Angel's Blog 2026-04-14T09:15:30Z Angel Copyright 2026, Angel SPHPBLOG JAVA: Initializing Spring Boot Application angelcool@lolcahost:~/code-learning/Java/spring-boot$ date
Sun Jun 1 12:30:32 PM PDT 2025
angelcool@lolcahost:~/code-learning/Java/spring-boot$ pwd
/home/angelcool/code-learning/Java/spring-boot

# INITIALIZE APPLICATION
angelcool@lolcahost:~/code-learning/Java/spring-boot$ spring init -a my-demo -l java --build maven -x my-demo
Using service at https://start.spring.io
Project extracted to '/home/angelcool/code-learning/Java/spring-boot/my-demo'
angelcool@lolcahost:~/code-learning/Java/spring-boot$

# INSTALL MAVEN
angelcool@localhost:~/code-learning/Java/spring-boot/my-demo$ sudo dnf install maven
...
angelcool@localhost:~/code-learning/Java/spring-boot/my-demo$ mvn --version
Apache Maven 3.9.6 (Red Hat 3.9.6-7)
...

# RUN APPLICATION, NOTE: I think I had to update the artifactId in pom.xml to 'spring-boot-starter-web'
angelcool@localhost:~/code-learning/Java/spring-boot/my-demo$ mvn spring-boot:run
...

# MAKE REQUEST
angelcool@localhost:~/code-learning/Java/spring-boot/my-demo$ http http://localhost:8080/coffees
HTTP/1.1 200
Connection: keep-alive
Content-Type: application/json
Date: Mon, 02 Jun 2025 03:13:46 GMT
Keep-Alive: timeout=60
Transfer-Encoding: chunked

[
{
"id": "3d1256a7-c5c8-4a9b-9ef3-60da3107b06b",
"name": "Black"
},
{
"id": "7fc475b2-7c39-4412-baeb-6ac01f46128c",
"name": "French Vanilla"
},
{
"id": "690c16af-3931-4dbd-b573-a9d8c86e0a3c",
"name": "Hazelnut"
}
]

# SOURCE CODE
angelcool@localhost:~/code-learning/Java/spring-boot/my-demo$ cat src/main/java/com/example/my_demo/DemoApplication.java
package com.example.my_demo;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
// import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
// import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestController;
// import org.springframework.ui.Model;
import java.util.ArrayList;
import java.util.List;
import org.springframework.web.bind.annotation.RequestMethod;
import java.util.UUID;

@SpringBootApplication
public class DemoApplication {

public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}

class Coffee {
private final String id;
private String name;

public Coffee(String id, String name) {
this.id = id;
this.name = name;
}

public Coffee (String name) {
this(UUID.randomUUID().toString(),name);
}

public String getId(){
return this.id;
}

public String getName(){
return this.name;
}

public void setName(String name){
this.name = name;
}
}

@RestController
class RestApiController{
private List<Coffee> coffees = new ArrayList<>();

public RestApiController(){
this.coffees.addAll(List.of(
new Coffee("Black"),
new Coffee("French Vanilla"),
new Coffee("Hazelnut")
));
}

@RequestMapping(value = "/coffees", method = RequestMethod.GET)
Iterable<Coffee> getCoffees() {
return this.coffees;
}
}
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry250602-032204 2025-06-02T00:00:00Z 2025-06-02T00:00:00Z Java: Installing Spring Boot CLI angelcool@localhost:~$
angelcool@localhost:~$ date
Sat May 31 04:57:16 PM PDT 2025
angelcool@localhost:~$ cat /etc/redhat-release
Fedora release 41 (Forty One)
angelcool@localhost:~$
# INSTALL SDKMAN
angelcool@localhost:~$ curl -s "https://get.sdkman.io" | bash
...
# CHECK SDKMAN VERSION
angelcool@localhost:~$ sdk version

SDKMAN!
script: 5.19.0
native: 0.7.4 (linux x86_64)

# INSTALL SPRING BOOT CLI
angelcool@localhost:~$ sdk install springboot
...
# CHECK SPRING BOOT CLI VERSION
angelcool@localhost:~$ spring --version
Spring CLI v3.5.0
angelcool@localhost:~$
angelcool@localhost:~$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry250601-000603 2025-06-01T00:00:00Z 2025-06-01T00:00:00Z Using GNU comm to compare sorted files line by line. 
angelcool@fedora-laptop$cat FILE1.txt 
1
2
3
4
5
5
angelcool@fedora-laptop$cat FILE2.txt 
1
2
3
4
5
6
7
8
9
angelcool@fedora-laptop$comm -13 <(sort FILE1.txt|uniq) <(sort FILE2.txt|uniq)
6
7
8
9
angelcool@fedora-laptop$ man comm
...
       Compare sorted files FILE1 and FILE2 line by line.

       When FILE1 or FILE2 (not both) is -, read standard input.

       With  no  options,  produce three-column output.  Column one contains lines unique to FILE1, column two con‐
       tains lines unique to FILE2, and column three contains lines common to both files.

       -1     suppress column 1 (lines unique to FILE1)

       -2     suppress column 2 (lines unique to FILE2)

       -3     suppress column 3 (lines that appear in both files)

       --check-order
              check that the input is correctly sorted, even if all input lines are pairable

       --nocheck-order
              do not check that the input is correctly sorted

       --output-delimiter=STR
              separate columns with STR

       --total
              output a summary

       -z, --zero-terminated
              line delimiter is NUL, not newline

       --help display this help and exit

       --version
              output version information and exit

       Note, comparisons honor the rules specified by 'LC_COLLATE'.
...
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry241218-034133 2024-12-18T00:00:00Z 2024-12-18T00:00:00Z Java: My First Servlet angelcool@fedora-laptop$date
Sat Nov 23 05:57:16 PM PST 2024
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$java --version
openjdk 17.0.13 2024-10-15
OpenJDK Runtime Environment (Red_Hat-17.0.13.0.11-1) (build 17.0.13+11)
OpenJDK 64-Bit Server VM (Red_Hat-17.0.13.0.11-1) (build 17.0.13+11, mixed mode, sharing)
angelcool@fedora-laptop$jar --version
jar 17.0.13
angelcool@fedora-laptop$
angelcool@fedora-laptop$pwd
/home/angelcool/java-practice/HelloWorldServlet
angelcool@fedora-laptop$tree
.
├── deploy
│   └── helloworld.war
├── Notes.txt
├── src
│   ├── HelloWorld.class
│   └── HelloWorld.java
└── web
└── WEB-INF
├── classes
│   └── com
│   └── coolwriter
│   └── helloworld
│   └── HelloWorld.class
└── web.xml

9 directories, 6 files
angelcool@fedora-laptop$
angelcool@fedora-laptop$cat Notes.txt
# Compile java class, this will create HelloWorld.class
angelcool@fedora-laptop$javac --class-path /usr/share/tomcat/lib/tomcat-servlet-api.jar src/HelloWorld.java

# Copy compiled .class file to WEB-INF
angelcool@fedora-laptop$cp src/HelloWorld.class web/WEB-INF/classes/com/coolwriter/helloworld/

# Create WAR file
angelcool@fedora-laptop$jar cvf deploy/helloworld.war -C web .

# Move WAR file to Tomcat webapps directory
angelcool@fedora-laptop$sudo cp deploy/helloworld.war /usr/share/tomcat/webapps/

# Reload servlet in /manager page ( or restart Tomcat I think )

# Access servlet: http://localhost:8080/helloworld/Hello
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$cat web/WEB-INF/web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="4.0" xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web- ... ">

<display-name>Hello World!</display-name>

<servlet>
<servlet-name>helloworld</servlet-name>
<servlet-class>com.coolwriter.helloworld.HelloWorld</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>helloworld</servlet-name>
<url-pattern>/Hello</url-pattern>
</servlet-mapping>

</web-app>
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$cat src/HelloWorld.java
package com.coolwriter.helloworld;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

public class HelloWorld extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");

PrintWriter out = response.getWriter();

String msg = this.getGreeting();

out.println(msg);
}

private String getGreeting()
{
String msg = null;

int rand = (int) (Math.random() * (6)) +1;

switch (rand) {
case 1:
msg = "Hello There!";
break;
case 2:
msg = "Hello Friend!";
break;
case 3:
msg = "Hello Stranger!";
break;
case 4:
msg = "Hello! My name is Angel!";
break;
default:
msg = "Hello World!";
}

return msg;
}
}
angelcool@fedora-laptop$
angelcool@fedora-laptop$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry241124-015310 2024-11-24T00:00:00Z 2024-11-24T00:00:00Z Java: Installing Tomcat in Fedora 39 angelcool@fedora-laptop$date
Sat Nov 23 12:00:14 PM PST 2024
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$cat /etc/redhat-release
Fedora release 39 (Thirty Nine)
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$dnf info tomcat
Last metadata expiration check: 0:42:59 ago on Sat 23 Nov 2024 11:18:54 AM PST.
Installed Packages
Name : tomcat
Epoch : 1
Version : 9.0.96
Release : 1.fc39
Architecture : noarch
Size : 323 k
Source : tomcat-9.0.96-1.fc39.src.rpm
Repository : @System
From repo : updates
Summary : Apache Servlet/JSP Engine, RI for Servlet 4.0/JSP 2.3 API
URL : http://tomcat.apache.org/
License : ASL 2.0
Description : Tomcat is the servlet container that is used in the official Reference
: Implementation for the Java Servlet and JavaServer Pages technologies.
: The Java Servlet and JavaServer Pages specifications are developed by
: Sun under the Java Community Process.
:
: Tomcat is developed in an open and participatory environment and
: released under the Apache Software License version 2.0. Tomcat is intended
: to be a collaboration of the best-of-breed developers from around the world.

angelcool@fedora-laptop$
angelcool@fedora-laptop$sudo dnf install tomcat
...
angelcool@fedora-laptop$sudo dnf install tomcat-admin-webapps
...
angelcool@fedora-laptop$sudo dnf install tomcat-docs-webapp
...
angelcool@fedora-laptop$sudo systemctl start tomcat.service
...

Enable admin user, uncomment the following in /etc/tomcat/tomcat-users.xml
<role rolename="admin"/>
<role rolename="admin-gui"/>
<role rolename="admin-script"/>
<role rolename="manager"/>
<role rolename="manager-gui"/>
<role rolename="manager-script"/>
<role rolename="manager-jmx"/>
<role rolename="manager-status"/>
<user name="admin" password="admin" roles="admin,manager,admin-gui,admin-script,manager-gui,manager-script,manager-jmx,manager-status" />


Restart server and go to: http://localhost:8080/manager/html

For reference:
angelcool@fedora-laptop$
angelcool@fedora-laptop$tree /usr/share/tomcat/webapps/
/usr/share/tomcat/webapps/
├── host-manager
│   ├── css
│   │   └── manager.css
│   ├── images
│   │   ├── asf-logo.svg
│   │   └── tomcat.svg
│   ├── index.jsp
│   ├── META-INF
│   │   └── context.xml
│   └── WEB-INF
│       ├── jsp
│       │   ├── 401.jsp
│       │   ├── 403.jsp
│       │   └── 404.jsp
│       ├── manager.xml
│       └── web.xml
└── manager
    ├── css
    │   └── manager.css
    ├── images
    │   ├── asf-logo.svg
    │   └── tomcat.svg
    ├── index.jsp
    ├── META-INF
    │   └── context.xml
    ├── status.xsd
    ├── WEB-INF
    │   ├── jsp
    │   │   ├── 401.jsp
    │   │   ├── 403.jsp
    │   │   ├── 404.jsp
    │   │   ├── connectorCerts.jsp
    │   │   ├── connectorCiphers.jsp
    │   │   ├── connectorTrustedCerts.jsp
    │   │   ├── sessionDetail.jsp
    │   │   └── sessionsList.jsp
    │   └── web.xml
    └── xform.xsl

13 directories, 26 files
angelcool@fedora-laptop$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry241123-202018 2024-11-23T00:00:00Z 2024-11-23T00:00:00Z Miscellaneous Notes 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ date
Sat 06 Jul 2024 04:44:24 PM PDT
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli --version
redis-cli 5.0.7
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### Find out node's role
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7000 INFO|grep role
role:master
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### If node is master...
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7000 INFO|grep slave0
slave0:ip=127.0.0.1,port=7005,state=online,offset=7532,lag=0
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### Verify this node is slave...
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7005 INFO|grep role
role:slave
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### Find out node's master...
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7005 INFO | egrep "master_(host|port)"
master_host:127.0.0.1
master_port:7000
acool@acool-HP-EliteBook-8440p:~/redis-cluster$
acool@acool-HP-EliteBook-8440p:~/redis-cluster$
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### Find out node's mode...
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7003 INFO | egrep mode
redis_mode:cluster
acool@acool-HP-EliteBook-8440p:~/redis-cluster$  ###  List all cluster nodes
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7004 CLUSTER NODES
99f95692421cd04661c93ef9f09e058a7a80a6e4 127.0.0.1:7002@17002 master - 0 1720310325000 3 connected 10923-16383
8589237392750f2df8618bcda4e92e3996dda07a 127.0.0.1:7005@17005 slave 02c090059770ba140c14a1f26a16b3457fd58bf1 0 1720310324000 6 connected
c53fa6a32d9646c21549346716f01a5147cb8bb9 127.0.0.1:7001@17001 master - 0 1720310325468 2 connected 5461-10922
02c090059770ba140c14a1f26a16b3457fd58bf1 127.0.0.1:7000@17000 master - 0 1720310325000 1 connected 0-5460
ed206ea99f372d34dee37433b7747b5f2b2a3a40 127.0.0.1:7003@17003 slave c53fa6a32d9646c21549346716f01a5147cb8bb9 0 1720310325567 4 connected
05fe8b609e4b13d0510ed9b32b27b84502898595 127.0.0.1:7004@17004 myself,slave 99f95692421cd04661c93ef9f09e058a7a80a6e4 0 1720310323000 5 connected
acool@acool-HP-EliteBook-8440p:~/redis-cluster$
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### This command seems to run INFO in all cluster nodes...                
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli --cluster call 127.0.0.1:7000 INFO|grep role
role:master
role:master
role:slave
role:slave
role:slave
role:master
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ### monitor node
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7005 monitor
...

Find out data directory and config path:
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ ####### FIND PATH for rdb AND aof FILES!!!! #######
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli -c -p 7000 CONFIG GET dir
1) "dir"
2) "/home/acool/redis-cluster/7000"
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli --cluster call 127.0.0.1:7000 CONFIG GET dir
>>> Calling CONFIG GET dir
127.0.0.1:7000: dir
/home/acool/redis-cluster/7000
127.0.0.1:7001: dir
/home/acool/redis-cluster/7001
127.0.0.1:7004: dir
/home/acool/redis-cluster/7004
127.0.0.1:7005: dir
/home/acool/redis-cluster/7005
127.0.0.1:7003: dir
/home/acool/redis-cluster/7003
127.0.0.1:7002: dir
/home/acool/redis-cluster/7002
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ 
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ redis-cli --cluster call 127.0.0.1:7000 INFO | grep -i config_file
...
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240706-235032 2024-07-06T00:00:00Z 2024-07-06T00:00:00Z Valkey Cluster Demo [acool@localhost ~]$ date
Fri Jul 5 01:48:53 PM PDT 2024
[acool@localhost ~]$ cat /etc/redhat-release
Fedora release 38 (Thirty Eight)
[acool@localhost ~]$ sudo dnf install valkey
...
[acool@localhost ~]$ valkey-cli --version
valkey-cli 7.2.4
[acool@localhost ~]$
[acool@localhost ~]$ # just in case...
[acool@localhost ~]$ systemctl stop valkey.service
[acool@localhost ~]$ systemctl status valkey.service
...
[acool@localhost ~]$ which valkey-server
/usr/bin/valkey-server
[acool@localhost ~]$
[acool@localhost ~]$ mkdir valkey-cluster-demo
[acool@localhost ~]$ cd valkey-cluster-demo/
[acool@localhost valkey-cluster-demo]$ vim valkey.conf
...
[acool@localhost valkey-cluster-demo]$ cat valkey.conf
port 7000
cluster-enabled yes
cluster-config-file nodes.conf
cluster-node-timeout 5000
appendonly yes
[acool@localhost valkey-cluster-demo]$
[acool@localhost valkey-cluster-demo]$ mkdir cluster-test
[acool@localhost valkey-cluster-demo]$ cd cluster-test/
[acool@localhost cluster-test]$ mkdir -p {7000..7005}
[acool@localhost cluster-test]$ for i in {7000..7005}; do cp ../valkey.conf $i; done
[acool@localhost cluster-test]$ # open 7 tabs, update ports and start servers
[acool@localhost cluster-test]$ # TIP to update ports: for i in {0..5}; do sed -i 's/7000/700'"$i"'/g' "700$i/redis.conf" ; done
[acool@localhost cluster-test]$ cd 7000/
[acool@localhost 7000]$ /usr/bin/valkey-server ./valkey.conf
...
[acool@localhost valkey-cluster-demo] # create cluster
[acool@localhost valkey-cluster-demo]$ valkey-cli --cluster create 127.0.0.1:7000 127.0.0.1:7001 127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:7004 127.0.0.1:7005 --cluster-replicas 1
...
[acool@localhost valkey-cluster-demo]$ valkey-cli -p 7000 cluster nodes
384d585df521f8588a03b57a38e871549c0e58c4 127.0.0.1:7001@17001 master - 0 1720214911355 2 connected 5461-10922
5d2edcbba8f394a612df5253bd19a9399f97f4ff 127.0.0.1:7002@17002 master - 0 1720214912358 3 connected 10923-16383
4cf4150f20ae444422f0dabbc29b0a75878b1a2d 127.0.0.1:7004@17004 slave c88d6bea070f64023a2c7f27831bbbd113b2ff03 0 1720214912000 1 connected
e40a58e318f277ce2d420f7cb77480d5643c28c4 127.0.0.1:7005@17005 slave 384d585df521f8588a03b57a38e871549c0e58c4 0 1720214913362 2 connected
c88d6bea070f64023a2c7f27831bbbd113b2ff03 127.0.0.1:7000@17000 myself,master - 0 1720214912000 1 connected 0-5460
5b13cd8e34b47890e88fb48e30a99174ba19b751 127.0.0.1:7003@17003 slave 5d2edcbba8f394a612df5253bd19a9399f97f4ff 0 1720214911354 3 connected
[acool@localhost valkey-cluster-demo]$
[acool@localhost valkey-cluster-demo]$
[acool@localhost valkey-cluster-demo]$ # To connect to Valkey Cluster, you'll need a cluster-aware Valkey client...
[acool@localhost valkey-cluster-demo]$ # ...store some keys
[acool@localhost valkey-cluster-demo]$ valkey-cli -c -p 7000
127.0.0.1:7000> set firstname Angel
-> Redirected to slot [7108] located at 127.0.0.1:7001
OK
127.0.0.1:7001> set lastname Cool
OK
127.0.0.1:7001>exit
[acool@localhost valkey-cluster-demo]$
[acool@localhost valkey-cluster-demo]$ # Retrive some keys
[acool@localhost valkey-cluster-demo]$ valkey-cli -c -p 7005
127.0.0.1:7005> get lastname
-> Redirected to slot [7726] located at 127.0.0.1:7001
"Cool"
127.0.0.1:7001> get firstname
"Angel"
127.0.0.1:7001>exit
[acool@localhost valkey-cluster-demo]$
[acool@localhost valkey-cluster-demo]$

TIP: Easy way to start all servers:
acool@acool-HP-EliteBook-8440p:~/redis-cluster$ for i in {0..5}; do  cd /home/acool/redis-cluster/700$i && /usr/bin/redis-server redis.conf --daemonize yes; done


Bonus: Pub/Sub demo

[acool@localhost valkey-cluster-demo]$ # TERMINAL 1
[acool@localhost valkey-cluster-demo]$ valkey-cli -c -p 7001
127.0.0.1:7001> SUBSCRIBE channel-a
...
[acool@localhost valkey-cluster-demo]$ # TERMINAL 2
[acool@localhost valkey-cluster-demo]$ valkey-cli -c -p 7002
127.0.0.1:7002> SUBSCRIBE channel-b
...

[acool@localhost valkey-cluster-demo]$ # TERMINAL 3
[acool@localhost valkey-cluster-demo]$ valkey-cli -c -p 7000
127.0.0.1:7000> PUBLISH channel-a "Hello channel a!"
(integer) 0
127.0.0.1:7000> PUBLISH channel-b "Hello channel b!"
(integer) 0
127.0.0.1:7000> 
127.0.0.1:7000> exit
[acool@localhost valkey-cluster-demo]$ # Monitor output in TERMINAL 1 and 2
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240705-213550 2024-07-05T00:00:00Z 2024-07-05T00:00:00Z Elixir: Making Concurrent API Calls angelcool@fedora-laptop$
angelcool@fedora-laptop$date
Fri Apr 12 07:51:16 PM PDT 2024
angelcool@fedora-laptop$ls lib/
coolprogram.ex coordinator.ex worker.ex
angelcool@fedora-laptop$cat lib/coolprogram.ex
defmodule CoolProgram do
def temperature_of(cities) do
coordinator_pid = spawn(CoolProgram.Coordinator, :loop, [[], Enum.count(cities)])
cities |> Enum.each(fn city ->
worker_pid = spawn(CoolProgram.Worker, :loop, [])
send(worker_pid, {coordinator_pid, city})
end)
end
end
angelcool@fedora-laptop$cat lib/coordinator.ex
defmodule CoolProgram.Coordinator do

def loop(results \\ [], results_expected) do
receive do
{:ok, result} ->
new_results = [result|results]
if results_expected == Enum.count(new_results) do
send(self(), :exit)
end
loop(new_results, results_expected)
:exit ->
IO.puts(results |> Enum.sort |> Enum.join(", "))
_->
loop(results, results_expected)
end
end

end
angelcool@fedora-laptop$cat lib/worker.ex
defmodule CoolProgram.Worker do

def temperature_of(location) do
result = url_for(location)
|> HTTPoison.get
|> parse_response
case result do
{:ok, temp} ->
"#{location}: #{temp}° C"
:error ->
"#{location} not found"
end
end

defp url_for(location) do
location = URI.encode(location)
"http://api.openweathermap.org/data/2.5/weather?q=#{location}&appid=#{apikey()}"
end

defp parse_response({:ok, %HTTPoison.Response{body: body, status_code: 200}}) do
body
|> JSON.decode!
|> compute_temperature()
end

defp parse_response(_) do
:error
end

defp compute_temperature(json) do
try do
temp = (json["main"]["temp"]-273.15)
|> Float.round(1)
{:ok, temp}
rescue
_-> :error
end
end

defp apikey do
"XXXXXXXXXXXXXXXXXXXXXXXXXXXX"
end

def loop do
receive do
{sender_pid, location}->
send(sender_pid, {:ok, temperature_of(location)})
_->
IO.puts "don't know how to process this message"
end
loop()
end
end
angelcool@fedora-laptop$
angelcool@fedora-laptop$iex --version
IEx 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$iex -S mix
Compiling 1 file (.ex)
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.7) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> cities=["San Diego", "Merida", "Singapore", "Los Angeles", "Mexico City", "Miami", "Temecula", "Buenos Aires", "Ojai" ]
["San Diego", "Merida", "Singapore", "Los Angeles", "Mexico City", "Miami",
"Temecula", "Buenos Aires", "Ojai"]
iex(2)> CoolProgram.temperature_of(cities)
:ok
Buenos Aires: 17.0° C, Los Angeles: 14.7° C, Merida: 25.0° C, Mexico City: 22.8° C, Miami: 22.0° C, Ojai: 14.2° C, San Diego: 15.2° C, Singapore: 30.8° C, Temecula: 13.1° C
iex(3)>
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240413-024712 2024-04-13T00:00:00Z 2024-04-13T00:00:00Z Elixir: Miscellaneous Notes # Filtering files in a directory by filename
angelcool@fedora-laptop$date
Fri Apr 12 12:02:42 PM PDT 2024
angelcool@fedora-laptop$iex
...
iex(90)> "/home/angelcool/Downloads" \
...(90)> |> Path.join("**/*.rpm") \
...(90)> |> Path.wildcard \
...(90)> |> Enum.filter(fn fname -> String.contains?(Path.basename(fname),"dbeaver") end)
["/home/angelcool/Downloads/dbeaver-ce-24.0.2-stable.x86_64.rpm"]

# Making an HTTP GET request
iex(18)> :inets.start()
:ok
iex(19)> :ssl.start()
:ok
iex(20)> :httpc.request(:get, {'https://www.angelcool.net', []}, [ssl: :httpc.ssl_verify_host_options(true)], [])
...
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240412-190002 2024-04-12T00:00:00Z 2024-04-12T00:00:00Z Elixir: Clustering Elixir Nodes - Updating Shared State.
angelcool@fedora-laptop$ # Let's get the date and versions used
angelcool@fedora-laptop$date
Sat Apr 6 11:51:08 AM PDT 2024
angelcool@fedora-laptop$iex --version
IEx 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$mix --version
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Mix 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$mix phx.new --version
Phoenix installer v1.7.11
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$
angelcool@fedora-laptop$ # The gist of this post...
angelcool@fedora-laptop$
angelcool@fedora-laptop$ # Terminal 1
angelcool@fedora-laptop$ iex --name a@127.0.0.1
iex(a@127.0.0.1)1>

angelcool@fedora-laptop$ #Terminal 2
angelcool@fedora-laptop$ iex --name b@127.0.0.1
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.7) - press Ctrl+C to exit (type h() ENTER for help)
iex(b@127.0.0.1)1> Node.connect :"a@127.0.0.1"
true
iex(b@127.0.0.1)2> Node.list
[:"a@127.0.0.1"]
iex(b@127.0.0.1)3>

# Terminal 1
iex(a@127.0.0.1)> Agent.start(
fn -> %{hello: "world"} end,
name: {:global, GlobalAgent}
)
{:ok, #PID<0.116.0>}

# Terminal 2
iex(b@127.0.0.1)4> Agent.get {:global,GlobalAgent}, &(&1)
%{hello: "world"}

# Terminal 2 - Update state
iex(b@127.0.0.1)5> Agent.update {:global, GlobalAgent}, fn _ -> %{hello: "everyone!"} end
:ok
iex(b@127.0.0.1)6>

# Terminal 2 - Get new state
iex(b@127.0.0.1)6> Agent.get {:global,GlobalAgent}, &(&1)
%{hello: "everyone!"}

# Terminal 1 - Get new state
iex(a@127.0.0.1)2> Agent.get {:global,GlobalAgent}, &(&1)
%{hello: "everyone!"}]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240406-184727 2024-04-06T00:00:00Z 2024-04-06T00:00:00Z Elixir: Processes Talking Amongst Themselves angelcool@fedora-laptop$date
Tue Apr 2 11:31:57 AM PDT 2024
angelcool@fedora-laptop$mix new process-demo --app process_a
* creating README.md
* creating .formatter.exs
* creating .gitignore
* creating mix.exs
* creating lib
* creating lib/process_a.ex
* creating test
* creating test/test_helper.exs
* creating test/process_a_test.exs

Your Mix project was created successfully.
You can use "mix" to compile it, test it, and more:

cd process-demo
mix test

Run "mix help" for more commands.
angelcool@fedora-laptop$
angelcool@fedora-laptop$cd process-demo/
angelcool@fedora-laptop$ls -l
total 8
drwxr-xr-x. 1 angelcool angelcool 24 Apr 2 11:31 lib
-rw-r--r--. 1 angelcool angelcool 575 Apr 2 11:31 mix.exs
-rw-r--r--. 1 angelcool angelcool 476 Apr 2 11:31 README.md
drwxr-xr-x. 1 angelcool angelcool 66 Apr 2 11:31 test
angelcool@fedora-laptop$
angelcool@fedora-laptop$cat lib/process_a.ex
defmodule ProcessA do
def receiverA(count) do
receive do
{from, message} -> send(from, {"Greetings from ProcessA!.", message})
receiverA(count+1)
end
end
end
angelcool@fedora-laptop$cat lib/process_b.ex
defmodule ProcessB do
def initialize do
pid_A = spawn(ProcessA, :receiverA, [1])
recieverB(pid_A)
end

def recieverB(pid_A) do
receive do
{message} ->
send(pid_A, {self(), message})
recieverB(pid_A)
{response, originalmessage} ->
IO.puts("Response: #{response}")
IO.puts("Original Message: #{originalmessage}")
recieverB(pid_A)
end
end
end
angelcool@fedora-laptop$
angelcool@fedora-laptop$iex --version
IEx 1.15.7 (compiled with Erlang/OTP 26)
angelcool@fedora-laptop$
angelcool@fedora-laptop$mix phx.new --version
Phoenix installer v1.7.11
angelcool@fedora-laptop$
angelcool@fedora-laptop$iex -S mix
Compiling 2 files (.ex)
Generated process_a app
Erlang/OTP 26 [erts-14.2.2] [source] [64-bit] [smp:16:16] [ds:16:16:10] [async-threads:1] [jit:ns]

Interactive Elixir (1.15.7) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> pid_B = spawn(ProcessB, :initialize, [])
#PID<0.166.0>
iex(2)> send(pid_B, {"Hi! This is a message from process B!"})
Response: Greetings from ProcessA!.
{"Hi! This is a message from process B!"}
Original Message: Hi! This is a message from process B!
iex(3)> ]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240402-184103 2024-04-02T00:00:00Z 2024-04-02T00:00:00Z Iperf - 1000BASE-LX SMF LC/LC Fiber Link Speed Test 

angelcool@2603-8000-6a00-5748-xxxx-xxxx-xxxx-xxxx:~$ date
Sun Mar  3 02:04:35 PM PST 2024

#IPv4
angelcool@2603-8000-6a00-5748-xxxx-xxxx-xxxx-xxxx:~$ iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
[  1] local 192.168.1.184 port 5001 connected with 192.168.1.192 port 57642 (icwnd/mss/irtt=14/1448/515)
[ ID] Interval       Transfer     Bandwidth
[  1] 0.00-10.01 sec  1.10 GBytes   941 Mbits/sec
angelcool@2603-8000-6a00-5748-xxxx-xxxx-xxxx-xxxx:~$
angelcool@2603-8000-6a00-5748-xxxx-xxxx-xxxx-xxxx:~$

# IPv6
angelcool@2603-8000-6a00-5748-xxxx-xxxx-xxxx-xxxx:~$ iperf -s -V
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
[  1] local 2603:8000:6a00:5748:xxxx:xxxx:xxxx:xxxx port 5001 connected with 2603:8000:6a00:5748:xxxx:xxxx:xxxx:xxxx port 56868 (icwnd/mss/irtt=13/1428/460)
[ ID] Interval       Transfer     Bandwidth
[  1] 0.00-10.02 sec  1.08 GBytes   928 Mbits/sec
angelcool@2603-8000-6a00-5748-xxxx-xxxx-xxxx-xxxx:~$


HOST B - CLIENT

acool@localhost ~]$
# IPv4
[acool@localhost ~]$ iperf -c 192.168.1.184
------------------------------------------------------------
Client connecting to 192.168.1.184, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  1] local 192.168.1.192 port 57642 connected with 192.168.1.184 port 5001 (icwnd/mss/irtt=14/1448/731)
[ ID] Interval       Transfer     Bandwidth
[  1] 0.00-10.02 sec  1.10 GBytes   940 Mbits/sec

# IPv6
[acool@localhost ~]$ iperf -c 2603:8000:6a00:xxxx:xxxx:xxxx:xxxx
------------------------------------------------------------
Client connecting to 2603:8000:6a00:xxxx:xxxx:xxxx:xxxx, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  1] local 2603:8000:6a00:5748:: port 56868 connected with 2603:8000:6a00:5748:xxxx:xxxx:xxxx:xxxx port 5001 (icwnd/mss/irtt=13/1428/783)
[ ID] Interval       Transfer     Bandwidth
[  1] 0.00-10.02 sec  1.08 GBytes   928 Mbits/sec
[acool@localhost ~]$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry240303-221911 2024-03-03T00:00:00Z 2024-03-03T00:00:00Z SSL/TLS: Wildcard Certificate Generation 
# Create root CA
[acool@localhost tls]$openssl req --x509 --nodes --days 3650 --newkey rsa:2048 --keyout ENT-CA.key --out ENT-CA.crt

# Crate new key and signing request (Tip: remove --aes256 to remove passphrase requirement... I think)
Passphrase: mypassphrase
[acool@localhost tls]$openssl genrsa --out star-dev-localhost.key --aes256 2048
[acool@localhost tls]$openssl req --new --key star-dev-localhost.key --out star-dev-localhost.csr

# Sign request
[acool@localhost tls]$openssl x509 --req --in star-dev-localhost.csr --CA ENT-CA.crt --CAkey ENT-CA.key --CAcreateserial --days 3650 --sha256 --extfile star-dev-localhost.cnf --out star-dev-localhost.crt

# remove passphrase
[acool@localhost tls]$openssl rsa --in star-dev-localhost.key --out star-dev-localhost-nopassphrase.key

[acool@localhost tls]$ cat star-dev-localhost.cnf 
authorityKeyIdentifier = keyid,issuer
basicConstraints = CA:FALSE
keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
subjectAltName = @alt_names

[alt_names]
DNS.1 = *.dev.localhost
[acool@localhost tls]$
[acool@localhost tls]


# finally, import ENT-CA.crt certificate in Chrome
# chrome://settings/certificates


Configure Nginx:
...
listen 443 ssl;
ssl_certificate /etc/ssl/certs/star-dev-localhost.crt;
ssl_certificate_key /etc/ssl/certs/star-dev-localhost-nopassphrase.key;
...
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry231116-031450 2023-11-16T00:00:00Z 2023-11-16T00:00:00Z C 101: Foreach loop macro [acool@localhost ~]$
[acool@localhost ~]$ date
Mon Apr 3 11:17:50 AM PDT 2023
[acool@localhost ~]$
[acool@localhost ~]$ cat c-foreach-macro.c
#include <stdio.h>

#define foreach(item, array) \
for(int keep = 1, \
count = 0,\
size = sizeof (array) / sizeof *(array); \
keep && count != size; \
keep = !keep, count++) \
for(item = (array) + count; keep; keep = !keep)

int main()
{
int mynumbers[] = {5,20,35,62,8,74,89};

char mygreeting[] = {"Hello world!"};

float myfloats[] = {1.6,6.9,5.8,43.5,1.1,0.9};

foreach(int *v, mynumbers) {
printf("value: %d\n", *v);
}

foreach(char *v, mygreeting) {
printf("value: %c\n", *v);
}

foreach(float *v, myfloats) {
printf("value: %.2f\n", *v);
}

return 0;
}
[acool@localhost ~]$
[acool@localhost ~]$ gcc c-foreach-macro.c -o c-foreach-macro
[acool@localhost ~]$
[acool@localhost ~]$ ./c-foreach-macro
value: 5
value: 20
value: 35
value: 62
value: 8
value: 74
value: 89
value: H
value: e
value: l
value: l
value: o
value:
value: w
value: o
value: r
value: l
value: d
value: !
value:
value: 1.60
value: 6.90
value: 5.80
value: 43.50
value: 1.10
value: 0.90
[acool@localhost ~]$

Bonus - dumping output from preprocessor.
[acool@localhost ~]$ 
[acool@localhost ~]$ gcc c-foreach-macro.c -E -o c-macro.preprocessed
[acool@localhost ~]$ 
[acool@localhost ~]$ cat c-macro.preprocessed
...
int main()
{
    int mynumbers[] = {5,20,35,62,8,74,89};

    char mygreeting[] = {"Hello world!"};

    float myfloats[] = {1.6,6.9,5.8,43.5,1.1,0.9};

    for(int keep = 1, count = 0, size = sizeof (mynumbers) / sizeof *(mynumbers); keep && count != size; keep = !keep, count++) for(int *v = (mynumbers) + count; keep; keep = !keep) {
        printf("value: %d\n", *v);
    }

    for(int keep = 1, count = 0, size = sizeof (mygreeting) / sizeof *(mygreeting); keep && count != size; keep = !keep, count++) for(char *v = (mygreeting) + count; keep; keep = !keep) {
        printf("value: %c\n", *v);
    }

    for(int keep = 1, count = 0, size = sizeof (myfloats) / sizeof *(myfloats); keep && count != size; keep = !keep, count++) for(float *v = (myfloats) + count; keep; keep = !keep) {
        printf("value: %.2f\n", *v);
    }

    return 0;
}
[acool@localhost ~]$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry230403-182101 2023-04-03T00:00:00Z 2023-04-03T00:00:00Z C 101: Creating Child Processes With A Loop #include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

void child( int seconds );

int children = 15;

int main(void)
{
printf("Parent ID %d, Main ID %d \n", getppid(), getpid());

for(int i=0;i<children;i++)
{
if(fork()==0)
{
child(children-i); // pass seconds to sleep
}
else
{
wait(NULL);
}
}
}

void child(int seconds)
{
printf("Parent ID %d, Child ID %d, Sleeping %d seconds.\n", getppid(), getpid(), seconds);
sleep(seconds);
exit(0);
}
[acool@localhost C-Exercises]$ date
Sun Oct 23 04:14:24 PM PDT 2022
[acool@localhost C-Exercises]$
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ gcc parent_children.c 
[acool@localhost C-Exercises]$ ./a.out 
Parent ID 4298, Main ID 10357 
Parent ID 10357, Child ID 10358, Sleeping 15 seconds.
Parent ID 10357, Child ID 10394, Sleeping 14 seconds.
Parent ID 10357, Child ID 10436, Sleeping 13 seconds.
Parent ID 10357, Child ID 10475, Sleeping 12 seconds.
Parent ID 10357, Child ID 10510, Sleeping 11 seconds.
Parent ID 10357, Child ID 10532, Sleeping 10 seconds.
Parent ID 10357, Child ID 10546, Sleeping 9 seconds.
Parent ID 10357, Child ID 10558, Sleeping 8 seconds.
Parent ID 10357, Child ID 10581, Sleeping 7 seconds.
Parent ID 10357, Child ID 10598, Sleeping 6 seconds.
Parent ID 10357, Child ID 10607, Sleeping 5 seconds.
Parent ID 10357, Child ID 10613, Sleeping 4 seconds.
Parent ID 10357, Child ID 10647, Sleeping 3 seconds.
Parent ID 10357, Child ID 10732, Sleeping 2 seconds.
Parent ID 10357, Child ID 10815, Sleeping 1 seconds.
[acool@localhost C-Exercises]$
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ ps -A |grep a.out
  10357 pts/0    00:00:00 a.out
  10394 pts/0    00:00:00 a.out
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ pstree -p 10357
a.out(10357)───a.out(10436)
[acool@localhost C-Exercises]$

Slightly different version, in this version we don't wait() for each child individually.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

void child( int seconds );

int children = 15;

int main(void)
{
  printf("Parent ID %d, Main ID %d \n", getppid(), getpid()); 

  for(int i=0;i<children;i++)
  {
    if(fork()==0)
    {
      child(children-i); // pass seconds to sleep
    }
  }

  while (wait(NULL) > 0); // wait for all children to finish
}

void child(int seconds)
{
  printf("Parent ID %d, Child ID %d, Sleeping %d seconds.\n", getppid(), getpid(), seconds); 
  sleep(seconds);
  exit(0);
}

[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ gcc parent_children.c 
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ ./a.out 
Parent ID 4298, Main ID 14322 
Parent ID 14322, Child ID 14323, Sleeping 15 seconds.
Parent ID 14322, Child ID 14324, Sleeping 14 seconds.
Parent ID 14322, Child ID 14325, Sleeping 13 seconds.
Parent ID 14322, Child ID 14326, Sleeping 12 seconds.
Parent ID 14322, Child ID 14327, Sleeping 11 seconds.
Parent ID 14322, Child ID 14328, Sleeping 10 seconds.
Parent ID 14322, Child ID 14329, Sleeping 9 seconds.
Parent ID 14322, Child ID 14330, Sleeping 8 seconds.
Parent ID 14322, Child ID 14331, Sleeping 7 seconds.
Parent ID 14322, Child ID 14332, Sleeping 6 seconds.
Parent ID 14322, Child ID 14333, Sleeping 5 seconds.
Parent ID 14322, Child ID 14334, Sleeping 4 seconds.
Parent ID 14322, Child ID 14335, Sleeping 3 seconds.
Parent ID 14322, Child ID 14336, Sleeping 2 seconds.
Parent ID 14322, Child ID 14337, Sleeping 1 seconds.
[acool@localhost C-Exercises]$
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ pstree -p 14322
a.out(14322)─┬─a.out(14323)
             ├─a.out(14324)
             ├─a.out(14325)
             ├─a.out(14326)
             ├─a.out(14327)
             ├─a.out(14328)
             ├─a.out(14329)
             ├─a.out(14330)
             ├─a.out(14331)
             ├─a.out(14332)
             ├─a.out(14333)
             ├─a.out(14334)
             └─a.out(14335)
[acool@localhost C-Exercises]$ ps -A |grep a.out
  14322 pts/0    00:00:00 a.out
  14323 pts/0    00:00:00 a.out
  14324 pts/0    00:00:00 a.out
  14325 pts/0    00:00:00 a.out
  14326 pts/0    00:00:00 a.out
  14327 pts/0    00:00:00 a.out
  14328 pts/0    00:00:00 a.out
  14329 pts/0    00:00:00 a.out
  14330 pts/0    00:00:00 a.out
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ 
[acool@localhost C-Exercises]$ pstree -p 14322
a.out(14322)─┬─a.out(14323)
             ├─a.out(14324)
             ├─a.out(14325)
             ├─a.out(14326)
             ├─a.out(14327)
             └─a.out(14328)
[acool@localhost C-Exercises]$
[acool@localhost C-Exercises]$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry221023-231122 2022-10-23T00:00:00Z 2022-10-23T00:00:00Z C101: Printing Emojis #include <stdio.h>
#include <wchar.h>
#include <locale.h>

// multibyte array, each character is 4 bytes long
wchar_t mystring[] = L"Angel Cool á 🤪 😁 ა";

// [acool@localhost other]$ gcc -Wall -ggdb emoji-multibyte-array.c -o emoji-multibyte-array
int main()
{
setlocale(LC_ALL,"");

// print total number of characters in string
wprintf(L"wcslen of wchar_t mystring[]: %ld\n", wcslen(mystring));

// output string
wprintf(L"%ls\n",mystring);

// print one character
wprintf(L"Emoji : %lc\n", mystring[13]);

// print all
for (int j = 0; j < wcslen(mystring); ++j)
{
wprintf(L"%lc,", mystring[j]);
}

wprintf(L"\n");

// size in bytes of string, it also includes 4 bytes for the null (\0) characters at the end it seems
wprintf(L"Size in bytes of mystring[]: %d\n", sizeof(mystring));

// print size of wchar_t data type
wprintf(L"wchar_t is %d bytes long!\n", sizeof(wchar_t));

return 0;
}
[acool@localhost other]$ date
Sat Oct 22 12:05:24 PM PDT 2022
[acool@localhost other]$ gcc emoji-multibyte-array.c 
[acool@localhost other]$ ./a.out 
wcslen of wchar_t mystring[]: 18
Angel Cool á 🤪 😁 ა
Emoji : 🤪
A,n,g,e,l, ,C,o,o,l, ,á, ,🤪, ,😁, ,ა,
Size in bytes of mystring[]: 76
wchar_t is 4 bytes long!
[acool@localhost other]$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry221022-190423 2022-10-22T00:00:00Z 2022-10-22T00:00:00Z C 101: Preventing Zombie Processes #include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>

int main()
{
pid_t pid;
int status;

pid = fork();

if(pid<0)
{
printf("Error: fork() returned %u.\n", pid);
return 1;
}

if(pid == 0)
{
printf("Child: PID is %u. Parent's PID is %u\n", getpid(), getppid());
sleep(10);
puts("Child: about to exit.\n");
return 33;
}
else
{
printf("Parent: PID is %u. Child's PID is %u\n", getpid(), pid);

while((pid=waitpid(-1,&status,WNOHANG)) == 0)
{
printf("Parent: No child has terminated.");
printf("Parent: Going to sleep for 1 second.\n");
sleep(1);
}
}

printf("Parent: child with PID %u ", pid);

if(WIFEXITED(status)!=0)
{
printf("exited with status %u\n",WIFEXITED(status));
}
else
{
printf("exited abnormally\n");
}

return 0;
}

Preventing Zombie Processes Using waitpid()
Listing 19.5 -Teach Yourself C For Linux Programming
[acool@localhost C-practice]$ gcc -Wall fork.c
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ ./a.out 
Parent: PID is 57544. Child's PID is 57545
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Child: PID is 57545. Parent's PID is 57544
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Parent: No child has terminated.Parent: Going to sleep for 1 second.
Child: about to exit.

Parent: child with PID 57545 exited with status 1
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry220923-200117 2022-09-23T00:00:00Z 2022-09-23T00:00:00Z C 101: Creating Structures 
// define it as a template
struct person {
 char first_name[50];
 char last_name[50];
};

// create two instances of person
struct person Person1, Person2;

// assign values to Person1
strcpy(Person1.first_name, "Angel");
strcpy(Person1.last_name, "Cool");

Method 2:
// define it and create two instances of it
struct car {
 char make[50];
 char color[50];
} Car1, Car2;

// assign values to Car1
strcpy(Car1.make, "Chevy");
strcpy(Car1.color, "red");

Method 3:
// use 'typedef' to create it
typedef struct {
 char first_name[50];
 char last_name[50];
} person;

// create two instances of person (no 'struct' keyword needed)
person Person1, Person2;

Method 1 example
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ cat method_1.c 
#include <stdio.h>
#include <string.h>

void main(){
    struct person {
      char first_name[50];
      char last_name[50];
    };

    // create two instances of person
    struct person Person1, Person2;

    // assign values to Person1
    strcpy(Person1.first_name, "Angel");
    strcpy(Person1.last_name, "Cool");
    
    // print assigned values 
    printf("Hello %s %s!\n", Person1.first_name, Person1.last_name);
}
[acool@localhost C-practice]$ gcc method_1.c -o method_1
[acool@localhost C-practice]$ ./method_1 
Hello Angel Cool!
[acool@localhost C-practice]$

Method 2 example
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ cat method_2.c 
#include <stdio.h>
#include <string.h>

void main(){
    // define it and create two instances of it
    struct car {
      char make[50];
      char color[50];
    } Car1, Car2;

    // assign values to Car1
    strcpy(Car1.make, "Chevy");
    strcpy(Car1.color, "red");

    // print assigned values
    printf("My %s %s.\n",Car1.color, Car1.make);
}
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ gcc method_2.c -o method_2
[acool@localhost C-practice]$ ./method_2
My red Chevy.
[acool@localhost C-practice]$

Method 3 example
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ cat method_3.c 
#include <stdio.h>
#include <string.h>

void main(){
    // use 'typedef' to create it
    typedef struct {
      char first_name[50];
      char last_name[50];
    } person;

    // create two instances of person (no 'struct' keyword needed)
    person Person1, Person2;

    // assign values to Person1
    strcpy(Person1.first_name, "Andres Manuel");
    strcpy(Person1.last_name, "Lopez-Obrador");

    printf("Viva la 4T! Viva %s %s!\n", Person1.first_name, Person1.last_name);
}
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$ gcc method_3.c -o method_3
[acool@localhost C-practice]$ ./method_3
Viva la 4T! Viva Andres Manuel Lopez-Obrador!
[acool@localhost C-practice]$ 
[acool@localhost C-practice]$


Another example:
[acool@localhost ~]$ 
[acool@localhost ~]$ 
[acool@localhost ~]$ date
Wed Apr  5 02:18:30 PM PDT 2023
[acool@localhost ~]$ 
[acool@localhost ~]$ cat books.c 
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct Books {
    char title[50];
    char author[50];
    char subject[100];
    int id;
};

typedef struct {
    char title[50];
    char author[50];
    char subject[100];
    int id;
} eBooks;

void printdetails(eBooks *myEbook, struct Books *myBook)
{
  printf( "myBook id : %d\n", myBook->id);
  printf( "myBook title : %s\n", myBook->title);
  printf( "myBook author : %s\n", myBook->author);
  printf( "myBook subject : %s\n", myBook->subject);
  
  printf("====================================\n");

  printf( "myEbook id : %d\n", myEbook->id);
  printf( "myEbook title : %s\n", myEbook->title);
  printf( "myEbook author : %s\n", myEbook->author);
  printf( "myEbook subject : %s\n", myEbook->subject);
}

int main()
{
    // Pay attention to this! ...two different ways to declare it.
   struct Books *myBook = (struct Books *) malloc(sizeof(struct Books));
   eBooks *myEbook = (eBooks *) malloc(sizeof(eBooks));

   strcpy( myBook->title, "C Programming");
   strcpy( myBook->author, "Angel Cool"); 
   strcpy( myBook->subject, "Programming C Structs Examples");
   myBook->id = 1;
 
   strcpy( myEbook->title, "C Programming (eBook)");
   strcpy( myEbook->author, "Angel Cool (eBook)"); 
   strcpy( myEbook->subject, "Programming C Structs Examples (eBook)");
   myEbook->id = 2;
 
   printdetails(myEbook,myBook);

   return 0;
}
[acool@localhost ~]$ 
[acool@localhost ~]$ 
[acool@localhost ~]$ gcc books.c -o books
[acool@localhost ~]$ 
[acool@localhost ~]$ ./books 
myBook id : 1
myBook title : C Programming
myBook author : Angel Cool
myBook subject : Programming C Structs Examples
====================================
myEbook id : 2
myEbook title : C Programming (eBook)
myEbook author : Angel Cool (eBook)
myEbook subject : Programming C Structs Examples (eBook)
[acool@localhost ~]$ 
[acool@localhost ~]$ file books
books: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=ea1090588d4c761da3060066a7d7a67b7db9caa6, for GNU/Linux 3.2.0, not stripped
[acool@localhost ~]$ 
[acool@localhost ~]$
]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry220823-035202 2022-08-23T00:00:00Z 2022-08-23T00:00:00Z Terraform: AWS VPC with IPV6 support [acool@localhost EC2-VPC]$
[acool@localhost EC2-VPC]$ date
Sun Jul 4 06:19:34 PM PDT 2021
[acool@localhost EC2-VPC]$ cat /etc/redhat-release
Fedora release 33 (Thirty Three)
[acool@localhost EC2-VPC]$ aws --version
aws-cli/1.18.223 Python/3.9.5 Linux/5.12.13-200.fc33.x86_64 botocore/1.19.63
[acool@localhost EC2-VPC]$ terraform -v
Terraform v1.0.1
on linux_amd64
+ provider registry.terraform.io/hashicorp/aws v3.48.0
[acool@localhost EC2-VPC]$

The gist of this post:
 
[acool@localhost EC2-VPC]$ 
[acool@localhost EC2-VPC]$ cat main.tf 
# extract public ssh key from private ssh key
# [acool@localhost EC2-VPC]$ ssh-keygen -y -f ./COOL_SSH_PRIVATEKEY.pem > COOL_SSH_PUBLICKEY.pub 

// a.- set region to use
provider "aws" {
    region = "us-east-2"
}

// b.- create ssh key pair
resource "aws_key_pair" "COOL_KEY_PAIR" {
  key_name   = "COOL_SSH_KEYPAIR"
  public_key = "${file("./COOL_SSH_PUBLICKEY.pub")}"
}

// c.- create vpc resource
resource "aws_vpc" "COOL_VPC" {
    enable_dns_support = true
    enable_dns_hostnames = true
    assign_generated_ipv6_cidr_block = true
    cidr_block = "10.0.0.0/16"
}

// d.- create subnet
resource "aws_subnet" "COOL_VPC_SUBNET" {
    vpc_id = "${aws_vpc.COOL_VPC.id}"
    cidr_block = "${cidrsubnet(aws_vpc.COOL_VPC.cidr_block, 4, 1)}"
    map_public_ip_on_launch = true

    ipv6_cidr_block = "${cidrsubnet(aws_vpc.COOL_VPC.ipv6_cidr_block, 8, 1)}"
    assign_ipv6_address_on_creation = true
}

// e.- create internet gateway
resource "aws_internet_gateway" "COOL_GATEWAY" {
    vpc_id = "${aws_vpc.COOL_VPC.id}"
}

// f.- create routing table
resource "aws_default_route_table" "COOL_VPC_ROUTING_TABLE" {
    default_route_table_id = "${aws_vpc.COOL_VPC.default_route_table_id}"

    route {
        cidr_block = "0.0.0.0/0"
        gateway_id = "${aws_internet_gateway.COOL_GATEWAY.id}"
    }

    route {
        ipv6_cidr_block = "::/0"
        gateway_id = "${aws_internet_gateway.COOL_GATEWAY.id}"
    }
}

// g.- create some sort of association needed
resource "aws_route_table_association" "COOL_SUBNET_ROUTE_TABLE_ASSOCIATION" {
    subnet_id      = "${aws_subnet.COOL_VPC_SUBNET.id}"
    route_table_id = "${aws_default_route_table.COOL_VPC_ROUTING_TABLE.id}"
}

// h.- create security group
resource "aws_security_group" "COOL_SECURITY_GROUP" {
    name = "COOL_SECURITY_GROUP"
    vpc_id = "${aws_vpc.COOL_VPC.id}"
    
    ingress {
        from_port = 22
        to_port = 22
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    ingress {
        from_port = 22
        to_port = 22
        protocol = "tcp"
        ipv6_cidr_blocks = ["::/0"]
    }

    // allow ping
    ingress{
        from_port = -1
        to_port = -1
        protocol = "icmp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    // allow ping
    ingress{
        from_port = -1
        to_port = -1
        protocol = "icmpv6"
        ipv6_cidr_blocks = ["::/0"]
    }

    egress {
      from_port = 0
      to_port = 0
      protocol = "-1"
      cidr_blocks = ["0.0.0.0/0"]
    }

    egress {
      from_port = 0
      to_port = 0
      protocol = "-1"
      ipv6_cidr_blocks = ["::/0"]
    }
}

// i.- create EC2 instance
resource "aws_instance" "COOL_INSTANCE_APP01" {
    ami = "ami-01d5ac8f5f8804300"
    key_name = "COOL_SSH_KEYPAIR"
    instance_type = "t2.micro"
    subnet_id = "${aws_subnet.COOL_VPC_SUBNET.id}"
    ipv6_address_count = 1
    vpc_security_group_ids = ["${aws_security_group.COOL_SECURITY_GROUP.id}"]

    tags = {
        Name = "COOL_INSTANCE_APP01"
    }

    depends_on = [aws_internet_gateway.COOL_GATEWAY]
}

//j.- print instance IPs
output "COOL_INSTANCE_APP01_IPv4" {
  value = "${aws_instance.COOL_INSTANCE_APP01.public_ip}"
}

output "COOL_INSTANCE_APP01_IPv6" {
  value = ["${aws_instance.COOL_INSTANCE_APP01.ipv6_addresses}"]
}
[acool@localhost EC2-VPC]$
[acool@localhost EC2-VPC]$ terraform init
...
[acool@localhost EC2-VPC]$ 
[acool@localhost EC2-VPC]$ terraform apply
...
[acool@localhost EC2-VPC]$


Happy 4th of July, 2021! and cheers!


UPDATE - November 9, 2021
Added 'app_servers' variable to create multiple aws_instances.
Commit message: 'Added EIP and specified private ip addresses.'

main.tf :

# extract public ssh key from private ssh key
# [acool@localhost EC2-VPC]$ ssh-keygen -y -f ./COOL_SSH_PRIVATEKEY.pem > COOL_SSH_PUBLICKEY.pub 

// set region to use
provider "aws" {
    region = "us-east-2"
}

// create ssh key pair
resource "aws_key_pair" "COOL_KEY_PAIR" {
  key_name   = "COOL_SSH_KEYPAIR"
  public_key = "${file("./COOL_SSH_PUBLICKEY.pub")}"
}

// create vpc resource
resource "aws_vpc" "COOL_VPC" {
    enable_dns_support = true
    enable_dns_hostnames = true
    assign_generated_ipv6_cidr_block = true
    cidr_block = "10.0.0.0/16"
}

// create subnet
resource "aws_subnet" "COOL_PVC_SUBNET" {
    vpc_id = "${aws_vpc.COOL_VPC.id}"
    cidr_block = "${cidrsubnet(aws_vpc.COOL_VPC.cidr_block, 4, 1)}"
    map_public_ip_on_launch = true

    ipv6_cidr_block = "${cidrsubnet(aws_vpc.COOL_VPC.ipv6_cidr_block, 8, 1)}"
    assign_ipv6_address_on_creation = true
}

// create internet gateway
resource "aws_internet_gateway" "COOL_GATEWAY" {
    vpc_id = "${aws_vpc.COOL_VPC.id}"
}

// create routing table
resource "aws_default_route_table" "COOL_VPC_ROUTING_TABLE" {
    default_route_table_id = "${aws_vpc.COOL_VPC.default_route_table_id}"

    route {
        cidr_block = "0.0.0.0/0"
        gateway_id = "${aws_internet_gateway.COOL_GATEWAY.id}"
    }

    route {
        ipv6_cidr_block = "::/0"
        gateway_id = "${aws_internet_gateway.COOL_GATEWAY.id}"
    }
}

// create some sort of association needed
resource "aws_route_table_association" "COOL_SUBNET_ROUTE_TABLE_ASSOCIATION" {
    subnet_id      = "${aws_subnet.COOL_PVC_SUBNET.id}"
    route_table_id = "${aws_default_route_table.COOL_VPC_ROUTING_TABLE.id}"
}

// create security group
resource "aws_security_group" "COOL_SECURITY_GROUP" {
    name = "COOL_SECURITY_GROUP"
    vpc_id = "${aws_vpc.COOL_VPC.id}"
    
    ingress {
        from_port = 22
        to_port = 22
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    ingress {
        from_port = 22
        to_port = 22
        protocol = "tcp"
        ipv6_cidr_blocks = ["::/0"]
    }

    // allow ping
    ingress{
        from_port = -1
        to_port = -1
        protocol = "icmp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    // allow ping
    ingress{
        from_port = -1
        to_port = -1
        protocol = "icmpv6"
        ipv6_cidr_blocks = ["::/0"]
    }

    egress {
      from_port = 0
      to_port = 0
      protocol = "-1"
      cidr_blocks = ["0.0.0.0/0"]
    }

    egress {
      from_port = 0
      to_port = 0
      protocol = "-1"
      ipv6_cidr_blocks = ["::/0"]
    }
}

// server names
variable app_servers {
    description = "name of app servers"
    type = list(map(any))
    default = [
        {name:"COOL_LB01", ip:"10.0.16.4"},
        {name:"COOL_LB02", ip:"10.0.16.5"},
        {name:"COOL_APP01", ip:"10.0.16.6"},
        {name:"COOL_APP02", ip:"10.0.16.7"},
    ]
}

// create EC2 instance
resource "aws_instance" "COOL_SERVERS" {
    ami = "ami-01d5ac8f5f8804300"
    key_name = "COOL_SSH_KEYPAIR"
    instance_type = "t2.micro"
    subnet_id = "${aws_subnet.COOL_PVC_SUBNET.id}"
    ipv6_address_count = 1
    vpc_security_group_ids = ["${aws_security_group.COOL_SECURITY_GROUP.id}"]
    for_each = {for server in var.app_servers:  server.name => server}
    private_ip = each.value["ip"]

    tags = {
        Name = each.value["name"]
    }

    depends_on = [aws_internet_gateway.COOL_GATEWAY]
}

// elastic IP
resource "aws_eip" "COOL_EIP" {
  instance = aws_instance.COOL_SERVERS["COOL_LB01"].id
  vpc      = true
}

// print instance IPs
output "COOL_INSTANCE_APP01_IPv4" {
    value = {for k, v in aws_instance.COOL_SERVERS: k => v.public_ip}
}

output "COOL_INSTANCE_APP01_IPv6" {
  value = {for k, v in aws_instance.COOL_SERVERS: k => v.ipv6_addresses}
}

output "COOL_VPC_IPV6_BLOCK" {
  value = aws_subnet.COOL_PVC_SUBNET.ipv6_cidr_block
}

// SSH to instance:
// [acool@localhost EC2-VPC]$ ssh -i ./COOL_SSH_PRIVATEKEY.pem centos@ip_address

// remove eip from COOL_LB01
// [acool@localhost EC2-VPC]$ aws ec2 disassociate-address --region us-east-2 --public-ip 3.131.249.150

// assign eip to COOL_LB02, adjust instance id to match LB02. The same commands work to return eip to LB01
// [acool@localhost EC2-VPC]$ aws ec2 associate-address --region us-east-2 --public-ip 3.131.249.150 --instance-id i-05a634252654b7b34

]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry210705-012044 2021-07-05T00:00:00Z 2021-07-05T00:00:00Z Terraform: AWS EC2 single instance example. [acool@localhost terraform-tests]$ terraform --version
Terraform v1.0.1
...
[acool@localhost terraform-tests]$ aws --version
aws-cli/1.18.223 Python/3.9.5 Linux/5.12.12-200.fc33.x86_64 botocore/1.19.63
...

The gist of this post:
[acool@localhost EC2-SINGLE-INSTANCE]$ cat main.tf 
provider "aws" {
    region = "us-east-2"
}

// create ssh key
resource "tls_private_key" "COOL_SSH_PK" {
  algorithm = "RSA"
  rsa_bits  = 4096
}

// create ssh key pair
resource "aws_key_pair" "COOL_KEY_PAIR" {
  key_name   = "COOL_SSH_KEYNAME"
  public_key = tls_private_key.COOL_SSH_PK.public_key_openssh

  provisioner "local-exec" { # Create "myKey.pem" to your computer!!
    command = "echo '${tls_private_key.COOL_SSH_PK.private_key_pem}' > ./COOL_SSH_PK.pem"
  }
}

// create aws ec2 instance
resource "aws_instance" "COOLAPP01" {
    ami = "ami-01d5ac8f5f8804300"
    instance_type = "t2.micro"
    key_name = aws_key_pair.COOL_KEY_PAIR.key_name
    vpc_security_group_ids = [aws_security_group.COOLAPP01_security_group.id]

  tags = {
    Name = "COOLAPP01_tag_name"
  }
}

// create security group
resource "aws_security_group" "COOLAPP01_security_group" {

    name="terraform_COOLAPP01_security_group"

    // allow port 80 tcp
    ingress{
        from_port = 80
        to_port = 80
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    // allow port 22 tcp
    ingress{
        from_port = 22
        to_port = 22
        protocol = "tcp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    // allow ping
    ingress{
        from_port = -1
        to_port = -1
        protocol = "icmp"
        cidr_blocks = ["0.0.0.0/0"]
    }

    // allow all outbound traffic
    egress {
        from_port   = 0
        to_port     = 0
        protocol    = "-1"
        cidr_blocks = ["0.0.0.0/0"]
    }
}

// TODO: enable IPV6

output "public_ip" {
    value = aws_instance.COOLAPP01.public_ip
    description = "public ip for COOLAPP01"
}
[acool@localhost EC2-SINGLE-INSTANCE]$ 
[acool@localhost EC2-SINGLE-INSTANCE]$terraform apply
...


Happy 4th of July, 2021 ya'll!!]]> https://angelcool.net/sphpblog/blog_index.php?entry=entry210704-200235 2021-07-04T00:00:00Z 2021-07-04T00:00:00Z