Technical Problems Record: April 2014

Thursday, 17 April 2014

VMWare Guest SDK

https://www.vmware.com/support/developer/guest-sdk/

The easiest way is to write your own application and call the combined, provided application to send heartbeat.

Spring roo simple example

http://edlovesjava.blogspot.hk/2011/07/getting-started-with-spring-roo-gwt-and.html

MsmqJava

Project Description
This is a JNI library for MSMQ. It allows Java applications to connect to MSMQ on Windows.

Summary

Many Java applications have the need to connect to MSMQ, for various reasons. For one, MSMQ can serve as a key interop conduit between Java and .NET applications. Outside of interop scenarios, Java applications can take advantage of MSMQ by themselves.
This library gives Java applications running on Windows, that basic connectivity into MSMQ.

Example

 try {
     Queue queue= new Queue(fullname);
     String label="testmessage";
     String body= "Hello, World!";
     byte[] correlationId = { 0,2,4,6,8,9 }; 
     Message msg= new Message(body, label, correlationId);
     queue.send(msg);
 }
 catch (MessageQueueException ex1) {
     System.out.println("Put failure: " + ex1.toString());
 }

Download

http://msmqjava.codeplex.com/

What's the best way to learn Smali (and how/when to use Dalvik VM opcodes)?

UPDATE: As I promised yesterday, I added some more links to the list.

Ufff. Not much documentation around! Best advice? Decompile, and read, and tweak, and see how it did, and start the cycle again and again. But you did not ask for that advice, right? ;)

Now, there are a few places out there that wil lhelp a little bit:

http://androidcracking.blogspot.com/search/label/smali This is the best one. I even asked the guy a question and he answered very quickly, so go and take a look.

http://pallergabor.uw.hu/androidblog/dalvik_opcodes.html Very comprehensive table - good reference!

http://webchat.freenode.net/?channels=smali I never tried it, but it's on the google code page of the baksmali author ( http://code.google.com/p/smali/ )

http://forum.xda-developers.com/showthread.php?t=777707 Lastly, this is a post I made some time ago describing some hacks to the Captivate camera. You can follow the diffs in there as I comment a little bit on what each .diff file is doing. The good stuff starts at the post #20.

http://www.slideshare.net/paller/understanding-the-dalvik-bytecode-with-the-dedexer-tool Interesting slide show with some basic concepts. Good way to start.

http://sites.google.com/site/haynesmathew/home/projects/dalvik-notes Even more low level than the typical .smali. A reference for later, but a good read.

http://jasmin.sourceforge.net/guide.html Smali syntax is based on Jasmin, so this gives good concepts.

http://groups.google.com/group/apktool?pli=1 Some discussions there are worth reading through. Also a good place to search for when you're stuck in something.

And last, but not least, the most helpful trick I used: start coding very basic classes and methods in java, compile them and then baksmali your own code. You know exactly what it does, so it will be a lot easier to follow.

Good luck!

http://stackoverflow.com/questions/5656804/whats-the-best-way-to-learn-smali-and-how-when-to-use-dalvik-vm-opcodes

Error compiling PHP on CentOS x64

configure: error: xml2-config not found. Please check your libxml2 installation.

yum install libxml2-devel.x86_64

configure: error: Cannot find OpenSSL's

yum install openssl-devel.x86_64

configure: error: Could not find pcre.h in /usr/local

yum install pcre-devel.x86_64

configure: error: Could not find pcre.h in /usr/local

"--with-pcre-regex=/usr/include" \

configure: error: Could not find libpcre.(a|so) in /usr/include

"--with-pcre-regex=/usr" \

configure: error: Please reinstall the libcurl distribution -
easy.h should be in /include/curl/

yum install curl-devel.x86_64

configure: error: libjpeg.(a|so) not found.

yum install libjpeg-devel.x86_64

configure: error: libpng.(a|so) not found.

yum install libpng-devel.x86_64

configure: error: freetype.h not found.

yum install freetype-devel.x86_64

configure: error: Please reinstall the iconv library.

"--with-iconv" \

configure: error: mcrypt.h not found. Please reinstall libmcrypt.

yum install libmcrypt.x86_64 libmcrypt-devel.x86_64

configure: error: Please reinstall libmhash – I cannot find mhash.h

yum install mhash.x86_64 mhash-devel.x86_64

Note that the MySQL client library is not bundled anymore!

yum install php-mysql.x86_64 mysql-devel.x86_64

configure: error: Please reinstall the BZip2 distribution

yum install bzip2-devel.x86_64

configure: error: utf8_mime2text() has new signature, but U8T_CANONICAL is missing. This should not happen. Check config.log for additional information.
DISABLE IMAP
configure: error: Cannot find pspell

yum install aspell-devel.x86_64

configure: error: Cannot find libtidy

yum install libtidy.x86_64 libtidy-devel.x86_64

error: xslt-config not found. Please reinstall the libxslt >= 1.1.0 distribution

yum install libxslt.x86_64 libxslt-devel.x86_64

collect2: ld returned 1 exit status

yum install glibc-utils.x86_64 libtool-ltdl-devel.x86_64

Step by step to guide PHP Compile

Step 1: Update & Install Development Tools & Libraries

yum update
yum group install "Development Tools"
yum group install "Development Libraries"

Step 2: Run the bellow bash script

#!/bin/sh
"./configure" \
"--prefix=/usr/local/php5" \
"--enable-force-cgi-redirect" \
"--enable-fastcgi" \
"--with-bz2" \
"--with-config-file-path=/usr/local/etc" \
"--with-config-file-scan-dir=/usr/local/etc/php.d" \
"--with-curl=/usr/local/lib" \
"--with-gd" \
"--with-gettext" \
"--with-jpeg-dir=/usr/local/lib" \
"--with-freetype-dir=/usr/local/lib" \
"--with-kerberos" \
"--with-mcrypt" \
"--with-mhash" \
"--with-mime-magic" \
"--with-mysql" \
"--with-mysqli" \
"--with-pcre-regex=/usr" \
"--with-pdo-mysql=shared" \
"--with-pdo-sqlite=shared" \
"--with-pear=/usr/local/lib/php" \
"--with-png-dir=/usr/local/lib" \
"--with-pspell" \
"--with-sqlite=shared" \
"--with-tidy" \
"--with-ttf" \
"--with-xmlrpc" \
"--with-xsl" \
"--with-zlib" \
"--with-zlib-dir=/usr/local/lib" \
"--with-openssl" \
"--with-iconv" \
"--with-libdir=lib64" \
"--enable-bcmath" \
"--enable-calendar" \
"--enable-exif" \
"--enable-ftp" \
"--enable-gd-native-ttf" \
"--enable-libxml" \
"--enable-magic-quotes" \
"--enable-soap" \
"--enable-sockets" \
"--enable-mbstring" \
"--enable-zip" \
"--enable-wddx"

http://www.lifelinux.com/error-compiling-php-on-centos-x64/

Wednesday, 16 April 2014

TCP RST before last packet you received

Upon reception of RST segment, the receiving side will immediately abort the connection. This statement has more implications than just meaning that you will not be able to receive or send any more data to/from this connection. It also implies that any unread data still in the TCP reception buffer will be lost. This information can be found in TCP/IP Internetworking volume 2 andUnix Network Programming Volume 1 third edition but in my opinion those books do not put enough emphasis on that detail and if you are not reading these books to find this exact detail, it might slip away from your attention.

Now, what are the conditions to receive a RST segment? The easiest way is to enable the SO_LINGER option with a timeout value of 0 on a server socket. As soon as the connection will be closed by the server, it will send a RST. You can learn more about SO_LINGER in the book Unix Network Programming Volume 1 third edition. The other possibility is if a server receives data after having closed the connection. If you enable the LINGER option, sending RST is the expected behavior but you can easily be bitten by the second possibility and here is an example on how it can happen.

Imagine a HTTP server that limits the number of simultaneous connections. Upon accepting a new connection, it might compare a global connection counter against a configured limit and if the counter has reached the limit then immediately send back a 503 error and close the connection. Do you see the problem? The server is closing the connection before receiving the HTTP request. There is a high probability that the client will never receive the 503 reply because a RST segment will immediately follow the reply.

A not too good solution would be to call shutdown(SHUT_WR) before closing the socket. What this will do is force the server to send a FIN segment before the RST segment. I have tried this solution and this seems to greatly improve the probability that the client application will receive the data before receiving the RST segment.

A better way is to program the server to read the request even if it has no intention to actually process it. This ensures that no RST will be sent unintentionally.

There remains one question. What exactly means data reception on a closed connection? Does that only include new received TCP segment or could data still in the TCP receive buffer of a closing connection be considered as data arrived after the connection has been closed? My intuition is that this question is open to interpretation and the TCP behavior will vary from one platform to the other. However, even if your platform does not react with a RST if a TCP connection receive buffer is not empty when it is closing it; my opinion is that you should not rely on that since this is a race condition. You could be closing the connection before or after receiving the client request depending on the RTT (Round Time Trip) of the connection.

http://blog.olivierlanglois.net/index.php/2010/02/06/tcp_rst_flag_subtleties

Monday, 14 April 2014

Conflicts while installing package via yum (Centos)

yum -y remove [package]
Example: yum -y remove mysql-libs-5.1.52*
yum install [package]

Technical Problems Record