/// <summary>
/// Creates an <see cref="IWebHostBuilder"/> as if the environment variables are set as per <paramref name="environment"/>.
/// The actual system environment variables are ignored. Command line arguments are not supported, as (by design) everything
/// that can be specified on the command line can also be specified via environment variables.
/// This method is primarily used for writing integration tests where a high degree of control is required,
/// for example to simulate the difference between running in a container or not.
/// </summary>
/// <param name="environment">The fake environment variables to use when constructing the host builder.</param>
/// <param name="functionAssembly">The assembly containing the target function. May be null, in which case the calling assembly
/// is used.</param>
/// <returns>A host builder that can be used for integration testing.</returns>
public static IHostBuilder CreateHostBuilder(IReadOnlyDictionary <string, string> environment, Assembly?functionAssembly = null)
{
var variables = ConfigurationVariableProvider.FromDictionary(environment);
var functionEnvironment = FunctionEnvironment.Create(functionAssembly ?? Assembly.GetCallingAssembly(), new string[0], variables);
return(functionEnvironment.CreateHostBuilder());
}
/// <summary>
/// Starts a web server to serve the function in the specified assembly. This method is called
/// automatically be the generated entry point.
/// </summary>
/// <param name="functionAssembly">The assembly containing the function to execute.</param>
/// <param name="args">Arguments to parse </param>
/// <returns>A task representing the asynchronous operation.
/// The result of the task is an exit code for the process, which is 0 for success or non-zero
/// for any failures.
/// </returns>
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);
// 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 environment = FunctionEnvironment.Create(functionAssembly, args, ConfigurationVariableProvider.System);
await environment.CreateHostBuilder().Build().RunAsync();
return(0);
}