Azure HTTP Functions Example - CUSIP Validation

Introduction

An Azure Function is an entirely serverless way of having common functionality available to your applications via the cloud without the overhead of managing virtual machines or configurations, etc. You only pay for the actual execution time spent and all of the scaling is taken care of for you.

Background

This example is a piece of functionality that is often used in financial systems which validates a CUSIP which is a special 9-digit identifier used to uniquely identify a financial security traded in the North American markets. The last digit of this number is a check sum digit used to check if the CUSIP is valid or not.

Since this validation is idempotent and requires no external storage, it is an ideal candidate for an Azure function.

Creating a New Azure Function

You create new functions in the Azure portal in the "App Services" section:

When you select this button, a quick-start screen allows you to select a language and starter template.

For this example, an API written in C# is selected.

The Function Wrapper (run.csx)

The template creates a wrapper that takes care of the connection and you then have to write the code that takes the inputs and returns an appropriate HTTP response.

#load "cusip.csx"

using System.Net;

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    log.Info("C# HTTP CUSIP validation function");

    // parse query parameter to get the cusip passed in
    string cusip = req.GetQueryNameValuePairs()
        .FirstOrDefault(q => string.Compare(q.Key, "cusip", true) == 0)
        .Value;

    // Get request body
    dynamic data = await req.Content.ReadAsAsync<object>();

    // Set name to query string or body data
    cusip = cusip ?? data?.cusip;

    if (IsValidCusip(cusip))
    {
        log.Info("Valid CUSIP : " + cusip);
       return req.CreateResponse(HttpStatusCode.OK, "true");
    }
    else
    {
       log.Info("Invalid CUSIP : " + cusip);
       return req.CreateResponse(HttpStatusCode.OK, "false");
    }
}

In this case, we just want to return "true" if the CUSIP is valid and "false" if it is not.

Custom (Shared) Functions

If you have functionality that you want to share between different Azure functions, you can have it in a separate code file that you can then reference in your Azure function. You need to use the #load command to reference this in your function wrapper.

public static bool IsValidCusip(string cusip)
{
    // CUSIP must not be empty
    if (string.IsNullOrWhiteSpace(cusip))
    {
        return false;
    }

    // CUSIP must be 9 digits
    if (cusip.Length == 9)
    {
        int checkDigit = getExpectedCheckDigit(cusip);
        int expectedCheckDigit = (int)Char.GetNumericValue(cusip[8]);
        return (checkDigit == expectedCheckDigit);
    }

    return false;
}

Triggering the Azure Function

To run the Azure function, you use the URL in the form https://{function app name}.azurewebsites.net/api/{function name} with any parameters passed in either in the query string or in the request body - for example, you could use https://fundadmin.azurewebsites.net/api/CUSIPValidation?cusip=00846U101.

History

• 17^th August, 2017 - First version