WeatherForecastController.cs

// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0

namespace Examples.AspNetCore.Controllers;

using System.Diagnostics;
using System.Diagnostics.Metrics;
using Examples.AspNetCore;
using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("[controller]")]
public class WeatherForecastController : ControllerBase
{
    private static readonly string[] Summaries = new[]
    {
        "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching",
    };

    private static readonly HttpClient HttpClient = new();

    private readonly ILogger<WeatherForecastController> logger;
    private readonly ActivitySource activitySource;
    private readonly Counter<long> freezingDaysCounter;

    public WeatherForecastController(ILogger<WeatherForecastController> logger, Instrumentation instrumentation)
    {
        this.logger = logger ?? throw new ArgumentNullException(nameof(logger));

        ArgumentNullException.ThrowIfNull(instrumentation);
        this.activitySource = instrumentation.ActivitySource;
        this.freezingDaysCounter = instrumentation.FreezingDaysCounter;
    }

    [HttpGet]
    public IEnumerable<WeatherForecast> Get()
    {
        using var scope = this.logger.BeginScope("{Id}", Guid.NewGuid().ToString("N"));

        // Making an http call here to serve as an example of
        // how dependency calls will be captured and treated
        // automatically as child of incoming request.
        var res = HttpClient.GetStringAsync("http://google.com").Result;

        // Optional: Manually create an activity. This will become a child of
        // the activity created from the instrumentation library for AspNetCore.
        // Manually created activities are useful when there is a desire to track
        // a specific subset of the request. In this example one could imagine
        // that calculating the forecast is an expensive operation and therefore
        // something to be distinguished from the overall request.
        // Note: Tags can be added to the current activity without the need for
        // a manual activity using Activity.Current?.SetTag()
        using var activity = this.activitySource.StartActivity("calculate forecast");

        var rng = new Random();
        var forecast = Enumerable.Range(1, 5).Select(index => new WeatherForecast
        {
            Date = DateTime.Now.AddDays(index),
            TemperatureC = rng.Next(-20, 55),
            Summary = Summaries[rng.Next(Summaries.Length)],
        })
        .ToArray();

        // Optional: Count the freezing days
        this.freezingDaysCounter.Add(forecast.Count(f => f.TemperatureC < 0));

        this.logger.LogInformation(
            "WeatherForecasts generated {count}: {forecasts}",
            forecast.Length,
            forecast);

        return forecast;
    }
}