Inceptions and Inspirations

Gurus and Readings

Gurus

Rod Johnson
- Spring Framework
Doug Lea
- Concurrent Programming in Java(1997), java.util.concurrent package
Joshua Bloch
- Effective Java(2001)
Douglas Crockford
- JSON, JSLint, JavaScript: The Good Parts(O'Reilly. 2008)

Books

Articles

The Ghost Who Codes: How Anonymity is Killing Your Programming Career(02.13.2013)

On Java

Basic

Constructor
- The first statement of a constructor body may be an explicit invocation of another constructor of the same class or of the direct superclass.
- If a constructor body does not begin with an explicit constructor invocation and the constructor being declared is not part of the primordial class Object, then the constructor body implicitly begins with a superclass constructor invocation "super();", an invocation of the constructor of its direct superclass that takes no arguments.
- source : 8.8.7. Constructor Body of The Java Language Specification of Java SE 8 Edition

Guidelines for Designing API

Minimize public members.

Prefer stateless over stateful

Provide factory, builder, facade or something that acts as an entrance point of the library.

Utilize JSR 305 annotations to clearly specify nullness and concurrency constraints.

Apply consistent pattern on the choice of primitive or wrapper for the return type and parameter type.

Apply consistent pattern on the choice of null or empty collection/array.

Apply consistent way to manage configuration.
- Define and describe the meaning of each configuration item.

Consider using with Spring framework.

Avoid get or set for the methods that's NOT trivial.

Don't miss the Javadoc for non-trivial public methods.
- Explain boundary conditions, contraints, or exceptional behavior as possible.

Use English in the source as possible.

Using Pattern

Design Patterns
GRASP (General Responsibility Assignment Software Patterns)
SOLID (Single responsibility, Open-closed, Liskov substitution, Interface segregation and Dependency inversion)
DRY (Don't Repeat Yourself)
Divide and Conquer

Design Patterns: Elements of Reusable Object-Oriented Software (by Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides)
Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development (by Craig Larman)

Core Patterns

High Cohesion
Low Coupling
Don't Talk to Strangers

Singleton pattern
Factory pattern
Builder pattern

Adapter pattern
Proxy pattern
Facade pattern

Observer pattern (Listener, Reacter, Callback)
Command pattern
Strategy pattern

Open-closed pattern

Builder Pattern

Builder pattern(Wikipedia)
The freeze thaw pattern

To make a class thread-safe escaping the state change during initializing, you can use *Builder pattern*. By delegating the thread unsafety to the builder object, the product object created by the builder can be thread safe.

Examples

jmxtrans

Concurrency

Immutables are thread-safe and shareable
Some mutables can be thread-safe and shareable
- When the mutables contains only global or shared variables
Partially thread-safe
- Thread safe after initial configuration
  - com.fasterxml.jackson.databind.ObjectMapper
  - Freeze/Thaw pattern

Formatting, conversion and validating of string, number or date type data

Available packages

Apache Commons Lang 3
- Homepage : http://commons.apache.org/lang/
- API : http://commons.apache.org/proper/commons-lang/javadocs/api-3.3.2/
- Lang provides a host of helper utilities for the java.lang API, notably String manipulation methods, basic numerical methods, object reflection, concurrency, creation and serialization and System properties. Additionally it contains basic enhancements to java.util.Date and a series of utilities dedicated to help with building methods, such as hashCode, toString and equals.

Apache Commons Validator
- Homepage : http://commons.apache.org/validator/
- API : http://commons.apache.org/proper/commons-validator/javadocs/api-1.4.0/
- Framework to define validators and validation rules in an xml file and include some much reusable method to validate and convert strings in terms of number, integer, date, time, IP address, e-mail address, credit card number and so on.

Available utilities by case

String manipulation
- org.apache.commons.lang3.StringUtils
  - general util. to investigate, join, split, substring or trim string
  - static methods, NullPointerException free
  - API
- org.apache.commons.lang3.StringEscapeUtils
  - escape or unescape string in terms of HTML, XML, Java, JavaScript or CVS
  - static methods, NullPointerException free and thread-safe
  - API
- org.apache.commons.lang3.text.WordUtils
  - capitalize, uncapitalize or wrap the string
  - static methods, NullPointerException free
  - API

Character manipulation
- org.apache.commons.lang3.CharUtils
  - static methods, NullPointerException free
  - API

Date manipulation and calculation
- org.apache.commons.lang3.DateUtils
  - java.util.Date type based basic calculations (add/subtract years/months/weeks/days/hours/minutes/seconds)
  - static method, NullPointerException free
  - API

Date formatting
- org.apache.commons.lang3.DateFormatUtils
  - one line formatting
  - static methods, NullPointerException free and thread-safe
  - API

String -> Number conversion
- org.apache.commons.lang3.math.NumberUtils
  - static methods, NullPointerException free, default definable style (like C)
  - API

String -> Date validation and conversion
- org.apache.commons.validator.routines.DateValidator
  - validate and parse string in terms of date
  - API
- org.apache.commons.validator.routines.TimeValidator
  - validate and parse string in terms of time
  - API

String -> Number validation and conversion
- org.apache.commons.validator.routines.DoubleValidator
  - validate and parse string in terms of double-precision floating-point number(double).
  - API
- org.apache.commons.validator.routines.FloatValidator
  - validate and parse string in terms of single-precision floating-point number(float).
  - API
- org.apache.commons.validator.routines.LongValidator
  - validate and parse string in terms of integer in long type.
  - API
- org.apache.commons.validator.routines.IntegerValidator
  - validate and parse string in terms of integer in int type.
  - API

General data container model

For meta modeling or untyped data transfer object(DTO), general data container model is necessary. A few real world samples are :

Open MBean descriptor classes.
- javax.management.openmbean package
- type for general data : CompositeData, TabularData
- type for general meta : SimpleType, ArrayType, CompositeType, TabularType

On Hadoop

Interesting point

Full landscape of Hadoop echo-system and the detailed features of each component in the echo-system

Cloudera
- the features and architectures of service and configuration management tool.

Leading products analysis

Cloudera Manager

Features
- Statement management
  - manage model state(shape) and runtime state
- Configuration management
- Process management
- Software distribution management
- Management services
  - Metric Collection and Display
  - Health Tests
  - Events and Alerts
Interfaces
- Web based admin tool
- Java API

Requisite

Full list of command line or API in Hadoop
- especially necessary or deeply related to admin or control the Hadoop system.

Running shell script from Java
- ProcessBuilder in JDK
- more elegant libraries or wrapper in open-source world ?

Distributed agent framework or library in Java

Data visualization UI framework or library
- Especially JavaScript
- other than D3.js

Monitoring and control Zookeeper from the application

On OpenShift

Background

Pain-point

Expectation

Workflow

Concepts

Applications, Cartridges, Gears, Nodes
- What are the cardinalies among concepts
  - application : cartridge = ?
  - cartridge : gear = ?
  - gear : node = ?
- "By default, for scalable applications, each cartridge resides on its own gears within its own group instance. However, sometimes it is required/preferred to have two cartridges be located together on the same set of gears." -> cartridge (instance) : gear = n : 1
- Considering domain scope cartridge, application : cartridge = n : m
- So, an application can be installed on top of multiple gears, and a gear can be involved with multiple applications.

Scope of cartridge
- domain scope cartridge seems to be suitable for shared services such as database and middle-wares.

Commands

command	action
`rhc help` command	view more information on a specific command.
`rhc authorization list`	view the tokens associated with your account.
`rhc apps`	display information about all the applications you have access to.
`rhc app show` appName	view information about an individual application.
`rhc app create` appName cartridge [... cartridge] [`-n` namespace]	create an application.
`rhc cartridge list`	view the current list of available cartridges.
`rhc cartridge add` cartType `-a` appName	add an add-on cartridge to an application.

Questions

Generally sources on a system consist of several source projects. Then how to map source projects on to applications of OpenShift ?
- Should consider the source configuration management view-points.

Can I use Subversion instead of built-in Git with OpenShift and how can I do that?

Can I share one database instance among multiple applications in OpenShift and how can I do that?
- Generally environment of software development process consist of
  - multiple source projects
  - single database
  - single application server
  - single configuration repository

Can I use my own value for $OPENSHIFT_GEAR_UUID ?

Is it possible to share Maven local repository among gears ?

Necessary Cartridges

Oracle database cartridge
- domain scope

Domain scope MySQL database cartridge
Domain scope PostgreSQL database cartridge

Jetty cartridge
Tomcat cartridge

Client env. cartridge
- contains install script of Eclipse and necessary plug-ins.

Source projects cartridge
- basically multiple source project.
- should be able to customized on the number and names of source projects at cartridge install time.

Front-end

On Hyperledger Fabric

Fabric CA
- 기본 설치 및 설정
- TCert, ECert 발급
- 인증서 갱신/재발급
- CA Server Clustering
- LDAP 연계

Fabric Network/Channel
- Fabric Peer 기본 설치/설정/구동
- Fabric Orderer 기본 설치/설정/구동
- Channel 설계/적용
- Endorsement Policy 설계/적용
- CouchDB 적용/최적화
- Kafka 적용/최적화
- Fabric Orderer Clustering
- TLS 적용
- Docker Swarm 구성
- Kubernete 구성
- ELK Stack 기반 Log 분석
- Gossip Protocol 분석
- gPRC 분석
- Transaction Tracing

성능/가용성 테스트
- JMeter 기본 테스트 방안
- JMeter 분산 테스트 방안
- 시스템 자원사용율 모니터링 - CPU
- 시스템 자원사용율 모니터링 - Memory
- 시스템 자원사용율 모니터링 - Network I/O
- 시스템 자원사용율 모니터링 - Disk I/O
- 서버 자원사용율 모니터링 - Fabric Peer
- 서버 자원사용율 모니터링 - Fabric Orderer
- 서버 자원사용율 모니터링 - Kafka
- 서버 자원사용율 모니터링 - CouchDB
- Go Profiling 적용
- Go Debugging 적용
- 표준 성능테스트 케이스 정의
- 표준 가용성테스트 케이스 정의

20 Node Test Network
- 기본 구성 (LevelDB, Solo Orderer, No TLS)
- 기본 구성 성능테스트
- CouchDB 적용 성능테스트
- Production 구성 (CouchDB, Clustered Orderer, TLS)
- Production 구성 성능 테스트
- Production 구성 가용성 테스트

100 Node Test Network
- 시스템 구성 설계
- 장비 구성
- 구축 (CouchDB, Clustered Orderer, TLS)
- 성능 테스트
- 가용성 테스트

Provisioning scripts design

Use JSON format metadata.
Use GNU parallel.
Use headquarter-station pattern.
Minimize file transfer.
Confirm pre-conditions and post-conditions.
Generate final report including architecture and useful endpoints of the network or cluster.

Architecture decision

What is the optimal ratio between Orders, Leader Peers and Nonleader Peers ?
What is the optimal values of block creation criteria ?
How to optimize the connection or link between Peer container and CouchDB container on the same host machine ?
What is the optimal values of gossip communications ?
How to optimize CouchDB ?
How to optimize Kafka ?
How to measure and optimize the network performance between machines ?
How to measure and optimize the disk I/O performance of machines ?

On OpenCV

IplImage Anatomy

Definition

typedef struct _IplImage {
    int             nSize;              /* size of iplImage struct         */
    int             ID;                 /* version                         */
    int             nChannels;
    int             alphaChannel;
    int             depth;              /* pixel depth in bits             */
    char            colorModel[4];
    char            channelSeq[4];
    int             dataOrder;
    int             origin;
    int             align;              /* 4 or 8 byte align               */
    int             width;
    int             height;
    struct _IplROI *roi;
    struct _IplImage
                   *maskROI;            /* poiner to maskROI if any        */
    void           *imageId;            /* use of the application          */
    struct
      _IplTileInfo *tileInfo;           /* contains information on tiling  */
    int             imageSize;          /* useful size in bytes            */
    char           *imageData;          /* pointer to aligned image        */
    int             widthStep;          /* size of aligned line in bytes   */
    int             BorderMode[4];      /*                                 */
    int             BorderConst[4];     /*                                 */
    char           *imageDataOrigin;    /* ptr to full, nonaligned image   */
} IplImage;

Member priority
- 1st : width, height,
- 2nd : depth, nChannels
- 3rd : origin, dataOrder

Constants for depth

Macro	Value	Type	Mat Equivalence	Mat Value
`IPL_DEPTH_8U`	8	unsigned 8-bit integer	`CV_8U`	0
`IPL_DEPTH_8S`		signed 8-bit integer	`CV_8S`	1
`IPL_DEPTH_16U`	16	unsigned 16-bit integer	`CV_16U`	2
`IPL_DEPTH_16S`		signed 8-bit integer	`CV_16S`	3
`IPL_DEPTH_32S`		signed 32-bit integer	`CV_32S`	4
`IPL_DEPTH_32F`	32	single-precision floating-point number	`CV_32F`	5
`IPL_DEPTH_64F`		64-bit floating-point double-precision	`CV_64F`	6

Constants for origin

Constants	Meaning
`IPL_ORIGIN_TL`	top-left origin
`IPL_ORIGIN_BL`	bottom-left origin (Windows bitmap style)

References

On Red5

RTMPClient

RTMPClient.connect(String host, int port, String app, IPendingServiceCallback connectCallback)
-> RTMPMinaIoHandler.messageSent(IoSession session, Object message)  (message = HeapBuffer[03 00 ...])
-> RTMPMinaIoHandler.messageReceived(IoSession session, Object message)   (message = HeapBuffer[...])
-> RTMPMinaIoHandler.messageSent(IoSession session, Object message)   (message = HeapBuffer[07 E8 ...])
-> RTMPClient.connectionOpened(RTMPConnection conn)
-> RTMPMinaIoHandler.messageSent(IoSession session, Object message)   (message = Packet[[header data type=20, ...] ...])
-> RTMPMinaIoHandler.messageReceived(IoSession session, Object message)   (message = Packet[[header data type=5, ...] ...])
-> RTMPMinaIoHandler.messageReceived(IoSession session, Object message)   (message = Packet[[header data type=6, ...] ...])
-> RTMPMinaIoHandler.messageReceived(IoSession session, Object message)   (message = Packet[[header data type=20, ...] ...])
...
-> connectCallback.resultReceived(IPendingServiceCall call)   (call.getServiceMethodName() = "connect")
-> RTMPMinaIoHandler.messageReceived(IoSession session, Object message)   (message = Packet[[header data type=4, ...] ...])
-> RTMPMinaIoHandler.messageSent(IoSession session, Object message)   (message = Packet[[header data type=4, ...] ...])

RTMPConnection.invoke("createStream", null, createStreamCallback)
-> BaseRTMPClientHandler.invoke("createStream", null, createStreamCallback)
-> RTMPConnection.invoke("createStream", null, createStreamCallback)
-> RTMPConnection.invoke(new PendingCall("createStream", null))
-> RTMPConnection.invoke(new PendingCall("createStream", null), 3)
-> RTMPConnection.getChannel(3).write(new Invoke().setCall(new PendingCall("createStream", null)))

On VirtualBox

Tips for CentOS on VirtualBox

Absolutely install the guest addition.
- CentOS as a Guest OS in VirtualBox
Use F10 for the Host Key.
- [VirtualBox Manager > File > Preference > Input > Virtual Machine > Host Key Combination]
Make Mini ToolBars visible as possible
- [Virtual Machine > Machine > Settings > General > Advanced > Mini ToolBars]
  - check "Show in Fullscreen/Seamless"
  - check "Show at Top of Screen"
- Use "Seamless Mode" as possible
- [Virtual Machine > View]

On Docker

Key Concerns

How to manage configuration per installation/instance, operation ?
How to manage logs ?
How to manage application deployments ?
How to manage persistent data ?
How to debug or monitor application in container ?
How to provide or access development tools ?
How to make containers collaborate or bind containers ?

Strategys and Tactics

Include development tools and environment into the docker image for developer local.
Make working copy of source code in local stored externalized storage or shared folder.
Externalize configuration. (using what ?)
Separate docker image from application source.
- Make docker image which can clone, build and deploy an application in some predefined format from source repository.
Make and enhance own management service for pods, containers and so on.

On Redmine

Customization

Target files

page template : $REDMINE_HOME/app/views/layouts/base.html.erb
initial page : $REDMINE_HOME/app/views/welcome/index.html.erb
i18n message bundle : $REDMINE_HOME/config/locales/*.yml
default style : $REDMINE_HOME/public/stylesheets/application.css

Custom style

body {
  font-family: "맑은 고딕", Georgia, Verdana, sans-serif;
  font-size: 1.0em; 
  line-height:1.5;
  color:black;
}
pre, code, tt {
  font-size:1.0em;
  line-height:1.5;
}
div.wiki.wiki-page, div.wiki.wiki-page pre, div,wiki.wiki-page code{
  font-size: 1.0em; 
  line-height:1.5;
}

div.syntaxhighlighter{
  padding-top:0.5em;
  padding-bottom:0.5em;
  padding-left:0.5em;
  border:thin solid lightgray;
  line-height:1.5 !important;
}
div.syntaxhighlighter div.line{
  line-height:1.5 !important;
}

div#header > h1 {
  font-family:Georgia, Tahoma, Verdana, serif;
  font-weight:bolder;
  font-size:2.5em;
}
div#sidebar { 
  width:15% !important;
  padding-right:0.0em;
  padding-left:0.5em;
}
div#content {
  margin-right:17% !important;
  padding-right:1.5em;
  padding-left:1.5em;
}

@media screen and (min-width:1024px){
  div#wrapper { width:90%;max-width:1600px;min-width:1000px }
}

/* styles for Headings */
h1, h2, h3, h4, h5, h6 {
  font-family: "맑은 고딕", Helvetica, "Trebuchet MS", Verdana;
  -webkit-font-smoothing: antialiased;
}

div.wiki.wiki-page h2, div.wiki.wiki-page h3, div.wiki.wiki-page h4, div.wiki.wiki-page h5, div.wiki.wiki-page h6{
  font-weight:bold;
  margin-top:1.0em;
  padding-top:0.1em;
  padding-bottom:0.1em;
  padding-left:0.4em;
}

h2, div.wiki h1, div.wiki.wiki-page h1 {font-size: 1.5em;}
h3, div.wiki h2, div.wiki.wiki-page h2 {font-size: 1.4em;}
h4, div.wiki h3, div.wiki.wiki-page h3 {font-size: 1.3em;}
h5, div.wiki h4, div.wiki.wiki-page h4 {font-size: 1.2em;}
h6, div.wiki h5, div.wiki.wiki-page h5 {font-size: 1.15em;}
.wiki h6, div.wiki.wiki-page h6 {font-size: 1.1em;color:black; }
#sidebar h3 {
  font-family: "맑은 고딕", Georgia, Verdana, sans-serif;
  font-size: 1.0em;   
}

div.wiki {
  counter-reset:step-for-h1;
  counter-reset:step-for-h2;
  counter-reset:step-for-h3;
}

div.wiki h1 {
  counter-reset:step-for-h2;
}
div.wiki h1:before {
  counter-increment:step-for-h1;
}
div.wiki h2 {
  counter-reset:step-for-h3;
  color:#000000;
  background-color:#99CC33;
  margin-right:15%;
  -moz-border-radius:3px;
  -webkit-border-radius:3px;
  border-radius:3px;
}
div.wiki h2:before {
  content: counter(step-for-h2) ". ";
  counter-increment:step-for-h2;
}
div.wiki h3 {
  color:#000000;
  background-color:#F5DEB3;
  -moz-border-radius:2px;
  -webkit-border-radius:2px;
  border-radius:2px;
}
div.wiki h3:before {
  content: counter(step-for-h2) "." counter(step-for-h3) ". ";
  counter-increment:step-for-h3;
}
div.wiki h4{
  text-decoration:underline;
}
div.wiki h5{
  text-decoration:underline;
}
div.wiki h6{
  text-decoration:underline;
}
/* end of styles for Headings */


/* styles for Table */
div.wiki.wiki-page td, div.wiki.wiki-page th  {
  padding:4px 2px 4px 2px;
}
/* end of styles for Table */


/* styles for Form elements */
input, textarea, select {
  /* font-family: "맑은 고딕", Georgia, Verdana, sans-serif; */
  font-family:serif;
  font-size:1.0em; 
  line-height:1.5;
}
/* end of styles for Form elements */

/* styles for menu */
#top-menu { font-size:1.0em; }
#top-menu li a { font-size:0.9em; } 
#top-menu li a, #main-menu li a { font-size:0.9em; }
#top-menu #loggedas { font-size:0.9em; }
/* end of styles for menu */

/* styles for TOC table */
div.wiki.wiki-page ul.toc { padding:0.5em; margin:0 0 0 0.5em }
div.wiki.wiki-page ul.toc li { font-size: 13px; }
div.wiki.wiki-page ul.toc li li { margin-left:0.9em }
/* end of styles for TOC table */

On TestLink

Installation

Overview

TestLink 1.9 needs PHP 5.2 or 5.3, MySQL database 4.1.x or higher, and Apache web server 2.x.
All of these can be prepared in oneshot using EasyPHP.

Procedure

Download "EasyPHP 12.0 with PHP 5.2.17" from www.easyphp.org/download.php
- Other than version 1.9 of TestLink, refer the installation guide or something like that to confirm the exact dependency of TestLink
Run the setup executable
- EasyPHP installation file is in forms of exe file like EasyPHP-12.0_with_PHP-5.2.17-setup.exe
Follow the instructions and specify the installation directory.
- All the files for PHP, Apache httpd server, MySQL database and those related files will be located under the specified directory.
- For windows, c:\servers\EasyPHP-12.0 would be proper and avoid to include white-space in the path like "c:\Program Files\EasyPHP-12.0"
Check the installation directory
- After the installation completed, you can see the following files or directories under the directory you specified during installation. Exact list could be different depending on the version and edition of EasyPHP

c:\servers\EasyPHP-12.0\ ----+--- apache\
                             |--- conf_files\
                             |--- home\
                             |--- modules\
                             |--- mysql\
                             |--- php\
                             |--- tmp\
                             |--- www\
                             |--- xdebug\
                             |--- EasyPHP-12.0.exe
                             |--- easyphp.ini
                             |--- EasyPHP.log
                             |--- gpl.txt
                             |--- langues.txt
                             |--- readme.txt
                             |--- unins000.dat
                             +--- unins000.exe

Run the EasyPHP and check around
- To run EasyPHP, execute the short cut of [Start > Programs > EasyPHP 12.0 > EasyPHP 12.0]
- Easy PHP will run Apache web server, MySQL database and make an icon appear on the right/bottom side of the Windows task bar nearby clock. The icon is like black lower-case alphabet "e", When you click the right mouse button on the icon, you can see meues like 'Help', 'Log Files', 'Configuration', 'Explorer', 'Administration', and so on. For more on these menus, refer http://www.easyphp.org/introduction.php

On Solidity

Compiler

The return of `solc.compile` function

After the following code executed

var output = solc.compile(data, 1)

The structure of output

"output" : {
   "contracts" : {
      contractName : {
         "assembly" : Object,
         "bytecode" : string,
         "functionHashes" : Object,
         "gasEstimates" : Object,
         "interface" : JsonArray,
         "metadata" : Json,
         "opcodes" : string,
         "runtimeBytecode" : string,
         "srcmap" : string,
         "srcmapRuntime" : string
      },
      formal : {
         "errors" : {
            errorNo " string
         }
      },
      "sourceList" : Object,
      "sources" : Object
   }
}

Smart Contract

Account White List
Whitelisted Token
Distingushiable Account
Distingushiable Polling

On Ethereum Signing

Signing of DSA
- when message m is given
- compute r from a random number k
- compute s from the random number k, private key, hashed message(hash(m)) and r
- signature : (r, s)

Signing of ECDSA
- when message m is given
- select a random number k
- compute a point (x₁, y₁) from the curve with the random number k
- compute r from x₁
- compute s from the random number k, private key, hashed message(hash(m)) and r

Signature doesn't have original message or hash of the message.
To verify the signature, the original message or hash of the message is necessary.

Signing and Verifying Messages in Ethereum (FEBRUARY 17, 2018)

ECDSA / Public key recovery

Using Python

eth-account.account.Account._recover_hash() methods source : Show how to obtain public key from the message (exactly Ethereum's unique hash of message) and signature.

@combomethod
def _recover_hash(self, message_hash, vrs=None, signature=None):
    hash_bytes = HexBytes(message_hash)
    if len(hash_bytes) != 32:
        raise ValueError("The message hash must be exactly 32-bytes")
    if vrs is not None:
        v, r, s = map(hexstr_if_str(to_int), vrs)
        v_standard = to_standard_v(v)
        signature_obj = self._keys.Signature(vrs=(v_standard, r, s))
    elif signature is not None:
        signature_bytes = HexBytes(signature)
        signature_bytes_standard = to_standard_signature_bytes(signature_bytes)
        signature_obj = self._keys.Signature(signature_bytes=signature_bytes_standard)
    else:
        raise TypeError("You must supply the vrs tuple or the signature bytes")
    pubkey = signature_obj.recover_public_key_from_msg_hash(hash_bytes)
    return pubkey.to_checksum_address()

Code Samples

Recovering address from the message and signature using wweb3.js (web3.eth.sign() and web3.eth.personal.ecRecover())

truffle(rinkeby)> accounts[0]
'0xb009cd53957c0D991CAbE184e884258a1D7b77D9'
truffle(rinkeby)> signature=await web3.eth.sign("We built this city.", accounts[0])
undefined
truffle(rinkeby)> signature
'0xfa02e8586f024c26dc34b262e2f768a3aba8b69d8d16b182d97e12d6a83fc0bf1bec454cdf875e77a26b82138e567a019cafe4310f3ebf7e64db19fb0e32d2db1b'
truffle(rinkeby)> acct=await web3.eth.personal.ecRecover("We built this city.", signature)
undefined
truffle(rinkeby)> acct
'0xb009cd53957c0d991cabe184e884258a1d7b77d9'
truffle(rinkeby)>

Using JavaScript

On Ethereum Layer 2

ZK-Rollups

ZK-Rollups

ZK-Rollups are one of the options being developed for layer 2 construction that increases scalability through mass transfer processing rolled into a single transaction.
Creating zero knowledge proofs requires a large amount of computing power.
The latency to block confirmation will increase because the SNARK proof will be delayed by a number of blocks.

Sidechains

This is sometimes referred to as a two-way peg. Since chains are independent of one another, resources are typically locked on one chain and minted(created) on another. When they are transferred back, they are burned(destroyed) and unlocked.

2-Way Peg

On NFT

Required features for assets
- offer/bidding
- lend/borrow
- buy/sell
- complex assets
- handprinting, tickering - my asset
- temporary, expiry
- locked
- categorized
- creator signature

>> Auction

On System Management

Production Systems Management Considerations

Don't use SSH users same with those on development or test environment.
Don't use SSH key/cert same with those on development or test environment.
Don't use sudoers

Don't use default port for system softwares or middle-wares.
Don't use default account for system softwares or middle-wares.
Close unnecessary ports.

On Blogging

Service	Description	Cost	Remarks
Medium
Wordpress.com
Tumblr
Ghost		Not Free
Wix

Writing Tumblr posts with Markdown (Sep 30, 2015)
Top 27 Tumblr Shortcuts to Navigate and Post Like a Pro (Windows and Mac) (11 Aug 2018)

Using Markdown in the Ghost editor - Full Markdown guide

Wix Answers Help Center Adding Markdown Text to an Article

On Finance

Concept	Description	Remark
Leverage	any technique involving the use of debt (borrowed funds) rather than fresh equity in the purchase of an asset, with the expectation that the after-tax profit to equity holders from the transaction will exceed the borrowing cost, frequently by several multiples⁠.
Margin	collateral that the holder of a financial instrument has to deposit with a counterparty (most often their broker or an exchange) to cover some or all of the credit risk the holder poses for the counterparty.
Position	the amount of a particular security, commodity or currency held or owned by a person or entity.	long position, short position, derivatives trading
Arbitrage	the practice of taking advantage of a price difference between two or more markets
Fungibility	the property of a good or a commodity whose individual units are essentially interchangeable, and each of its parts is indistinguishable from another part.	company shares, bonds, precious metals, currencies

Entry	Meaning	Position	Korean
Debit	a transfer of value to that account	right side	차변
Credit	a transfer of value from the account	left side	대변

Financial Instrument

Financial instrument
- monetary contracts between parties which can be created, traded, modified and settled.

Instrument	Description	Remark
Bond	an instrument of indebtedness of the bond issuer to the holders.	debt security
Loan	the lending of money by one or more individuals, organizations, or other entities to other individuals, organizations etc.
Deposit	any other type of bank account that allows money to be deposited and withdrawn by the account holder.

Margin

Margin (Wikipedia)

In finance, margin is the collateral that a holder of a financial instrument has to deposit with a counterparty (most often their broker or an exchange) to cover some or all of the credit risk the holder poses for the counterparty.

What Is Margin Trading? (13.01.2020)
- This ability to expand trading results makes margin trading especially popular in low-volatility markets, particularly the international Forex market. Still, margin trading is also used in stock, commodity, and cryptocurrency markets.
Margin (Jun 25, 2019)
Leverage (Mar 19, 2021)

MARGIN AND LEVERAGE EXPLIANED
- Trading on margin is used to increase an investor’s buying power.
The Relationship Between Margin and Leverage
- You use margin to create leverage.
Leveraging and Deleveraging

Model

initial margin              : A
initial margin-equity ratio : x  (예. 1.5, 2, ... 10)
equity drop ratio           : y   (예. 0.1, 0.2, ...)
loss                        : A * x * y
revised margin              : A * (1 - y)

margin-call at : loss = revised margin ---> A * x * y = A * (1 - y) ---> y = 1/(x + 1)

Concept	Formula	Remarks
Initial	$p_{0}\longrightarrow v_{0}=(1+\alpha )p_{0}$	$p_{0}$ : initial price, margin $v_{0}$ : initial value(volume) $\alpha$ : leverage factor
Current	$p\longrightarrow v=(1+\alpha )p=(1+\alpha )p_{0}(1+{\frac {p-p_{0}}{p_{0}}})=v_{0}(1+{\frac {d}{p_{0}}})$	$p$ : current price $v$ : current value(volume) $d$ : price delta (= $p-p_{0}$ )
Gain/Loss	$v-v_{0}=(1+\alpha )(p-p_{0})$
Loss Limit	$v_{0}-v_{t}=(1+\alpha )(p_{0}-p_{t})=(1+\beta )p_{0}$ $p_{t}={\frac {\alpha -\beta }{1+\alpha }}p_{0}$	$p_{t}$ : threshold price $\beta$ : minimum factor (< $\alpha$ )

Margin Calls

Concept	Formula	Remarks
Initial	$p_{0}=r_{0}v_{0}$ $b_{0}=v_{0}-p_{0}={\frac {1-r_{0}}{r_{0}}}p_{0}$	$p_{0}$ : margin $v_{0}$ : initial volume(value) $b_{0}$ : borrowed $r_{0}$ : initial margin requirement
Current	$v={\frac {p}{r_{0}}}$	$p$ : current price
Loss Limit	$v_{t}-b_{0}=r_{m}v_{t}$ $(1-r_{m})v_{t}=(1-r_{m}){\frac {p_{t}}{r_{0}}}=b_{0}={\frac {1-r_{0}}{r_{0}}}p_{0}$ $p_{t}={\frac {1-r_{0}}{1-r_{m}}}p_{0}$	$r_{m}$ : minimum(maintenance) margin requirement $p_{t}$ : threshold price (margin call)

ETF

ETF (Exchange-Traded Fund)
- a type of investment fund and exchange-traded product, i.e. they are traded on stock exchanges.
ETF (Korean)
The Comprehensive Guide to Understanding ETF

How ETFs work (Vanguard)
Authorized participants and market makers (BlackRock)
Who Are the ETF Giants? (Mar 22, 2021)
- BlackRock, The Vanguard Group, ...

Credit Card

Credit Card Authentication (Mar 16, 2018)
- Credit Card Transaction = Credit Card Authentication + Credit Card Authorization

What is a credit card network and how do they work? (April 12, 2020)
- The four major credit card networks in the U.S. are Visa, Mastercard, Discover and American Express.

Auction

Auction (Wikipedia)
Auction theory (Wikipedia)
Auction
Auctions

Glossary	Description	Remarks
Reserve Price	The minimum amount that a seller will accept as the winning bid	Reservation Price
Blind Auction	All bidders simultaneously submit sealed bids so that no bidder knows the bid of any other participant.	FPSBA(First-Price Sealed-Bid Auction)
Bid Price	a price for which somebody is willing to buy something, whether it be a security, asset, commodity, service, or contract.	offered price, ask price

Differentiating Open Auction, Private Auction & Preferred Deal
- Private auction is similar to open auction, except publishers restrict participation to selected advertisers only.

On Healthcare

Item	Description	Remarks
HL7 (Health Level 7)	a set of international standards for transfer of clinical and administrative data between software applications used by various healthcare providers.
FHIR (Fast Healthcare Interoperability Resources)	a standard describing data formats and elements (known as "resources") and an API for exchanging electronic health records (EHR)
SNOMED (Systematized Nomenclature of Medicine)	a systematic, computer-processable collection of medical terms, in human and veterinary medicine, to provide codes, terms, synonyms and definitions which cover anatomy, diseases, findings, procedures, microorganisms, substances, etc.

EMR

openEHR / EHR Information Model

FHIR

Medication

Resource	Description	Remarks
`MedicationRequest`	An order or request for both supply of the medication and the instructions for administration of the medication to a patient. a single medication.	medication prescription, medication order
`MedicationAdministration`	Describes the event of a patient consuming or otherwise being administered a medication.
`MedicationDispense`	Indicates that a medication product is to be or has been dispensed for a named person/patient. the result of a pharmacy system responding to a medication order.
`DiagnosticReport`	the set of information that is typically provided by a diagnostic service when investigations are complete.

misc

File abstraction

path, directory, name, extension
- path = directory + file-separator + name + '.' + extension

full-name = path
short-name = name + '.' + extension

Samples
- c:\windows\system32\kernel32.dll
  - path : c:\windows\system32\kernel32.dll
  - directory : c:\windows\system32
  - name : kernel32
  - extension : dll

References
- Filename (Wikipedia)
- java.nio.file.Path API
- java.io.File API

Message scheme

General message header

Item	Meaning	Value Space	Remarks
Start of message
Message type	the unique identifier for this type of message

Message mapping

Mapping rules
- unit rules
  - concatenation
    - concatenation of <emp>n</emp> items of source
  - split
    - split by index
    - split by delimiter
  - replacement
  - formatting
    - pre defined formatting
    - user defined formatting using formatt pattern
  - format conversion
    - pre defined conversion : eg) 2013/01/01 -> 2013-01-01
    - user defined - is it possible ?
    - two step : unformat and apply new format
  - arithmetic calculations
    - addition of two items
    - subtraction of two items
    - multiplication of item and constant number
    - division of item
  - logical calculations
  - code to code conversion
  - to boolean conversion : different from logical calculation ?
  - regex conversion : ?
- combined rules
- free-form using expression directly
  - how to validate

Mapping rule unit test case

Things you MUST know about DEBUGGING

Eclipse debugger
- How to setup debugging.
  - on server-side
  - on Eclipse
- How to start debugging.
  - when launched by Eclipse
  - when externally launched.
- How to make or delete break point.
- How to view static fields in the Variables view.
- How to view inherited fields in the Variable view.
- How to view only logical structure of collection or map objects.
- How to use Display view.
- What is stack trace and how to trace it.
- How to move forward.
  - resume, step into, step over, step return
- How to list breakpoints while debugging
- How to config debugging step filter.
- How to config debugging stack filter. Is it possible?
- How to change variable value and execute forward while debugging.
- How to add or remove breakpoints on-the-fly (while debugging).

General strategy and tactics on development environment

Source projects

Concepts
- portfolio = product+
- product = module+
  - module ~ package
- module = class+, resource+

Tactics
- Construct source project per module not product.
- Construct source repository per product.
  - Do not ...
  - Dependencies among products should be defined on binary repository, not source repository of dependent products.
- The structure of trunk and tag or release directory in source repository.
- Eclipse launcher and configuration
  - eclipse.bat and eclipse.ini under the trunk or the tag/0.0.0 directory.
  - JAVA_6_HOME, ECLIPSE_422_HOME
- Readme files
  - under the trunk or the tag/0.0.0 directory for Readme on scale of product.
  - under the per module Eclipse project directory for Readme on scale of module.
  - contents
    - requirement on environment. specially necessary environment variables and their meaning.

Configuration management

Naming environment variables, configuration property or variable placeholder
- an item (environment variable or configuration property) whose value is a directory should have a name that ends in _DIR or .dir and the value should have a trailing slash.
- an item whose data-type is boolean should have a name that includes ....
  - example ; ALLOWS_DELETE

Software Distributable Packaging

Concepts and terms

source, binary, resource
library, runtime
file types
- C/C++ : *.lib, *.dll, *.pdb, *.h
- Java : *.jar

Directory layout of deployed

JBoss AS 4.x directory structure
- bin, client, docs, lib, conf, data, log, tmp, work

UI(User Interface) design

Delete or Reset action should be reconfirmed by the user.
Internatiolization(i18n) or Localization(l10n) should be applied intrinsically for buttons, labels and titles.

Software development guideline

Guides source project layout
Guides selection of programming languages, software frameworks, and development tools
Guides coding convention
Guides design patterns and common libraries
Guides software build and packaging
Guides unit testing
Guides debugging
Guides static code analysis
Guides technical documentation
Provides boilerplate or scaffold artifacts

Blogging Service

Service	Cost	Remarks
WordPress	Free
Blogger	Free	Goggled
Medium	Free/Paid
Tumblr	Free
Wix
Ghost	Paid

10 Best Tumblr Alternatives You Can Use (February 25, 2020)
- WordPress, Blogger, Soup, Medium, Mastodon, Posthaven, Ghost, Typepad
17 Best Tumblr Alternatives in 2020 for Creators and Bloggers (Aug 13, 2020)
- WordPress, Ghost, ShareSome, Wix, Pinterest

PC Optimization

Disable services

Disable auto-starts

Disable auto-updates
- Google auto-update
- Notepad ++ auto-update
- Hancom auto-update

Inceptions and Inspirations

Gurus and Readings

Gurus

Books

Articles

On Java

Basic

Guidelines for Designing API

Using Pattern

Core Patterns

Builder Pattern

Examples

Concurrency

Formatting, conversion and validating of string, number or date type data

Available packages

Available utilities by case

General data container model

On Hadoop

Interesting point

Leading products analysis

Cloudera Manager

Related topics

Requisite

On OpenShift

Background

Pain-point

Expectation

Workflow

Concepts

Commands

Questions

Necessary Cartridges

Front-end

On Hyperledger Fabric

Provisioning scripts design

Architecture decision

On OpenCV

IplImage Anatomy

References

On Red5

RTMPClient

On VirtualBox

Tips for CentOS on VirtualBox

On Docker

Key Concerns

Strategys and Tactics

On Redmine

Customization

Target files

Custom style

On TestLink

Installation

Overview

Procedure

On Solidity

Compiler

The return of solc.compile function

Smart Contract

On Ethereum Signing

Using Python

Code Samples

Using JavaScript

On Ethereum Layer 2

ZK-Rollups

Sidechains

2-Way Peg

On NFT

On System Management

Production Systems Management Considerations

On Blogging

On Finance

Financial Instrument

Margin

Model

ETF

Credit Card

Auction

On Healthcare

EMR

FHIR

The return of `solc.compile` function