Async FileStreams: Example of how to produce correct OpenAPI docs for returning files as streams and byte arrays.

AsyncFileStreamMinApi.cs

async Task Main()
{
	var builder = WebApplication.CreateBuilder();
	builder.Services.AddEndpointsApiExplorer();
	builder.Services.AddSwaggerGen(s => s.SwaggerDoc("v1", new OpenApiInfo
	{
		Title = "Report API",
		Description = "Manager all of your reporting needs.",
		Version = "v1",
		TermsOfService = null,
		License = new OpenApiLicense
		{
			Url = new Uri("https://www.apache.org/licenses/LICENSE-2.0.html"),
			Name = "Apache 2.0"
		},
		Contact = new OpenApiContact
		{
			Email = "support@example.com",
			Name = "Chris Carter",
			Url = new Uri("https://chrisjcarter.com")
		}
	}));

	var app = builder.Build();

	app.UseSwagger();
	app.UseSwaggerUI(s => s.SwaggerEndpoint("/swagger/v1/swagger.json", "Todo API V1"));

	// The file we're going to return from the apis
	const string file = @"C:\code\SCA_InfrastructureSecurity_Process.pdf";

	// OpenAPI yaml generated for /reports/{id:int}/stream:
	/*
	  '/reports/{id}/stream':
	    get:
	      tags:
	        - Streaming is super cool
	      operationId: GetReportStream
	      parameters:
	        - name: id
	          in: path
	          required: true
	          schema:
	            type: integer
	            format: int32
	      responses:
	        '200':
	          description: Success
	          content:
	            application/pdf:
	              schema:
	                type: string
	                format: binary
	*/
	app.MapGet("/reports/{id:int}/stream", (int id) =>
	{
		var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, FileOptions.Asynchronous);
		return Results.File(fileStream, "application/pdf", $"SCA_InfrastructureSecurity_Process_{id}.pdf");
	})
	.WithName("GetReportStream")
	.WithTags("Streaming is super cool")
	.Produces((int)HttpStatusCode.OK, typeof(FileStreamResult), "application/pdf");

	// OpenAPI yaml generated for /reports/{id:int}/byte-array:
	/*
	  '/reports/{id}/byte-array':
	    get:
	      tags:
	        - Byte arrays are the bees knees.
	      operationId: GetReportByteArray
	      parameters:
	        - name: id
	          in: path
	          required: true
	          schema:
	            type: integer
	            format: int32
	      responses:
	        '200':
	          description: Success
	          content:
	            application/pdf:
	              schema:
	                type: string
	                format: byte	
	*/
	app.MapGet("/reports/{id:int}/byte-array", async (int id) =>
	{
		var fileBytes = await File.ReadAllBytesAsync(file);
		return Results.File(fileBytes, "application/pdf");
	})
	.WithName("GetReportByteArray")
	.WithTags("Byte arrays are the bees knees.")
	.Produces((int)HttpStatusCode.OK, typeof(byte[]), "application/pdf");
	
	await app.RunAsync();
}