Startup.cs

// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
using System;
using System.Linq;
using System.Threading.Tasks;
using CloudNative.CloudEvents;
using Google.Cloud.Vision.V1;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json.Linq;

namespace vision
{
    public class Startup
    {
        public void ConfigureServices(IServiceCollection services)
        {
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILogger<Startup> logger)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            logger.LogInformation("Service is starting...");

            app.UseRouting();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapPost("/", async context =>
                {
                    var cloudEvent = await context.Request.ReadCloudEventAsync();

                    logger.LogInformation("Received CloudEvent\n" + GetEventLog(cloudEvent));

                    try
                    {
                        dynamic data = JValue.Parse((string)cloudEvent.Data);
                        var storageUrl = (string)ConstructStorageUrl(data);
                        logger.LogInformation($"Storage url: {storageUrl}");

                        var labels = await ExtractLabelsAsync(storageUrl);

                        var message = "This picture is labelled: " + labels;
                        logger.LogInformation(message);

                        await context.Response.WriteAsync(message);
                    }
                    catch (Exception e)
                    {
                        logger.LogError("Something went wrong: " + e.Message);
                        context.Response.StatusCode = 500;
                        await context.Response.WriteAsync(e.Message);
                    }
                });
            });
        }

        private string ConstructStorageUrl(dynamic data)
        {
            return data == null? null
                : string.Format("gs://{0}/{1}", data.bucket, data.name);
        }

        private async Task<string> ExtractLabelsAsync(string storageUrl)
        {
            var visionClient = ImageAnnotatorClient.Create();
            var labels = await visionClient.DetectLabelsAsync(Image.FromUri(storageUrl), maxResults: 10);

            var orderedLabels = labels
                .OrderByDescending(x => x.Score)
                .TakeWhile((x, i) => i <= 2 || x.Score > 0.50)
                .Select(x => x.Description)
                .ToList();

            return string.Join(",", orderedLabels.ToArray());
        }

        private string GetEventLog(CloudEvent cloudEvent)
        {
            return $"ID: {cloudEvent.Id}\n"
                + $"Source: {cloudEvent.Source}\n"
                + $"Type: {cloudEvent.Type}\n"
                + $"Subject: {cloudEvent.Subject}\n"
                + $"DataSchema: {cloudEvent.DataSchema}\n"
                + $"DataContentType: {cloudEvent.DataContentType}\n"
                + $"Time: {cloudEvent.Time?.ToUniversalTime():yyyy-MM-dd'T'HH:mm:ss.fff'Z'}\n"
                + $"SpecVersion: {cloudEvent.SpecVersion}\n"
                + $"Data: {cloudEvent.Data}";
        }
    }
}