in src/Google.Cloud.Functions.Hosting/EntryPoint.cs [52:91]
public static async Task<int> StartAsync(Assembly functionAssembly, string[] args)
{
// Clear out the ASPNETCORE_URLS environment variable in order to avoid a warning when we start the server.
// An alternative would be to *use* the environment variable, but as it's populated (with a non-ideal value) by
// default, I suspect that would be tricky.
Environment.SetEnvironmentVariable("ASPNETCORE_URLS", null);
// Guess the function type by creating a configuration with just the environment variables and command line
// arguments in it. We do this so we can work out the function startup classes to use - and then validate that
// when we've used those functions startups and worked out the actual function target, the set of
// function startups is still valid. Note that it's possible for this to return null, if an assembly-specified
// function startup determines the actual function target. That's valid, so long as the function target doesn't
// later require any specific startups. (It would be very, very rare for a startup to affect which function is
// used, but I can imagine some scenarios where it's useful.)
var expectedFunctionTarget = GuessFunctionTarget();
// TODO: Catch exceptions and return 1, or just let the exception propagate? It probably
// doesn't matter much. Potentially catch exceptions during configuration, but let any
// during web server execution propagate.
var host = Host.CreateDefaultBuilder()
.ConfigureWebHostDefaults(webHostBuilder => webHostBuilder
.ConfigureAppConfiguration(builder => builder.AddFunctionsEnvironment().AddFunctionsCommandLine(args))
.ConfigureLogging((context, logging) => logging.ClearProviders().AddFunctionsConsoleLogging(context))
.ConfigureKestrelForFunctionsFramework()
.ConfigureServices((context, services) => services.AddFunctionTarget(context, functionAssembly))
.UseFunctionsStartups(functionAssembly, expectedFunctionTarget)
.Configure((context, app) => app.UseFunctionsFramework(context, validateStartups: true)))
.Build();
await host.RunAsync();
return 0;
Type? GuessFunctionTarget()
{
var configuration = new ConfigurationBuilder()
.AddFunctionsEnvironment()
.AddFunctionsCommandLine(args)
.Build();
return HostingInternals.TryGetFunctionTarget(configuration, functionAssembly);
}
}