How to merge a branch in git

Follow the commands below to do the auto merge the branch in git:

$ git checkout -b {new-branch-name}

$ git merge --no-ff {old-branch-name}

$ git push -u origin {new-branch-name}

Concatenating and combining lists in Python

CODE:

[4, None, 'foo'] + [7, 8, (2, 3)]

or

x = [4, None, 'foo']

x.extend([7, 8, (2, 3)])

print(x)

OUTPUT:

[4, None, 'foo', 7, 8, (2, 3)]

Ternary expressions in Python

A ternary expression in Python allows you to combine an if-else block that produces

a value into a single line or expression. The syntax for this in Python is:

value = true-expr if condition else false-expr

Here, true-expr and false-expr can be any Python expressions. It has the identical

effect as the more verbose:

if condition:

    value = true-expr

else:

    value = false-expr

This is a more concrete example:

CODE:

x = 5

'Non-negative' if x >= 0 else 'Negative'

OUTPUT:

'Non-negative'

What is pass in Python

pass is the "no-op" statement in Python. It can be used in blocks where no action is to

be taken (or as a placeholder for code not yet implemented); it is only required

because Python uses whitespace to delimit blocks:

Eg:

if x < 0:

    print('negative!')

elif x == 0:

    # TODO: put something smart here

    pass

else:

    print('positive!')

How to chain comparisons in Python

CODE:

print(4 > 3 > 2 > 1)

OUTPUT:

True

What are the datetime format specifications (ISO C89 compatible) in Python

Below are the Datetime format specification (ISO C89 compatible) in Python:

Why triple quotes (" " ") are used in Python

For multiline strings with line breaks, you can use triple quotes, either ''' or " " ":

c = """

This is a long string that

spans multiple lines

"""

Standard Python scalar types

Below are the standard Python scalar types:

Type: Description

None: The Python "null" value (only one instance of the None object exists)

str: String type; holds Unicode (UTF-8 encoded) strings

bytes: Raw ASCII bytes (or Unicode encoded as bytes)

float: Double-precision (64-bit) floating-point number (note there is no separate double type)

bool: A True or False value

int: Arbitrary precision signed integer

How to check/get/set an attribute or a method in Python (Reflection)

Python allows an easy way to check whether an object contains/has an attribute or method with the specified name as follows:

1) getattr:

Gets the attribute/method with the specified name, usage as follows:

usage: getattr(obj, 'method/attribute name')

eg: 

a='RK'; 

getattr(a, 'split')

2) hasattr:

Checks whether object has the attribute/method with the specified name, usage as follows:

usage: hasattr(obj, 'method/attribute name')

eg: 

a='RK'; 

hasattr(a, 'split')

3) setattr:

Sets the attribute/method with the specified name, usage as follows:

usage: setattr(obj, 'method/attribute name', value)

eg: 

a=Employee(23)

setattr(a, 'id', 45)

Python assignments are by references

When assigning a variable (or name) in Python, you are creating a reference, have a look at below:

CODE:

a=[1,2]

b=a

print("Before append: ", b)

b.append(3)

print("Shows a & b are same references, after append to b, a: ", a)

OUTPUT:

Before append:  [1, 2]

Shows a & b are same references, after append to b, a:  [1, 2, 3]

How to get rid of `grep: warning: GREP_OPTIONS is deprecated; please use an alias or script`?

Need to have an alias for grep to make the output colored as follows and unset the GREP_OPTIONS.

alias grep="grep --color=auto"
unset GREP_OPTIONS

How to create a self signed certificate, and how to validate the JWT token using Nimbus

This post will help you to generate a self-signed certificate and show you how to validate the JWT token using Nimbus Jose JWT library.

package com.varra.samples;

import java.io.IOException;

import java.math.BigInteger;

import java.security.GeneralSecurityException;

import java.security.KeyFactory;

import java.security.KeyPair;

import java.security.KeyPairGenerator;

import java.security.PrivateKey;

import java.security.SecureRandom;

import java.security.cert.X509Certificate;

import java.security.interfaces.RSAPrivateKey;

import java.security.interfaces.RSAPublicKey;

import java.security.spec.X509EncodedKeySpec;

import java.util.Base64;

import java.util.Date;

import com.nimbusds.jose.JWSAlgorithm;

import com.nimbusds.jose.JWSHeader;

import com.nimbusds.jose.JWSSigner;

import com.nimbusds.jose.crypto.RSASSASigner;

import com.nimbusds.jose.crypto.RSASSAVerifier;

import com.nimbusds.jwt.JWTClaimsSet;

import com.nimbusds.jwt.SignedJWT;

import sun.security.rsa.RSAPublicKeyImpl;

import sun.security.x509.AlgorithmId;

import sun.security.x509.CertificateAlgorithmId;

import sun.security.x509.CertificateSerialNumber;

import sun.security.x509.CertificateValidity;

import sun.security.x509.CertificateVersion;

import sun.security.x509.CertificateX509Key;

import sun.security.x509.X500Name;

import sun.security.x509.X509CertImpl;

import sun.security.x509.X509CertInfo;

public class JWTTokenUtils {

/** 

* Create a self-signed X.509 Certificate

* @param dn the X.509 Distinguished Name, eg "CN=RK, L=Hyderabad, C=Hyderabad"

* @param pair the KeyPair

* @param days how many days from now the Certificate is valid for

* @param algorithm the signing algorithm, eg "SHA1withRSA"

*/ 

public static X509Certificate generateCertificate(String dn, KeyPair pair, int days, String algorithm)

  throws GeneralSecurityException, IOException

{

  PrivateKey privkey = pair.getPrivate();

  X509CertInfo info = new X509CertInfo();

  Date from = new Date();

  Date to = new Date(from.getTime() + days * 86400000l);

  CertificateValidity interval = new CertificateValidity(from, to);

  BigInteger sn = new BigInteger(64, new SecureRandom());

  X500Name owner = new X500Name(dn);

 

  info.set(X509CertInfo.VALIDITY, interval);

  info.set(X509CertInfo.SERIAL_NUMBER, new CertificateSerialNumber(sn));

  //info.set(X509CertInfo.SUBJECT, new CertificateSubjectName(owner));

  info.set(X509CertInfo.SUBJECT, owner);

  info.set(X509CertInfo.ISSUER, owner);

  info.set(X509CertInfo.KEY, new CertificateX509Key(pair.getPublic()));

  info.set(X509CertInfo.VERSION, new CertificateVersion(CertificateVersion.V3));

  AlgorithmId algo = new AlgorithmId(AlgorithmId.md5WithRSAEncryption_oid);

  info.set(X509CertInfo.ALGORITHM_ID, new CertificateAlgorithmId(algo));

 

  // Sign the cert to identify the algorithm that's used.

  X509CertImpl cert = new X509CertImpl(info);

  cert.sign(privkey, algorithm);

 

  // Update the algorith, and resign.

  algo = (AlgorithmId)cert.get(X509CertImpl.SIG_ALG);

  info.set(CertificateAlgorithmId.NAME + "." + CertificateAlgorithmId.ALGORITHM, algo);

  cert = new X509CertImpl(info);

  cert.sign(privkey, algorithm);

  return cert;

}

public static String generateToken(RSAPrivateKey privateKey) throws Exception

{

// Create RSA-signer with the private key

final JWSSigner signer = new RSASSASigner(privateKey);

// Prepare JWT with claims set

final JWTClaimsSet claimsSet = new JWTClaimsSet.Builder()

    .subject("alice")

    .issuer("Rajakrishna Reddy")

    .claim("user", "Rajakrishna Reddy")

    .claim("email", "abc@xyz.com")

    .claim("tenantId", "123")

    .expirationTime(new Date(new Date().getTime() + 60 * 1000))

    .build();

final SignedJWT signedJWT = new SignedJWT(new JWSHeader(JWSAlgorithm.RS256), claimsSet);

signedJWT.sign(signer);

return signedJWT.serialize();

}

public static boolean isValidToken(String token, RSAPublicKey publicKey) throws Exception

{

return SignedJWT.parse(token).verify(new RSASSAVerifier(publicKey));

}

public static boolean isValidToken(String token, String publicKey) throws Exception

{

byte[] decoded = Base64.getDecoder().decode(publicKey);

    X509EncodedKeySpec spec = new X509EncodedKeySpec(decoded);

    KeyFactory kf = KeyFactory.getInstance("RSA");

    RSAPublicKey generatePublic = (RSAPublicKey) kf.generatePublic(spec);

    BigInteger modulus = generatePublic.getModulus();

    BigInteger exponent = generatePublic.getPublicExponent();

    return SignedJWT.parse(token).verify(new RSASSAVerifier(new RSAPublicKeyImpl(modulus, exponent)));

//return SignedJWT.parse(token).verify(new RSASSAVerifier(publicKey));

}

public static void main(String[] args) throws Exception {

final String algorithmType = "RSA";

final String algorithm = "SHA256withRSA";

final String dn = "CN=Rajakrishna Reddy, OU=OU, O=varra, L=Hyderabad, ST=TL, C=IN";

final int days = 365;

final KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(algorithmType);

keyGenerator.initialize(2048);

final KeyPair kp = keyGenerator.genKeyPair();

final X509Certificate certificate = generateCertificate(dn, kp, days, algorithm);

System.out.println("X09.Certificate: "+certificate);

//final String token = generateToken((RSAPrivateKey) kp.getPrivate());

final String token = "eyJhbGciOiJSUzI1NiJ9.eyJleHAiOjE1MjUyNDUyMDAsInN1YiI6IkpXVCIsInVzZXJfbWV0YWRhdGEiOiJ7XCJVc2VybmFtZVwiOlwibWNzYVwifSIsImlhdCI6MTUyNTE1ODgwMH0.wbroKZfrdGPGnk3OaPWbRr56rRzkg4DFO999jmSsut8IYAthKU0f26CIjWfrNPXD5asV74JYIS49VFNkFwbWfnIFETY1CaLIIm6F6NP5cFE7LW5G-y0qNRaCJgOLaFV4z4lsQOi0KAfuFVckiL5EHxhyBks-MCQEXMWO2JIBBZjAxhIH7fmhMHsYQQUxvm8Tx1dpnbvyh9E6x5F9BNZeS2DcBCqvzCuSUAz2DbgsJ-gVyrDRJgcItiCnscZy2u3sZq3XBTK2qBiSIpS4zVZupVS0f-5v57y7BvdVX2siuu-StN5614zvON_MJRgNLdo1yA1Y5F8eJ9IZrelMWB5GZw";

final String publiKey = "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA2hg1nqteEY12r5AO/enYD14aXEUaoqgvhtcHDwEPQwf9KqGpwoeC8jQE1qHfb2K1Wm/o4ug60Kv02f7AEJiNrUuKe9MYJdTr/DhekVrE0ttJkGCjLoNiVgMZHKH557Ouf6RsWJc5QjUiqxg6azwYUuHu2U199MZzFXvAVVUQR+hh8YqQM4KIQytOpj1JhxH7hQehth9vF5kIhA+K8htIIO04UF9+8ScrBHMQgj9q0RLperVQLxGsYT8cEZIn9tv1r47jynrTS0z/Vq2uVMGRg/bRPuo598++XUIglM92Ehbih87j//ATcHtsabefzBAVQuN4OaqLTT375JRAWpoWmQIDAQAB";

System.out.println("Token: "+token);

//System.out.println("Is valid?: "+isValidToken(token, (RSAPublicKey) kp.getPublic()));

System.out.println("Is valid?: "+isValidToken(token, publiKey));

//System.out.println(isValidToken(token, CertificateUtil.parseRSAPublicKey()));

}

}