public BodyStatistics(BodyStatistics statistics)
{
this.Minimum = statistics.Minimum;
this.Maximum = statistics.Maximum;
this.Average = statistics.Average;
this.Total = statistics.Total;
this.Count = statistics.Count;
}
public async Task InvokeAsync(HttpContext context, RequestDelegate next)
{
// Record start time of request.
var startTime = DateTime.Now;
// Save a reference to the original body of the response.
var originalBody = context.Response.Body;
try
{
// Need to change response body to a stream that has a length.
using (var memoryStream = new MemoryStream())
{
// Swap the response body with a MemoryStream, which can read and seek.
context.Response.Body = memoryStream;
// Send request down pipeline.
await next(context);
// Get the content type of the response to determine encoding.
var contentType = new ContentType(context.Response.ContentType);
context.Response.Body.SeekToBegining();
BodyStatistics requestBodyStatistics;
lock (lockObj)
{
// Add the request data to the statistics data.
this.bodyStatistics.AddRequest(context.Response.Body.Length);
// Create a new variable with a copy of the body statistics for thread safety.
requestBodyStatistics = new BodyStatistics(this.bodyStatistics);
}
// Calculate the length of time the request took.
var interval = DateTime.Now - startTime;
// Write the gathered information to any HTML page.
await WriteContent(memoryStream, contentType, requestBodyStatistics, interval);
// Copy the data in the local MemoryStream to the original body.
await memoryStream.CopyToAsync(originalBody);
}
}
finally
{
// Set the reference to the original body in the response object so it gets returned to the client.
context.Response.Body = originalBody;
}
}
private static async Task WriteContent(Stream stream, ContentType contentType, BodyStatistics bodyStatistics, TimeSpan interval)
{
// Only inject the gathered information into HTML pages.
if (contentType.MediaType == "text/html")
{
// Get an encoding object for use later.
var encoding = Encoding.GetEncoding(contentType.CharSet);
stream.SeekToBegining();
// Construct the HTML to be injected.
var content = $"Time: {interval.TotalMilliseconds} ms<br/ >Body length minimum: {bodyStatistics.Minimum}<br/ >Body length maximum: {bodyStatistics.Maximum}<br/ >Body length average: {bodyStatistics.Average}";
// Parse the HTML that is to be returned to the client.
var parser = new HtmlParser();
var document = await parser.ParseDocumentAsync(stream);
// Create a new HTML div element to hold the injected informatin.
var div = document.CreateElement("div");
div.InnerHtml = content;
// Add the new HTML div to the document.
document.Body.Prepend(div);
stream.SeekToBegining();
// Truncate the stream that will be sent to the client so as to not return anything that shouldn't.
stream.SetLength(0);
// Write the HTML with the injected information to the response stream.
using (var writer = new StreamWriter(stream, encoding, 4096, true))
{
await writer.WriteAsync(document.DocumentElement.OuterHtml);
}
stream.SeekToBegining();
}
}
