Does NancyFX support static content caching via the ETag and Last-Modified headers? - browser-cache

Question

I want my static content (images, javascript files, css files etc) to served in full only after the file has been updated.
If a file has not changed since it was last requested (as determined by the ETag and Last-Modified response header values) then I want the cached versions of the files to be used by the client browser.
Does Nancy support this functionality?

Answer 1

Nancy does partially support the ETag and the Last-Modified headers. It sets them for all static files but as of version 0.13 it does nothing with these values. here is the Nancy code:
Nancy.Responses.GenericFileResponse.cs
if (IsSafeFilePath(rootPath, fullPath))
{
Filename = Path.GetFileName(fullPath);
var fi = new FileInfo(fullPath);
// TODO - set a standard caching time and/or public?
Headers["ETag"] = fi.LastWriteTimeUtc.Ticks.ToString("x");
Headers["Last-Modified"] = fi.LastWriteTimeUtc.ToString("R");
Contents = GetFileContent(fullPath);
ContentType = contentType;
StatusCode = HttpStatusCode.OK;
return;
}
To make use of the ETag and Last-Modified header values you need to add a couple of modified extensions methods. I borrowed these directly from the Nancy source code in GitHub (as this functionality is planned for a future release) but the original idea came from Simon Cropp - Conditional responses with NancyFX
Extension Methods
public static void CheckForIfNonMatch(this NancyContext context)
{
var request = context.Request;
var response = context.Response;
string responseETag;
if (!response.Headers.TryGetValue("ETag", out responseETag)) return;
if (request.Headers.IfNoneMatch.Contains(responseETag))
{
context.Response = HttpStatusCode.NotModified;
}
}
public static void CheckForIfModifiedSince(this NancyContext context)
{
var request = context.Request;
var response = context.Response;
string responseLastModified;
if (!response.Headers.TryGetValue("Last-Modified", out responseLastModified)) return;
DateTime lastModified;
if (!request.Headers.IfModifiedSince.HasValue || !DateTime.TryParseExact(responseLastModified, "R", CultureInfo.InvariantCulture, DateTimeStyles.None, out lastModified)) return;
if (lastModified <= request.Headers.IfModifiedSince.Value)
{
context.Response = HttpStatusCode.NotModified;
}
}
Finally you need to call these methods using the AfterRequest hook in your Nancy BootStrapper.
BootStrapper
public class MyBootstrapper :DefaultNancyBootstrapper
{
protected override void ApplicationStartup(TinyIoCContainer container, IPipelines pipelines)
{
pipelines.AfterRequest += ctx =>
{
ctx.CheckForIfNoneMatch();
ctx.CheckForIfModifiedSince();
};
base.ApplicationStartup(container, pipelines);
}
//more stuff
}
Watching the responses with Fiddler you will see the first hit to your static files downloads them with a 200 - OK Status Code.
Thereafter each request returns a 304 - Not Modified Status Code. After a file is updated, requesting it once again downloads it with a 200 - OK Status Code ... and so on.