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I have been researching Asp.Net Security and I found some surprising code:
context.Response.ContentType = "text/html";
await context.Response.WriteAsync("<html><body>");
await context.Response.WriteAsync("An remote error has occured: " + context.Request.Query["ErrorMessage"] + "<br>");
await context.Response.WriteAsync("<a href=\"/\">Home</a>");
await context.Response.WriteAsync("</body></html>");
What surprised me is the multiple calls to WriteAsync with short strings.
I would have used a template with String.Format or a StringBuilder to concatenate the strings and then write that in a single call:
var template = @"
<html><body>
An remote error has occured:{0}<br>
<a href=\"/\">Home</a>
</body></html>
";
var html = string.format(template, context.Request.Query["ErrorMessage"]);
await context.Response.WriteAsync(html);
If string concatenation should be avoided, this part should be broken up:
"An remote error has occured: " + context.Request.Query["ErrorMessage"] + "<br>"
For the purposes of discussion. Let's assume that this is in the context of a web server with an average of ~10,000 simultaneous active users: So performance is important.
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I created an Azure website (running on Basic 1 - 1 Small Instance) to benchmark this. Then I used the free service at https://loader.io to run each test at 100 users/second over 1 minute.
I ran each test 3 times in different orders. The times for each test run were within 200ms of each other.
The results were clear: StringBuilder won significantly. The cost of each async call far out weighs the cost of any form of string concatenation (even String.Format performed better than the multiple async calls).
Here is the code for each test:
// Do not write this code - It is ugly and performs terribly
private async Task TestWriteAsync(HttpContext context)
{
var r = context.Response;
var id = "id";
var size = "12";
var text = "text";
await r.WriteAsync("<div style='display:none'>");
for (int i = 0; i < 10000; i++)
{
await r.WriteAsync("<li id='");
await r.WriteAsync(id);
await r.WriteAsync("' style='font-size:");
await r.WriteAsync(size);
await r.WriteAsync("'>");
await r.WriteAsync(text);
await r.WriteAsync("</li>");
}
await r.WriteAsync("</div>");
}
// This is much better, but still not great
private async Task TestWriteAsyncFormat(HttpContext context)
{
var r = context.Response;
var id = "id";
var size = "12";
var text = "text";
var template = "<li id='{0}' style='font-size:{1}'>{2}</li>";
await r.WriteAsync("<div style='display:none'>");
for (int i = 0; i < 10000; i++)
{
await r.WriteAsync(string.Format(template, id, size, text));
}
await r.WriteAsync("</div>");
}
// The Performance Winner, but ugly code
private async Task TestStringBuilder(HttpContext context)
{
var sb = new StringBuilder();
var id = "id";
var size = "12";
var text = "text";
sb.Append("<div style='display:none'>");
for (int i = 0; i < 10000; i++)
{
sb.Append("<li id='");
sb.Append(id);
sb.Append("' style='font-size:");
sb.Append(size);
sb.Append("'>");
sb.Append(text);
sb.Append("</li>");
}
sb.Append("</div>");
await context.Response.WriteAsync(sb.ToString());
}
// Decent performance and Clean Code
private async Task TestStringBuilderFormat(HttpContext context)
{
var sb = new StringBuilder();
var id = "id";
var size = "12";
var text = "text";
var template = "<li id='{0}' style='font-size:{1}'>{2}</li>";
sb.Append("<div style='display:none'>");
for (int i = 0; i < 10000; i++)
{
sb.AppendFormat(template, id, size, text);
}
sb.Append("</div>");
await context.Response.WriteAsync(sb.ToString());
}
So although the old "Response.Write" is faster than StringBuilder with synchronous requests, "await Response.WriteAsync" is much slower (because of the async overhead).
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