NetCat (nc) is used to read and write to TCP and UDP network connections. It is an excellent tool for diagnosing network connectivity issues.
sudo apt-get install netcatTo listen to a specific port.
nc -l -p 8000To write to a specific port
nc 127.0.0.1 8000
nc -v 127.0.0.1 8000Database access is a core aspect of many applications. C# can interface with many different databases such as Oracle, Microsoft SQL, and MongoDB. In this case, we will be working with MySQL. The first step is to add the MySQL package to your project.
dotnet add package MySql.Data
When you run a client program to connect to the MySQL server, it is inadvisable to specify your password in a way that exposes it to discovery by other users. We will store our credentials in a .env file and load them into the environment variables. The code to load .env files is trivial, so we will just add it directly to the project. Add the .env file to your .gitignore so that you don’t upload your credentials to your code repository.
class DotEnv {
public static void Load() {
string filepath = Path.Combine(
Directory.GetCurrentDirectory(),
".env"
);
DotEnv.Load(filepath);
}
public static void Load(string filePath) {
if (!File.Exists(filePath)) return;
foreach (var line in File.ReadAllLines(filePath)) {
var parts = line.Split('=',StringSplitOptions.RemoveEmptyEntries);
if (parts.Length != 2) continue;
if (Environment.GetEnvironmentVariable(parts[0]) != null) continue;
Environment.SetEnvironmentVariable(parts[0], parts[1]);
}
}
}
SQL_USER=username
SQL_PW=supersecret
SQL_SERVER=localhost
Before you can perform database operations, you need to establish a connection. This is achieved with a MySqlConnection object. We will add the variables from the .env file with string interpolation.
using MySql.Data.MySqlClient;
DotEnv.Load();
var env = Environment.GetEnvironmentVariables();
string cs = @$"
server={env["SQL_SERVER"]};
userid={env["SQL_USER"]};
password={env["SQL_PW"]};
database={env["SQL_DB"]}
";
var con = new MySqlConnection(cs);
con.Open();
Console.WriteLine($"MySQL version : {con.ServerVersion}");
con.Close();
After the connection has been established you will typically perform one or more operations, this is enabled by the MySqlCommand object. There are three primary methods that you will usually use:
Although possible to build SQL queries using string interpolation, it is not advisable to put query values directly in the query string. Doing so leaves your database open to injection attacks. Instead of placing the value into the query directly, we will use placeholders, prefixed with ‘@’.
string sql = $"SELECT Name FROM Country WHERE Continent = {continent};string sql = "SELECT Name FROM Country WHERE Continent = @continent;When using parameterized strings the values are added using the Parameters field of the MySqlCommand object.
To insert a new record into the database we use the ExecuteNonQuery method.
Executes a SQL statement returning the affected row count. [*]
string sql = "INSERT INTO users(username, password, email) values (@username, @password, @email)";
using var cmd = new MySqlCommand(sql, con);
cmd.Parameters.AddWithValue("@username", username);
cmd.Parameters.AddWithValue("@password", password);
cmd.Parameters.AddWithValue("@email", email);
cmd.ExecuteNonQuery();
Sends the CommandText value to MySqlConnection and builds a MySqlDataReader object.
The Reader object contains the rows that result from the SQL command execution. The Read method advances the reader to the next row, returning true if a row exists. The using keyword ensures that classes that implement the IDisposable interface call their dispose method.
using (MySqlDataReader reader = cmd.ExecuteReader()){
while (reader.Read()) {
...
}
}
You retrieve values from the current row with the class indexer which can retrieve values by column index or name. There are also several methods to retrieve a value by type, for example, GetInt32. The following statements perform the same action.
var name = reader[0];
var name = reader["name"];
var name = reader.GetString(0);
var name = reader.GetString("name");
Official MySQL/Net Tutorial
https://dev.mysql.com/doc/connector-net/en/connector-net-tutorials-sql-command.html
Nuget MySQL Package
https://www.nuget.org/packages/MySql.Data/
MySQL/Net API
<form action="/multipart-data?id=x" method="post" enctype="multipart/form-data">
<b>multipart/form-data</b><br>
<span>jobid</span>
<input type="number" name="jobid" value="0"><br>
<span>jobname</span>
<input type="text" name="jobname" value=""><br>
<input type="submit"><br>
</form>
import express from "express";
import bodyParser from "body-parser";
const router = express.Router();
router.post("/multipart-data",
log,
multer({ dest: 'uploads/' }).none(),
printBody
);
function log(req, res, next) {
console.log(req.method + ` ` + req.originalUrl);
next();
}
function printBody(req, res, next){
console.log(req.body);
console.log(req.query);
next();
}
export default router;
POST /justdata
{ jobid: '0', jobname: 'asdf' }
{ id: 'x' }
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate, br
Accept-Language: en-CA,en-GB;q=0.9,en-US;q=0.8,en;q=0.7
Cache-Control: no-cache
Connection: keep-alive
Content-Length: 234
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryB2AGWn1yYcOCi0T9
------WebKitFormBoundaryB2AGWn1yYcOCi0T9
Content-Disposition: form-data; name="jobid"
0
------WebKitFormBoundaryB2AGWn1yYcOCi0T9
Content-Disposition: form-data; name="jobname"
sdf
------WebKitFormBoundaryB2AGWn1yYcOCi0T9--
<form action="/justdata?id=x" method="post" enctype="application/x-www-form-urlencoded">
<b>application/x-www-form-urlencoded</b><br>
<span>jobid</span>
<input type="number" name="jobid" value="0"><br>
<span>jobname</span>
<input type="text" name="jobname" value=""><br>
<input type="submit"><br>
</form>
import express from "express";
import bodyParser from "body-parser";
const router = express.Router();
router.post("/justdata",
log,
bodyParser.urlencoded({ extended: true }),
printBody
);
function log(req, res, next) {
console.log(req.method + ` ` + req.originalUrl);
next();
}
function printBody(req, res, next){
console.log(req.body);
console.log(req.query);
next();
}
export default router;
POST /justdata
{ jobid: '0', jobname: 'asdf' }
{ id: 'x' }
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9
Accept-Encoding: gzip, deflate, br
Accept-Language: en-CA,en-GB;q=0.9,en-US;q=0.8,en;q=0.7
Cache-Control: no-cache
Connection: keep-alive
Content-Length: 20
Content-Type: application/x-www-form-urlencoded
jobid=0&jobname=asdf
sudo apt update
sudo apt upgrade
sudo apt install mysql-server
sudo service mysql start
sudo service mysql status
sudo mysql
sql> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password by 'password';
sudo mysql_secure_installation
mysql -u root -p
sql> CREATE USER 'MyUsername'@'localhost' IDENTIFIED BY 'password';
sql> CREATE DATABASE datebase_name;
sql> GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, INDEX, DROP, ALTER, CREATE TEMPORARY TABLES, LOCK TABLES ON database_name.* TO 'MyUsername'@'localhost';
sql> quit
mysql -u MyUsername -p
sql> show databases;
sql> use database_name;
GRANT ALL ON demo.* TO 'demo'@'localhost';
mysql --login-path=demo