How to Validate Addresses with USPS API in C#

Setting Up the Environment

• Install the RestSharp library from NuGet, a popular library for making HTTP requests in C#. Execute the following command in your Package Manager Console: Install-Package RestSharp.

 

• Ensure that you have access to the USPS API by obtaining the necessary credentials (User ID) from USPS.

Create a Function to Make the API Request

• Create a function that formulates a request to the USPS API. You will utilize the RestSharp library to simplify HTTP requests.

using RestSharp;
using System;

public class USPSAddressValidator
{
    private readonly string _uspsUserId;

    public USPSAddressValidator(string uspsUserId)
    {
        _uspsUserId = uspsUserId;
    }

    public string ValidateAddress(string firmName, string address1, string address2, string city, string state, string zip5, string zip4)
    {
        var client = new RestClient("https://secure.shippingapis.com/ShippingAPI.dll");
        var request = new RestRequest(Method.GET);
        
        request.AddParameter("API", "Verify");
        request.AddParameter("XML", 
            $"<AddressValidateRequest USERID=\"{_uspsUserId}\"><Revision>1</Revision><Address ID=\"0\">" +
            $"<FirmName>{firmName}</FirmName><Address1>{address1}</Address1><Address2>{address2}</Address2>" +
            $"<City>{city}</City><State>{state}</State><Zip5>{zip5}</Zip5><Zip4>{zip4}</Zip4></Address></AddressValidateRequest>");
        
        var response = client.Execute(request);
        return response.Content;
    }
}

Parse the API Response

• After receiving the response from the USPS API, parse the XML response to extract the validated address components.

using System.Xml;

public Address ParseUSPSResponse(string response)
{
    XmlDocument doc = new XmlDocument();
    doc.LoadXml(response);

    XmlNode addressNode = doc.SelectSingleNode("//Address");
    if (addressNode == null)
        throw new Exception("Invalid response from USPS API.");

    return new Address
    {
        FirmName = addressNode.SelectSingleNode("FirmName")?.InnerText,
        Address1 = addressNode.SelectSingleNode("Address1")?.InnerText,
        Address2 = addressNode.SelectSingleNode("Address2")?.InnerText,
        City = addressNode.SelectSingleNode("City")?.InnerText,
        State = addressNode.SelectSingleNode("State")?.InnerText,
        Zip5 = addressNode.SelectSingleNode("Zip5")?.InnerText,
        Zip4 = addressNode.SelectSingleNode("Zip4")?.InnerText
    };
}

Handle Errors and Edge Cases

• Ensure that your code gracefully handles errors from the API, such as malformed input or connectivity issues.

 

• Implement retry logic for network-related issues or consider caching API responses to reduce redundant checks.

 

• Employ exception handling around API calls and XML parsing to manage unexpected scenarios smoothly.

Integrate and Test the Solution

• Integrate the address validation into your application where address validation is necessary. Ensure seamless communication between components.

 

• Create unit tests using frameworks like NUnit or xUnit to validate the robustness and correctness of your address validation logic.

 

• Verify your implementation with various sample addresses to check for completeness and correctness of the API response parsing.