schema-validation.md

Schema Validation

This is a schema validation library that consumes a JSON schema from the schema registry and validate event/message payload against the schema. Schema registry is accessible through SchemaConsumer.

NuGet Package Status

Package	Download	Version
Aliencube.AzureMessaging.SchemaValidation

Usage

ISchemaValidator and SchemaValidator

As an interface, and as an abstract class, both ISchemaValidator and SchemaValidator declare the following properties and methods:

• Consumer: Declares the ISchemaConsumer instance.
• WithSchemaConsumer(ISchemaConsumer consumer): Adds the ISchemaConsumer instance to the validator.
• ValidateAsync(string payload, string path): Validates the payload against the schema through the SchemaConsumer instance.

var sink = new BlobStorageSchemaSink();
var consumer = new SchemaConsumer()
                   .WithSink(sink);

var validator = new SchemaValidator()
                    .WithSchemaConsumer(consumer);

var payload = "{ \"hello\": \"world\" }";
var path = $"v1/schema.json";

var validated = await validator.ValidateAsync(payload, path)
                               .ConfigureAwait(false);

Schema Validation Extension

There is an extension method, StringExtensions.ValidateAsync(this string payload, ISchemaValidator validator, string path) that directly applies to the event/message payload. It is particularly useful for Azure Function triggers. The following function code is to apply the validation for Azure Service Bus, but it can be applied to any message triggers.

public static class ServiceBusTopicSubscriptionTrigger
{
    [FunctionName(nameof(ServiceBusTopicSubscriptionTrigger))]
    public static async Task Run(
        [ServiceBusTrigger(/* OMITTED */)] string message,
        ILogger log)
    {
        var path = "default.json";

        var sink = new BlobStorageSchemaSink();
        var consumer = new SchemaConsumer()
                           .WithSink(sink);
        var validator = new SchemaValidator()
                            .WithSchemaConsumer(consumer);

        var validated = await message.ValidateAsync(validator, path)
                                     .ConfigureAwait(false);
    }
}

There is another extension method, StringExtensions.ValidateAsStringAsync(this string payload, ISchemaValidator validator, string path) that directly applies to the event/message payload. It is particularly useful for Azure Function outputs. The following function code is to apply the validation for Azure Service Bus, but it can be applied to any message output bindings.

public static class ServiceBusTopicPublishHttpTrigger
{
    [FunctionName(nameof(ServiceBusTopicPublishHttpTrigger))]
    public static async Task<IActionResult> Run(
        [HttpTrigger(/* OMITTED */)] HttpRequest req,
        [ServiceBus(/* OMITTED */)] IAsyncCollector<string> collector,
        ILogger log)
    {
        var path = "default.json";
        var sink = new BlobStorageSchemaSink();
        var consumer = new SchemaConsumer()
                           .WithSink(sink);
        var validator = new SchemaValidator()
                            .WithSchemaConsumer(consumer);

        var sample = new SampleClass();

        var payload = await JsonConvert.SerializeObject(sample)
                                       .ValidateAsStringAsync(validator, path)
                                       .ConfigureAwait(false);

        await collector.AddAsync(payload)
                       .ConfigureAwait(false);

        return new StatusCodeResult((int)HttpStatusCode.Created);
    }
}