Convert from byte[] to string in C#.NET

Recently I had to convert a byte[] array to a string in .NET. I knew that there should be some method somewhere which takes a encoding and returns the string accordingly.
I searched in the "byte[]" class, then in the "string" class, but could not find any appropriate method. Finally I found it in the System.Text.Encoding class. It has other subclasses such as
System.Text.ASCIIEncoding,
System.Text.UnicodeEncoding,
System.Text.UTF7Encoding,
System.Text.UTF8Encoding.

Code snippet:

System.Text.Encoding enc = System.Text.Encoding.ASCII;
string myString = enc.GetString(myByteArray );

I would have preferred a String Constructor which takes a byte[] and a encoding string. Much more intuitive...

Unix /dev/null

In quite a few unix programs ( shell scripts) I see the following command =

someprog > /dev/null 2>&1

The > /dev/null 2>&1 part means to send any standard output to /dev/null (the linux trash can) and to redirect standard error (2) to the same place as the standard output (1). Basically it runs the command without any output to a terminal etc.

Enabling FTP on Solaris

Recently I wanted to enable FTP on my Solaris box and had to make quite a few changes to start the FTP server. I got a summary of all the things that should be done/checked :

#vi /etc/services - uncomment
-> ftp 21/tcp
#vi /etc/inetd.conf - uncomment
-> ftp stream tcp nowail root /usr/sbin/in.ftpd in.ftpd
# vi /etc/ftpd/ftpuser - to uncomment "root" out
-> # root
#vi /etc/shells - put in all the shell as possible
-> /usr/sbin/ksh
#vi /etc/default/login - to uncomment
-> CONSOLE=/dev/console
check ftp.allow and ftp.deny files as well
#kill -HUP pid - to restart #/usr/sbin/inetd -s

If U need to enable FTP upload, then U need to make changes in one more file. (/etc/ftpd/ftpaccess) For more details see this link:
http://docs.sun.com/app/docs/doc/816-4555/6maoquinp?a=view

More info about VNC

I have been using VNC for years and I always assumed it to be a product of a company named RealVNC. It was only recently that I realised that VNC (Virtual Network Computing) is a open-source technology and had been first developmed on the Unix platform !!!...(I thought VNC works only on Windows)
We have VNC servers available for all platforms such as Unix X-window, Solaris CDE, Linux, Windows XP etc.

More info can be found at :
http://www.softpanorama.org/Xwindows/vnc.shtml
http://www.realvnc.com

Debugging in Java

When I was first introduced to Java, most of the program debugging was done through console/file logging. (using the ubiquitous System.out.println).

But today, we have so many GUI debuggers at our disposal. IDEs contain their own debuggers (such as IBM VisualAge for Java, Symantec VisualCafe, and Borland JBuilder, IBM Eclipse), Stand-alone GUIs (such as Jikes, Java Platform Debugger Architecture javadt, and JProbe) ,Text-based and command-line driven (such as Sun JDB)
My favourite is the Eclipse Debugger and it serves most of my purposes.
But there are some other cool stand-alone debuggers available too. Here are links to a few of them:
http://www.bluemarsh.com/java/jswat/
http://www.debugtools.com/index.html
http://freshmeat.net/projects/jikesdebugger/

If any of the above still do not meet your needs, the Java platform has introduced the JavaDebugging APIs, which you may use to create a debugger that specifically meets yourneeds. The revised Java Debugger (JDB) serves as both a proof of concept for the Java DebuggingAPI, and as a useful debugging tool. It was rewritten to use the Java Debug Interface (JDI)and is part of the JDK.

JProbe - A cool cool tool

I had used JProbe in my earlier project for some basic memory profiling and performance bottleneck detection. JProbe suite consists of 3 important components:

JProbe Profiler: Identify Method and Line-level Performance Bottlenecks
JProbe Memory Debugger: Investigate Memory Leaks and Garbage Collection Activity
JProbe Coverage: Measure Code Coverage After Testing

Recently on visiting their site, I saw a free version of JProbe Profiler which I belive would be immensely useful to anyone doing development in Java.
http://www.quest.com/jprobe/profiler_freeware.asp

Java XML processing APIs

It's been some time that I have worked on any new XML processing program. My favaourite Java XML library had always been JDOM (promoted by Jason Hunter) JDOM was so intutive to use for Java developers and also made excellent use of Java collections.

But today, there are quite a number of alternatives that one needs to study before deciding on which library to use.

A good tutorial using Java standard APIs is available here - http://www.mkyong.com/java/how-to-read-xml-file-in-java-dom-parser/

Check out the following links to learn more:
http://www.artima.com/intv/jdomP.html
http://www-128.ibm.com/developerworks/xml/library/x-injava/index.html http://xml.apache.org/xerces-j/index.html
http://www.extreme.indiana.edu/soap/xpp/
http://xml.apache.org/crimson/index.html
http://jdom.org/index.html

Diff btw "java.exe" and "javaw.exe"

This is what the SUN documentation says:

The javaw command is identical to java, except that with javaw there is no associated console window. Use javaw when you don't want a command prompt window to appear. The javaw launcher will, however, display a dialog box with error information if a launch fails for some reason.

So If Ur application is 100% GUI, then U can use javaw to launch it instead of java.exe

Java 1.4 and 1.5 compatibility problems

Recently I faced a peculiar problem when I had compiled a application using JDK 1.5 and then tried to run it inside TOMCAT running Java 1.4. And I got an runtime exception - Version mismatch -- 0.49 should be 0.48
I was bewildered, but later on searching the NET understood that the class files generated by the JDK 1.5 compiler(v 0.49) and JDK 1.4(v 0.48) compiler are not same.

My application was not using any of the new JDK 1.5 features, even then this problem was arising. I think the reason for this being the host of new features introduced in JDK1.5
For e.g. in Java 1.5, U can write:
Integer I=7; and it will compile with Java1.5 and also run inside a Java 1.5 JVM.

But if the above code is run inside a Java 1.4 JVM, then it will fail. Hence SUN has put a check to ensure that there is a runtime error shown if the class files are of different versions than that of the JVM.

Code coverage tools

Even if we are using JUnit and NUnit for executing our unit test cases, there are still some loopholes left. For e.g. how do we test that all paths in the code have been covered in the test cases? What code are the tests actually testing? What code isn't being tested? Is the test suite getting out of date?

Code coverage tools prove to be invaluable in such occasions. These tools instrument the code/binaries to discover those sections of the code that have not been tested.

Two such tools for Java and .NET are provided by Clover:
http://www.cenqua.com/clover/
http://www.cenqua.com/clover.net/

Check out the trail versions and see the benefits Urself..

Changing the bootstrap classes in javac.exe

Sometimes we may wish to change the default bootstrap classes that are loaded by the java compiler while compiling.

javac.exe provides us with a '-bootclasspath' option for that.

I found this option useful, when I was using a older version of CORBA interfaces, which were not compatible with the "org.omg.*" CORBA interfaces in JDK 1.5. So I included the old CORBA interfaces jar file before rt.jar in the bootstrap classpath and the problem was solved.

In Eclipse, the problem was solved just by changing the order of jar files in the "Build path" menu.

Specify java files names in a text file for javac.exe

Found out that there was an alternative way to pass Java source files names to the javac compiler :)

Here's what the Java docs say:
There are two ways to pass source code file names to javac:
- For a small number of source files, simply list the file names on the command line.
- For a large number of source files, list the file names in a file, separated by blanks or line breaks. Then use the list file name on the javac command line, preceded by an @ character.

Some good Wiki sites on the web.

I cam upon this wiki as I was surfing the web, searching for more info on XP...It turned out to be a gold mine of information..

http://c2.com/cgi/wiki?CategoryCategory

Design By Contract

When I first heard about DBC 4 years back, little did I know how important a role it can play in software development. But my experience in the past few years have made me wiser. I have seen so much of cluttered code where inside each method call, the first thing that is seen is the checking of all the parameters. (This is sometimes also replicated on the client side). How many times I have seen a try/catch for a condition that will never occur if the method is called correctly.

The "Design By Contract" paradigm eliminates all this. It specifies that a method should have a pre-condition, a post-condition and an invariant. At first, I found the concept of invariant a bit foggy to understand.

Well, actually it is very simple. An invariant is something (in a class) which does not change. Classes should specify their invariants: what is true before and after executing any public method.

If U are planning to incorporate DBC in Ur code, then check out :
http://jcontractor.sourceforge.net/
http://c2.com/cgi/wiki?DesignByContract

I feel "Unit Tests" can also play the role of checking Contracts as it is used in Extreme Programming. But may be both can be used to complement each other.

UnitTests tests for things which should happen. DesignByContract watches for things which shouldn't. These two categories overlap somewhat, but both techniques are still useful.

Proxy setting for Java programs

Quite often whenever we need to connect to the internet thru the company firewall, we need to set the proxy details for the Java interpreter.

Here is the syntax:
java -DproxySet=true -DproxyHost=localhost -DproxyPort=80

In Ant, we need to set it as:

set ANT_OPTS=-DproxySet=true -DproxyHost=localhost -DproxyPort=80
ant mytarget

Alternately, your application can specify proxy settings before using a URLConnection :

// Modify system properties
Properties sysProperties = System.getProperties();
// Specify proxy settings
sysProperties.put("proxyHost", "myhost");
sysProperties.put("proxyPort", "myport");
sysProperties.put("proxySet", "true");

Java Decompilers and Obfuscators

Was looking for a comprehensive list of Java decompilers and obfuscators..Found a nice article here:
http://www.program-transformation.org/Transform/JavaDecompilers

Java Classpaths on Cygwin

The problem with using Java on Cygwin is that Java.exe is a windows program and expects the path to be in windows style. Whereas Cygwin expects paths to be in Unix style.

Hence if U run a simple Java command like the below, U will get an error:
java -classpath /cygdrive/d/naren MyJavaProgram

Even the following would give an error, bcoz cygwin cannot understand windows path on the command prompt
java -classpath d:\naren MyJavaProgram

So, the solution is to use a cygwin utility known as cygpath.exe. This tool converts from unix paths to windows path, before passing it to the shell.
java -classpath `cygpath -wp $CLASSPATH` [arguments]

Java and .NET interop

Came across a cool tool today that can be used to convert Java byte-code to .NET IL.
What does this mean to developers..Well, it means that if U have a Java library, U need not 'manually' port the Java library to .NET. Just use the IKVM tool to do this for U...

For furthur details, check out the following links:
http://www.ikvm.net/index.html
http://www.onjava.com/pub/a/onjava/2004/08/18/ikvm.html

Diff btw a Corba object and a servant

I have been perplexed by the concepts of Corba object and servant. Finally after a lot of reading, things are falling into place. The following articles give a good explanation of the same:

http://www.javaworld.com/javaworld/jw-09-2002/jw-0927-corba_p.html
http://www4.informatik.uni-erlangen.de/~geier/corba-faq/poa.html

Excerpt from the above articles:

In the CORBA world, an object is a programming entity with an identity, an IDL (interface definition language)-defined interface, and an implementation. An object is an abstract concept and cannot serve client requests. To do so, an object must be incarnated or given bodily form—that is, its implementation must be activated. The servant gives the CORBA object its implementation. At any moment, only one servant incarnates a given object, but over an object's lifetime, many (different) servants can incarnate the object at different points in time.
The terms creation and destruction apply to objects, while the terms incarnation and etherealization apply to servants.
Once an object is created, it can alternate between many activations and deactivations during its lifetime. To serve requests, an object must:
1)Be activated if it is not active.
2)Be associated with a servant if it does not already have one. Just because an object is active does not mean that it has an associated servant. You can configure/program the POA to use a new servant upon request.

A client views a CORBA object as an object reference. The fact that a client has an object reference does not mean that a servant is incarnating the object at that time. In fact, the object reference's existence does not indicate an object's existence. If the object does not exist (that is, it has been destroyed), the client will receive an OBJECT_NOT_EXIST error when it tries to access the object using the object reference. However, as noted above, if the object is in a deactivated condition, it will activate, a process transparent to the client.

Servant: A programming language entity that exists in the context of a server and implements a CORBA object. In non-OO languages like C and COBOL, a servant is implemented as a collection of functions that manipulate data (e.g., an instance of a struct or record) that represent the state of a CORBA object. In OO languages like C++ and Java, servants are object instances of a particular class.

The POA distinguishes between the CORBA object reference (IOR) and the implementation object that does the work. This implementation object is called a servant. A BOA-based approach has the IOR and servant existing at the same time. A POA-based approach can support this, but can also support IORs existing without being associated with servants, and also servants existing without being associated with IORs.

Obviously, the association between an IOR and a servant has to be made at some point, to make the servant a useable CORBA object. But this association can be done on-demand. Consider the following example scenarios to motivate the advantages of on-demand association:

• A pool of servants can be instantiated, and then associated in turn with IORs, as needed.
• A set of IORs can be created for the purposes of publishing the references to the Name Service, without going through the work to actually instantiate the servants.

Moreover, the POA allows a single servant to simultaneously support several IORs.
All of the above significantly contribute to scalable applications.

HOW DOES THE POA MAKE THE ASSOCIATION BETWEEN SERVANTS AND CORBA OBJECTS?

This is where the Object ID and and POA Active Object Map come in. So, for a given POA, the Object ID identifies a specific CORBA object, which is used in the Active Object Map to identify the servant.

IPC channel in .NET 2.0 (remoting)

Good news is that MS has finally included the 'named-pipe' channel into the core .NET 2.0 remoting framework. The channel is known as IPC channel and enables on-box communication between processes on the same m/c.
It has, additionally, the capability to secure that channel with an ACL. You can use an Access Control List with this particular channel to limit the number of users that can access it.

More information here.

Named pipes in Linux

In computing, a named pipe (also FIFO for its behaviour) is an extension to the classical pipe concept on UNIX and UNIX-like systems, and is one of the methods of interprocess communication. The concept is also found in Windows, albeit the semantics are largely different.
A good article is available at http://www2.linuxjournal.com/article/2156
Snippet from the article:

We often used "un-named" pipes on the command prompt. For e.g. ls grep x
The other sort of pipe is a "named'' pipe, which is sometimes called a FIFO. FIFO stands for "First In, First Out'' and refers to the property that the order of bytes going in is the same coming out. The "name'' of a named pipe is actually a file name within the file system. Pipes are shown by ls as any other file with a couple of differences:
% ls -l fifo1
prw-r--r-- 1 andy users 0 Jan 22 23:11 fifo1

The p in the leftmost column indicates that fifo1 is a pipe. The rest of the permission bits control who can read or write to the pipe just like a regular file. On systems with a modern ls, the character at the end of the file name is another clue, and on Linux systems with the color option enabled, fifo is printed in red by default.

To make a pipe named pipe1

% mkfifo pipe
Then open 2 console windows:
% ls -l > pipe1 { in one window }
% cat <>

Voila! The output of the command run on the first console shows up on the second console. Note that the order in which you run the commands doesn't matter.

Chatty interfaces Vs Chunky interfaces

In distributed applications, we need to put special emphasis on issues such as network latency, low bandwidth. Hence as a good design principle, we should make our interfaces 'chunky' and not 'chatty'

Chatty interfaces are interfaces that make a lot of transitions(between layers, processes etc.) without doing any significant work on the other side. For example, property setters and getters are chatty. Chunky interfaces are interfaces that make only a few transitions and work done on the other side is significant. For example, method that opens a database connection and retrieves some data is chunky.

This does not mean that U return unnecessary data in Ur calls...U need to take a decision based on 'balance' and the 'problem situation'

Problems with CAO in .NET remoting.

In his excellent article here, Ingo Rammer states the points why CAO is not a good option for many scenarios.

Excerpt from the article:
CAOs are always bound to the machine on which they have been created. This means that you can't use load balancing or failover clustering for these objects. If on the other hand you'd use SingleCall SAOs, you could use Windows Network Load Balancing (NLB) quite easily to randomly dispatch the method invocations to one out of a number of available servers.
If you are running a single-server application, this doesn't matter too much for you. If however there is the slightest chance that the application has to scale out to a server-side cluster, than CAOs will definitely limit its scalability.
CAOs also affect you on a single server. When running SingleCall SAOs (and when strictly keeping all state information in a database) you can shutdown and restart your server on demand. You could for example upgrade to a newer version or apply some bug fix without having to tell any user to close and restart your client-side application. As soon as you use CAOs however, you instantly lose this feature. If you restart a server in which you host CAOs, the client application will receive exceptions when calling any methods on these objects. CAOs are not restored after restarting your server. Don't use them if you care about restartability or scalability.

Important points regarding Sponsors in .NET remoting

• The lease manager calls ISponsor's single method, Renewal, when the lease expires, asking for new lease time. Because the sponsor is called across an AppDomain boundary, the sponsor must be a remotable object, i.e. extend from MarshalByRef object.
• We need to override the InitializeLifetimeService() method to return null, so that the sponsor object itself has infinite lease.
• Also the client needs to register a channel so that the server can make the lease renewal calls.

Access a .NET webserice using proxy generated from SoapSuds.exe

Both WSDL.exe and Soapsuds.exe generate proxies that can be used to access a web service.
But we need to be aware of the SOAP encoding differences.

SoapSuds.exe expects a RPC style WSDL/Web Service but ASP. NET Web Services are Document style per default. These different styles imply different XML message encoding.

In order for a Soapsuds-generated proxy to communicate with a ASP.NET webservice, we need to apply an attribute to your ASP.NET Web Service class to achieve 'compatibility': [SoapRpcService()]

SOAP encoding concepts

Web Services Description Language (WSDL) defines two styles for how an XML Web service method, which it calls an operation, can be encoded in a SOAP request or a SOAP response: RPC and Document. The RPC style refers to encoding the XML Web service method according to the SOAP specification for using SOAP for RPC; otherwise known as Section 7 of the SOAP specification. This style specifies that all parameters are encapsulated within a single element named after the XML Web service method, and that each element within that element represents a parameter named after their respective parameter name.

A more detailed explanation can be found at MSDN here.

Elements in the .NET remoting chain

There are a lot of components/elements that play a role in the .NET remoting architecture:

Client --> Proxy {Converts the stack frame into a message}
-- > Message Sink (chain) { Intercepts the message }
-- > Formatter { Converts the message into a stream }
-- > Channel Sink (chain) {Intercepts the stream }
-- > Transport Sink { Transfers the stream from one process to the other }
====================================
-- > Transport Sink { On Server side }
-- > Channel Sink
-- > Formatter
-- > Message Sink
-- > Dispatcher { Converts the message into a stack frame }
-- > Remote Object

.NET Remoting Proxies

In .NET remoting, proxies are generated transparently by the remoting runtime, hence it is necessary to have the remote object metadata at the client side.
This metadata can be obtained in many ways. I only knew of the 'sharing interfaces' and 'soapsuds.exe' utility, but there are a couple more --

– Shared interfaces
– Shared base classes
– Shared implementation (implementation is copied to server and client)
– SoapSuds.exe (lets you extract metadata from running server or from an Assembly)

Data Concurrency Violations in ADO.NET

Bcoz the DataSet is a disconnected data model, quite often we may have to handle concurrency problems. There are basically 3 ways in which data concurrency is handled:

• Pessimistic locking-- A range lock is obtained on the required rows and no one else can modify the rows during that time. Fully fool-proof, but reduces the scalibility drastically
• Optimistic locking -- If there are data changes that has happened in between the user updates, then the user is given the choice to either overwrite the changes or discard his changes.
• Last wins -- Whoever updates last will overwrite everything.

ADO.NET used Optimistic concurrency and hence it is possible to alert the user of any concurrency violations. An excellent article regarding the same is available here.

Object Activation in .NET remoting

I have often been confused on when the 'new()' operator can be used for remote server activation? Can it be used only for CAO (client activated objects) or SAO (server activated objects) or for both?

The answer is that the 'new' operator can be used to activate any kind of remote object-both CAO and SAO. The only difference between GetObject/CreateInstance and 'new' is that the former allows you to specify a URL as a parameter, where the latter obtains the URL from the configuration. (I belive the 'new' operator can be used only when U have the remote object implementation on the client side?)

Another imp point regarding activation is that the remote object on the server is 'not' actually created when the 'new' operator or the GetObject() methods are called.

Here's a snippet of what MSDN says:

GetObject or new can be used for server activation. It is important to note that the remote object is not instantiated when either of these calls is made. As a matter of fact, no network calls are generated at all. The framework obtains enough information from the metadata to create the proxy without connecting to the remote object at all. A network connection is only established when the client calls a method on the proxy. When the call arrives at the server, the framework extracts the URI from the message, examines the remoting framework tables to locate the reference for the object that matches the URI, and then instantiates the object if necessary, forwarding the method call to the object. If the object is registered as SingleCall, it is destroyed after the method call is completed. A new instance of the object is created for each method called.

But for CAO, the new operator or the CreateInstance methods send a Activation message to the server machine when the client creates the object and a proxy is created on the client side. Constructors with parameters are supported.