Generate SHA-512 hashes using Python

python -c "import crypt, getpass, pwd; \
             print(crypt.crypt('password', '\$6\$saltsalt\$'))"

Pagination in Solidity

Simple working Solidity code to paginate arrays returned from a Smart Contract:

pragma solidity >=0.4.22 <0.6.0;

contract ArrayPagination {
    uint[] arr;

    function add(uint data) public {
        arr.push(data);
    }

    function fetchPage(uint cursor, uint howMany) public view returns (uint[] memory valueset, uint newCursor) {
        uint length = howMany;
        if (length > arr.length - cursor) {
            length = arr.length - cursor;
        }

        uint[] memory values = new uint[] (length);
        for (uint i = 0; i < length; i++) {
            values[i] = arr[cursor + i];
        }

        return (values, cursor + length);
    }
}

Mapping network connections to Process ID's in Windows

One of the cool features in Linux is the ability to map network requests with process id's (PIDs). This can help any system administrator troubleshoot a number of things, such as "What process is using port 80?".


I struggled for a long time to do the same thing on Windows machines, but I have recently found out that with netstat, run in administrator mode, you can actually get something similar:


Microsoft Windows [Version 10.0.17763.592]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\WINDOWS\system32>netstat -aon

Active Connections

  Proto  Local Address          Foreign Address        State           PID
  TCP    0.0.0.0:80             0.0.0.0:0              LISTENING       4
  TCP    0.0.0.0:135            0.0.0.0:0              LISTENING       1072
  TCP    0.0.0.0:445            0.0.0.0:0              LISTENING       4
  TCP    0.0.0.0:2179           0.0.0.0:0              LISTENING       4428
  TCP    0.0.0.0:2701           0.0.0.0:0              LISTENING       11140
  TCP    0.0.0.0:3000           0.0.0.0:0              LISTENING       10204
  TCP    0.0.0.0:5040           0.0.0.0:0              LISTENING       6916
  TCP    0.0.0.0:8732           0.0.0.0:0              LISTENING       4

Remove all Docker images and containers

Very handy and fundamental commands to delete ALL Docker images and containers:

First start by deleting the containers (since these are dependencies of images):
docker rm $(docker ps -a -q)

Then we can proceed to delete all the images:
docker rmi $(docker images -a -q)

Render Material-UI Modal in the center of the Screen

The Material-UI Modal component is a very powerful and commonly used component in the ReactJS community. Unfortunately it is badly documented. One of the most common questions is how to center the modal to the center of the screen. Well the solution is actually quite simple, just add a style prop as follows:

        <Modal
          style={{ alignItems: "center", justifyContent: "center" }}
          open={this.state.openModal}
          onClose={this.handleCloseModal}
        >
          ...
        </Modal>


Hot Reloading Node and React on Docker Windows

Ever since I moved my development environment to Windows, it has been a constant struggle to emulate the previous environment that I had built on OSX.

Probably one of the most critical components in my projects is the fact that all of my projects run on a Docker microservice architecture. In addition to the usual isolation and scalability advantages, development becomes a joy especially when you use filesystem watchers on NodeJS (nodemon) and ReactJS (react-scripts) that enable hot-reloading.

The problem is that, out of the box, these file watchers do not work on Windows 10. The reason is that to run Linux container on Windows 10, you need to have Hypervisor, which acts as a virtualization layer - hence all virtualization rules apply to hot-reloading!

In other words, in order for hot reloading to work on Docker Windows, you need to enable Chokidar polling.

How do fix Hot Reloading with Chokidar?


For NodeJS, just modify the package.json file to use the legacy mode when starting nodemon. This can be easily done using the -L flag.

  "scripts": {
    "server": "nodemon -L index.js"
  },

For ReactJS, it is equally simple. Just add a .env file inside the project parent directory (/usr/src/app) with the following line:

CHOKIDAR_USEPOLLING=true

Trigger TeamCity job when specific branch is merged to Master

Any DevOps who has been involved in some serious CI/CD pipeline architectures have met these particular requirements at least once in his life:

  1. Detect hotfix* branches that are merged to Master
  2. Detect feature* branches that are merged to Master
  3. Automatically trigger a job if (1) is true
Although most build systems support this feature (I know for a fact that this is the case for Bamboo and Jenkins) and the methodologies are similar, this blogpost will focus on Teamcity, probably because I saw a lack of documentation on the matter.

Teamcity is notorious for being tricky! The only way to trigger merges is by listening to the commit messages. With this in mind, we will bake our commit messages to reflect our needs.

Assumptions:

We will assume that the commit message looks something like:
git commit -m "hotfix-*"

Trigger when HotFix branch merged to Master:







Trigger when Feature branch merged to Master:







In both cases, the VCS should be only monitoring the Master branch: