;
    while(data[it] != '\0') {
        inc++;
        it++;
    }
    inc/=2;
	
    while(inc2

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Generating UML diagram from Java source code

Published 2011/05/02 by Daoyuan Li

Sometimes we may need to generate UML diagrams from source codes. Here’s what I do for Java code: graphviz + ant + UMLGraph. Details below:

1. Install graphviz and ant, download UMLGraph from http://www.umlgraph.org/

2. Place UMLGraph.jar in your project, for example, under
lib/

3. Write or modify your ant script, for example:


   
   The specification for the Java-based umlgraph build processes.

4. Run this ant script.

ant javadocs

5. You will get the UML class diagram as expected in the generated Java docs. Here’s one example (click to enlarge):

com.andryy.hccdroid

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码农

Published 2010/11/11 by Daoyuan Li

最近看系统编程准备面试，顺便找点儿小算法练练手。在面试书上看到写冒泡排序的面试题，心血来潮也来练练手。闭着眼睛敲完代码，编译竟然没有错误，运行了一下结果也竟然是对的。

于是重新打开代码，怀着无比复杂的心情来审视自己的代码，郁闷的是看不懂自己5秒钟之前写的代码。我一边很囧的看着书上给出的代码，一边对着自己的代码检查。迷迷糊糊五分钟过去之后还是看不出来自己的代码是不是冒泡排序……

无奈之下拿出笔在草稿上画图一步一步推，终于验证了自己代码的正确性……30秒写完代码，300+秒来读自己写了什么，确实够囧的，
不知道是大一的时候代码背的太熟了的缘故……

估计以后当了码农会经常出现这种状况吧：噼里啪啦的一顿敲代码，敲完之后对着显示器一顿发愣，TMD刚才都敲了些啥？就像真正的农民种田一样，种久了之后做事情完全不过脑，偶尔思考一下的时候就会感慨：我靠，我这块地为啥要撒这么多种子，用这么多化肥啊。第二天睡觉前恍然大悟：就应该放这么多才对！之前折腾个什么劲儿阿！

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Qt画图

Published 2010/10/27 by Daoyuan Li

Qt提供了一个QPainter来画图，可以用来绘制矢量图，也可以用来装载图片。今天实现的是一个给照片加边框的功能，为了练习，将PicFrame构造成一个继承自QWidget的自定义Widget。这时QPainter不能直接在自己定义的Widget中使用，而需要在paintEvent(QPaintEvent *event)中实现，否则会有类似于“QPainter::begin: Paint
device returned engine == 0, type: 1”的错误消息出现。

void PicFrame::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    QRect rect(0, 0, image.width()*(1+frameSize), image.height()*(1+frameSize));
    painter.fillRect(rect,color);
    QPoint point(frameSize*image.width()/2, frameSize*image.height()/2);
    painter.drawImage(point, image);
}

=============================心情分割线=============================

今天NordSec2010开始，又见到了很多老朋友。再聚首总是有很多要交流的，大家都在为毕设发愁，都在为前途迷茫。从来没有像现在这样反感学术，当初不去美国的决定似乎是对的。

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一步一脚印

Published 2010/10/26 by Daoyuan Li

咱虽然笨，一步一步慢慢来还不行么。

用正则表达式改进了昨天的计算器，用来限制用户输入。

regExp.setPattern("^\\d*.?\\d+[\\+\\-\\*\\/]\\d*.?\\d+$");
lineEdit->setValidator(new QRegExpValidator(regExp,this));

因为这个匹配模式是字符串，而字符串中”是转义字符，所以’d’放到字符串中就应该写成’\d’。类似的，如果要匹配一个”，则应该写成’\\’。

另外今天还写了个记事本，实现了最基本的打开，修改，保存和修改字体功能。Qt
Designer用的不太熟，于是手工添加控件，那叫一个麻烦。基本控件大致了解了，对文件的操作还不熟。中间由于把保存文件的对话框写成了打开文件的对话框而导致一直不能保存文件，原来这两个还不一样，虽然长得很像，汗。

QString filename = QFileDialog::getOpenFileName(this, tr("Open file"), ".", tr("Text files (*.txt)"));
QString filename = QFileDialog::getSaveFileName(this, tr("Save text file"), ".", tr("Text files(*.txt)"));

对Signal-Slot机制的了解基本到了可以用的程度，但是对于中间的参数传递过程还一无所知。明天继续。

=============================心情分割线=============================

最近一直比较抑郁，算来差不多郁闷了将近二十年了。当然中间也会有间歇性的亢奋，但总体来说太微不足道了。以前总是对过去恋恋不舍，对未来不知所措，对当下却不能把握。总是过于重视别人的看法，过多的考虑别人的感受。从来不知道自己需要什么，现在回首看看，自己竟然不认识自己。

于是我打算跟自己一刀两断，我从今天开始就是我而且只是我，不再在乎他人的评价，不去关心我不愿关心的人和事，只做自己想做的事情。锲而不舍，勇往直前，纵然头破血流也在所不惜。不是做回自己，因为以前的我没有自己。

这几天一直听李宗盛，把他的四首歌翻来覆去的听。他那沙哑的声音切割者我的心，想哭却无法从干枯的眼睛中挤出半滴泪水。真爱难寻，我会继续等待，孤傲的常驻于此。直到你出现在我面前，I’ll love as if I’ve never been in love before.

思维之混乱，阅者了然。

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千里之行

Published 2010/10/25 by Daoyuan Li

用Qt写计算器，花了我一个晚上终于写出来一个能用的了，能赶上大二学Java时写计算器的速度了。

用Qt Designer设计界面比较方便，用熟之后效率会更高。把界面设计好之后可以通过继承的方式给自己的类添加逻辑。如果设计的界面保存为mycaculator.ui的话，uic将会自动将这个XML文件转换成ui_mycaculator.h，其中的namespace为Ui。

#include"ui_mycaculator.h"
class Caculator : public QMainWindow, public Ui::MyCaculator

另外，Qt对字符串的处理简直跟Java一样了：

QString s1 = expStr.split(QRegExp("[+-*/]"))[0]; 
QString s2 = expStr.split(QRegExp("[+-*/]"))[1];
double d1 = s1.toDouble();
double d2 =s2.toDouble();
resStr = QVariant(d1+d2).toString();
expStr.append(resStr);

总算是迈出了第一步，再接再厉。

更新：上面的正则表达式不对，因为’+’, ‘-‘和’*’在正则表达式中有特殊意义。应该为如下：

QString s1 = expStr.split(QRegExp("[\\+\\-\\*/]"))[0];
QString s2 =expStr.split(QRegExp("[\\+\\-\\*/]"))[1];
double d1 = s1.toDouble();
double d2 = s2.toDouble();
resStr = QVariant(d1+d2).toString();
expStr.append(resStr);
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