DDevelopment & Design

NetCat in Java

Recently, I tried to run netcat under Windows and I failed to compile it. So I decided to write a simple equivalent in Java, which works under all platforms.

NetCat is a very simple and useful tool, which allows to see contents of TCP/IP requests, like HTTP etc., both server and client side. With NetCat it is possible to either set up TCP/IP listener on a port and receive data or send TCP/IP request to remote server.

The code and executable for Java version of NetCat is available on GitHub:
http://github.com/rafalrusin/netcat/downloads

I used Jakarta Commons CLI to handle commandline parameters. The code is as simple as that:

In order to handle stream I/O I implemented a simple StreamTransferer class like this:

The only issue I had was that whenever I closed Java I/O stream using OutputStream.close(), it was closing the whole socket. So I couldn’t receive any response back from server. So instead of doing that I had to use Socket shutdownOutput method, like in the code below.

It worked perfectly then.

So it is possible to send HTTP GET requests to google using this tool. In order to do that, you need to connect to google.com and type GET and enter. CTRL+Z and enter is for closing input stream under Windows. CTRL+D is for Linux.

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GeeCON 2012 review

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DDevelopment & Design

Need to make a quick json fixes – JSONPath for rescue

From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.

First of all you can try it without pain online: http://jsonpath.curiousconcept.com/. Full syntax is described at http://goessner.net/articles/JsonPath/



But also you can download python binding and run it from command line:
$ sudo apt-get install python-jsonpath-rw
$ sudo apt-get install python-setuptools
$ sudo easy_install -U jsonpath

After that you can use inside python or with simple cli wrapper:
#!/usr/bin/python
import sys, json, jsonpath

path = sys.argv[1]

result = jsonpath.jsonpath(json.load(sys.stdin), path)
print json.dumps(result, indent=2)

… you can use it in your shell e.g. for json:
{
"store": {
"book": [
      {
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
      },
      {
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
      },
      {
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
      },
      {
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
      }
    ],
"bicycle": {
"color": "red",
"price": 19.95
    }
  }
}

You can print only book nodes with price lower than 10 by:
$ jsonpath '$..book[?(@.price

Result:
[
  {
"category": "reference",
"price": 8.95,
"title": "Sayings of the Century",
"author": "Nigel Rees"
  },
  {
"category": "fiction",
"price": 8.99,
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"author": "Herman Melville"
  }
]

Have a nice JSON hacking!From time to time I have a need to do some fixes in my json data. In a world of flat files I do this with grep/sed/awk tool chain. How to handle it for JSON? Searching for a solution I came across the JSONPath. It quite mature tool (from 2007) but I haven't hear about it so I decided to share my experience with others.
DDevelopment & Design

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I've been to 4Developers in 2009 in Cracow, together with Tomasz Przybysz and we had very nice impressions, no wonder then I wanted to signed up for 2010 edition in Poznań as well. Tomasz was sick, but Jakub Kurlenda decided to come with me. This time...I've been to 4Developers in 2009 in Cracow, together with Tomasz Przybysz and we had very nice impressions, no wonder then I wanted to signed up for 2010 edition in Poznań as well. Tomasz was sick, but Jakub Kurlenda decided to come with me. This time...