Customize HTTP Server Response Header in WSO2 API Manager / WSO2 ESB

You may know that in the response header from WSO2 ESB invocations or WSO2 API Manager invocations, You are getting "Server" header as bellow.

HTTP/1.1 200 OK
Access-Control-Allow-Headers: authorization,Access-Control-Allow-Origin,Content-Type,SOAPAction
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: POST,GET,DELETE,PUT,HEAD
Content-Type: application/json
Access-Control-Allow-Credentials: true
Date: Sat, 09 Apr 2016 20:02:58 GMT
Server: WSO2-PassThrough-HTTP
Transfer-Encoding: chunked
Connection: Keep-Alive

{
  "origin": "50.185.34.119"
}

You can see that Server Header Contains WSO2 as bellow.

Server: WSO2-PassThrough-HTTP

Sometimes there are situations like It needs to customize this header.

Eg: If we need to customize this as bellow.

Server: PassThrough-HTTP

What we need to do is , Add the http.origin-server to passthru-http.properties file located in ESB_HOME/repository/conf/ directory with customized value as bellow.

http.origin-server=PassThrough-HTTP

Once you restart the server, Above response will be changed as bellow.

HTTP/1.1 200 OK
Access-Control-Allow-Headers: authorization,Access-Control-Allow-Origin,Content-Type,SOAPAction
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: POST,GET,DELETE,PUT,HEAD
Content-Type: application/json
Access-Control-Allow-Credentials: true
Date: Sat, 09 Apr 2016 20:11:47 GMT
Server: PassThrough-HTTP
Transfer-Encoding: chunked
Connection: Keep-Alive

{
  "origin": "50.185.34.119"
}

ActiveMQ - WSO2 ESB - Redelivery Delay - MaximumRedeliveries Configuration

There are use cases which we need to configure Redelivery Delay and the Maximum Redeliveries for Message Consumers of Activemq.

When consuming ActiveMq Queue, we can configure these parameters as mentioned in [1]

WSO2 ESB also can act as a message consumer and a message producer. Information of configuring that can be found in ESB documentation. [2]  Then we can find Consumer / Producer configurations in [3]

In ESB JMS proxy, we can configure Redelivery Delay and MaximumRedeliveries with using following parameters.

Eg:  By default Redelivery Delay in ActiveMq is one second and MaximumRedelivery count is 6. If you need to change the as bellow, you can do it with following parameters in the proxy service.

Redelivery Delay - 3 Seconds
MaximumRedelivery Count - 2

   <parameter name="redeliveryPolicy.maximumRedeliveries">2</parameter>
   <parameter name="transport.jms.SessionTransacted">true</parameter>
   <parameter name="redeliveryPolicy.redeliveryDelay">3000</parameter>
   <parameter name="transport.jms.CacheLevel">consumer</parameter>

Other than enabling the default configurations for JMS transport receiver, you dont need to add any other parameters to the axis2.xml to achive this.

Here is a sample proxy service which i have added above parameters.

Tested Versions : ESB 4.9.0 / Apache ActiveMQ 5.10.0

<proxy xmlns="http://ws.apache.org/ns/synapse"
       name="JMStoHTTPStockQuoteProxy"
       transports="jms"
       statistics="disable"
       trace="disable"
       startOnLoad="true">
    <target>
        <inSequence>
            <log level="full">
                <property name="Status" value=" Consuming the message"/>
                <property name="transactionID" expression="get-property('MessageID')"/>
            </log>
            <property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>
            <drop/>
        </inSequence>
    </target>
    <parameter name="redeliveryPolicy.maximumRedeliveries">2</parameter>
    <parameter name="transport.jms.DestinationType">queue</parameter>
    <parameter name="transport.jms.SessionTransacted">true</parameter>
    <parameter name="transport.jms.Destination">JMStoHTTPStockQuoteProxy</parameter>
    <parameter name="redeliveryPolicy.redeliveryDelay">3000</parameter>
    <parameter name="transport.jms.CacheLevel">consumer</parameter>
    <description/>
</proxy>

When we configure these redelivery parameters, we need to make sure that we have enabled transactions for the proxy. We have done it using following parameter.

<parameter name="transport.jms.SessionTransacted">true</parameter>

Once we enable transactions, If the transaction is successful there is no redelivery happens.  So, in order to test the redelivery functionality, After consuming the message, we need to RollBack the transaction. In order to do that we need add following parameter inside the InSequence of the proxy service.

<property name="SET_ROLLBACK_ONLY" value="true" scope="axis2"/>

With above property, we notify the server that, The tranaction is Rollbacked.

All these properties are passed in to the server when we make the connection from ESB to the Message Broker. So, at that time we need to specify all these parameters.


[1] http://activemq.apache.org/redelivery-policy.html
[2] https://docs.wso2.com/display/ESB490/Configure+with+ActiveMQ
[3] https://docs.wso2.com/display/ESB490/ESB+as+a+JMS+Consumer

Introduction to BITCOIN

 What is the price of a Lamborghini in BitCoins ???

You should contact Lamborghini to find the today's price :). But you have to believe that this is real and world is moving towards digital currency. [1]

In this post, I would like to provide you a brief introduction to BitCoins after attending to a Meetup on introduction to BitCoins held on Silicon Valley yesterday.

There were plenty of questions I had in my mind before I attend to this meetup. So I thought many people will have the same and sharing the answers I got will help everyone.

What is a BitCoin?

BitCoin is a decentralized digital currency. It is virtual and you can not touch and feel. But you can transfer bitcoins from person to person or one organization to another organization. Basically, it is like normal cash or gold. But no any government or organization controls it.  As we have USD for US Dollars, BitCoins are identified as BTC. and its symbol is as in the bellow image.

In order to identify anything as a currency it should have four properties

1. Divisible (Broken into small amounts)
2. Durable ( Stands for a long time)
3. Fungible 
4. Verifiable (Verify that it is real)

All the currencies we trade for goods and services have all these properties. BitCoin also has the same four properties. The difference is, the currencies we use subjected to inflation. But BitCoins are not and it automatically controls the inflation.

As we know, US government can print US Dollars and issue to the market. There is no limit in how many bills it going to print over time. It makes the inflation. But in BitCoins, there is a limit of BitCoins which can be exchanged ever in the market. Currently, it has not reached that limit and that limit is 21 Million BitCoins.

How many BitCoins we have in the market at the moment?

At the moment I am writing this blog post, it has the amount in the following image.

You can get the most updated information on the count in [2]. BitCoins are not coming into the market automatically. BitCoins are mined by BitCoin miners. Approximately, in every ~10 mins, 25 new BitCoins are introduced to the market in the time I am writing this blog post. Reason behind saying that "at the time I am writing is", after another few years or months this rate of mining BitCoins become half of the current value.

Who Invented BitCoin?

Satoshi Nakamoto
In 2008 satoshi published a whitepaper on Bitcoin: A Peer-to-Peer Electronic Cash System[3]. Then he released the first client version of the bitcoin software in 2009. You can read more on satoshi with [4].

Who are BitCoin Miners?  

As I mentioned previously, BitCoins are not come into circulation automatically. They are mined by BitCoin miners. Satoshi was the first BitCoin miner and now there are huge amount of BitCoin miners in the world.

What is the task of a BitCoin Miner? Do they dig the soil to mine?

It is more than Digging :).  BitCoin mining comes into the picture with a transaction. Lets assume as following.

Alice has 50 BTC in her wallet. Then she needs to give 30 BTC to Bob and She needs to get 19 BTC as change and 1 BTC as transaction fee.  This is a particular transaction as we do in normal currency. Lets assume Alice has a 50$ bill. She gives it to intermediate party to give which Alice and Bob trust to give 30$ to Bob and get 19$ back to Alice as change. Then she asks intermediate party to keep 1$ as transaction fee.

So, in this digital currency transaction it is as same. But here this 50BTC is kept in an address which has a public key and a private key. This address is encrypted and the public key of this address can be used to decrypt and find the amount of BTC has in this address. But only the private key of this address can be used to send BitCoins from this address to another address.

So, it is important that this private key is stored very securely since once a hacker has this private key, it is like a thief got the wallet. When Alice wants to send money to Bob, what she does is three steps.

She uses a BitCoin Client application. She provides the address of Bob's wallet which she wants to send money. Then she provides the amount she expects to send to Bob, change she expects and the transaction fee. Once she confirms the transaction with her private key, this transaction is done.

Then this transaction is going to all the miners in the world through a distributed communication system. Like this transaction, there are plenty of transactions happening in the BitCoin world and all those transactions are received to the minors.

When there is some number of transactions received by the Miners,  Then they start to validate those transactions first. After validating all those transactions, they need to use a hashing algorithm to hash these set of transactions into a 10 digit number. When hashing these set of transactions to into a 10 digit number, they have to use a random number to make it happens. So it is not an easy task.

As I mentioned previously there are plenty of BitCoin miners in the world. It is like a contest and everybody tries to come up with this 10 digit number and the first one to come up with that number gets the reward.

The reward is 25BTC and all the transaction fees in this transaction. At the moment, the value of a BitCoin in USD is $456.77. So, what do you think? How much you can earn?

Ok, From where this 25BTC comes from?

It comes from Nowhere. That is called mining. When the minor starts to hash and find this 10 digit number, He adds this as a transaction like bellow.  This address 1axxas... is the public address of this miner. So this 25BTC is mined with this transaction.

25 BTC To Address 1axxas...

After finding 10 Digit number What happens?

Once a minor found this 10 digit number for the set of transactions, he broadcasts this number to the entire world.  These is common ledger called "Block Chain". Every minor has the same copy of this common ledger in the world and it has each and every transaction happen from the first BitCoin.
So, once the above 10 Digit number is broadcasted, everybody who mines adds this set of transactions with this number to their ledger. This set of transactions and the number is called a "Block".

The above mentioned 10 digit number is the link from one block to another block. As everybody agrees to use the same key over the entire world, this block is getting saved in everyone's block chain.
After this block is get saved in every ones ledger and it was added three more blocks, the transaction is confirmed.

You can read more information about block chains and how it works in [5].

Can I be a Miner?

Of course, you can. But you will get 25BTC only if you win the contest. You 'll need huge computational power to be the winner. Currently, there is huge computation power used to my miners to mine. Following is a BitCoin mining farm.

Where can I buy BitCoins?

You can buy BitCoins from BitCoin ATMs who are selling BitCoins[6]. You can pay with USDs if you are in USA and you can pay in Yens if you are in Japan.

Who accept BitCoins?

As I mentioned in the beginning, world is moving to the digital currency. So there will be most of the people accepting BitCoins for transactions like buying a coffee to buying a Lamborghini.

Conclusion
This is just an introduction to BitCoins and how it works. There are plenty of resources in the web which you can learn about BitCoins and how it works. Here I am listing few of them for your convenience.

Finally, I would like to thank to Donn Lee who held this meetup and Prabath Siriwardene who asked me to come to this Meetup.

[1] https://www.cryptocoinsnews.com/buying-cars-bitcoin-lamborghini-jeep-everything/
[2] http://realtimebitcoin.info
[3] http://www.coindesk.com/bitcoin-peer-to-peer-electronic-cash-system/
[4] http://www.coindesk.com/information/who-is-satoshi-nakamoto/
[5] http://www.coindesk.com/information/how-do-bitcoin-transactions-work/
[6] http://www.coindesk.com/bitcoin-atm-map/

Additional Resources

• https://www.youtube.com/watch?v=000UtKtm7kU
• https://www.coursera.org/course/bitcointech
• http://chimera.labs.oreilly.com/books/1234000001802

WSO2 Carbon LogViewer Admin Service

Most of the WSO2 Products contains so many Admin Services. All of the available admin services can be seen by starting the server with -DosgiConsole command as guided in documentation [1]

In those admin services, there is an Admin service called "LogViewer". This service provides so many operations as listed in WSDL. In order to access this WSDL locally, you need to change the carbon.xml file as mentioned in link [1]

In those operations, "getApplicationLogs " operation can be used to filter out logs about deployed carbon applications.

Eg: In WSO2 ESB, when we deploy a carbon application, it will print a log like bellow.

[2015-12-17 14:01:07,531]  INFO - ApplicationManager Undeploying Carbon Application : LocalEntryTestProject...
[2015-12-17 14:01:07,552]  INFO - ApplicationManager Successfully Undeployed Carbon Application : LocalEntryTestProject {super-tenant}

[2015-12-17 14:01:22,558]  INFO - LocalEntryDeployer LocalEntry named 'foo1' has been undeployed

So, with the above operation in "Log Viewer" admin service, we can obtain all the logs related to Carbon application deployment.

To verify this we can access this Admin Service with SOAP UI as bellow and provide required input parameters and get the log.

It is important to have proper input parameters to use this admin service.

With the provided input parameters, it filters out the complete log and returns the filtered log.

Type - The log type, It can be ALL, DEBUG, INFO, ERROR, WARN

keyword - This string will be searched in the log and it will return only this keyword presents in the log

appName - This is the application name to be used. We can keep this blank, if we dont know the specific app name

domain - This is the tenant domain, For super admin, the domain is "carbon.super". For others, we can use the proper tenant domain.

serverKey - What is the server we expect to get the log. eg: ESB, AS, GREG

[1] https://docs.wso2.com/display/AM160/WSO2+Admin+Services

MySql Start / Stop / Restart

I was experiencing following error in my mac after i upgraded to Yosemite.

Shammis-MacBook-Pro:~ shammi$ mysql
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)


Then i went through so many ways to get rid of the issue. Finally this advise made it working. I found that from here.

Create /Library/LaunchDaemons/com.mysql.mysql.plist and save it with the following plist:

1. xml version="1.0" encoding="UTF-8"?>  
2. >  

<plist version="1.0">  

  <dict>  

   <key>KeepAlive</key>  

   <true/>  

   <key>Label</key>  

   <string>com.mysql.mysqld</string>  

   <key>ProgramArguments</key>  

   <array>  

   <string>/usr/local/mysql/bin/mysqld_safe</string>  

   <string>--user=mysql</string>  

   </array>  

  </dict>  

</plist>  

And also changing some permisions to the file:

sudo chown root /Library/LaunchDaemons/com.mysql.mysql.plist
sudo chgrp wheel /Library/LaunchDaemons/com.mysql.mysql.plist
sudo chmod 644 /Library/LaunchDaemons/com.mysql.mysql.plist

And finally load the plist:

sudo launchctl load -w /Library/LaunchDaemons/com.mysql.mysql.plist







In the same time, It will be useful to know following which i found from [1]




To restart, start or stop MySQL server from the command line, type the following at the shell prompt…

On Linux start/stop/restart from the command line:

 /etc/init.d/mysqld start

 /etc/init.d/mysqld stop

 /etc/init.d/mysqld restart

Some Linux flavours offer the service command too

 service mysqld start

 service mysqld stop

 service mysqld restart

or

 service mysql start

 service mysql stop

 service mysql restart

On OS X to start/stop/restart MySQL from the command line:

 sudo /usr/local/mysql/support-files/mysql.server start

 sudo /usr/local/mysql/support-files/mysql.server stop

 sudo /usr/local/mysql/support-files/mysql.server restart

ERROR java.io.InvalidClassException: org.apache.synapse.message.store.impl.jms.SynapseMessage; local class incompatible

Recently i was working with Message Store /Message Processor scenario in WSO2 ESB. In that i developed a CAR file with Dev Studio and used it with ESB 4.8.1.

Then i executed the scenario of sending some messages to Message Store while making the Backend unavailable which leaded to remain some messages in the queue.

Then , i used the same CAR file in ESB 4.8.0 and once i deploy the CAR file , i was getting following exception continuously.

ERROR - JmsConsumer [TestMessageStore-C-263] cannot receive message from store. Error:Failed to build body from bytes. Reason: java.io.InvalidClassException: org.apache.synapse.message.store.impl.jms.SynapseMessage; local class incompatible: stream classdesc serialVersionUID = -7391992645087640122, local class serialVersionUID = -8457646720705005296

Then i initially thought that this can be due to some incompatibility of Dev Studio version with ESB 4.8.1 and 4.8.0. But i was wrong.

Actual problem was my previous act before i shutdown ESB 4.8.1. Because the message processor could not process the messages previously due to the un availability of the back end, There were some messages remaining which i sent with ESB 4.8.1.

Then when i started 4.8.0 and deploy the CAR file, it tried to process those existing messages from the queue. Since those message were sent from different serialVersionUID of the same class org.apache.synapse.message.store.impl.jms.SynapseMessage  It is not possible to deserialise them with different serialVersionUID.

So , once i removed all the previous messages from the queue, it worked perfectly.

How to setup networking for Virtualbox VMs in Mac

By default when we configure Virtual box VM for  Mac we are getting networking with NAT. The configuration looks like bellow.

But with that i could not PING from my Mac to the Windows VM or vice-versa.  As usual i changed the connection to Bridge mode but no success. Then contacted my Networking friend "Dhanushka Ranasinge" and with his guide i could get it done.

Following is the TIP.

For the VM
1. Change the  network interface to "Host-Only Adapter" as in the bellow image.

2. Then start the VM and disable to windows firewall.

Now you are in a STATE that you can PING from your MAC to WINDOWS.

Now we need to set up internet for the VM.

3. Shutdown the VM and add second Network adaptor for NAT

With this NAT interface , it will connect your VM to internet. Now it is all done. Start your VM and you should be able to connect to INTERNET and you should be able to PING from MAC to WINDOWS and vice-versa.