Web Development 701 ~ OpenFaas ~ Creating a Function

With assessment 2 finished now it’s time to focus back on assessment 3, which serverless via OpenFaas. In this blog I am going to create the function, and it will be with a program I’ve already made; sbh. The first thing to do is create a new directory to store the code in, this will be done via mkdir web701.

The next thing to do is scaffold a new function via faas-cli new --lang python3 sbh --prefix="<dockerhub-username>"

Now with our scaffolded function it’s time to add the following to handler.py.

import hashlib
import os
import random
from string import ascii_lowercase, digits, printable
import sys

SYMBOLS = printable[62:]

def handle(req):
    return sbh()

def cc(rot, plaintext):
    plaintext = plaintext.replace(' ', '')
    encrypted = ''
    for n in plaintext:
        if n.isalpha():
            encrypted += ascii_lowercase[(ascii_lowercase.index(n.lower()) + rot) % len(ascii_lowercase)]
        elif n.isdigit():
            encrypted += digits[(digits.index(n) + rot) % len(digits)]
        else:
            encrypted += SYMBOLS[(SYMBOLS.index(n) + rot) % len(SYMBOLS)]
    return hashlib.sha256(bytes(encrypted, 'UTF-8')).hexdigest()

def sbh():
        query = os.getenv('Http_Query').split(',')
        plaintext = query[0].split('=')[1]
        nrots = int(query[1].split('=')[1])
        seed = int(query[2].split('=')[1])

        random.seed(seed)
        text = cc(random.randint(1, sys.maxsize), plainText)
        for _ in range(1, nrots):
            rot = random.randint(1, sys.maxsize)
            text = cc(rot, text)

        return text

Now to build/deploy the function via faas-cli up -f sbh.yml

Once it’s finished we invoke the function via echo "" | faas-cli invoke sbh --query plaintext=test,nrots=3,seed=3

It should print 89c00164680e5e77266515e02005ed9e81ec0b8b448f997dfb192b6f05a3f41b

Works!